The Donut In The Trunk

We've hashed and rehashed issues relating to the pressures to run in the road tires, now what about the one in the trunk!

Most care tire information and loading placards on a vehicle equipped with a spare 'donut' specify keeping that tire at its maximum inflation pressure, typically 60psi.

I have faithfully maintained this pressure in the spares in both mine and my wife's car. Some knowns:

It is known that the donut in my wife's 2004 Toyota Corolla is the orginal, because she bought the car practically new - it was either a lease or trade from that model year, and she got an incredible deal buying it that way, less than 6 months old, around 10,000 miles on it. This knowledge will come into play momentarily.

Not known: The age/vintage of the donut in my 2010 Honda Accord. I bought this car in 2020, unlike the Toyota which was 6 or so months old. So I do not know if this is the original donut back there. But since the car itself is 6 years newer than the Corolla, it is possible that mine might be the original spare, or it might have been replaced at some point between 2011 and 2020. The tread depth appears to be quite even, with little scuffing aside from my trunk-to-driveway movement to fill it.


Back to the Corolla. 17-18 year old car, presumably with a spare donut of that vintage, which I have personally had to mount for my stranded wife some years ago.

Just the other day, I topped it off. Now my procedure for spare donuts is to use my automatic inflator set to 62-64psi. Why? Because both screwing the inflator chuck onto, and unscrewing it from, the spare's valve, releases far more air per second than doing so on a lower pressure standard road tire.

Just gauging the spare donut releases about 1psi! So it checked out at 52psi last week. Connecting the inflator probably let out another 2-3. At an inflator indication of 63psi I decided to turn the inflator off and remove it from the tire valve. Then I noticed something odd: one whole side of the donut was swolen, and there were gaps in the rubber on that side, in the transition zone from sidewall to tread!

I gauged the tire: 60.4psi with my high pressure Jaco digital. That gauge reads about 1psi high in general, so good enough. But I know this temp tire should no longer serve as a spare lawn ornament, let alone service a car.


Soooooooh, my question is:

Is it gospel to keep temp donuts at the maximum cold psi as indicated both on the donut and the vehicle's tire/load placard? Or should I just set my automatic inflator to 60psi exactly, and lose a litte air upon unscrewing it from the tire valve? And, was I doing a disservice to this tire by overinflating 3psi or so to compensate for what would seep out upon removing the inflator chuck?

As I said previously, if I didn't overinflate just a couple psi, and inflated exactly to 60, I'd always end up wth a 57-58psi pressured donut, owing to how quickly air escapes from its valve when pressed. Personally I think the safety margin on spare donuts is too thin, keeping their max pressure as the cold inflation pressure.

Do any of you maintain, IE: 55 in your spare donut, if you still have one?

I inflate my spares to the max, but pretty much only check then either when I'm waiting for the oil to finish draining during an oil change or when I'm preparing for a road trip.

-Rod

We've hashed and rehashed issues relating to the pressures to run in the road tires, now what about the one in the trunk!

Most care tire information and loading placards on a vehicle equipped with a spare 'donut' specify keeping that tire at its maximum inflation pressure, typically 60psi.

I have faithfully maintained this pressure in the spares in both mine and my wife's car. Some knowns:

It is known that the donut in my wife's 2004 Toyota Corolla is the orginal, because she bought the car practically new - it was either a lease or trade from that model year, and she got an incredible deal buying it that way, less than 6 months old, around 10,000 miles on it. This knowledge will come into play momentarily.

Not known: The age/vintage of the donut in my 2010 Honda Accord. I bought this car in 2020, unlike the Toyota which was 6 or so months old. So I do not know if this is the original donut back there. But since the car itself is 6 years newer than the Corolla, it is possible that mine might be the original spare, or it might have been replaced at some point between 2011 and 2020. The tread depth appears to be quite even, with little scuffing aside from my trunk-to-driveway movement to fill it.


Back to the Corolla. 17-18 year old car, presumably with a spare donut of that vintage, which I have personally had to mount for my stranded wife some years ago.

Just the other day, I topped it off. Now my procedure for spare donuts is to use my automatic inflator set to 62-64psi. Why? Because both screwing the inflator chuck onto, and unscrewing it from, the spare's valve, releases far more air per second than doing so on a lower pressure standard road tire.

Just gauging the spare donut releases about 1psi! So it checked out at 52psi last week. Connecting the inflator probably let out another 2-3. At an inflator indication of 63psi I decided to turn the inflator off and remove it from the tire valve. Then I noticed something odd: one whole side of the donut was swolen, and there were gaps in the rubber on that side, in the transition zone from sidewall to tread!

I gauged the tire: 60.4psi with my high pressure Jaco digital. That gauge reads about 1psi high in general, so good enough. But I know this temp tire should no longer serve as a spare lawn ornament, let alone service a car.


Soooooooh, my question is:

Is it gospel to keep temp donuts at the maximum cold psi as indicated both on the donut and the vehicle's tire/load placard? Or should I just set my automatic inflator to 60psi exactly, and lose a litte air upon unscrewing it from the tire valve? And, was I doing a disservice to this tire by overinflating 3psi or so to compensate for what would seep out upon removing the inflator chuck?

As I said previously, if I didn't overinflate just a couple psi, and inflated exactly to 60, I'd always end up wth a 57-58psi pressured donut, owing to how quickly air escapes from its valve when pressed. Personally I think the safety margin on spare donuts is too thin, keeping their max pressure as the cold inflation pressure.

Do any of you maintain, IE: 55 in your spare donut, if you still have one?

First, the date of manufacture is on tires - even donut spares! It's encoded in the TIN (Tire Identification Number) commonly called the DOT number. The DOT code is a 9 to 13 digit code that is located near the letters "DOT". More detail here: http://barrystiretech.com/dotcoding.html

Short version: The date code is the last 4 digits in a week/week/year/year format. So a 3115 is the 31st week of 2015.

An 18 year old tire coming apart is due to the age, not the inflation pressure. Over time, the rubber loses adhesion to the steel belt. That's why tire manufacturers recommend replacing tires after 10 years - and sooner in some instances.

So check your 12 year old Accord spare for the manufacture date. I'll bet its original to the car.

And just an FYI. the burst pressure of a tire is many times the max pressure. Even that 60 psi donut spare will not burst until over 150 psi - except when it gets damaged or is very old!

So what to do about that failed spare? Tire Rack does sell donut spares. If they don't have the size, you can try something close or get a regular wheel and normal tire.

First, the date of manufacture is on tires - even donut spares! It's encoded in the TIN (Tire Identification Number) commonly called the DOT number. The DOT code is a 9 to 13 digit code that is located near the letters "DOT". More detail here: http://barrystiretech.com/dotcoding.html

Short version: The date code is the last 4 digits in a week/week/year/year format. So a 3115 is the 31st week of 2015.

An 18 year old tire coming apart is due to the age, not the inflation pressure. Over time, the rubber loses adhesion to the steel belt. That's why tire manufacturers recommend replacing tires after 10 years - and sooner in some instances.

So check your 12 year old Accord spare for the manufacture date. I'll bet its original to the car.

And just an FYI. the burst pressure of a tire is many times the max pressure. Even that 60 psi donut spare will not burst until over 150 psi - except when it gets damaged or is very old!

So what to do about that failed spare? Tire Rack does sell donut spares. If they don't have the size, you can try something close or get a regular wheel and normal tire.

Thanks Barry!

My concern was not bursting the donuts, although I wasn't sure just how high above that establashed Max. the bursting point was.

Which leads me to another question:

At this point I'm fairly knowledgeable, thanks to you and other experts, of how vehicle mfgs. arrive at the recommended/specified cold tire pressures printed on the Tire/Load placards on their vehicles.

So, my question is, by what process do tire mfgs establish a Maximum Inflation pressure for their products?

IE: If the bursting pressure of a given tire is 'B'psi, then how do tire makers determine how low to set that published Maximum Inflation point 'M'psi?

My formula 'M = B/2' (or B/3 or B/4)

I'm going to start in a completely different place.

Please note, I am only going to talk about the US based tire standardization organization - The Tire and Rim Association (TRA). I am also only going to talk about Standard Load Passenger Car tires. I am not going to talk about metric based tire systems or Extra Load (XL) tires. Those are done similarly, but talking about them just complicates things

TRA sets the max pressure. They indicate that only 35 psi, 44 psi, and 51 psi are acceptable max tire pressures for Standard Load Passenger Car (SL PC) tires.

If you look at the load tables, you'll notice that for SL PC tires, the load maxes out at 35 psi. Please note that it doesn't matter if the tire says 44 psi max or 51 psi max on the sidewall. The load table is the same.

From an engineering perspective, tires are all about fatigue - and one of the principles of Fatigue is that if you make something stronger, it takes more cycles before it fails. So plies are made considerably stronger than 35 psi requires - about 4 or 5 times as strong.

That means a 35 psi rated tire should burst at about 140 to 175 psi - and that's about where that happens.

And remembering that tires marked 44 psi max or 51 psi max are built like 35 psi tires, you now have a picture of the relationship between max pressure and burst pressure.

I'm going to start in a completely different place.

Please note, I am only going to talk about the US based tire standardization organization - The Tire and Rim
Association (TRA). I am also only going to talk about Standard Load Passenger Car tires. I am not going to
talk about metric based tire systems or Extra Load (XL) tires. Those are done similarly, but talking about them
just complicates things

TRA sets the max pressure. They indicate that only 35 psi, 44 psi, and 51 psi are acceptable max tire pressures
for Standard Load Passenger Car (SL PC) tires.

If you look at the load tables, you'll notice that for SL PC tires, the load maxes out at 35 psi. Please note that it
doesn't matter if the tire says 44 psi max or 51 psi max on the sidewall. The load table is the same.

From an engineering perspective, tires are all about fatigue - and one of the principles of Fatigue is that if you
make something stronger, it takes more cycles before it fails. So plies are made considerably stronger than 35 psi
requires - about 4 or 5 times as strong.

That means a 35 psi rated tire should burst at about 140 to 175 psi - and that's about where that happens.

And remembering that tires marked 44 psi max or 51 psi max are built like 35 psi tires, you now have a picture of
the relationship between max pressure and burst pressure.

I'm starting to believe that a 44 or 51psi max on a tire sidewall is marketing, and not a valid basis for determining vehicle specific tire pressure. All those two values do is tempt the, let's just say 'less knowledgeable', into inflating their tires to an even more ridiculously high pressure! So just assume standard load tables, 35psi, for passenger applicatations.

So burst is safely 3-4x any maximum cold pressure listed on a tire's sidewall.

I guess for tractor trailer and bus tires, oft pressurized to 90-105psi, have even a higher maximum pressure stamped on them, and an even higher burst pressure: 300psi and up...

I'm starting to believe that a 44 or 51psi max on a tire sidewall is marketing, and not a valid basis for determining vehicle specific tire pressure. All those two values do is tempt the, let's just say 'less knowledgeable', into inflating their tires to an even more ridiculously high pressure! So just assume standard load tables, 35psi, for passenger applications.

So burst is safely 3-4x any maximum cold pressure listed on a tire's sidewall.

I guess for tractor trailer and bus tires, oft pressurized to 90-105psi, have even a higher maximum pressure stamped on them, and an even higher burst pressure: 300psi and up...

While I knew the marketing folks, I never asked them the question of how they determined the max pressure, but I agree with you: Marketing. Fooling the public they are getting more than they actually are. Not that it matters, because max pressure doesn't really mean anything. It seems to me to be a case of telling a white lie.

But there is a thing about speed rated tires tested at more than 35 psi - and that's where the 44 psi and 51 psi came from.

Truck/Bus tires? They don't have a max pressure printed on the sidewall. They use this form: Max Load XXXX at YY pressure.

What I found was that many people think that the above way of stating the max load means that is the max pressure, too. Sorry, but that is not the case. There are situations where a bit more pressure can be used. It just isn't a hard and fast rule.

(1)While I knew the marketing folks, I never asked them the question of how they determined the max
pressure, but I agree with you: Marketing. Fooling the public they are getting more than they actually
are. Not that it matters, because max pressure doesn't really mean anything. It seems to me to be a
case of telling a white lie.

But there is a thing about speed rated tires tested at more than 35 psi - and that's where the 44 psi and
51 psi came from.

Truck/Bus tires? They don't have a max pressure printed on the sidewall. They use this form: Max Load
XXXX at YY pressure.

(2)What I found was that many people think that the above way of stating the max load means that is the
max pressure, too. Sorry, but that is not the case. There are situations where a bit more pressure can be
used. It just isn't a hard and fast rule.


(1) Which is why I've advocated for not listing any pressure on a tire sidewall. Drivers(at least non-commercial private ones here in the States) are mostly too ignorant to know where to source the correct pressure for their specific vehicle. And they take it so politically when you show them the correct way to set it. ,

So "Max Load XXXXlbs @ 44/51psi" on such a speed rated tire means the max load - at those higher pressures? As in, you can carry that max load at 35psi as long as you are maintaining speeds lower than the tires' full rating, buuut, inflate to the 44 rating if at speed? I can see where such reasoning, on part of the tire maker, could confuse drivers as to what the true "max" pressure is.


(2) Toward the end of this paragraph it looks as though you are saying it is ok, on occasion, to run tire pressures higher than the value on the tire sidewall, at least on the commercial side. Is that your assertion?

That might be why I read so many schoolbus forums where I hear about bus tires maintained at 110+? :o

Once in a while someone chimes in that they run 95psi cold, and both the bus ride and tire wear patterns are far more satisfactory. Someone - who thinks things through - a rare commodity in this new century!


Well, I'm still afraid to let folks I help, with tire pressures, know that their tires won't just explode at 36psi, or at 45, 52, or LT 81! That will only embolden them to use those sidewall values instead of the pressures carefully arrived at by the vehicle mfgs themselves.

They'll use the Ford "Exploder" case as rebuttal, not realizing that that was just one blatant outlier among mostly successful tire pressure recommendations. If more folks had observed the pressure offset specified on earlier Corvairs, we might not have heard - as much - from Ralph Nader.

(1) Which is why I've advocated for not listing any pressure on a tire sidewall. Drivers(at least non-commercial private ones here in the States) are mostly too ignorant to know where to source the correct pressure for their specific vehicle. And they take it so politically when you show them the correct way to set it. .....

I think the government regulation needs to be updated to indicate the max load and its corresponding pressure. Not a max pressure. Right now it's confusing as to what is supposed to be written on the sidewall.

.....
So "Max Load XXXXlbs @ 44/51psi" on such a speed rated tire means the max load - at those higher pressures? As in, you can carry that max load at 35psi as long as you are maintaining speeds lower than the tires' full rating, buuut, inflate to the 44 rating if at speed? I can see where such reasoning, on part of the tire maker, could confuse drivers as to what the true "max" pressure is....

See, it is confusing for those folks in the US - and those are the regulations I am talking about. Let the rest of the world figure out what they want to do about higher speeds.

.....(2) Toward the end of this paragraph it looks as though you are saying it is ok, on occasion, to run tire pressures higher than the value on the tire sidewall, at least on the commercial side. Is that your assertion? ......

Yes

......That might be why I read so many schoolbus forums where I hear about bus tires maintained at 110+? :o .....

It's also possible that the tires call for that pressure. Some Truck/Bus tires can have even higher pressures!

..... Once in a while someone chimes in that they run 95psi cold, and both the bus ride and tire wear patterns are far more satisfactory. Someone - who thinks things through - a rare commodity in this new century!

Well, I'm still afraid to let folks I help, with tire pressures, know that their tires won't just explode at 36psi, or at 45, 52, or LT 81! That will only embolden them to use those sidewall values instead of the pressures carefully arrived at by the vehicle mfgs themselves. ....

I always struggle to understand why some folks just can not understand that the placard has some good science behind it.

...... They'll use the Ford "Exploder" case as rebuttal, not realizing that that was just one blatant outlier among mostly successful tire pressure recommendations. If more folks had observed the pressure offset specified on earlier Corvairs, we might not have heard - as much - from Ralph Nader.

I have a whole webpage devoted to the Ford/Firestone controversy. http://barrystiretech.com/fordfirestone.html

On that page, I have a photo of the infamous Explorer placard - and I do the math to prove the pressure is adequate.

But what I usually do is point out that if that pressure was too low, the vehicle would have been recalled - and it wasn't! Only the tire!

I think the government regulation needs to be
updated to indicate the max load and its corresponding
pressure. Not a max pressure. Right now it's confusing
as to what is supposed to be written on the sidewall.



See, it is confusing for those folks in the US - and those
are the regulations I am talking about. Let the rest of
the world figure out what they want to do about higher
speeds.



Yes


(1) It's also possible that the tires call for that pressure.
Some Truck/Bus tires can have even higher pressures!



(2)I always struggle to understand why some folks just
can not understand that the placard has some good science
behind it.



(3)I have a whole webpage devoted to the Ford/Firestone controversy.
http://barrystiretech.com/fordfirestone.html

On that page, I have a photo of the infamous Explorer
placard - and I do the math to prove the pressure is adequate.

But what I usually do is point out that if that pressure was
too low, the vehicle would have been recalled - and it
wasn't! Only the tire!


(1) With all due respect Barry, the tires shouldn't be calling their mom - let alone calling for any specific air pressure. A tire won't step forward and proclaim "use me!" on this or that vehicle.

The application itself - be it a Schwinn, a riding mower, a Yugo, a Cadillac, a Suburban, a school bus, a tractor trailer, an Airbus A320, a DC-10, or a 747 - should be "calling for" a specified tire pressure - as determined by the engineers who designed them. (notice I went in size/weight order there :) ).

The tires manufactured for each of those vehicle classifications should have a max-load rating that is at least 110-125% of the maximum capacity(passengers, cargo, and fuel) of each of those vehicles I mentioned.

(2) It's called 'pride', Barry - the oldest flaw in the Bible!
People generally like to think they know better - better than each other, even better than those educated and or certified in areas of expertise.

Some of the biggest complaints(and proclamantions) I hear made about the tire pressures specified on Tire/Load decals on cars:

"They feel mushy"

"The tires 'look' flat" (radial bulge on the ground)

"They handle like crap at the vehicle pressure"

And the following gem:

"The car maker doesn't make tires - what do they know about proper air pressures?" :rolleyes:

....etc.



(3) A lot to unpack there regarding the early generations of Explorer, starting in 1991.

What I gleaned from it mainly was, that certain plant locations assigned to manufacture OEM tires for the first Explorer were producing tires that were defective in the bonding capacities of the rubber between the plies and the tread layer.

As for pressures? Ok, so while the 26psi specified by Ford for those early Explorers was approx 110% of that required to carry the maximum weight of the heaviest axle, then why, on more recent generations of Explorer, are cold pressures of 35psi and up specified?

One reason could be the aspect ratios of the tire/wheel combo has evolved, from 75-series higher profile tires to the 50-series and lower, profile tire and larger wheel size currently in fashion(!). A wider tire with shorter sidewalls, all other things being equal, requires a higher pressure to maintain an even contact patch with the road.

Another reason could be that the original - 1980s Ranger-based - Explorers possessed a high C/G (center of gravity).

Thirdly: Fuel economy - it is common knowledge that higher tire pressures reduce rolling resistance.

Barry, I beg of you: WHAT is the sticker on the drivers door pillar properly called??? - the one with GVWR and GAWR, and manufacture date on it, not the Tire pressure sticker.

I searched for an HOUR online and could not find GAWR specs published for recent generations of Ford Explorer, to compare to those specs for the 1991 model year Explorer. And I am not about to go roaming through a Ford parking lot opening doors on a dozen Explorers to determine Gross vehicle and Gross Axle weights, lol!

So I'm unable to determine if the front & rear gross axle ratings on Explorers from the last 5 years are significantly heavier than those for the first-gen Explorer, requiring a higher cold tire pressure.

Even a dinky little 2018-present Escape specifies cold tire pressures much higher than the 26psi specified for a larger 1991 Explorer.

(1) With all due respect Barry, the tires shouldn't be calling their mom - let alone calling for any specific air pressure. A tire won't step forward and proclaim "use me!" on this or that vehicle. .....

We're talking Federal Regulations here. I doubt we could change them, but if we could, I just know they would not want to get rid of the pressure on the sidewall - plus, they absolutely would want the max load - ergo, referencing the load table. It's the same for everyone including the government.

........The application itself - be it a Schwinn, a riding mower, a Yugo, a Cadillac, a Suburban, a school bus, a tractor trailer, an Airbus A320, a DC-10, or a 747 - should be "calling for" a specified tire pressure - as determined by the engineers who designed them. (notice I went in size/weight order there :) ).

The tires manufactured for each of those vehicle classifications should have a max-load rating that is at least 110-125% of the maximum capacity(passengers, cargo, and fuel) of each of those vehicles I mentioned. .....

Well, that's the system we have now. On light vehicles (cars, pickups, SUV's, trailers), they have a placard that's supposed to be on the driver's side doorframe.

For other vehicles, the government has been reluctant to get into the mess. Over-the-Road Trucks, for example, are ordered special - that is every truck is individualized for the buyer - and that could mean a variety of tire sizes. For many trucking outfits, they have a tire rep that helps with issues - and one of those is setting pressure.

...... (3) A lot to unpack there regarding the early generations of Explorer, starting in 1991.

What I gleaned from it mainly was, that certain plant locations assigned to manufacture OEM tires for the first Explorer were producing tires that were defective in the bonding capacities of the rubber between the plies and the tread layer. ......

Not exactly. The problem was an odd one: A combination of the tread pattern and a peculiar way of processing rubber (which is probably what you were referring to.)

...... As for pressures? Ok, so while the 26psi specified by Ford for those early Explorers was approx 110% of that required to carry the maximum weight of the heaviest axle, then why, on more recent generations of Explorer, are cold pressures of 35psi and up specified? ...

Don't fall for the trap others have fallen into - that the unusual pressure spec is somehow the reason for the failures. If Ford had specified a smaller tire with a more common pressure spec, there still would have been failures. The problem would still be there - and Firestone wasn't the only tire manufacturer with the problem - albeit different versions.

......One reason could be the aspect ratios of the tire/wheel combo has evolved, from 75-series higher profile tires to the 50-series and lower, profile tire and larger wheel size currently in fashion(!). A wider tire with shorter sidewalls, all other things being equal, requires a higher pressure to maintain an even contact patch with the road. ......

Ah ....... No!!

A wider tire with shorter sidewalls does NOT require more pressure to maintain an even contact patch with the road. Even contact with the road is achieved by careful attention to a thing called the tread profile - and chief among those is tread radius. Those things can be adjusted regardless of the aspect ratio of the tire.


...... Another reason could be that the original - 1980s Ranger-based - Explorers possessed a high C/G (center of gravity). .....

You mean the Bronco II?

An interesting tidbit is that in 1989 I saw protypes of the Explorer operating at Ford's Naples Proving Grounds with Bronco II badging. Shortly after that, the Bronco II was lambasted as being unsafe due it's high CG, narrow track, and short wheelbase - all of which that replacement vehicle was supposed to address. But it was too late to fix the name, so Ford opted to change it to something untarnished - hence the "Explorer" name that had been used in the past. In retrospect, it's kind of ironic.


....... Thirdly: Fuel economy - it is common knowledge that higher tire pressures reduce rolling resistance.

Barry, I beg of you: WHAT is the sticker on the drivers door pillar properly called??? - the one with GVWR and GAWR, and manufacture date on it, not the Tire pressure sticker. ....

I think it is called the certification sticker.

.........I searched for an HOUR online and could not find GAWR specs published for recent generations of Ford Explorer, to compare to those specs for the 1991 model year Explorer. And I am not about to go roaming through a Ford parking lot opening doors on a dozen Explorers to determine Gross vehicle and Gross Axle weights, lol!

So I'm unable to determine if the front & rear gross axle ratings on Explorers from the last 5 years are significantly heavier than those for the first-gen Explorer, requiring a higher cold tire pressure.

Even a dinky little 2018-present Escape specifies cold tire pressures much higher than the 26psi specified for a larger 1991 Explorer.

Again, don't fall into the trap of thinking that an unusual pressure spec means that it is somehow faulty. Larger tires require less pressure to carry the same load.

So when you go to compare pre-2000's Explorers to post 2008 Explorers, you will find something kind of interesting.

Prior to the Firestone recall in 2000, it was common for pickups, SUV's, and Vans regardless of manufacturer to be spec'd with tires that closely matched the GAWR's. In other words, the tires were the limiting factor for payloads in these vehicles.

One way of expressing this is that there was no tire reserve load capacity.

But after 2008, the vehicle manufacturers added reserve capacity by going to larger tires and more conventional inflation pressures. (It did not go unnoticed that there was prejudice towards lower inflation pressures!) And I mean more than just Ford - GM, Toyota, Nissan, etc.

Between 2000 and 2008 was the transition as vehicle manufacturers introduced vehicles that had bigger fenderwells to accommodate the larger sized tires.

Why 2008? Because that was when the new laws concerning tire placards, TPMS, etc. went into effect. Some vehicle manufacturers were quicker than others, but everyone met the 2008 deadline.

We're talking Federal Regulations here. I doubt we could change them, but if we could, I just know they
would not want to get rid of the pressure on the sidewall - plus, they absolutely would want the max load - ergo, referencing the load
table. It's the same for everyone including the government.



Well, that's the system we have now. On light vehicles (cars, pickups, SUV's, trailers), they have a placard that's supposed to be on
the driver's side doorframe.

For other vehicles, the government has been reluctant to get into the mess. Over-the-Road Trucks, for example, are ordered
special - that is every truck is individualized for the buyer - and that could mean a variety of tire sizes. For many trucking outfits, they
have a tire rep that helps with issues - and one of those is setting pressure.



Not exactly. The problem was an odd one: A combination of the tread pattern and a peculiar way of processing rubber (which is
probably what you were referring to.)



Don't fall for the trap others have fallen into - that the unusual pressure spec is somehow the reason for the failures. If Ford had
specified a smaller tire with a more common pressure spec, there still would have been failures. The problem would still be there -
and Firestone wasn't the only tire manufacturer with the problem - albeit different versions.



(1) Ah ....... No!!

A wider tire with shorter sidewalls does NOT require more pressure to maintain an even contact patch with the road. Even
contact with the road is achieved by careful attention to a thing called the tread profile - and chief among those is tread radius.
Those things can be adjusted regardless of the aspect ratio of the tire.




(2) You mean the Bronco II?

An interesting tidbit is that in 1989 I saw protypes of the Explorer operating at Ford's Naples Proving Grounds with Bronco II badging.
Shortly after that, the Bronco II was lambasted as being unsafe due it's high CG, narrow track, and short wheelbase - all of which
that replacement vehicle was supposed to address. But it was too late to fix the name, so Ford opted to change it to something
untarnished - hence the "Explorer" name that had been used in the past. In retrospect, it's kind of ironic.




(3) I think it is called the certification sticker.



Again, don't fall into the trap of thinking that an unusual pressure spec means that it is somehow faulty. Larger tires require
less pressure to carry the same load.

So when you go to compare pre-2000's Explorers to post 2008 Explorers, you will find something kind of interesting.

Prior to the Firestone recall in 2000, it was common for pickups, SUV's, and Vans regardless of manufacturer to be spec'd
with tires that closely matched the GAWR's. In other words, the tires were the limiting factor for payloads in these vehicles.

One way of expressing this is that there was no tire reserve load capacity.

But after 2008, the vehicle manufacturers added reserve capacity by going to larger tires and more conventional inflation
pressures. (It did not go unnoticed that there was prejudice towards lower inflation pressures!) And I mean more than just
Ford - GM, Toyota, Nissan, etc.

(4) Between 2000 and 2008 was the transition as vehicle manufacturers introduced vehicles that had bigger fenderwells to
accommodate the larger sized tires.

Why 2008? Because that was when the new laws concerning tire placards, TPMS, etc. went into effect. Some vehicle manufacturers
were quicker than others, but everyone met the 2008 deadline.

_________________________
Re: Tread pattern and rubber processing.

I see. I wonder if the specific tread pattern arrived by the partners(Ford / Firestone) on the project might have produced oscillation issues that slowly led to the separation of the tread from the carcass.

Where I now live, off a state highway, I hear the 'RO RO RO RO RO' of a knobby tread outside the window. I look, and sure enough its a SUV, pickup, or other such vehicle with monster 'knobby' tread tires going by!



1) Lower profile tire pressure and "tread radius"

The reason I made this assertion is because a friend of mine and I both have similar year Honda Accords of the same generation.

She has a 2009 base(LX) Accord, specifiying 215/60R16 94H tires @30psi cold. (I may be off on that speed letter though)

Mine is an 2010 Accord EX, specifying 225/50R17 93V tires @32psi cold.
My specific tires, and most tires currently available for my car, are 94V, since that OEM 93V has become a scarcer combination than hens teeth. lol

Searching through sites such as tirepressure dot com, I noticed a similar pattern, of car trim levels with wider lower profile tires specifying cold pressures 1-2psi higher than on trims with the narrower tires.

So then why are they doing that?

And also, I would appreciate more info, hopefully from you, regarding concepts of the "tread profile" and "tread radius" you mentioned.



2) Bronco II / Ranger as the starting point for Explorer platform.

Barry, on-line I have seen both referenced as such, adding to my natural confusion. And in reality, the Bronco II of that era(1980s) was just a covered Ranger!



3) Certification Sticker. I will search with that term. Not expecting miracles!

I even called it the "axle weight sticker" or "GVWR" placard - no dice on Google. The sticker itself does not have a name or part no. on it.



4) 2008.

So around THEN began the industry-wide transition toward the ridiculously wide tires and hideously huge wheels we now see on passenger vehicles from Sentras up to Sequoias.

I still maintain that something could have been done for brakes without resorting to rim and wheel sizes seen normally on 10- and upward - wheel trucks not that long ago.

I may, Barry, be alone in this regard: But I simply do not like the feel/handling on vehicles with such large wheels and low profile rubber. I have been (teasingly) referred to as "pizza cutter" for my preference for narrower, higher sidewall tires! lol

_________________________
Re: Tread pattern and rubber processing.

I see. I wonder if the specific tread pattern arrived by the partners(Ford / Firestone) on the project might have produced oscillation issues that slowly led to the separation of the tread from the carcass.

Where I now live, off a state highway, I hear the 'RO RO RO RO RO' of a knobby tread outside the window. I look, and sure enough its a SUV, pickup, or other such vehicle with monster 'knobby' tread tires going by! ....

The Firestone tire in question had an unusual tread pattern that squeezed out some of the rubber from between the belts during molding. That rubber is critical towards preventing separations - which is what happened.

____1) Lower profile tire pressure and "tread radius"

The reason I made this assertion is because a friend of mine and I both have similar year Honda Accords of the same generation.

She has a 2009 base(LX) Accord, specifiying 215/60R16 94H tires @30psi cold. (I may be off on that speed letter though)

Mine is an 2010 Accord EX, specifying 225/50R17 93V tires @32psi cold.
My specific tires, and most tires currently available for my car, are 94V, since that OEM 93V has become a scarcer combination than hens teeth. lol

Searching through sites such as tirepressure dot com, I noticed a similar pattern, of car trim levels with wider lower profile tires specifying cold pressures 1-2psi higher than on trims with the narrower tires.

So then why are they doing that? ......

I can think of several reasons:

1) The models in question might be ever so slightly heavier, justifying an increase in pressure to carry the additional load.

2) The sporty nature of the lower profile tire is benefited by increased inflation pressure.

____And also, I would appreciate more info, hopefully from you, regarding concepts of the "tread profile" and "tread radius" you mentioned. ....

Lay a straight edge across the face of the tread of a tire - shoulder to shoulder. You will notice that the tread is not flat - it's a curve. You can measure the radius of that curve. That curve affects the distributio of the pressure in the footprint - and that, in turn, affects wear and grip.

____ 4) 2008.

So around THEN began the industry-wide transition toward the ridiculously wide tires and hideously huge wheels we now see on passenger vehicles from Sentras up to Sequoias. ....

I think it started in the late 1980's. By the time the 2008 rolled around, the car industry had taken full advantage of the opportunity and the process was more or less complete by then.

____I still maintain that something could have been done for brakes without resorting to rim and wheel sizes seen normally on 10- and upward - wheel trucks not that long ago......

Yeah but making the brakes larger is soooo much easier.


____I may, Barry, be alone in this regard: But I simply do not like the feel/handling on vehicles with such large wheels and low profile rubber. I have been (teasingly) referred to as "pizza cutter" for my preference for narrower, higher sidewall tires! lol

I, too, am not a fan of lower profile tires - except for handling purposes, but the car manufacturers and shock manufacturers have done a remarkable job of mitigated the issues inherent with those lower profiles.

The Firestone tire in question had an unusual tread pattern
that squeezed out some of the rubber from between the belts
during molding. That rubber is critical towards preventing
separations - which is what happened.



I can think of several reasons:

1) The models in question might be ever so slightly heavier, justifying an increase in pressure to carry the additional load.

2) The sporty nature of the lower profile tire is benefited by increased inflation pressure.



Lay a straight edge across the face of the tread of a tire - shoulder to shoulder. You will notice that the tread is not flat - it's a curve. You can measure the radius of that curve. That curve affects the distributio of the pressure in the footprint - and that, in turn, affects wear and grip.



I think it started in the late 1980's. By the time the 2008 rolled around, the car industry had taken full advantage of the opportunity and the process was more or less complete by then.



Yeah but making the brakes larger is soooo much easier.




I, too, am not a fan of lower profile tires - except for handling purposes, but the car manufacturers and shock manufacturers have done a remarkable job of mitigated the issues inherent with those lower profiles.

A. Tread radius, and a slight curve across the tread.

I'm sure this flattens out at the portion in the contact patch, correct?

B. Wider Low profile tires and handling

I'm over 40, and no longer drive like I did in my high school or college years, so F1-wide tires and corresponding suspension are wasted on me, :D

As far as mitigating issues associated with low profiles go:

1. Increasing certain alignment angles to increase self-aligning/self centering from turns. IE: Kingpin and Caster. An 'ancient' 75R14 tire might need just a tough of Caster and a little Kingpin angle to keep going straight. A more recent, wider 50R17 combo might need, at minimum, 3-4 degrees Caster angle, and 10 or more degrees of Kingpin, to center the wheels from turns.

2. Power steering assist can also be reduced slightly on models with wider tires, since they respond more rapidly to smaller steering inputs.

3. On the suspension side, the stiffer ride from shorter sidewall tires can be compensated for with lower, and variable spring-rate coils.

Still, more straightforward engineering can be accomplished by going back - halfway, to 'pizza cutter' narrow wheels with higher profile tires!

By 'tread radius' is this what you are referring to?

(Note blue line added by me) - And how does that influence contact patch maintenance in wider/lower profile tires?

A search of "tread radius" yields results not quite relevant to what I'm attaching, so let me know if I'm going in the wrong direction
with it.

Like this (in green):

And the tread profile would be the distance between the top of the tread down and the top of the belt (or cap plies).


http://barrystiretech.com/Tread%20Radius.jpg

Like this (in green):

And the tread profile would be the distance between the top
of the tread down and the top of the belt (or cap plies).


http://barrystiretech.com/Tread%20Radius.jpg

And what is the significance of that in maintaining even contact patch in wider, lower profile tires?

And what is the significance of that in maintaining even contact patch in wider, lower profile tires?

The lower the tread radius, the more pressure in the middle of the contact patch. This has implications for treadwear and grip.

The lower the tread radius, the more pressure in
the middle of the contact patch. This has implications for
treadwear and grip.

Ok, first things first: On a higher tread radius tire, is the tread section rounder(your green line), and on a lower tread radius tire, is it flatter/straighter?

Because what you said, above, goes completely counter to my gut. Remember Barry, I think with my belly(gut instinct), not that thing upstairs. ;)

So first, I am pleased that when I changed that photo, that this website picked that up. This version is sooooo much easier to deal with.

Ok, first things first: On a higher tread radius tire, is the tread section rounder(your green line), and on a lower tread radius tire, is it flatter/straighter? .....

You have it exactly backwards. I am puzzled that you don't know that a small radius results in a smaller circle, and that a larger radius results in a larger circle - and that if I am measuring an arc (part of a circle) a larger radius results in a flatter arc.

...... Because what you said, above, goes completely counter to my gut. Remember Barry, I think with my belly(gut instinct), not that thing upstairs. ;)

Does your gut feel better, now?

So first, I am pleased that when I changed that photo, that this website picked that up.
This version is sooooo much easier to deal with.



You have it exactly backwards. I am puzzled that you don't know that a small radius results
in a smaller circle, and that a larger radius results in a larger circle - and that if I am measuring
an arc (part of a circle) a larger radius results in a flatter arc.



Does your gut feel better, now?


You're "puzzled"?

Barry:
.
.
.

I can't even multiply or divide! Let alone understand basic radii theory.

I had to get a deferment - for lack of better term - to be allowed to attend university and get a degree, my secondary math grades were so poor. Goes back to issues in early childhood.

In subjects I could could care less about: social studies, history, English, I averaged A-PLUS. And I'm not proud of that.

So please break it down, this radius thing, for me.

Well, the smaller the tread radius, the more pressure along the centerline of the footprint. That means there is an optimal tread radius where the footprint pressure is such that it promotes even tread wear and max grip.

Well, the smaller the tread radius, the more pressure along the centerline of the footprint. That means there is
an optimal tread radius where the footprint pressure is such that it promotes even tread wear and max grip.


Can this tread radius be engineered into a wider tire so that, at a given pressure, that footprint pressure against the gound is equally distributed?

Can this tread radius be engineered into a wider tire so that, at a given pressure, that footprint pressure against the ground is equally distributed?

This question seems to say that you think there is something wrong with wide tires that might be fixed by applying "tread radius". Would you please explain?

This question seems to say that you think there is something
wrong with wide tires that might be fixed by applying "tread radius". Would you please explain?


"Lay a straight edge across the face of the tread of a
tire - shoulder to shoulder. You will notice that the tread
is not flat - it's a curve. You can measure the radius of
that curve. That curve affects the distributio of the pressure
in the footprint - and that, in turn, affects wear and grip."


Your words - not mine. The onus is on you to explain how that curve, the tread radius curve that you highlighted in reply #17 I believe, can be adjusted in manufacturing to affect load distrib. across a wider tires' contact patch.

Now that I've thought about the basic concepts, and finally grasp, them, I'll continue to wait patiently for your explanation.

The reason I asked the question is that I am confused about why you would think wide tires and narrow tires would be different when it comes to tread radius. Perhaps if I answer your question, it can serve as a basis so you can answer mine.

Let’s start with an assumption that in the contact patch, a flat belt is needed to get an even pressure distribution. That means that the tread thickness is the same shoulder to shoulder. Remember this is an assumption, which we will revisit later.

If I measure the tread radius when the tire is completely unloaded (commonly called Freestanding), I can get a value – and I can translate that back to the radius in the mold, because I know the relationship between freestanding and molded tire shapes.
But what if my initial assumption about the belt needing to be parallel to the road surface is wrong? I can add or subtract rubber as needed. And I don’t even have to change the tread depth. I can change what we tire engineers call the undertread – the rubber between the bottom of the grooves and the top of the belt. The net result would be I’d get a different freestanding tread radius.

What if it takes different freestanding tread radii for different tire sizes? Well it doesn’t matter, I just do the same thing for each size.
In the old days, that was time consuming, because you’d have to build tires. But today, we can do that in virtual space – lots easier and faster. And, of course, once its been done for one tire line, the same thing can be applied to different tire lines.

So back to the question I asked, why do you think there is a difference between wide tires and narrow tires when it comes to tread radius?

The reason I asked the question is that I am confused about why you would think wide tires and narrow tires would be different when it comes to tread radius. Perhaps if I answer your question, it can serve as a basis so you can answer mine.

Let’s start with an assumption that in the contact patch, a flat belt is needed to get an even pressure distribution. That means that the tread thickness is the same shoulder to shoulder. Remember this is an assumption, which we will revisit later.

If I measure the tread radius when the tire is completely unloaded (commonly called Freestanding), I can get a value – and I can translate that back to the radius in the mold, because I know the relationship between freestanding and molded tire shapes.
But what if my initial assumption about the belt needing to be parallel to the road surface is wrong? I can add or subtract rubber as needed. And I don’t even have to change the tread depth. I can change what we tire engineers call the undertread – the rubber between the bottom of the grooves and the top of the belt. The net result would be I’d get a different freestanding tread radius.

What if it takes different freestanding tread radii for different tire sizes? Well it doesn’t matter, I just do the same thing for each size.
In the old days, that was time consuming, because you’d have to build tires. But today, we can do that in virtual space – lots easier and faster. And, of course, once its been done for one tire line, the same thing can be applied to different tire lines.

So back to the question I asked, why do you think there is a difference between wide tires and narrow tires when it comes to tread radius?

Before I related it to tread radius, let's discuss the relative integrity of, IE, the 195-75R14 off my 1981 Buick and the 225-50R17 off my 2010 Honda.

The Century's tire consists of a narrower action surface(tread) spanning two taller sidewalls.

The Accord's tire consistes of a significantly wider tread, spanning two shorter sidewalls.

Going by my gut again, Capri, with the wider tread, something - either the tread's construction itself, its free-wheeling shape, or, what fills the tire to maintain the tread's shape integrity and thus equal force across its contact patch - must be changed from what worked for that narrower Buick tire.

Please tell me what that is. If not a change in the tread radius(what you illustrated with the green line), then something else. Just tell me what that is, or what combination of properties.

Before I related it to tread radius, let's discuss the relative integrity of, IE, the 195-75R14 off my 1981 Buick and the 225-50R17 off my 2010 Honda.

The Century's tire consists of a narrower action surface(tread) spanning two taller sidewalls.

The Accord's tire consistes of a significantly wider tread, spanning two shorter sidewalls.

Going by my gut again, Capri, with the wider tread, something - either the tread's construction itself, its free-wheeling shape, or, what fills the tire to maintain the tread's shape integrity and thus equal force across its contact patch - must be changed from what worked for that narrower Buick tire.

Please tell me what that is. If not a change in the tread radius(what you illustrated with the green line), then something else. Just tell me what that is, or what combination of properties.

I'm a little unclear what you are asking. Could you reword the question a bit?

I'm a little unclear what you are asking.
Could you reword the question a bit?

Alright, in laymans terms: Is the tread on a wider tire with shorter sidewalls “floppier” more prone to flexing than the tread on a narrow tire with taller sides?

That’s why I arrived at the conclusion that a 45- or 50-series tire, on the same car in place of 60-or higher series tire required higher air pressure to maintain the same rigidity across the patch.

Thanks for the clarification. A part of me wondered if you were asking me to compare a 40 year old tire to a 10 year old tires - and that was going to be difficult! Im glad its current tires.

OK, on to the question. What's different? Actually not much.

First, the steel belt consists of 2 layers of rubber coated steel wire, with the wires running parallel to each other in each layer. If you were to look through the 2 layers, it would look like a cross hatch pattern.

But those are the same to each tire, the only difference is that the wider tire has wider belts - and within each tire, the belts are the same underneath the treadface, except for the ends - meaning the strength of the belts are the same throughout either tire except at the ends - no difference.

But there is a difference in that the wider tire has wider belts so each individual wire wraps further around the circumference of the tire. I don't think that makes a difference in how the tire behaves, but it is a difference, but probably in the wrong direction for your theory.

So let's look at your assertion that lower profile tires get more pressure. According to Tire Guides, 2010 Honda Accord. It came with P215/60R16 94H at 30 psi and P225/50R17 93V at 32 psi. If I do the math, the load carrying capacity of each is the same - which would explain why there's a difference in specified pressure. But the Accord also came with P235/45R16 94V at 34 psi. That seems to be the odd man out, but I note that Tire Guides says this was only for the EX-L Coupe V-6, and that for the 2011 and 2012 model year, that same entry is listed as 32 psi. That's doubly odd. Can't tell what is going on there.

Maybe we could get some insight if we looked at the Civic. In 2010 it came with P195/65R15 89 S &H at 32 psi, P205/55R16 89H at 32 psi, and P215/45R17 87V at 32 psi. Huh?

What about the Accord in 2013? 205/55R16 95H at 32/32, 215/55R17 94V at 33/33, 235/45R18at 33/32. That doesn't seem to follow any pattern at all!

So I don't think your theory holds up.

Thanks for the clarification. A part of me wondered if you were asking me to compare a 40 year old tire to a 10 year old tires - and
that was going to be difficult! Im glad its current tires.

OK, on to the question. What's different? Actually not much.

First, the steel belt consists of 2 layers of rubber coated steel wire, with the wires running parallel to each other in each layer.
If you were to look through the 2 layers, it would look like a cross hatch pattern.

But those are the same to each tire, the only difference is that the wider tire has wider belts - and within each tire, the belts are the same
underneath the treadface, except for the ends - meaning the strength of the belts are the same throughout either tire except at the ends -
no difference.

But there is a difference in that the wider tire has wider belts so each individual wire wraps further around the circumference of the tire.
I don't think that makes a difference in how the tire behaves, but it is a difference, but probably in the wrong direction for your theory.

So let's look at your assertion that lower profile tires get more pressure. According to Tire Guides, 2010 Honda Accord. It came with
P215/60R16 94H at 30 psi and P225/50R17 93V at 32 psi. If I do the math, the load carrying capacity of each is the same - which
would explain why there's a difference in specified pressure. But the Accord also came with P235/45R16 94V at 34 psi. That seems
to be the odd man out, but I note that Tire Guides says this was only for the EX-L Coupe V-6, and that for the 2011 and 2012 model
year, that same entry is listed as 32 psi. That's doubly odd. Can't tell what is going on there.

Maybe we could get some insight if we looked at the Civic. In 2010 it came with P195/65R15 89 S &H at 32 psi, P205/55R16 89H
at 32 psi, and P215/45R17 87V at 32 psi. Huh?

What about the Accord in 2013? 205/55R16 95H at 32/32, 215/55R17 94V at 33/33, 235/45R18at 33/32. That doesn't seem to
follow any pattern at all!

So I don't think your theory holds up.

For the wider tire, with wider belts, are the belts beefed up with additional 'windings', or strands of wires? In other words, are the belts scaled up in size along with the size of a given tire section?

IE: The size record-breaking Olympic Trio of ocean liners were originally designed with scaled up hull and deck plating in mind: Two inch thick steel hull plating, for example, in place of time-honored 1 inch steel plating. Ultimately, they were built with 1 inch, but I'm sure their framing was beefed up by some percentage over that of the Cunarders they were built to out-class.

Does such scaling up of interior elements of tires occur with tires of greater width, diameter, and overall size?

For the wider tire, with wider belts, are the belts beefed up with additional 'windings', or strands of wires? In other words, are the belts scaled up in size along with the size of a given tire section? .....

No.

While this is something I've wondered about - that is, why doesn't this happen - manufacturing complexity is the reason. There has to be a certain level of standardization within the plant for the plant to remain efficient.

.....IE: The size record-breaking Olympic Trio of ocean liners were originally designed with scaled up hull and deck plating in mind: Two inch thick steel hull plating, for example, in place of time-honored 1 inch steel plating. Ultimately, they were built with 1 inch, but I'm sure their framing was beefed up by some percentage over that of the Cunarders they were built to out-class.

Does such scaling up of interior elements of tires occur with tires of greater width, diameter, and overall size?

There is a certain amount of scaling up just due to the bigger dimensions - that is, wider tires have wider belts and that means more wires across the tread width. Larger diameter tires obviously get more belt material.

But also consider that the purpose of the belt is stiffness, not strength. It's sort of like how they size the smoke stacks on a cruise ship so they look in proportion to the size of the ship and not because they need to be bigger.

No.

While this is something I've wondered about - that is, why doesn't this happen - manufacturing complexity is the reason.
There has to be a certain level of standardization within the plant for the plant to remain efficient.



There is a certain amount of scaling up just due to the bigger dimensions - that is, wider tires have wider belts and that
means more wires across the tread width. Larger diameter tires obviously get more belt material.

But also consider that the purpose of the belt is stiffness, not strength. It's sort of like how they size the smoke stacks
on a cruise ship so they look in proportion to the size of the ship and not because they need to be bigger.


So in theory, if I divide my heavier gross axle weight of the two in half, and find out that my tire size and load designation satisfies that capacity at a lower pressure, IE, in my case 30psi instead of 32, can I run my Accord's wider, lower profile tires at that?


Your analogy of the tire belts and ocean liner(by the way!) smoke stacks is not exactly correct. Scaling up the radial tire belts is being done for a physical property. Scaling up the funnels on the liner was done for looks. Two different goals.

So in theory, if I divide my heavier gross axle weight of the two in half, and find out that my tire size and load designation satisfies that capacity at a lower pressure, IE, in my case 30psi instead of 32, can I run my Accord's wider, lower profile tires at that? .......

You and I have had this discussion before.

The spring rate of a tire varies according to the inflation pressure. Vehicle engineers set the springs, shocks and sway bars at the target inflation pressure, so following the vehicle tire placard is the correct way to do this.

You and I have had this discussion before.


The spring rate of a tire varies according to the
inflation pressure. Vehicle engineers set the springs,
shocks and sway bars at the target inflation pressure,
so following the vehicle tire placard is the
correct way to do this.

This should be on a placque on every garage wall - and on its own page in the drivers/owners manual!

Thank you - point well taken!

Now how do I get all the naysayers and know-it-alls - even those with 'ASE' embroidered on their shirt - on board?

This should be on a placque on every garage wall - and on its own page in the drivers/owners manual!

Thank you - point well taken!

Now how do I get all the naysayers and know-it-alls - even those with 'ASE' embroidered on their shirt - on board?

I have taken to certain tactics:

1) Repeating it whenever I get a chance. I always include the explanation as well as the advice.

2) Recognize that some folks are resistant to new information. I had a friend who called this "First Learnings" - that is the first time some folks hear some bit of information, is the last time they learn.

3) Also recognize that some people (and in this case, I mean you) aren't going to be able to pass on this information successfully. Not because of any personal flaw, but because the recipient isn't going to be receptive of information from certain sources.

I have taken to certain tactics:

1) Repeating it whenever I get a chance. I always include the explanation as well as the advice.

2) Recognize that some folks are resistant to new information. I had a friend who called this "First Learnings" -
that is the first time some folks hear some bit of information, is the last time they learn.

3) Also recognize that some people (and in this case, I mean you) aren't going to be able to pass on this information
successfully. Not because of any personal flaw, but because the recipient isn't going to be receptive of information
from certain sources.

Well, I use the following art analogy:

The tire is the 'canvas' and the vehicle is the 'art form'

IE: You have a 51" or 44" canvas to paint on, but that doesn't mean you have to use every square inch of that surface for your painting. That 51" is just the maximum dimension of that canvas.

They sort of get where I'm going, after that explanation.


This question popped into my mind while I was typing that:

On vehicles where there is a tire pressure split/offset of the recommended cold pressures: Front=34, Rear=40, for instance.

How does a car's TPMS and other body control systems reconcile that difference?

I'm sure the axle with the lower pressure will accumulate several dozen more revolutions per mile.

........ This question popped into my mind while I was typing that:

On vehicles where there is a tire pressure split/offset of the recommended cold pressures: Front=34, Rear=40, for instance.

How does a car's TPMS and other body control systems reconcile that difference?

I'm sure the axle with the lower pressure will accumulate several dozen more revolutions per mile.

First, the revs per mile statement:

RPM is a function of inflation pressure AND load. On a tire with a light load, the rpm's will lower.

Plus, on ABS based braking systems, the computer notices the DIFFERENCE in revs. I am sure computers can be programmed to ignore steady, but different RPM's.

But ABS systems is not my area of expertise, so what I just said is a guess.

First, the revs per mile statement:

RPM is a function of inflation pressure AND load. On a tire with a light load, the rpm's will lower.

Plus, on ABS based braking systems, the computer notices the DIFFERENCE in revs. I am sure computers
can be programmed to ignore steady, but different RPM's.

But ABS systems is not my area of expertise, so what I just said is a guess.

So for vehicles that do recommend disparate front and rear cold tire pressures, this has(in theory at least) been accounted for by the engineers, with regards to sensors, TPMS, transmission ratios(in AWD cars), etc.?

Several 9th generation(2013-17) Accord trims specified, IE, 33 Front 32 Rear cold. That also was accounted for during design of those machines?

So for vehicles that do recommend disparate front and rear cold tire pressures, this has(in theory at least) been accounted for by the engineers, with regards to sensors, TPMS, transmission ratios(in AWD cars), etc.?

Several 9th generation(2013-17) Accord trims specified, IE, 33 Front 32 Rear cold. That also was accounted for during design of those machines?

Vehicle engineers are responsible for the entire package as presented - and that includes the tire inflation pressures specified on the vehicle tire placard. If it doesn't work, THEY are responsible - and if that leads to a recall, then that's what it does. The engineers - in the form of the manufacturing company - are responsible for addressing anything recallable.

That made for an interesting dynamic in the Ford/Firestone situation. While The tire manufacturer was responsible for the issue, the fact that the vehicle manufacturer approved that tire for their vehicle pot the vehicle manufacturer in an interesting position. Eventually, Ford recalled those tires - and I can't remember how they did it without issuing an official (as in recorded by the Federal government) recall notice. I suppose I could look it up and figure it out, but I know the situation was complex.

Vehicle engineers are responsible for the entire package as presented - and that includes the tire inflation pressures
specified on the vehicle tire placard. If it doesn't work, THEY are responsible - and if that leads to a recall, then that's
what it does. The engineers - in the form of the manufacturing company - are responsible for addressing anything
recallable.

That made for an interesting dynamic in the Ford/Firestone situation. While The tire manufacturer was responsible
for the issue, the fact that the vehicle manufacturer approved that tire for their vehicle pot the vehicle manufacturer
in an interesting position. Eventually, Ford recalled those tires - and I can't remember how they did it without
issuing an official (as in recorded by the Federal government) recall notice. I suppose I could look it up and figure
it out, but I know the situation was complex.


Along this pattern of thought:

Some vehicles' TPMS systems use a rudimentary RPM(iles)-based system of monitoring, where if one tire's pressure drops enough to increase it's revs-per-mile/km indication by enough of a difference from the other three, it will trigger a light on the drivers instrument panel.

My 2010 Accord might be one such vehicle. So if I do experiment with different front/rear tire pressures, enough of a difference could trigger such a light on my dash - albeit inadvertantly! Best for me to keep them all evenly inflated, if that's what's on the door placard and in the manual.

On vehicles where a different front/rear axle pressure is specified, Barry, I would assume the TPMS system(which ever type is used) is factory calibrated to account for the difference in rolling revs-per-mile caused by a two - or more - psi inflation offset between rear and front axles.will

More sophisticated RF(radio frequency) TPMS units transmit the actual PSI/kPa/Bar to the BCM(body control) or whatevever receptacle receives this info. If any/all tires are more than below a specified threshold, IE: 75% of door-placard pressure, regardless of differencs in specified front/rear pressures, an indication will occur for those tires - the excessive low pressures on each tire on the dash may be displayed in amber or red, for instance, instead of normal color.