For Anyone Who Owns a Digital Tire Gauge


RidingOnRailz
06-21-2019, 05:28 PM
Hi!

I need some recommendations for a digital tire pressure gauge. I'm getting the dropsies in old age and do not have the budget to keep replacing my clock-face analog bleeder models from Slime and Accu-Gage after dropping them only from the height of a tire, and finding out they are no longer accurate from even such a short fall onto pavement.
My priorities are:

1. Must read down to 1/10th - not 1/2, not a whole - but one-tenth PSI, IE: 32.7 or 29.2psi (yes, it matters!)
2. Have a bleeder valve as my clock-face gauges all did.
3. Price: approx $$$ on a scale of $(cheapo) - $$$$$(military pentagon grade).

Any suggestions, models you have had good experience with?

Thanks!

RidingOnRailz
06-22-2019, 07:55 AM
Come on!

I'm not asking about how far apart to plant geraniums here, lol!

shorod
06-22-2019, 09:49 AM
I don't own this one, but Amazon reviews (https://www.amazon.com/dp/B07JL8YB36/ref=sspa_dk_detail_1?psc=1&pd_rd_i=B07JL8YB36&pd_rd_w=UQLPl&pf_rd_p=8a8f3917-7900-4ce8-ad90-adf0d53c0985&pd_rd_wg=lkiR3&pf_rd_r=RVY1RKWGEX868N0X5RKX&pd_rd_r=48bf3df8-94f2-11e9-bd29-f56f00babb57) suggest it's pretty good. It's probably a bit on the inexpensive side of your required price scale (considering I work on military grade components and know how expensive such trivial items can cost). It fits your other requirements, but unfortunately you didn't mention what the full-scale accuracy needs to be. It reads to 0.1 psi resolution, but with a full-scale accuracy of 0.5% which apparently is good enough to be considered "professional racing accuracy standards."

From a quick search I didn't find anything that provided a lower full scale AND also listed the full scale accuracy.

FWIW, finding out the recommended distance to plant geraniums from one another is much easier to find.

-Rod

RidingOnRailz
06-23-2019, 07:01 AM
Getting the tire pressures this precise could help eliminate them in cases of pull or drift to one side or another, or unequal steering effort on one side, etc, except in hopefully rarer cases of conicity - tires with different tread circumferences from one sidewall to the other.

shorod
06-23-2019, 09:55 AM
So you're looking more for consistency and resolution more so than accuracy. In that case, the one I linked to seems like it should check most of your boxes.


-Rod

RidingOnRailz
06-23-2019, 01:16 PM
So you're looking more for consistency and resolution more so than accuracy. In that case, the one I linked to seems like it should check most of your boxes.


-Rod

Actually, both: Higher resolution, RE: Having all four tires read precisely 32.7PSI(just an example!) is easier to achieve than trying to eyeball such with a dial or stick gauge.

shorod
06-23-2019, 05:36 PM
Right. My accuracy comment pertains to the 0.5% full scale accuracy. Since that particular unit can measure up to 200 psi, that translates to a 1 psi accuracy. Your readings may be off by as much as 1 psi, but as long as the reading is consistent with 0.1 psi resolution, the accuracy is less important to you. If you wanted accuracy as well, you'd want to find one with either a lower full scale capability or better than 0.5% accuracy.

-Rod

RidingOnRailz
06-23-2019, 08:15 PM
Right. My accuracy comment pertains to the 0.5% full scale accuracy. Since that particular unit can measure up to 200 psi, that translates to a 1 psi accuracy. Your readings may be off by as much as 1 psi, but as long as the reading is consistent with 0.1 psi resolution, the accuracy is less important to you. If you wanted accuracy as well, you'd want to find one with either a lower full scale capability or better than 0.5% accuracy.

-Rod

So, if hypothetically, I adjust all my tires to indicate exactly 32.0PSI, one tire might actually have 33, another one 31, and so on?

So how do I know if the gauge is indicating low(causing me to overinflate) or indicating high(resulting in underinflation)?

By "lower full scale capability" do you mean, buying a 5-60psi gauge vs a 5-100 model?

RidingOnRailz
06-25-2019, 07:07 AM
Bump!

shorod
06-25-2019, 07:56 PM
So, if hypothetically, I adjust all my tires to indicate exactly 32.0PSI, one tire might actually have 33, another one 31, and so on?

So how do I know if the gauge is indicating low(causing me to overinflate) or indicating high(resulting in underinflation)?

By "lower full scale capability" do you mean, buying a 5-60psi gauge vs a 5-100 model?

I would expect the gauge to be consistent, it just might be consistently high by as much as 1psi or consistently low by as much as 1psi. I would not expect it to read high 1 reading and then low on the next though.

Regarding lower full scale capability, yes, you interpreted my comment correctly. For a gauge that can read up to 100 psi, 0.5% full scale would be 0.5 psi. For one that has a 60 psi full scale, 0.5% would be 0.3 psi.

-Rod

RidingOnRailz
06-25-2019, 10:28 PM
I would expect the gauge to be consistent, it just might be consistently high by as much as 1psi or consistently low by as much as 1psi. I would not expect it to read high 1 reading and then low on the next though.

Regarding lower full scale capability, yes, you interpreted my comment correctly. For a gauge that can read up to 100 psi, 0.5% full scale would be 0.5 psi. For one that has a 60 psi full scale, 0.5% would be 0.3 psi.

-Rod


Thanks! I know it's just tire pressure, set & forget, come back in a month, but, it's my F-18- I mean, Hyundai! And I just want things as evenly set as possible.

By the way shorod, there's a set of calculations out there that I learned, that returns a set of front and rear cold pressures even more exact than the ones listed on a car's b-pillar load sticker:

It involves knowing the max load and inflation pressure of the original tires, and the front and rear GAWR(gross axle weight rating).

IE: The load sticker on my 2015 Hyundai recommend 33psi cold, front and rear.

Plugging the information about my car and the tires in, and the formula returns 35psi front and 32 rear - to account for the front weight bias in a typical front wheel drive econo-sedan. The car really sticks to the road in turns, smoother ride, and 1-2mpg better highway mileage. Same for my wife's 2004 Toyota:

Recommended: 30psi all around. Calculated: 32psi front, 29 rear. She says she presses the gas less, and the brakes more! Fuel economy improved too.

For a friend's 2005 Legacy GT sedan however, the calculated pressures made ZERO sense: 48psi front, 49 rear! WT... ?! Sound more like TRUCK pressures, ehh?

Actual recommended pressures on that Subaru's sticker: 35psi front, 33rear. I think she will stick with those! lol

It's tires are 45-series 17" wagon wheels, vs my Hyundai's - 65-series normal tires. That might explain why I got the wonky figures on the Subaru.

Ordinarily, most vehicles I've done it for are predictable: They add 1-2psi for the heavier GAWR axle, and reduce 1-2psi for the lighter axle.

CapriRacer
06-26-2019, 08:24 AM
……. By the way shorod, there's a set of calculations out there that I learned, that returns a set of front and rear cold pressures even more exact than the ones listed on a car's b-pillar load sticker: …..

Do you mind sharing? As a tire engineer who has been told how the vehicle tire placard values are calculated, it would be interesting to know what other methods exist.

RidingOnRailz
06-26-2019, 04:30 PM
Do you mind sharing? As a tire engineer who has been told how the vehicle tire placard values are calculated, it would be interesting to know what other methods exist.

1. Obtain the following information(mostly on the tires, and stickers on vehicle door frame):

GAWR(gross axle weight) values for front and rear axles.

Max. cold pressure and USTA max load rating from OEM tire, if possible. *Some replacement tires, even with exact same size, speed-rating letter code, and maximum cold pressure as the OEMs, might have a different USTA max load stamped on them. Use it in those cases.

2. Divide both front and rear GAWR/2 - remember: you want final pressure per tire, not per axle!

3. Plug figures into following formula:

Front: [(GAWR/2) /USTA max load] * Max Cold Pressure from OEM tires.

Repeat for Rear axle.

My 2015 Hyundai example: The B-pillar sticker specifies 33psi cold, front & rear - nice n easy for average Schmoe consumer to remember and set their tires to!

B-pillar Front GAWR: 2,160lbs. Rear GAWR: 2006lbs.

OEM Tires: 44psi Max cold, USTA max load 1,356lbs.


So for front tires:

Half of front GAWR = 1,080. Half of Rear GAWR = 1003

(1080/1,356 )
= 0.7964601 * 44 = 35.04psi

For rear tires:

(1003/1356)
= 0.7396755 * 44 = 32.5psi(I rounded down to 32psi for convenience!)


35psi front, 32 rears.
Or alternatively(for summer): 34 front, 31 rear - as long as that difference is maintained.


Essentially it calculates GAWR/2 as a percentage of the USTA maximum load
(in my case, 1,356lbs) per tire. 1080lbs = 79% of max load for the front tires, and 1003lbs = 73% of max load for the rear tires.

It does not work for all vehicles! Like I said previously, the formulas above returned some ridiculous figures for my friend's 2005 Subaru Legacy.

Your mileage - and pressures - may vary ;)

CapriRacer
06-27-2019, 08:35 AM
Thanks,

OK, that's not a new one for me - however, it is one I debunked quite a while ago. Here are the flaws:

1) The max pressure on the tire is NOT related to max load - at least for P type tires.

US regulations say that the max load and the max pressure must be imprinted on the sidewall of any tire that is to be used on the street. Usually it is expressed this way: Max Load XXXX at YY pressure. Notice the relationship. This is the way pretty much the way every tire is done except for P type tires.

For P type tires, it is usually expressed this way: Max Load XXXX, Max pressure YY. Notice that no relationship is expressed - and there's a reason for that. The pressure where the load maxes out for Standard Load P type tires is 35 psi (or if using metric units, 36.3 psi), but it is permissible to use higher pressures for certain conditions. The values specified by The Tire and Rim Association are 44 and 51 psi. I show where those values come from here (about 1/3 the way down): http://barrystiretech.com/loadtables.html

2) The load curve is NOT proportional to the inflation pressure, nor is it linear. So the formula won't match what the tire manufacturers (through The Tire and Rim Association) publish.

3) Nowadays, it is common practice for the GAWR's to be 85% of the load carrying capacity of the tire at the placard pressure. This is a change that result from the Ford/Firestone situation back in 2001.

The net effect is that you won't get what the vehicle manufacturers specify. The fear is that you will get a value lower than what the vehicle manufacturers specify and that could be dangerous.

Plus, the spring rate of a tire is relatively proportional to its inflation pressure, so the vehicle will handle differently if a different pressure is used.

RidingOnRailz
06-27-2019, 03:58 PM
CapriRacer wrote: "The net effect is that you won't
get what the vehicle manufacturers specify."

I wasn't expecting it to!

"The fear is that you will get a value lower
than what the vehicle manufacturers specify
and that could be dangerous."

I did - on both mine and my wife's car -only for the rear axle tire pressures.

My wife's Toyota load decal specifies 30psi both front & rear. So easy a caveman could set tire pressure

The formula yielded 32psi front and 29 rear.


My Hyundai load decal specifies 33psi front & rear - easy for the masses to set.

The formula yielded 35front and 32 rear.

We both like the way our cars steer, handle, and roll with cold pressures set accordingly.
Notice that for both of our cars the formula successfully took into account the front-end weight bias - lowering the tire pressure a tad in the rear and adding some in the front.

My friend's AWD 2005 Subaru calls for 34psi front, and 35 rear.

However, for reasons yet unknown, the formula returned suggested cold psi of 48 front and 49 rear!

The only thing I could possibly think of, is, even though the tires currently on her Subaru match the size on the door placard, they might not be the same speed or USTA load weight rating. That could be throwing things off in her case.

At any rate, it shows that Subaru appreciates that its customers love to drive, and took the time to calculate and recommend the exact front and rear pressures for tires on their vehicles - not just an average pressure for both front and rear - as in mine and my wife's cars cases.

CapriRacer
06-28-2019, 08:21 AM
...…… My friend's AWD 2005 Subaru calls for 34psi front, and 35 rear.

However, for reasons yet unknown, the formula returned suggested cold psi of 48 front and 49 rear! ……..

Remember when I said that the max pressure is NOT related to the max load? I suspect the answer you are getting for the Subaru is because the tire's max pressure is 51 psi, where the actual rating pressure is 35 psi.

RidingOnRailz
06-28-2019, 08:31 AM
Remember when I said that the max pressure is NOT related to the max load? I suspect the answer you are getting for the Subaru is because the tire's max pressure is 51 psi, where the actual rating pressure is 35 psi.

So if I plug 35psi max cold, or even 44(my Hyundai tires) into the formula, I might get actual sane recommended pressures for that Legacy?

And secondly, it's 2019, not 1989: I haven't seen a Max Cold PSI of 35 stamped on a passenger tire since nearly back to then. Since the '90s, 44 and 51psi max cold appear on every pax tire I've had the pleasure of kneeling before. :D

Are you suggesting that those current max cold stampings might lack some validity?

RidingOnRailz
06-28-2019, 10:04 AM
Remember when I said that the max pressure is NOT related to the max load? I suspect the answer you are getting for the Subaru is because the tire's max pressure is 51 psi, where the actual rating pressure is 35 psi.

Wait - HOLLLLLLLLD everything!

I just noticed something odd: The USTA load stamped on the Subaru tires(1201lbs) is LOWER than it is on my SMALLER Hyundai(1356lbs), and even smallllller Corolla, also 1356lbs. I'm surprised - and actually embarrassed - that I didn't pick up on that weeks ago!

This changes everything! Apparently her tires are NOT of the OEM specified on her door B-pillar: "215/45ZR17". I neglected to photograph the size stamped on the tires, so while I do recall the size, I don't remember exactly what speed/load ratings the tire place sold someone who owned the car before my friend! Will it be a risk for her to keep these lower load, NON-oem tires on her car, since it is mostly just her driving across town to work, and sometimes with her kid?

So I found a Continental Extreme Contact in that exact size as indicated on the Subaru door sticker, BUT: That "Z" is NOT the speed rating! The speed rating, acc. to Continental's own page for that tire, is W! With a load index of 91(1,356lbs).

So I don't know WHY there is a Z in the middle of that tire size if it does not refer to the speed rating. As Trump would say: "Misleading - VERRY misleading!" :D


Anywho, I ran the formula with the new 1,356lb USTA figure, and get something a *little* less truckish for my friend's poor Legacy:

F: 43psi, R: 44.


Also Capri, when I left in the original USTA load - the one actually on her car - and used 35psi max cold in the formula, I got:

F: 33psi, R: 34 (basically the opposite of her door placard: F: 35, R: 33).


When I used the correct USTA load(1,356) annnd 35 max cold(as you mentioned), I got:

F: 29psi R: 30

BOTH axles calculated under the door sticker cold pressures! Although those are the exact cold "normal load" pressures I saw on my boss's 2015 Forester. Cosmic.....


So the second to last set of pressures seem the most sensible, to me anyway, for this 2005 Legacy sedan. LOL! Notice though, how in each scenario, the formula flips the pressure difference between front and rear. Interesting.


Long n short: The tire pressure formula I shared happens to work perfectly with the tires on the cars in my household, adding pressure to the heavier axle and subtracting it from the lighter one.

Now for the greatest mystery of the tire universe:

How, in 1994, Ford came up with the recommendations for my 1996 Contour - remember, Mondeo? World car? Driver extraordinaire?

Front: 31psi, Rear: 34!

Wait, wasn't Mondeo/Contour a FRONT-drive econobox - or econobubble?

Why would Ford specify higher tire pressures on the LIGHTER axle?

Anywho, from 20 to 17 years ago, when I drove the Contour, I tried Ford's pressures for one week - and never looked back. One of my favorite drivers! If it had a moonroof, I might still be driving it today!

CapriRacer
06-29-2019, 08:44 AM
Whoa!! So much to unpack.

Let's start by having you read this web page: http://barrystiretech.com/loadtables.html

This will ask you if you read the page on Tire Standardizing Organizations. Do that, too.

3 things you should pick up:

1) That the rating pressure for Standard Load P metric tires is 35 psi - and even though the max pressures may be at 44 or 51 psi, this value still holds.

2) That there is a note that it is PERMISSIBLE to use 44 psi and 51 psi - hence some tire manufacturers will list one of those as the max pressure. So don't read too much into that, because it doesn't say when to use either, so the decision is relatively arbitrary.

3) That the load curve is NOT proportion to the inflation pressure, so the formula you are using is wrong.


And a couple of tidbits:

What is the USTA? Did you mean the USTMA - US Tire Manufacturers Association? If so, then be aware they don't publish load and inflation information - but the tire standardizing organizations do, hence why I want you to read my page on the subject.

The 1996 Ford Contour? Only the SE version had that pressure split. All the other versions used the same pressure front to rear. (Source: The Old Timers Tire Guide)

Why would Ford do that? It has been known for vehicle manufacturers to tweak the tire pressure to get certain handling characteristics. My opinion is that they shouldn't do this, but they don't listen to me.

There are more things I want to talk about, but I don't want to overload you with information, so I'm doing this in steps.

RidingOnRailz
06-30-2019, 12:47 AM
CapriRacer wrote: "The 1996 Ford Contour? Only the SE
version had that pressure split. All the other versions used
the same pressure front to rear. (Source: The Old Timers Tire
Guide)"

ERRRR - Wrong!

My GL also had that Front/Rear pressure difference on its B-pillar placard, and I went by it.

So I suppose you'll accuse Ford of putting the wrong tire decal on the wrong trim-level Contour.



Yes, I was using USTA arbitrarily - If you suffered the damage I did during youth you might, also.

So exactly who determines those max loads, and thus max cold pressures(35, 44, 51, etc) that get stamped on tires?

By the way, your load tables link is more a text book explaining load theory. I was expecting an actual table where I could look up my specific tire size - or that on my friend's Subaru - and glean some actual load data from it.

It just shows an example of a load table, which helps only those whose tires happen to be listed in that excerpt.

CapriRacer
06-30-2019, 08:50 AM
…… So I suppose you'll accuse Ford of putting the wrong tire decal on the wrong trim-level Contour. ….

No, I'll be accusing Tire Guides of making a mistake in their book. This wouldn't be the first time I found one.

I wonder what the placards actually say for the other versions. Put another way, it is unusual to specify more inflation pressure for the rear tires on a FWD, and if all the Contours had that pressure split, why did Tire Guides only indicate it for the one combination? I wonder if it was that way for the 1995 models and the 15" - which only came on the 1995 SE model - had that pressure split and Tire Guides just didn't pick up on the change made in later model years.

……Yes, I was using USTA arbitrarily - If you suffered the damage I did during youth you might, also.

So exactly who determines those max loads, and thus max cold pressures(35, 44, 51, etc) that get stamped on tires? ……..

The tire standardizing organizations publish load tables - max load vs inflation pressures - in the form of a book published every year. While a tire manufacturer is not under any obligation to follow those, not only would it be foolish not to do so, there have only been a few cases where the tire manufacturer did something other than what was published - and eventually, those exceptions disappeared.

The US government accepts those standards and requires the tire manufacturers to imprint the max load and the max inflation pressure on the sidewall of each tire designated for street usage.

And here's where the confusion comes in: Officially, all Standard Load passenger type tires will have their load max out at 35 psi (or 2.5 bar (36.3 psi) if the standard is written in metric units), the tire standards allow 44 or 51 psi (3.0 bar and 3.5 bar) to be used as well - and the tire manufacturer deicides what to place on the sidewall. The sort of exception to this is that for the speed rating test, while S and T rated tires are tested at 35 psi, H rated tires are tested at 44 psi and V and higher rated tires are tested at 51 psi. Needless to say, tires with those speed rating HAVE to have max pressure of at least that value.

Note: The speed rating test is the only standard test where the inflation pressures are as indicated in the above paragraph. Standard load tests use 35 psi or 2.5 bar, whichever is appropriate.

……By the way, your load tables link is more a text book explaining load theory. I was expecting an actual table where I could look up my specific tire size - or that on my friend's Subaru - and glean some actual load data from it.

It just shows an example of a load table, which helps only those whose tires happen to be listed in that excerpt.

Unfortunately, those tables are copyrighted and can not be reproduced without permission - which I don't have. You will occasionally find portions of those load tables published by tire manufacturers on the web. But since there is a yearbook published every year with new sizes (and old sizes removed), you will not always find a particular size - although the information on a given size doesn't change from year to year.

Besides, the current TRA yearbook has 60 pages for the passenger tire section alone. For me to publish those would be a lot of work and I risk a copyright infringement lawsuit. Not to mention there are 3 major tire yearbooks in common usage with about the same number of pages - also covered by copyright law.

However, I did publish a few pages from the TRA yearbook for educational purposes (allowed under copyright law), and pages of old yearbooks for obsolete tire sizes - like size G78-15 or 7.35-15. Those old pages don't represent much of a legal risk as TRA would have to show monetary damage to their business and information about old tire sizes just doesn't sell.

Now allow me to return to an earlier conversation we were having:
…… So I found a Continental Extreme Contact in that exact size as indicated on the Subaru door sticker, BUT: That "Z" is NOT the speed rating! The speed rating, acc. to Continental's own page for that tire, is W! With a load index of 91(1,356lbs).

So I don't know WHY there is a Z in the middle of that tire size if it does not refer to the speed rating. …..

At one point in time, there were only 3 speed ratings and Z was the highest - above V - and the speed rating was to be imbedded in the size designation. But when W and Y speed ratings were added, the Z speed rating couldn't be changed, so technically Z speed ratings include W and Y, but are further restrictions - plus it is still permissible for tire manufacturers to place the speed rating in the size if they want to, but with the advent of service descriptions, there is no longer the need - EXCEPT, it seems that some tire manufacturers imbed the Z in the size for W and Y speed rated tires. I don't understand why.

RidingOnRailz
06-30-2019, 11:21 AM
See my 'Railz' responses, within:

No, I'll be accusing Tire Guides of making a mistake in their book. This wouldn't be the first time I found one.

I wonder what the placards actually say for the other versions. Put another way, it is unusual to specify more inflation pressure for the rear tires on a FWD, and if all the Contours had that pressure split, why did Tire Guides only indicate it for the one combination? I wonder if it was that way for the 1995 models and the 15" - which only came on the 1995 SE model - had that pressure split and Tire Guides just didn't pick up on the change made in later model years.

Railz: My 1996 GL had 205/60R15 tires on it. At this point I don't recall the speed rating, but I replaced them with H-rated, same size.



The tire standardizing organizations publish load tables - max load vs inflation pressures - in the form of a book published every year. While a tire manufacturer is not under any obligation to follow those, not only would it be foolish not to do so, there have only been a few cases where the tire manufacturer did something other than what was published - and eventually, those exceptions disappeared.

The US government accepts those standards and requires the tire manufacturers to imprint the max load and the max inflation pressure on the sidewall of each tire designated for street usage.

And here's where the confusion comes in: Officially, all Standard Load passenger type tires will have their load max out at 35 psi (or 2.5 bar (36.3 psi) if the standard is written in metric units), the tire standards allow 44 or 51 psi (3.0 bar and 3.5 bar) to be used as well - and the tire manufacturer deicides what to place on the sidewall. The sort of exception to this is that for the speed rating test, while S and T rated tires are tested at 35 psi, H rated tires are tested at 44 psi and V and higher rated tires are tested at 51 psi. Needless to say, tires with those speed rating HAVE to have max pressure of at least that value.

Note: The speed rating test is the only standard test where the inflation pressures are as indicated in the above paragraph. Standard load tests use 35 psi or 2.5 bar, whichever is appropriate.

Railz: So the max cold stamped on a tire(35, 44, 51psi) is based on that speed rating?


Unfortunately, those tables are copyrighted and can not be reproduced without permission - which I don't have. You will occasionally find portions of those load tables published by tire manufacturers on the web. But since there is a yearbook published every year with new sizes (and old sizes removed), you will not always find a particular size - although the information on a given size doesn't change from year to year.

Railz: Communists! :D

Besides, the current TRA yearbook has 60 pages for the passenger tire section alone. For me to publish those would be a lot of work and I risk a copyright infringement lawsuit. Not to mention there are 3 major tire yearbooks in common usage with about the same number of pages - also covered by copyright law.

However, I did publish a few pages from the TRA yearbook for educational purposes (allowed under copyright law), and pages of old yearbooks for obsolete tire sizes - like size G78-15 or 7.35-15. Those old pages don't represent much of a legal risk as TRA would have to show monetary damage to their business and information about old tire sizes just doesn't sell.

Now allow me to return to an earlier conversation we were having:


At one point in time, there were only 3 speed ratings and Z was the highest - above V - and the speed rating was to be imbedded in the size designation. But when W and Y speed ratings were added, the Z speed rating couldn't be changed, so technically Z speed ratings include W and Y, but are further restrictions - plus it is still permissible for tire manufacturers to place the speed rating in the size if they want to, but with the advent of service descriptions, there is no longer the need - EXCEPT, it seems that some tire manufacturers imbed the Z in the size for W and Y speed rated tires. I don't understand why.

Railz: I will have to look at the size section on her sidewall again for that load index and speed letter, IE: '89T', 91V' or which ever hers might be. BTW on my Contour, the replacement tires did have the H embedded inside the size, and they were in fact H-rated tires.


So Capri: Would you consider it just happy coincidence that the formula I shared here worked for mine and my wife's cars and tires, yielding as it did a perfect split just above and below the equal recommended tire pressure on our door placards? Because we both really like how our cars drive after setting them to the values I derived.

CapriRacer
07-01-2019, 08:23 AM
See my 'Railz' responses, within:

…… Railz: My 1996 GL had 205/60R15 tires on it. At this point I don't recall the speed rating, but I replaced them with H-rated, same size. …..

That would seem to confirm that it is the 15" option that has the pressure split


……… Railz: So the max cold stamped on a tire(35, 44, 51psi) is based on that speed rating? ……..

Oh, if it were just that simple. The tire manufacturer is the one who decides what max pressure is to be imprinted and he is constrained to use those 3 pressures, and by the speed rating. You will find S and T rated tires with a max pressure of 44 or 51 psi, even though the speed rating test is performed at 35 psi.

……… Railz: Communists! ……

No, this is the height of capitalism. Making money off of selling information.

……… Railz: I will have to look at the size section on her sidewall again for that load index and speed letter, IE: '89T', 91V' or which ever hers might be. BTW on my Contour, the replacement tires did have the H embedded inside the size, and they were in fact H-rated tires.


So Capri: Would you consider it just happy coincidence that the formula I shared here worked for mine and my wife's cars and tires, yielding as it did a perfect split just above and below the equal recommended tire pressure on our door placards? Because we both really like how our cars drive after setting them to the values I derived.

No, the formula you shared is tantalizingly close. It just uses some faulty assumptions. The result it provides will be within shouting distance of what it would get if it hadn't made those assumptions.

Then there is the issue of what people like in the way of vehicle handling. When I was calling on Ford, I talked to the ride engineers - the ones the specify the spring, shock, and sway bar settings. Their job was to ignore their own preferences and delivery a product that met the goals as determined by the management team. But one of the items NOT on the agenda was tire pressure. That had been predetermined based on a procedure the company had loads of experience with.

However, that result of tire pressure, spring rate, sway bar size, and shock damping didn't always appeal to every driver and it is common for folks to tune their car by using a tire pressure different than what is on the vehicle tire placard. The danger is not using enough tire pressure - which increases the risk of a structural tire failure - or using too much that wet traction is significantly reduced.

RidingOnRailz
07-01-2019, 10:22 PM
That would seem to confirm that it is the 15" option that has the pressure split




Oh, if it were just that simple. The tire manufacturer is the one who decides what max pressure is to be imprinted and he is constrained to use those 3 pressures, and by the speed rating. You will find S and T rated tires with a max pressure of 44 or 51 psi, even though the speed rating test is performed at 35 psi.



No, this is the height of capitalism. Making money off of selling information.



No, the formula you shared is tantalizingly close. It just uses some faulty assumptions. The result it provides will be within shouting distance of what it would get if it hadn't made those assumptions.

Then there is the issue of what people like in the way of vehicle handling. When I was calling on Ford, I talked to the ride engineers - the ones the specify the spring, shock, and sway bar settings. Their job was to ignore their own preferences and delivery a product that met the goals as determined by the management team. But one of the items NOT on the agenda was tire pressure. That had been predetermined based on a procedure the company had loads of experience with.

However, that result of tire pressure, spring rate, sway bar size, and shock damping didn't always appeal to every driver and it is common for folks to tune their car by using a tire pressure different than what is on the vehicle tire placard. The danger is not using enough tire pressure - which increases the risk of a structural tire failure - or using too much that wet traction is significantly reduced.


So, as far as my friend's 2005 Subaru Legacy GT is concerned:

I checked the size listed on the GY Eagles currently on the vehicle: 'P215/45R17', load & speed index: 87W.

87 load index = 1,201 lbs.

Now here's the kicker:
Her door placard lists original tire size: '215/45ZR17'.

So her current tires are not of the original Z speed rating, but are W. Probably saved whoever had them put on at least $50 per tire! This is a 15 year old car, so the exact size listed on that door placard is probably no longer available.

My smaller Hyundai's OEM T-rated(lower speed rating than W or Z!) tires have a higher load index - 91(1,356lbs) - on a smaller car! As well as my wife's: H-Rated 91's. That likely explains why the formula worked for both our rides, and why it didn't, initially, with my friend's Legacy GT. It's got the wrong tires on it! LOL

I've already run the formula under alll the scenarios, several posts above, so I'm not going to repeat here, but I do know that I got more reasonable results for that particular Subaru with the correct load & speed rated tires plugged into it.

RidingOnRailz
07-06-2019, 01:35 PM
That would seem to confirm that it is the 15" option that has the pressure split




Oh, if it were just that simple. The tire manufacturer is the one who decides what max pressure is to be imprinted and he is constrained to use those 3 pressures, and by the speed rating. You will find S and T rated tires with a max pressure of 44 or 51 psi, even though the speed rating test is performed at 35 psi.



No, this is the height of capitalism. Making money off of selling information.



No, the formula you shared is tantalizingly close. It just uses some faulty assumptions. The result it provides will be within shouting distance of what it would get if it hadn't made those assumptions.

Then there is the issue of what people like in the way of vehicle handling. When I was calling on Ford, I talked to the ride engineers - the ones the specify the spring, shock, and sway bar settings. Their job was to ignore their own preferences and delivery a product that met the goals as determined by the management team. But one of the items NOT on the agenda was tire pressure. That had been predetermined based on a procedure the company had loads of experience with.

However, that result of tire pressure, spring rate, sway bar size, and shock damping didn't always appeal to every driver and it is common for folks to tune their car by using a tire pressure different than what is on the vehicle tire placard. The danger is not using enough tire pressure - which increases the risk of a structural tire failure - or using too much that wet traction is significantly reduced.

ZZZZZZ....zzzzzz-snorrre..zzz- Whoa, WAIT - Oh!

Where am I, what day is.. Oh!, how was your Fourth? :D


We just had our off-Site storage guy come for a pick up with his 2019 Nissan NV150 van.

Tires: LT245/70R17E, Max load 3000lbs, 2,755lbs 'dual' - assuming that means four per axle? Max cold pressure on tire 80psi. These tires match the B-pillar placard, of course probably OEM since the thing is less than one year old.

Anywho, ran my trusty-rusty formula for this van in its four-tire config., and got the following:

B-Pillar sticker on the van recommends: F 50psi, R 80psi, cold.

My calculations: F 51psi, R 78psi.

Tantalizing! :D


Do you know what that means, Capri?...

RidingOnRailz
07-08-2019, 09:06 AM
ZZZZZZ....zzzzzz-snorrre..zzz- Whoa, WAIT - Oh!

Where am I, what day is.. Oh!, how was your Fourth? :D


We just had our off-Site storage guy come for a pick up with his 2019 Nissan NV150 van.

Tires: LT245/70R17E, Max load 3000lbs, 2,755lbs 'dual' - assuming that means four per axle? Max cold pressure on tire 80psi. These tires match the B-pillar placard, of course probably OEM since the thing is less than one year old.

Anywho, ran my trusty-rusty formula for this van in its four-tire config., and got the following:

B-Pillar sticker on the van recommends: F 50psi, R 80psi, cold.

My calculations: F 51psi, R 78psi.

Tantalizing! :D


Do you know what that means, Capri?...


It means that that 2005 Subaru is one WEIRD car, that's what it means, lol!

Even with specs for the correct OEM tires, my formula still returns relatively high recommendations for that Legacy GT - low 40s-psi vs low 30s on the B-pillar sticker.

It's the only car I've used the formula for that has returned such 'out-there' results.

I suspect it has something to do with the factory low-profile tires. Vehicles with wider, lower-profile tires on larger rims more often than not are speced with higher recommended cold pressures than vehicles with skinny high-profiles.

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