Recommended psi verses Max psi.


mchapman
05-15-2003, 09:40 AM
I read the forums fixed post, "Tire tech" by Luke@tirerack. It was good reading, however, it did not quite answer a question that I have had for 20 years regarding max tire pressure.

Regarding tire inflation technique, the forum post stated, '....recommended tire pressure...cold...'. The problem is that the tires all say, "max tire pressure", instead of 'recommended'. Here's my question. If a tire says 'max 35 psi' and it is 70 degrees cold, parked overnight, etc, and by late afternoon it will be 90 degrees, then; should I fill the tire to 33 psi, so that I do not exceed the max psi later on when the tire heats up?

I have always underinflated my tires by 3 psi from the 'max psi' printed on the tire, in a calculated effort to not exceed the 'max psi' as the tire heats up.

Venger10
05-15-2003, 01:02 PM
MAX cold psi means exactly that..that is the most you should inflate the tire to when COLD , it takes into account what tire pressure will be when it warms up;)
For example , The tires on my WRX said "max cold psi 44" which I did. Next day it was 70+ degrees and when I checked them they were about 55 psi......:bloated:
As long as you don't exceed the max cold psi rating , the tire should be fine.....

A few years ago I worked at a gas station ..... had a guy come in one day , complaining that his car was riding VERY hard..... said he'd put air in his tires a few weeks before , but since he did not have an air guage , he had to guess by how "hard" the tire felt....
When I check his tires , a couple of them were over 100 psi:eek: :eek: And this was on a Honda....:smoker2: :smoker2:

Cy@tirerack
05-15-2003, 02:14 PM
Ditto

Also figure about 1 psi change for every 10 deg change in temp. Cold pressure is generally based on an ambient temperature of 60 deg Fahrenheit.

So if car has been sitting out in the sun with an ambient temperature of 80 deg Fahrenheit, then when you check and adjust pressure you want to compensate by setting at 2 deg below your intended pressure. So if you want to run 30, inflate to 32.

mchapman
05-16-2003, 02:11 AM
Thanks, those two answers were just what I was looking for. Thank you both ever so much.

marzo7
05-20-2003, 11:29 AM
You guys are the experts, so I'm a little hesitant to disagree, but.....it seems strange to me that the maximum pressure stated on the sidewall would be for a "cold" pressure. If that was the case, then it would not really be a "maximum" at all, just another "recommendation".

Presumably a tire manufacturer has done some testing to determine what is the maximum safe pressure that a tire can sustain. By definition, this would be a "hot" pressure. Why then would the manufacturer fool around with listing a supposed maximum cold pressure on the sidewall, making the consumer guess as to how much air the tires were designed to sustain safely?

A maximum of 44 psi hot would be just that, the maximum, no if's and's or but's. A "maximum" of 44 psi cold is totally meaningless. Why would the manufacturer even bother to list such a thing?

marzo7
05-20-2003, 12:58 PM
OK, I did a bit of research, and of course you guys are right. I still think it doesn't make much sense, but at least now I know why: it's government regulations that mandate the rating!

FWIW, every tire I've owned has simply stated "Max. load of xx at max. pressure of xx." IMO, all manufacturers should do like that of Venger10's tires and explicitly state that the max. pressure is "cold".

Venger10
05-20-2003, 04:38 PM
They do.......:D

Its further around the edge of the tire and it should be in () << like so.....

(Max cold pressure 44 Psi)


Every tire I've seen had that on the side......:confused: :confused: :alien2:

marzo7
05-20-2003, 05:00 PM
Hmm... I just double-double-checked both sets of tires in my garage (Kumho Ecsta 712 and Toyo Proxes RA1). Nope, neither make any mention of whether the max. pressure is cold or hot (unless they've molded it into the tread in braille ;)).

I'll check our BF Goodrich Long Trails when my wife gets home, but like I said, I've never seen it before...

Venger10
05-20-2003, 07:55 PM
How weird......:bloated: I've never seen a tire without them.
My Potenza's had it , my Eagle GS-Z's had it , my Kumho's had it , I just looked outside and my Signet DH-60's have it .
Sure you are looking in the right place?? its VERY close to the edge of the rim.

Also , I'm thinking perhaps that maybe only H and up rated tires may have it on there....:cool:

Inflation pressure is more crucial on a performance tire than on a regular Passenger car tire:rolleyes: :smoka:

marzo7
05-21-2003, 01:21 AM
Well, I just checked the Long Trails, and nope, no mention of the word "cold".

All three tires I've listed say the same thing: "Max load of xxxx lbs at max pressure of xx psi". Absolutely no mention of the word "cold".

I don't think speed rating has anything to do with it: my Kumhos are V-rated and the Toyos are Z-rated.

The only thing I can think of is that manufacturers make a different production run for Canada (which is where I am). Seems unlikely, but maybe that's it. Now that I think about it, my tires also state the maximum load in kilograms and the maximum pressure in kilopascals. Is that the case in the U.S. also?

Venger10
05-21-2003, 09:45 PM
Yes , they do state Kpa and max load in kilo's.......

Maybe they don't think inclusion of the word COLD is quite as important in Canada....:rolleyes: :alien2: :alien2:

CapriRacer
05-21-2003, 10:00 PM
Perhaps I can help explain.

Tires are standardized. In the US the standards organization is the Tire and Rim Association (TRA). In Europe, it's the European Tire and Rim Technical Organization (ETRTO). There are others.

It is these bodies that set the nominal dimensions AND the loading standards, which includes the maximum psi. It is a US government regulation that the maximum load and the maximum pressure be stamped on the sidewall and it is must conform to one of these standards.

In all cases, these pressures are specified as cold. It is the tire manufacturer's responsibility to account for the pressure build up in their design. Doesn't matter how much it is, but it must be factored in.

For practical matters, the static bursting pressure of passenger car tires is well over 100 psi. So 44 psi, which is what is now standard max pressure on most passenger car tires, is well within design capabilities.

Hope this helps.

marzo7
05-28-2003, 05:20 PM
Thanks CapriRacer...

Not to beat this to death, but I just had a look at the two sets of winter tires buried in the corner of my garage:

Bridgestone Blizzak LM-22 - no mention of the word "cold"

Yokohama Geolandar I/T - well whaddaya know, yep they specify that the maximum pressure is 50 psi COLD.

For me, that's only one out of five that specifically indicates "cold". I wonder why there isn't more consistency in the labelling?

Venger10
05-28-2003, 09:34 PM
Originally posted by marzo7
Thanks CapriRacer...

Not to beat this to death, but I just had a look at the two sets of winter tires buried in the corner of my garage:

Bridgestone Blizzak LM-22 - no mention of the word "cold"

Yokohama Geolandar I/T - well whaddaya know, yep they specify that the maximum pressure is 50 psi COLD.

For me, that's only one out of five that specifically indicates "cold". I wonder why there isn't more consistency in the labelling?

Its a government thing......:rolleyes:

captain_tinker
08-15-2003, 03:39 PM
Venger10, you said earlier in this post that you had Signet DH-60's? I just bought a 2000 Grand Am SE1, I am trying to find some information on my tires that came on it. It says Signet, then Dark Horse on it. I have looked all over on Google.com trying to find anything about tires and Signet, and Dark Horse and I keep getting nothing. Is Signet the actual brand name then? Or are they made by another company like Pirelli, or something? I did find a Korean website, http://www.nexentire.co.kr/business-E/catalog_radial.htm that showed some tires, and had Dark Horse next to them, but I am not sure if these are the same ones... I am not home right now, and did not drive that car here, so I can't go and check to see anything more about it right now.
Mainly, I am just trying to get some information on them to see if they are good tires. They really look nice...

-captain_tinker

ginostats
02-03-2015, 07:26 AM
The MAx PSI is listed as "Cold" Because : here is an example…you are driving at 55mph on an 80 degree day, the temp of your tires would be in the 130 degree range…you stop and check your tires and find that your one tire is riding at 30 psi when the max cold is 44….so you fill the tire up to 44..with air that is probably not super cold because it is in fact an 80 degree day….Cold tires are usually "cold" at about 50 degrees..and 44 max psi at 50 degrees is the max you should use…if you drive an heat up your tires that are at 44…after a while you will see the gauge up to as high as 60psi or so, But as someone else posted above, about an increase of one psi per ten degrees..it is actually about one percent per ten degrees…so tires at 44 at 500 degrees should babout 50psi at 100 degrees, however, the shape and thickness of tires definitely comes into play in this area, a high performance tire heats up more than a large tread "wrangler" type tire…so in a jeep you may see the psi go to 48-50- where the same psi in a corvette under the same conditions will go as high as 65-70….see next post…

ginostats
02-03-2015, 07:36 AM
I made a mistake or two above and am new to this and do not know how to edit LOl..But the point is..If Someone fills to the "Cold" max the new air going in is cold and can only expand so much, at 44 psi as an example, that cold air is the safe limit, that will not cause a heated tire to over expand and potentially blow out..and even though those numbers come with a safety buffer by the manufacturer( you could easily go to 50psi safely) it is best to adhere to the max number or slightly below..HOWEVER the Number on your Car Door for "manuafatuers Suggested PSI" is the lowest you should even keep your tires inflated…This Number is in direct contrast too the Tire Number..the carmaker number is about smooth ride and comfort, and does not care about tire care and fuel milage…While the Tire Makers, does not care about comfort and leans toward tire wear and safety and file mileage…Here is the BEST BET..Lean Towards the TIREMAKERS NUMBER…if the door says 33 and the tire says 44….go to a middle number and add 2 pSi so the mid number of 33-44 would be 38.5 add two and you got 40.5… level it off to 40 and you have the best possible combination, of Ride, Handling, Tire wear, tire Safety, and Fuel Mileage !

shorod
02-03-2015, 06:28 PM
Although the "max pressure" listing on the tire sidewall is irrelevant as long as the tire is the correct size and load rating as the vehicle calls out. The tire inflation should always be per the vehicle door sticker, not the max pressure listed on the tire sidewall.

-Rod

CapriRacer
02-04-2015, 06:07 AM
I hope everyone realizes this is an 11 year old post that has been revived.

But I do want to correct one thing that was said.


......... HOWEVER the Number on your Car Door for "manuafatuers Suggested PSI" is the lowest you should even keep your tires inflated…This Number is in direct contrast too the Tire Number..the carmaker number is about smooth ride and comfort, and does not care about tire care and fuel milage…While the Tire Makers, does not care about comfort and leans toward tire wear and safety and file mileage…...

The max pressure listed on the sidewall of the tire is just that - a maximum. It does not take into account anything about the vehicle. It is like saying you have a pickup truck that can haul 3,000 lbs. That only means that is the maximum allowable, not a recommendation for everyday usage.

Further, the number the car manufacturer put on the vehicle tire placard, may or may not be be strictly for comfort. It depends on what the vehicle was designed to do. Sometimes these pressures are biased towards handling - sometimes not. In the case of pickup truck, the inflation pressure is set to carry the load in the bed and ride and handling come secondary.

And lastly, the combination of tire size and inflation pressure determine the load carrying capacity. Some vehicle manufacturers will specify a large tire to get a low pressure (so they get a soft ride). If you put the max pressure in the tire, you could wind up with half the size of the footprint - and that causes traction problems.

RidingOnRailz
02-23-2019, 10:22 AM
Earlier this month, I posted a poll about where people get their tire pressure info from, before realizing that this Tire and Wheel subforum existed. It got very few responses, but the majority of those that did vote said they went by the vehical load decal.

I'm sure none of those respondants were mechanics, as most mechanics and service techs I have used lately inflate at or just below the Max. Cold number on the tire itself!

This concerns me, since many mechs. I know do have ASE on their work shirts, and should know which numbers to inflate to. I would expect this from the public, since the vast majority of the public still don't know where the correct recommended cold tire pressures are posted for their specific vehicles.

I'm sure my poll would have gotten more votes here, so I will ask here:

What source do you refer to when inflating/adjusting your every day vehicle cold tire pressures?

CapriRacer
02-24-2019, 08:16 AM
Like you, I am puzzled over why mechanics don't know about the vehicle tire placard - except to say, they probably got their information from their fellow workers, and that's not always a reliable place to get correct info.

Having been a tire engineer for over 40 years, I know where both sets of numbers come from and I know that what is printed on the sidewall is relatively arbitrary. See my webpage on the subject of load tables :

http://www.barrystiretech.com/loadtables.html

About 1/3 of the way down, I talk about "The Notes on page 1-34" and that is where the sidewall number comes from.

RidingOnRailz
02-24-2019, 10:25 AM
Like you, I am puzzled over why mechanics don't know about the vehicle tire placard - except to say, they probably got their information from their fellow workers, and that's not always a reliable place to get correct info.

Having been a tire engineer for over 40 years, I know where both sets of numbers come from and I know that what is printed on the sidewall is relatively arbitrary. See my webpage on the subject of load tables :

http://www.barrystiretech.com/loadtables.html

About 1/3 of the way down, I talk about "The Notes on page 1-34" and that is where the sidewall number comes from.


Well, the owner at the place that recently did my brakes responded to my question about the importance of the load decal with "The pressures on that sticker are a joke" "I always set tire pressure to a pound or two under what's on the tire - The handling is way better"

So these mechanics - and many customers - do know where the correct cold pressures specific to a vehicle can be found. They just choose to do things their way instead of the right way, or at least by what is recommended. And it probably extends to other things in their lives beyond the air pressure in their tires.

Stealthee
02-24-2019, 10:43 AM
That owner is a moron. There is no way it handles better with more pressure. It goes against the laws of vehicular physics.

I got into an argument with a guy at work about this exact same issue a few weeks back. He tried to say you always run max psi and I told him he was an idiot. He tried to tell me me knew better than I did because he used to sell tires.

Just because one sells/installs tires doesn't mean they know anything about tires.

RidingOnRailz
02-24-2019, 10:48 AM
Like you, I am puzzled over why mechanics don't know about the vehicle tire placard - except to say, they probably got their information from their fellow workers, and that's not always a reliable place to get correct info.

Having been a tire engineer for over 40 years, I know where both sets of numbers come from and I know that what is printed on the sidewall is relatively arbitrary. See my webpage on the subject of load tables :

http://www.barrystiretech.com/loadtables.html

About 1/3 of the way down, I talk about "The Notes on page 1-34" and that is where the sidewall number comes from.


Where are the complete load tables? My size is not listed there: 195/65R15

RidingOnRailz
02-24-2019, 10:50 AM
That owner is a moron. There is no way it handles better with more pressure. It goes against the laws of vehicular physics.

I got into an argument with a guy at work about this exact same issue a few weeks back. He tried to say you always run max psi and I told him he was an idiot. He tried to tell me me knew better than I did because he used to sell tires.

Just because one sells/installs tires doesn't mean they know anything about tires.

I think your conversation with that person became an argument after the name-calling began. If on the other hand he first called you a name, then I would have responded with "This conversation is OVER if it degrades to name-calling", and then walked away.

I can't believe this tire pressure thing is taken more personally, by some, than politics and elections! Sheez..

CapriRacer
02-25-2019, 08:52 AM
...…. There is no way it handles better with more pressure. It goes against the laws of vehicular physics. ……

Not exactly. Using a higher inflation pressure makes the tire respond quicker to steering input. If that's what is being used as the definition of "Handling", then the statement is correct.

Where are the complete load tables? My size is not listed there: 195/65R15

The tables are published in a yearbook issued by the various tire standardizing organizations. They are copyrighted and can't be reproduced without permission.

However, you can find abbreviated versions if you search on the term "Tire Load Tables". Just be aware that each standardizing organization uses a SLIGHTLY different formula, so the values will be SLIGHTLY different - close, but different. I've found one for passenger car tires from Toyo, and I am sure there are others.

…..I can't believe this tire pressure thing is taken more personally, by some, than politics and elections! Sheez..

Been in the business over 40 years and it's always been like that.

RidingOnRailz
02-25-2019, 03:05 PM
Not exactly. Using a higher inflation pressure makes the tire respond quicker to steering input. If that's what is being used as the definition of "Handling", then the statement is correct.



The tables are published in a yearbook issued by the various tire standardizing organizations. They are copyrighted and can't be reproduced without permission.

However, you can find abbreviated versions if you search on the term "Tire Load Tables". Just be aware that each standardizing organization uses a SLIGHTLY different formula, so the values will be SLIGHTLY different - close, but different. I've found one for passenger car tires from Toyo, and I am sure there are others.



Been in the business over 40 years and it's always been like that.
Well, it's science and engineering, nothing personal. People shouldn't get so worked up over it or think they know better than those that designed and built the vehicle.

RidingOnRailz
02-26-2019, 08:46 AM
My 2015 base Elantra sedan, OEM T-rated 195/65R15, calls for Fr/Rr 33psi cold. For the 2011-13 of that same trim level, Fr/Rr 32psi is specified.

At 33psi cold to all four corners, my Elantra accelerates fine, gets mid-20s to mid-30s MPG gas mileage according to the gauge cluster, but handles/rides nervously and a little rough over gravelly, bumpy roads. I experienced this both with the Kumho stock tires that came on the car, and with the True-Contacts I had installed two winters ago and am still riding on.

Cutting the rear tires back to 2011 pressures(32psi cold), tames some of that rear hop and there is no hit on that indicated gas mileage.

Cut to 2011 pressures all around, and this 2015 Elantra feels like a CAR again: nicely weighted steering even in Normal steering mode - and that rear end minds its business. I still use Sport mode on highways, for maximum steering weight. Avg. mileage does suffer a bit though at those pressures, with city falling to low 20s, and highways around 30mpg.


In retrospect: This Elantra, with 32 all around psi, out-handles the 2013 Sonata LTD I traded for it. That Sonata, with its wider 55-series 17s set even at 33psi, and history of 'self steering' issues - particularly on first through third model years of that body style - steered lighter in the dealer-set Sport mode than my Elantra set for COMFORT! It was a white-knuckle experience on highways, esp. after dark, and after dark plus raining. I just could not feel where the car was in its lane!

Not to mention on my specific Sonata the Caster angle was equally half a degree below the minimum range for some reason(previous driver mounted a curb at 30mph by mistake??). That was not adjustable unfortunately. I do miss the moonroof though: turns any car cabin into a cathedral! :D

Verdict: If acceleration and one-finger Tom Cruise-maneuverabilty matter most to you, go with wider lower profile tires. But for myself, and many others, higher narrower profile tires at modest pressures keep things tight on the straight and narrow. And we don't mind using actual muscle to turn the steering wheel. ;D

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