What air pressure for new tires

[BillyHW]

You have the size, load range, as well as the air pressure range molded right into the sidewall of every tire manufactured. Including the tires that are shipped on the car when you buy it.

What more do you need to know? That being the case, who cares what the sticker say's?

The "more you need to know" is the weight of your car on each axle, technically. The tire doesn't know how much your car weighs.

 

[OVERKILL]

Been running that way for over 50 years, on both bias ply and radial tires. In weather from -20F to over 120F, and never had a blowout or a problem. And have gotten good tire and fuel mileage from doing so.

Far more tires suffer from under inflation than over inflation. And it's one of the main causes for premature tire wear and blowouts.

Just because somebody has been doing something a certain way for a long time doesn't make it right. The placard pressure is arrived at based on testing performed by the OEM as to what they've deemed optimal for the vehicle and its intended operating profile. The sidewall pressure is just the maximum pressure that carcass is rated for and doesn't, in any way, take how the tire is planned to be used, or what it is fitted to, into account.

 

[BillyHW]

Not always.

I have seen same size, same load rating, same speed rating tires, installed on a car, with factory door jamb pressures, and the car is unsafe to drive. Unstable. Not safe. Sways all over the road.

Running door jamb pressure on this car, with this set of tires, and you'll be in an accident within weeks. So not safe. Seen it a few times.

If you haven't experienced or seen it yourself, I guess you would just believe the text books. But life teaches lessons, learned with actual experience.

I stand by my comment.

The door jamb ONLY applies to the tires that were on the car at retail delivery. If you change the tires after that, the door jamb is a guide.

Were you going from Goodyear tires to Goodride tires?

 

[OVERKILL]

It's not as prevalent today as it used to be. But just going by max pressure on the sidewall, (if that's all that's listed, and backing off 5 or even 10 PSI), is better than going by the door sticker. Simply because it's common for people change not only size, but load range as well. Especially on trucks.

My truck was delivered with P235 X 15 tires. They weren't even LT rated. I replaced them with 31 X 10.5 X 15's. The door sticker showed an inflation range from 28 to 32 PSI for the P235's. The 31's I had installed had a max inflation pressure of 55 PSI. (The tire dealer pumped 45 PSI into them).

I always go by what the tire states, (or slightly less), not the door jam sticker, because many times it's no longer applicable. And could even be dangerous if minimum door jam pressure was in the tire under maximum load with a larger and higher load range tire.

Half ton trucks rarely come fitted with LT tires because the additional load carrying capacity isn't necessary for the payload and GVWR and LT tires increase the required tire pressure to hit the same load carrying capacity, negatively impacting ride quality. This is why large SUV's also come with P-Metric tires instead of LT's.

Of course when you change the tire type from P-Metric to LT, you have to use the load tables to determine what the correct pressure is to match the original load carrying capacity because you've now invalidated the testing performed by the OEM that resulted in the pressure indicated on the placard.

This is from the Toyo guide, which can be found here: https://www.toyotires.com/media/3729/application_of_load_inflation_tables_20200723.pdf

EDIT to add: Toyo also indicates that the individual that performs the above fitment apply a new sticker with the size and new pressure to the placard location so that anybody dealing with the tires in the future is aware of the change. I suspect this is rarely done in application however, which is unfortunate.

 

[kschachn]

Not always.

I have seen same size, same load rating, same speed rating tires, installed on a car, with factory door jamb pressures, and the car is unsafe to drive. Unstable. Not safe. Sways all over the road.

Running door jamb pressure on this car, with this set of tires, and you'll be in an accident within weeks. So not safe. Seen it a few times.

If you haven't experienced or seen it yourself, I guess you would just believe the text books. But life teaches lessons, learned with actual experience.

I stand by my comment.

The door jamb ONLY applies to the tires that were on the car at retail delivery. If you change the tires after that, the door jamb is a guide.

Give it up, football.

 

[OVERKILL]

Not always.

I have seen same size, same load rating, same speed rating tires, installed on a car, with factory door jamb pressures, and the car is unsafe to drive. Unstable. Not safe. Sways all over the road.

Running door jamb pressure on this car, with this set of tires, and you'll be in an accident within weeks. So not safe. Seen it a few times.

If you haven't experienced or seen it yourself, I guess you would just believe the text books. But life teaches lessons, learned with actual experience.

I stand by my comment.

The door jamb ONLY applies to the tires that were on the car at retail delivery. If you change the tires after that, the door jamb is a guide.

No, it doesn't. Your anecdote is not only invalidated by @CapriRacer's comments, who is a tire engineer, but also by the various OEM's. This statement from Toyo for example:

 

[billt460]

Toyo also indicates that the individual that performs the above fitment apply a new sticker with the size and new pressure to the placard location so that anybody dealing with the tires in the future is aware of the change. I suspect this is rarely done in application however, which is unfortunate.

I'm surprised that tire dealers don't automatically do this when they install a set of new tires on every car. Much like they do an oil change sticker at "Quick Lube", or wherever.

It would take any questions about tire pressure out of play. As well as give the new owner knowledge of when, (date and mileage), as well as where they were installed.

 

[OVERKILL]

I'm surprised that tire dealers don't automatically do this when they install a set of new tires on every car. Much like they do an oil change sticker at "Quick Lube", or wherever.

It would take any questions about tire pressure out of play. As well as give the new owner knowledge of when, (date and mileage), as well as where they were installed.

Unfortunately, as demonstrated even on this forum, a lot of people, including techs, don't understand how this process works. But yes, IF this process was properly followed, and everybody knew to go to the placard for accurate information, this would eliminate a lot of the posturing, guessing, and downright wrong information about this subject in circulation and in practice.

 

[OilMagnate]

So since clearly my training having worked in the business is in the minority opinion, let's hear exactly why from those who differ.

Here's an example case to be argued:
My mother drives a 2010 Honda CR-V. Door placard recommends 30psi.

OEM Tires: Bridgestone Duelers - P225/65R17 102T

Newest installed set: Pirelli Scorpion All Terrain Plus - P225/65R17 102H

OEM set was okay at 30psi. These Pirellis are underinflated at 30psi and show a clear flat indention on the ground instead of being appropriately round. Yes, they have different speed ratings, but we're talking about pressure and it's therefore irrelevant. Both have the same load index at 102. So if the door placard is correct, why the noticeably visually low tires?

 

[OVERKILL]

So since clearly my training having worked in the business is in the minority opinion, let's hear exactly why from those who differ.

Here's an example case to be argued:
My mother drives a 2010 Honda CR-V. Door placard recommends 30psi.

OEM Tires: Bridgestone Duelers - P225/65R17 102T

Newest installed set: Pirelli Scorpion All Terrain Plus - P225/65R17 102H

OEM set was okay at 30psi. These Pirellis are underinflated at 30psi and show a clear flat indention on the ground instead of being appropriately round. Yes, they have different speed ratings, but we're talking about pressure and it's therefore irrelevant. Both have the same load index at 102. So if the door placard is correct, why the noticeably visually low tires?

You need to describe why you feel they are underinflated, are you observing significant wear on the shoulders and not the centre or are you just basing this on the radial sidewall bulge, which will vary significantly depending on carcass construction and sidewall stiffness. @CapriRacer is the expert on the subject, and I generally defer to his expertise.

 

[krzyss]

So since clearly my training having worked in the business is in the minority opinion, let's hear exactly why from those who differ.

Here's an example case to be argued:
My mother drives a 2010 Honda CR-V. Door placard recommends 30psi.

OEM Tires: Bridgestone Duelers - P225/65R17 102T

Newest installed set: Pirelli Scorpion All Terrain Plus - P225/65R17 102H

OEM set was okay at 30psi. These Pirellis are underinflated at 30psi and show a clear flat indention on the ground instead of being appropriately round. Yes, they have different speed ratings, but we're talking about pressure and it's therefore irrelevant. Both have the same load index at 102. So if the door placard is correct, why the noticeably visually low tires?

If they wear properly at 30PSI and just look underinflated, you need better glasses or just ignore the look.
Could it be that AT tire has softer sidewall for better off road capabilities?

Krzys

 

[billt460]

....... OEM set was okay at 30psi. These Pirellis are underinflated at 30psi and show a clear flat indention on the ground instead of being appropriately round. Yes, they have different speed ratings, but we're talking about pressure and it's therefore irrelevant. Both have the same load index at 102. So if the door placard is correct, why the noticeably visually low tires?

Pump them up to 40 PSI and drive them for a while. (That's most likely still well under the max pressure on the sidewall). They'll look better, most likely ride and drive better, and you can happily motor on.

 

[jadatis]

So since clearly my training having worked in the business is in the minority opinion, let's hear exactly why from those who differ.

Here's an example case to be argued:
My mother drives a 2010 Honda CR-V. Door placard recommends 30psi.

OEM Tires: Bridgestone Duelers - P225/65R17 102T

Newest installed set: Pirelli Scorpion All Terrain Plus - P225/65R17 102H

OEM set was okay at 30psi. These Pirellis are underinflated at 30psi and show a clear flat indention on the ground instead of being appropriately round. Yes, they have different speed ratings, but we're talking about pressure and it's therefore irrelevant. Both have the same load index at 102. So if the door placard is correct, why the noticeably visually low tires?

Mayby the pirelli's are less rigid tires, and for that reason have more surfacelength on the ground at the same deflection .
And the deflection counts for heatproduction, so determining maxload of tire.
You could simply measure the deflection to check if the same for both tires , if the same ( with same weight on them, and pressure), its OK.
Then they only look flatter.
Same is with energysaving tires.
My brother had them and also noticed that they looked flatter.
Can see an advantage for AT, if they are less rigid, so they deform better over rocks.

 

[OilMagnate]

You need to describe why you feel they are underinflated, are you observing significant wear on the shoulders and not the centre or are you just basing this on the radial sidewall bulge, which will vary significantly depending on carcass construction and sidewall stiffness. @CapriRacer is the expert on the subject, and I generally defer to his expertise.

They are clearly visually underinflated. I changed tires for a living for a major chain for 5 years. I know what underinflated looks like. Bulge is different from a large flat spot where the tire contacts the pavement. Bulge is fine to a point, until it's not. Not trying to be argumentative, I just know if I leave these tires at 30 there will be massive wear on the edges of the tread.

 

[OilMagnate]

If they wear properly at 30PSI and just look underinflated, you need better glasses or just ignore the look.
Could it be that AT tire has softer sidewall for better off road capabilities?

Krzys

That's a backwards mentality. Why would I send her on her way with underinflated tires to see if there is tire wear? They would prematurely wear or blow out prior to seeing enough evidence. Not a gamble I'm willing to take with my own mother.

Nobody has ever been harmed by a small amount of what you would call 'overinflation,' as long as it is under the individual tire's maximum pressure. But don't get it twisted, I'm against airing them up to the max also. This has a negative effect in rain/snow.

 

[OilMagnate]

Pump them up to 40 PSI and drive them for a while. (That's most likely still well under the max pressure on the sidewall). They'll look better, most likely ride and drive better, and you can happily motor on.

I have them at about 38 and they appear to be wearing perfectly. Maximum pressure is 51. I'm perfectly happy with how they look and feel. They aren't overly flat on the pavement and aren't bulging excessively like they were at 30.

 

[OilMagnate]

Mayby the pirelli's are less rigid tires, and for that reason have more surfacelength on the ground at the same deflection .
And the deflection counts for heatproduction, so determining maxload of tire.
You could simply measure the deflection to check if the same for both tires , if the same ( with same weight on them, and pressure), its OK.
Then they only look flatter.
Same is with energysaving tires.
My brother had them and also noticed that they looked flatter.
Can see an advantage for AT, if they are less rigid, so they deform better over rocks.

She sees nothing but pavement and basic gravel. The less contact patch/rolling resistance, the better. I'm not saying air them up to the max, I'm just not a fan of a tire that has to overly deform itself at 70+mph to contact the pavement. It should be round, with an appropriately-sized (small), flat contact patch. It shouldn't act as a tank tread.

 

[billt460]

I have them at about 38 and they appear to be wearing perfectly. Maximum pressure is 51. I'm perfectly happy with how they look and feel. They aren't overly flat on the pavement and aren't bulging excessively like they were at 30.

Perfect. Problem solved. I've found in over 50 years of driving in most all conditions, with both older bias ply, and newer radial tires, you're better off with a little more pressure, than you are with less. Besides, I've never heard of air leaking into a tire.

 

[CapriRacer]

So since clearly my training having worked in the business is in the minority opinion, let's hear exactly why from those who differ.

Here's an example case to be argued:
My mother drives a 2010 Honda CR-V. Door placard recommends 30psi.

OEM Tires: Bridgestone Duelers - P225/65R17 102T

Newest installed set: Pirelli Scorpion All Terrain Plus - P225/65R17 102H

OEM set was okay at 30psi. These Pirellis are underinflated at 30psi and show a clear flat indention on the ground instead of being appropriately round. Yes, they have different speed ratings, but we're talking about pressure and it's therefore irrelevant. Both have the same load index at 102. So if the door placard is correct, why the noticeably visually low tires?

First, the steel belts in a tire can be manipulated to affect the wear pattern. There is a wedge of rubber under the edge of the steel belts and you can make the belt concave or convex depending on how large those wedges are. Needless to say that tire designers try to get a good wear pattern at the loads and inflation pressures specified by the vehicle manufacturers.

HOWEVER, sometimes there is a different goal and the result is a tire that doesn't wear well. For example, if the goal is better rolling resistance, the tire can be made such that the amount of rubber on the edges of the tread is reduced, and the wear pattern resembles an underinflated tire. It's also possible for a mistake to be made in manufacturing that results in a less than optimal wear pattern. Don't ask how I know.

And in this case, the H speed rated tire will likely have a cap ply and that affects the wear pattern, so the belts have to be adjusted to compensate - and sometimes, they aren't.

Plus, there is a way to get a good wear pattern for a wide range of loads and inflation pressures. (I don't know what it is, but I have seen the results.) That's why "The Chalk Test" doesn't work.

And to complete the picture: Inflation pressure isn't the largest effect when it comes to even wear. Steer tires tend to wear in the shoulders and drive tires tend to wear in the center - and this effect is larger than inflation pressure. Even a FWD car where both those functions are on the same axle, if one drives a lot in the city, where there are a lot of turns, the shoulder wear effect will come out.

The primary design goal for a tire is the load table. This is a MUST as it is part of a government regulation. The wear pattern comes after that and isn't covered by a regulation - and sometimes things don't go the way they should.

The pressure listed on the vehicle placard is also derived from the load tables. So there's a direct connection between the placard and the tire's durability. The wear pattern isn't so well connected and you can get odd wear patterns, even at the proper inflation pressure.

Side note: I know that there's lots of illustrations showing that underinflation generates a certain wear pattern, but it is a gross generalization. It's done to encourage people to check their tire pressures and needs to be understood in that context. Things are NOT as black and white as that is portrayed.

 

[OilMagnate]

HOWEVER, sometimes there is a different goal and the result is a tire that doesn't wear well.

It's also possible for a mistake to be made in manufacturing that results in a less than optimal wear pattern. Don't ask how I know.

And in this case, the H speed rated tire will likely have a cap ply and that affects the wear pattern, so the belts have to be adjusted to compensate - and sometimes, they aren't.

The primary design goal for a tire is the load table. This is a MUST as it is part of a government regulation. The wear pattern comes after that and isn't covered by a regulation - and sometimes things don't go the way they should.

The pressure listed on the vehicle placard is also derived from the load tables. So there's a direct connection between the placard and the tire's durability. The wear pattern isn't so well connected and you can get odd wear patterns, even at the proper inflation pressure.

You clearly are more knowledgeable about tire construction than I am, but I can't help but point out that all of the above sound to me like there isn't a one-size-fits-all with tires. This is the point I was trying to prove. Every tire is unique, and every driving habit is unique. Therefore a one-size-fits-all door placard is not to be automatically trusted in absolute.