Is maximum tire pressure (sidewall) any indicator

[PandaBear]

for quality?

I am just splitting hair, trying to see between 2 tires which one is "better" after all else is compared.

What determines the maximum sidewall pressure?

 

[Quattro Pete]

I thought max tire pressure was a direct result of the tire's size/load/speed rating. So, if you have two tires in exact same size/load/speed rating, they should have the exact same max tire pressure. Are you finding it not to be the case?

 

[PandaBear]

Originally Posted By: Quattro Pete
I thought max tire pressure was a direct result of the tire's size/load/speed rating. So, if you have two tires in exact same size/load/speed rating, they should have the exact same max tire pressure. Are you finding it not to be the case?


I didn't really pay attention to the max load rating because i was looking for a small tire (195 60 14), just notice some tires have 44 and some have 51 psi max. So if the load rating is the reason of higher psi, does load rating make a big difference in passenger tires for a small car?

 

[Corvette Owner]

Indirectly it is. As stated by Quattro Pete, higher speed rated tires generally have higher pressure limits. Also, a higher speed rated tire could be considered to be a higher "quality tire", in that it usually handles better and is definitely safer at higher speeds.

Having said all that, you really don't need a higher speed rated tire than your car's OEM specifications call for. Most tires are S or T speed rated. High performance tires are usually H or V rated. Super high performance tires are W, Y, or Z rated.

L 75 mph 120 km/h Off-Road & Light Truck Tires
M 81 mph 130 km/h
N 87 mph 140km/h Temporary Spare Tires
P 93 mph 150 km/h
Q 99 mph 160 km/h Studless & Studdable Winter Tires
R 106 mph 170 km/h H.D. Light Truck Tires
S 112 mph 180 km/h Family Sedans & Vans
T 118 mph 190 km/h Family Sedans & Vans
U 124 mph 200 km/h
H 130 mph 210 km/h Sport Sedans & Coupes
V 149 mph 240 km/h Sport Sedans, Coupes & Sports Cars

When Z-speed rated tires were first introduced, they were thought to reflect the highest tire speed rating that would ever be required, in excess of 240 km/h or 149 mph. While Z-speed rated tires are capable of speeds in excess of 149 mph, how far above 149 mph was not identified. That ultimately caused the automotive industry to add W- and Y-speed ratings to identify the tires that meet the needs of new vehicles that have extremely high top-speed capabilities.
W 168 mph 270 km/h Exotic Sports Cars
Y 186 mph 300 km/h Exotic Sports Cars

While a Z-speed rating still often appears in the tire size designation of these tires, such as 225/50ZR16 91W, the Z in the size signifies a maximum speed capability in excess of 149 mph, 240 km/h; the W in the service description indicates the tire's 168 mph, 270 km/h maximum speed.

 

[Quattro Pete]

Originally Posted By: Quattro Pete
I thought max tire pressure was a direct result of the tire's size/load/speed rating. So, if you have two tires in exact same size/load/speed rating, they should have the exact same max tire pressure.

Now that I've looked at tires in this size on TireRack, my previous statement does not hold water. There are tires there with exact same load and speed ratings, yet different max PSI. Sorry about the confusion. I'll shut up now and wait for Capri to explain.

 

[Colt45ws]

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

This note means that in spite of the load curve ending at 35 (or 41 for XL) psi, it is permissible to stamp the sidewall of the tire as having a maximum inflation of 35 psi, or 44 psi or 51 psi. (41 or 50 psi for XL).

If you were to dig to find the US regulation that covers what is supposed to be stamped on the sidewall of the tire (In this yearbook, it is FMVSS109, but this was superseded by FMVSS139 in 2007, but this part reads the same for both), the regulation is unclear which of those values it is supposed to be.

Most everyone in the tire industry reads the regulation that either 44 psi or 51 psi is the proper value for SL tires. However, a few tire manufacturers - notably the Michelin group (Michelin, Uniroyal, and Goodrich) have interpreted this differently and read the regulation to mean that for S and T speed rated tires, 35 psi should be stamped on the sidewall, while H and higher are supposed to read 44 or 51 psi.

That means for otherwise comparable tires, you will find different maximum pressures stamped on the sidewall. This means you SHOULD NOT use the pressure stamped on the sidewall as any sort of reference point, except, of course, what it says - a maximum.
and there are a couple exceptions to that!!

 

[PandaBear]

Thanks.

 

[mechtech2]

Don't you guys see the corresponding WEIGHT in the same sidewall pressure statement?
They go together and tell a better tale.

 

[kr_bitog]

Originally Posted By: PandaBear
for quality?

I am just splitting hair, trying to see between 2 tires which one is "better" after all else is compared.

What determines the maximum sidewall pressure?


It depends on what properties you want it better.
Higher maximum psi normally only shows that the sidewall can stand more pressure (but does not mean they can carry more load). So this normally only help to determine whether the tyre is more versatile to be matched with the suspension characteristic.

Speed rating is a better gauge to determine how good the tyre can handle speed and extra heat.

For me, I would focus more on the speed rating, treadwear, traction and sidewall characteristic to match with the suspension rather than putting much consideration on the maximum tire pressure.

 

[CapriRacer]

Originally Posted By: mechtech2
Don't you guys see the corresponding WEIGHT in the same sidewall pressure statement?
They go together and tell a better tale.


Ah ..... not exactly.

You will find the sidewall will express this in 2 ways:

Max Load XXXX at YY pressure: That indicates a relationship, but doesn't tell you what the max pressure is.

Max Load XXXX, Max pressure YY: That indicates the max pressure, but doesn't say anything about a relationship.

I hope that clears this up.

 

[SteveSRT8]

I just recently waded through all this and bought summer only tires for my car.

It was interesting in that several tires were obviously aimed at much lighter weight vehicles than mine. My choice eventually was helped along by the weight ratings posted online. Since I'm not a Vette or an S2000 I bought a tire much more suited to a car that weighs two tons.