Vehicle manufactures tire pressure or Dealers tire pressure? 1

[DAVIDSTECKER]

Every winter I change my rear light truck rear tires over to more of an off-road “Snow” tire.
Last year I damaged one of them and the dealer said that I should have had the pressure up to the maximum 50 PSI listed on the tire instead of the 35 PSI listed on the trucks data plate.
I have just put the replacement tires on this weekend and I would like to know which pressure is the correct one or if I should be somewhere in between.
Best regards, David

 

[GregLocock]

I'd have thought the plate pressure would refer to the original tires that were fitted. In general there is no harm to modern tires to run them at higher pressures than the plate, so long as they are less than the max pressure on the sidewall, although you can alter the handling of the vehicle by doing so.

Rear tires on trucks are a bit of a problem, since if you inflate them correctly for full load they may be too hard for unladen, and may get a bit skittish.

Having said all that I've never used snow tires.

Cheers

Greg Locock

I rarely exceed 1.79 x 10^12 furlongs per fortnight

 

[DAVIDSTECKER]

I'm not so much concerned with the truck getting skittish at the higher pressure as I am about wearing more in the center of the tread which is a problem with over inflation.
That happened to the very first set of snow tires I had.

 

[GregLocock]

Oh, I thought that issue was long gone.

Well, seems like you need a bit more pressure but not too much. Sorry that isn't much help.

Anyway, I can confirm that at least in Australia and the UK the plate refers to the tires that were originally fitted, it is not a general recommendation.

Cheers

Greg Locock

I rarely exceed 1.79 x 10^12 furlongs per fortnight

 

[CapriRacer]

There's a quite a few different issues here, so this is going to be a long post.

First, I think we need to know the year, make, and model of the vehicle we are talking about.

Second, what does the vehicle tire placard say about the original tire size and pressure?

Third, what tire size are you using?

Be sure you include the letters in front of and behind the tire size, because they are important. For example, "LT" tires are different than "P" type tires.

You should be aware that drive tires tend to wear in the center, while steer tires tend to wear in the shoulders. So if you are putting snow tires only on the drive end of a 4X2 pickup, you should expect the tires to wearout in the center.

You should also be aware that stopping is as important as getting started, so winter tires should be on all 4 positions.

And lastly, if you consider the situation, which makes the most sense: A vehicle manufacturer who has thousands of engineers with a lot of expertise, who can consult with the engineers at the tire manufacturer and who is required by law to place a sticker on the vehicle (and, of course, that means that every lawyer in the country can see it!)

- OR -

the guy at the tire store who might have a high school education and who might know somebody from a tire manufacturer and who didn't write anything down (or sign it!)

 

[NormPeterson]

Consider that 50 psi sidewall marking as the maximum for the tire, no matter what vehicle it may be fitted to, whether or not it's a proper size for that vehicle, or maybe even if it isn't fitted to any vehicle at all. The tire mfr is only responsible for providing a safe maximum inflation pressure for his product. While he can provide guidance for its proper use, he cannot enforce rigid control over it.

It's the vehicle mfr who chooses an appropriate tire size (or sizes) for his vehicles and sets his recommended inflation pressures accordingly. Assuming that your snow tires are the same size as the OE size, the vehicle sticker pressures are the ones that you should be working with. Or at least starting from.

Just what (which?) inflation pressures were you running on the set of tires that wore the tread centers out at an apparently unsatisfactory rate?


Norm

 

[evelrod]

I think we are overthinking the OP's request. As stated, inflating the tire to the mfgrs max on the sidewall will do no harm as long as the tire is mounted to the required rim.
However, the idea these days, at least, that if inflated to the stated pres will cause the center of the tire to wear abnormally is as Greg put it "...I thought that issue was long gone". With most over the counter tires being of the belted/steel belted radial design, where the tread belt is super stiff, the wear problem of the old bias ply days is truly 'moot'. Your gonna hafta go to wild extremes to get the type of wear you seem to fear, David. If your comfortable at 35psi and the truck handles to your requirements, by all means, run 35. You might try 50 and see what happens...you might like it better. On my Dodge duelly I typically run the rears at 50 (placard is 85) cause it rides a bit better. If I load it up, I simply inflate the tires to 85.

Now, as to "winter only" tires...When I did live in the snow belt, I used a set of "snow tires" occasionally and found out the hard way that they should be renewed around five years or so, no matter what the tread looked like.

Rod

 

[DAVIDSTECKER]

Thanks to everyone for your input, it was very informative.
Special thanks to EVELROD for a great job of summing up what the other gentlemen were telling me.
Best regards, David

 

[MikeHalloran]

Greg, that issue is not long gone.
It's not gone.
It's worse than before.

My most recent five Camaros all used roughly the same tires:
245/50ZR16-ish.
All strongly preferred the same tire pressures:
34 psi front
32 psi rear
+1 psi produced center wear
-1 psi produced edge wear
Without regard to brand, over a statistically significant number of sets of tires over a statistically significant number of miles.


Mike Halloran
Pembroke Pines, FL, USA

 

[rmw]

Mike,

What about the pressure change when you drove them hard (or long) and they heated up? Did you get out and let air out to maintain correct pressure?

rmw

 

[MikeHalloran]

NASCAR tried automatic pressure releasing valve caps a few seasons ago. When the cars slowed down in response to a caution, the tires cooled off, lost pressure, got all wonky and caused more crashes. They gave up on the idea of bleeding off the overpressure.
So did I.

Besides, I don't drive hard enough to get the tires real hot anyway. The tires are damn expensive, so I try not to chew 'em up. Smoky burnouts are for journalists who don't buy the tires.







Mike Halloran
Pembroke Pines, FL, USA

 

[CapriRacer]

Contrary to what Dave and Evelrod think, the problem has not been over-thought. Here's an example:

If the truck came with P235/75R15's and new tires of LT235/75R15's were put on, then the difference in the load carrying capacities of the tires results in a 15 psi difference in proper inflation pressure.

Since we do not know if we are talking about LT metric or P metric tires - except what the snow tires are - then we can not know what answer to give. There is a technically supportable answer, but we need to know what the vehicle's tire placard says for size and pressure (I think the OP gave us the pressure) and the size of the snow tires.

 

[evelrod]

Mike, I've been a fan or yours for many years. I've followed your posts, even given you a star on occasion....However, in the case of street tire wear, radical wear differences, from +1/-1 psi changes....Nope. Your way off base here. I suspect your problems are generated from some other cause.

As to the pressure bleeders, yes, your right with them. I experienced the same problems (plus a couple others) with them and no longer use them.

Capri, it really is not a matter of load carrying capacity. Most trucks are equipped with tires that exceed rated capacity and in the case of "snow tires", it's mostly a case of "ride" and "handling"...Those can be very subjective.

Rod

 

[LionelHutz]

I'd agree it's a combination of ride, handling and wear for normal driving. For example, you might want to run the rears a little lower in pressure to compensate for less unloaded weight or to help keep the center from wearing. If the truck is being used to haul a load then the pressure should be checked to ensure you have the load handling you require.

Mike, you're lucky - try to get 305/30ZR19 rubber to wear evenly. And you're complaining about cost... I run 28psi even though the car has 32psi on the door tag and the wear isn't too bad so far.

 

[MikeHalloran]

So ... I'm _not_ crazy? ...Don't answer that.

It took me three sets of tires to get the pressures right, and that's with 45..55 aspect ratio.

If low profile/ aspect ratio is indeed responsible for the wear asymmetry/ pressure, then the /30s could be even more sensitive to pressure. You might need to resolve tenths of a psi.





Mike Halloran
Pembroke Pines, FL, USA

 

[DAVIDSTECKER]

Well here's an up-date, we received 3-4" of snow here last night.
Yesterday I put about 900# of steel on a pallet in the back of the truck with about 70% of the load just forward of the center of the axle then filled the rear tires to 45PSI.
The truck was very stable and went straight as an arrow even at 45MPH on the snow covered high ways.
I have an extra set of wheels now so maybe in the near future I'll get a matching set of tires for the front. Right now the regular front tires are more like boat rudders, but that’s OK, I used to have 35' boat so I'm used to that mode of transportation too.

 

[CapriRacer]

Rod,

"......Capri, it really is not a matter of load carrying capacity. Most trucks are equipped with tires that exceed rated capacity and in the case of "snow tires", it's mostly a case of "ride" and "handling"...Those can be very subjective.

Rod...."

Oh, contrare! The load carrying capacity vs pressure relationship controls the size and the shape of the footprint - which, needless to say has a profound affect on both the ride and the handling.

Again, we still don't know if the vehicle originally came with P metric or LT metric tires - and I suspect P metric, and Dave is currently running LT metric tires, which would explain why such as high pressure (compared to the placard) and the additional weight had a positive affect. A P metric tire would have been saturated and not performed as well.

 

[evelrod]

Perhaps I did not make my point clear enough. In the case of heavy loads, rain, etc. perhaps it is clearly advantageous to use the high pressure as rated...no argument. For snow, where it is obvious the load is nowhere near rated capacity, the "high" pressure could/would definitely be a problem. The "footprint", at least the length of the footprint, is the determining factor as I see it. I've had to lower my tire pressure just as if I were in sand in order to make it over the pass from Colorado Springs to Canyon City, more than once!

Rod

 

[CapriRacer]

Rod,

I understand your point, but I think you are missing mine. Let me illustrate it for you.

Same truck, but there is a difference in the type of tire on the truck - P245/75R16 vs LT245/75R16.

P245/75R16 has a maximum load carrying capacity of 2271# @ 35 psi - but because this is a truck it has to be derated 10% - to 2065#.

LT245/75R16: come in a variety of load ranges - but Load Range C has a maximum load carrying capacity of 2205# at 50 psi. At 35 psi, it only has a 1700# capacity - and put another way, for a load capacity of 2065#, the pressure has to be 46 psi.

Since there is this difference, the tires are going to be designed differently:

1) The heat generation will be different, so the tire designer will select different rubber compounds.

Side note: One of the problems with LT tires is that they can carry such a high load compared to the size of the footprint, that rubber compounds will be more prone to - and the term escapes me for the moment so I'll use the term stress flow (or creep), meaning the rubber will not rebound to the same shape, but is permanently distorted. This limits what rubber compounds can be used in LT metric tires.

2) The footprint will be designed differently to accommodate the difference in pressure for the various load conditions.

For this reason, if the truck originally came with P metric tires - and that's what is posted on the vehicle tire placard - then putting LT metric tires on calls for a different pressure. You won't get exactly the same behavior between the 2 types of tires, but given the differences in the way the tires are designed, you have to use different pressures to accommodate the difference the load carrying capacities.

And that goes directly back to the original question: What pressure is supposed to be used - the placard or what the tire dealer put in?

My answer is that it makes a difference what answer you give if there is a mixing of P metric and LT metric tires.

 

[NormPeterson]

Let me see if I've got this straight.

The answer that should be given when there is a mixing of Pmetric and LTmetric tires needs to acknowledge that the proper inflation pressure will differ from the vehicle placard pressure(s).

Except by coincidence, the specific proper inflation pressure will not be the maximum pressure molded into the sidewall of the tire being installed either.

You might still end up at the sidewall max pressure after a little individual pressure tuning to suit very specific conditions/vehicle behavior preferences. But it would be outside the typical tire installer's cognizance to recommend that the sidewall max pressure be used as a starting point.


Norm