My tire pressure vs. door sticker

jbones

Original poster
Member
Dec 5, 2011
658
I know it well go by the door sticker, and it’s also my understanding that when tire size goes up one, like in my case from P245/65/17 to P255/65/17 you still go the door sticker. My sticker like many others reads cold recommended 35psi rear and 30psi front. Now 35 in the rear looks, performs, and rides just fine with the new size, but the 30 front looks underinflated, sidewalls darn near dragging

My question boils down to this: should I leave them at thirty (door sticker) expecting ambient and driving to increase the pressure, but not beyond unsafe limits, and just check more often (already check a few times a week) to ensure I don’t go below 30psi. Or, pump up cold pressure 1 or 2psi expecting ambient and driving increases not to exceed what’s considered unsafe, or hard on tire wear?

Old 245/65/17 Michelin Cross Terrains
New 255/65/17 Michelin LTX MS2
 

HARDTRAILZ

Moderator
Nov 18, 2011
49,665
Just do a chalk test and see what PSI works and wears correctly.
 

Rubberman

Member
Dec 14, 2011
117
I never go by the door sticker. You go by the stamped tire pressure.
 

HARDTRAILZ

Moderator
Nov 18, 2011
49,665
Rubberman said:
I never go by the door sticker. You go by the stamped tire pressure.

The only stamp is max tire pressure, not the proper pressure for the type and weight of vehicle. The same tire on an s-10 and a crew cab dually will need far different pressure than the MAX listed on the tire.
 

jbones

Original poster
Member
Dec 5, 2011
658
Sounds like a good start, never occured, never done it, since I've always ran OEM size, and used recommened pressure.

I assume it's the best cold pressure, matching an even across chalk/tread I'm searching for after some short chalked up drives with different cold inflations?
 

HARDTRAILZ

Moderator
Nov 18, 2011
49,665
You can do it in an empty parking lot if you have a small compressor and chalk. You chalk and drive about 100 feet, see how the wear is and adjust pressure accordingly. You want nice and even all across. ---If center wears off first, then lower pressure
 

jbones

Original poster
Member
Dec 5, 2011
658
HARDTRAILZ said:
The only stamp is max tire pressure, not the proper pressure for the type and weight of vehicle.

That's how I've always know it to be, I've always looked at it as a pressure vessel, the hydrostatic test pressure being greater than the fill/working pressure. Double, or darn near in the cylinders I worked with the Navy.

HARDTRAILZ said:
You can do it in an empty parking lot if you have a small compressor and chalk. You chalk and drive about 100 feet, see how the wear is and adjust pressure accordingly. You want nice and even all across. ---If center wears off first, then lower pressure

I know just the location, even has a free air source. The Navy Exchange down the road, big empty parking lot before and after hours.
 

HARDTRAILZ

Moderator
Nov 18, 2011
49,665
You may need different front and rear pressures as well. More weight with the engine up front. I find good luck with a 2 psi difference, but your is set up differently than my big wide tires.
 

Chickenhawk

Member
Dec 6, 2011
781
The thing to remember about tire pressures are that there are MINIMUM, SAFE tire pressures for the average driver on the street, and there are OPTIMUM tire pressures for the drivers who can tell the difference.

It is a myth that door sticker pressures no longer apply if you change tire brands. The reality is that these are the safe tire pressures no matter the brand, simply because there are no tires available in the OEM sizes that would be unsafe at these pressures. As long as the tire construction type (P-metric) and size are the same (or the equivalent rolling diameter in a different size) then door sticker pressures are acceptable.

But these are not the best pressures for enthusiast drivers who want to optimize their traction.

The chalk test will show you the best contact area, but a general rule of thumb is that optimum traction occurs at 80% to 90% of the maximum pressure listed on the tire sidewall. I generally keep my fronts towards the 90% end of the spectrum to prevent tuck-under if I need to corner hard, and rears at 80% to maximize comfort. If I was carrying more of a load in the rear, I would go with closer to 90% for the rears as well, and if I was carrying a load near my maximum vehicle rated capacity, I would even go to 100% of the maximum sidewall pressure.

Keep in mind that this rule of thumb only applies to P passenger tires on the street. It does not apply to off-roading, nor does it apply to LT tires.

(LT tires have much stiffer sidewalls so they can carry much higher loads, and they are at their optimum traction at closer to 70% of the maximum tire pressure listed on the sidewall.)

Therefore, with my Michelin LTX M/S tires, I run 39 PSI in the front and 36 PSI in the rear. I can go to a maximum of 44 PSI in the rear if I need to when carrying a heavy load. Door sticker, 30 front, 35 rear is safe, but it is not optimum.
 

jbones

Original poster
Member
Dec 5, 2011
658
Chickenhawk said:
The thing to remember about tire pressures are that there are MINIMUM, SAFE tire pressures for the average driver on the street...

Sadly that that's me:no::yes::no::yes:it is...:smile:

Wondering, did you arrive at your minimum from a chalk test? Your rear min doesn’t seem extreme, only 1 psi over, was more curious about your front at 9psi over average driver psi. You’ve had no road hazard issues, or premature wear issues @ 9 over?
 

blazinlow89

Member
Jan 25, 2012
2,088
I run front and rear at 40 psi. If I tow then I drop it down to 37 for each tire.

I have been running like this for years, and my tires last pretty wrong, never had any issues other than a nail here and there.

I run the GF's VW at 38 psi, they are low pro 18" tires. Car rides alot smoother and handles a sh!t ton better. I can tell when my tires are low by even a few psi. The ride feels off.

I will see if I can find the article but it was in like car and driver or something talking about a stunt school. The instructor said he runs tires at a minimum of about 85% of the max rated value, sort of like how chickenhawk is talking about the "safe" pressure.
 

Chickenhawk

Member
Dec 6, 2011
781
If max. sidewall pressure is 44 PSI like mine are, then at 39, I don't consider 9 PSI over the door sticker to be too high.

If you want a nice ride with those tires, I would suggest you at least try 36 PSI all around and see how you like it. That will maximize your traction at both ends. The Michelin LTX M/S is one of the best tires ever made for our platform, and responds well to pressures that approach 85% TO 90% of the max. sidewall pressure cold.

Always keep in mind that most manufacturers want to induce understeer in their vehicles because it is safer for granny. She goes too fast into a corner; the front end keeps going straight when she wants it to turn; she panics and takes her foot off the gas, it transfers weight forward and it self-corrects. (Unless she has really screwed up badly.) Therefore, the manufacturer wants the fronts to be safe but below the maximum traction point.

If a vehicle is in perfect dynamic balance and neither understeers nor oversteers, if a driver cooks a corner too fast and takes their foot off the gas, it transfers weight forward but in this case, the front is already at maximum traction so it effectively reduces weight off the rear, lessening the rear traction, and the rear end can start to swing around. (This is called throttle-off oversteer.) It takes more skill - according to liability-shy manufacturers - to stay in control of the average car when it oversteers than when it understeers.

An extreme example is a 1980's-vintage Porsche 911 Turbo; 90% of them are now wrecked after spinning ass backwards out of curves by drivers who wanted the look and the rarity but didn't have the skills to control a car that would not just begin to get light on the rear end if you took your foot off the gas in a corner; it would lose control.

However, keep in mind we are dealing with a heavy SUV and it will never be a Porsche no matter what colour we paint our brake rotors. We will never get a perfectly neutral vehicle on our platform. I am the type of driver who wants to minimize understeer as much as possible. This is why I run slightly higher pressures in front and why I run a stiffer aftermarket sway bar in the rear.

If you find a quiet paved parking lot where you can safely and legally go round and round in a tight circle, you will also begin to instantly understand what I mean by preventing "tuck-under" of the front tires in sudden corners. If the circle is tight, you do not need to be going very fast at all.

Mark Donohue, for those of us old enough to remember him, was not just a skilled race driver, he was a brilliant engineer. Before he took any race car out on the track, he would remove the body work (to eliminate aerodynamic forces) and test the chassis and suspension on a very tight skid pad. In the 1970's, he could dial in more 240 MPH Can-Am and Le Mans race cars going 30 MPH in a tight circle than most engineers could do with all the computer power and test tracks at their disposal today.

Thankfully, in all the years I have been driving, I can only think of one occasion when I really needed those extra few PSI in the front (aside from the race track.) I was going down the highway approaching a cross road when I saw a car that I somehow sensed wasn't going to stop at the stop sign. I saw her turn her head to the right to look for traffic and then drive straight through.

Sadly ... I was coming from her left.

A sixth sense had me back off the gas but she was directly in front of me before I could react. Someone in my truck nailed the gas as hard as they could, swerved to the left only enough to miss her by an inch, immediately corrected to the right before any appreciable weight transfer had taken place and then straightened the wheel to put me back in my lane like nothing had taken place. To this day, I still don't know who it was that was doing the steering but I know one thing; if that person had even tried for the brake pedal, we would both be dead.
 

HARDTRAILZ

Moderator
Nov 18, 2011
49,665
blazinlow89 said:
If I tow then I drop it down to 37 for each tire

Why??
 

blazinlow89

Member
Jan 25, 2012
2,088
Always lowered the pressure when towing, I usually only tow a pop up, and load the back with bags and stuff. I always lowered to compensate for the extra weight. Never done much towing (other than work, no tongue weight. We use towbars). Never really though about the pressure difference, just something I have always done.
 

djthumper

Administrator
Nov 20, 2011
14,950
North Las Vegas
I run a higher pressure when I tow. The max pressure is with a load anyhow, I am far from my max pressure.
 

jbones

Original poster
Member
Dec 5, 2011
658
Chickenhawk said:
If you want a nice ride with those tires, I would suggest you at least try 36 PSI all around and see how you like it. That will maximize your traction at both ends.

And of course rolling resistance is important to me for the fuel economy, will 36psi facilitate this?

At any rate I might as well take some time and try both; 36 PSI, and chalking to see why works best.
 

gmcman

Member
Dec 12, 2011
4,656
blazinlow89 said:
I run front and rear at 40 psi. If I tow then I drop it down to 37 for each tire.

I run mine at 36 for all 4 and when I tow I go up to 40. You don't want to drop down to tow....you need the extra weight carrying capacity.

The sidewall pressure reads exactly how it should........"MAX LOAD XXXX LBS at XX PSI" You can run them at 44 but will be slightly harsh.

I don't go by the door sticker either but use it as a reference, 30 is too light IMO.

I have been running 36 for 165K miles and the tires wear very even, and handle well.
 

ScarabEpic22

Member
Nov 20, 2011
728
Run the recommended pressure for your tires, not what the door says.

My winter setup (17s, Dueler AT Revo 2s 255/65R17) I run at 35psi front/rear and tire wear is uniform plus the ride is great. Summer setup (stock 20s, Goodyear RS-As 255/50R20) I run at 35psi front/rear as well, ride is firmer, but I expect that because of the rim size difference.

Ive run whatever pressure the dealer tells me to ha, Ive played with +2 and +5 psi on my winter setup and the ride went to $hit when I went +5. +2 was ok, but Im worried about over-inflation and extra wear on the tires in the center.

Just my .02.
 

Mark20

Member
Dec 6, 2011
1,630
Been running 35 all around on stock size Goodyear Forteras. At first I could definietely feel the difference on the front as compared to the factory spec of 30. I'm used to it now. As it is, time to park by the loading dock at work and exercise that nice compressor we have.

As mentioned before ride comfort and handling for less capable drivers go into determing factory tire pressure.
 

HARDTRAILZ

Moderator
Nov 18, 2011
49,665
You can also call the tire manufacturer and give them your vehicle info and which tires you got and they will give you their specific recommendations
 

jbones

Original poster
Member
Dec 5, 2011
658
HARDTRAILZ said:
You can also call the tire manufacturer and give them your vehicle info and which tires you got and they will give you their specific recommendations

So this morning I called Michelin, give the info requested, put on hold for some time, and she comes back with 20-25 front, and 30-33 rear. I said what! there’s no way that’s below the OEM pressure's, and this is a bigger tire. I told her 30 front OEM pressure on the new tire looks like the sidewalls are dragging on the ground, her reply was “what do you mean”, then says well try 35 front, and 40 rear, just like that! I thanked her and hung up, had no more time to spend on the phone, will call back later hoping for a different tech. :confused:
 
Feb 24, 2012
133
blazinlow89 said:
Always lowered the pressure when towing, I usually only tow a pop up, and load the back with bags and stuff. I always lowered to compensate for the extra weight. Never done much towing (other than work, no tongue weight. We use towbars). Never really though about the pressure difference, just something I have always done.

Always increase tire pressure when you increase load. Stiffens the tire so it responds better, helps dissapate heat better. That's why there is a Max load at Max pressure rating on the sidewall of the tire. You should be at/near max pressure.

Only lower tire pressure when doing something that requires MORE flexible tires (offroading/sand driving/etc). When towing you want stiffer tires for more stability.
 

jbones

Original poster
Member
Dec 5, 2011
658
jbones said:
So this morning I called Michelin, give the info requested, put on hold for some time, and she comes back with 20-25 front, and 30-33 rear. I said what! there’s no way that’s below the OEM pressure's, and this is a bigger tire. I told her 30 front OEM pressure on the new tire looks like the sidewalls are dragging on the ground, her reply was “what do you mean”, then says well try 35 front, and 40 rear, just like that! I thanked her and hung up, had no more time to spend on the phone, will call back later hoping for a different tech. :confused:

I also sent an email, Michilen's reply:

Hello Jeff,

Thank you for your email. We welcome the opportunity to serve you.

We appreciate you purchasing LTX M/S2 tires for your Trailblazer.

I would recommend continuing to use 30 psi front and 35 psi rear, measured when the tires are cold.

We appreciate your business and thank you for choosing Michelin.

It is our goal to ensure that your issue has been resolved or your question answered to your satisfaction. If we can assist you further, please respond to this email or call us at 1-800-642-4354 (toll free) between 8:00AM and 8:00PM Eastern Time Monday through Friday or between 8:30AM and 4:30PM Eastern Time on Saturday.

Sincerely,

Mike


Consumer Care Department
Certified Michelin Product Expert

That's three (3) different PSI's from the tire manufacture. :crazy:
 

gmcman

Member
Dec 12, 2011
4,656
It's your call but I wouldn't go down to 30 in the front. Those tires aren't cheap and there's alot of weight in the front rolling around turns. The consensus here is at least 34, I won't let mine get below 34.

Factor in possibly not checking the air often then you get into some really low numbers. Reminds me of the days when the explorer debuted and they ran low pressure to attract buyers to the smooth ride of a "truck" and Firestone took the hit for failing tires being the smaller fish.
 

jbones

Original poster
Member
Dec 5, 2011
658
gmcman said:
It's your call but I wouldn't go down to 30 in the front. Those tires aren't cheap and there's alot of weight in the front rolling around turns. The consensus here is at least 34, I won't let mine get below 34....

I know what you’re saying, but it's on record (email) from Michelin, 30/35, they recommend going with auto manufacture psi, if they wear wrong it's on their dime. I always do my part checking pressure and rotating. I did call a second time today and got 30/35 and to go with with on the manufactures placard, again.

The OEM's had a lower load rating and lasted 54,000 at 30/35 psi, they were at 5/32 when I replaced a few weeks back.
 

djthumper

Administrator
Nov 20, 2011
14,950
North Las Vegas
I would probably try 35 all the way around and then go from there.
 

gmcman

Member
Dec 12, 2011
4,656
I have an 02 4WD SWB and my door sticker reads Front 32, Rear 32, Spare 35.


I can't understand how a 30/35 bias can be recommended when the front is as near the weight of the rear if not more.

For sake of arguement has anyone split the axle weight of said platforms?

Just curious.
 

sevendj

Member
Dec 9, 2011
52
jbones said:
I know it well go by the door sticker, and it’s also my understanding that when tire size goes up one, like in my case from P245/65/17 to P255/65/17 you still go the door sticker. My sticker like many others reads cold recommended 35psi rear and 30psi front. Now 35 in the rear looks, performs, and rides just fine with the new size, but the 30 front looks underinflated, sidewalls darn near dragging

My question boils down to this: should I leave them at thirty (door sticker) expecting ambient and driving to increase the pressure, but not beyond unsafe limits, and just check more often (already check a few times a week) to ensure I don’t go below 30psi. Or, pump up cold pressure 1 or 2psi expecting ambient and driving increases not to exceed what’s considered unsafe, or hard on tire wear?

Old 245/65/17 Michelin Cross Terrains
New 255/65/17 Michelin LTX MS2

Have you gotten a chance to try these in snow at all? I've had such good experiences with my cross terrains that I just threw another set on, but saw this tire as well. Doesn't sound like it would be any better in the snow though...
 

Chickenhawk

Member
Dec 6, 2011
781
The reason why many SUVs have higher pressure requirements for the rear are simple. The front is probably never going to get much heavier than it is, but if you load three heavy passengers in the rear, a full tank of gas, full cargo and trailer tongue weight, and all that weight is added to the rear axle.

Basically, manufacturers are saying that most drivers aren't bright enough to know to add extra pressure in the rear tires when you are carrying a heavier load, so they want you to run it all the time.

(If you think about the average brainless driver out there, they are probably right!)
 

jbones

Original poster
Member
Dec 5, 2011
658
sevendj said:
Have you gotten a chance to try these in snow at all? I've had such good experiences with my cross terrains that I just threw another set on, but saw this tire as well. Doesn't sound like it would be any better in the snow though...

The CT's I took off ran great in snow as you also experienced, the MS2 is rated even better for snow and ice with tire rack and Consumers Report, and rated both their #1 AS tire. I believe the winter snow and ice is gone for the season I my area, will have to wait to compare. So far wet and dry, and all around handling feels way better with the MS2. even at 30/35.

Waiting for dry weather for the chalk test.

Bumping the pressure up today for comparison, and figuring mileage today at the 30/35 after I fill up again. Then pressure up and burn some more gas over the next week or so and check mileage again, and of course compare handing under the wet and dry conditions.
 

gmcman

Member
Dec 12, 2011
4,656
jbones said:
Bumping the pressure up today for comparison, and figuring mileage today at the 30/35 after I fill up again. Then pressure up and burn some more gas over the next week or so and check mileage again, and of course compare handing under the wet and dry conditions.

Definately keep an eye on the shoulders for any increased wear running at 30 PSI. If you stick with that pressure you may need to rotate more often.
 

jbones

Original poster
Member
Dec 5, 2011
658
Chalk test at 30/35, and 31/36 looked Ok, but clearly room for improvement in the shoulders. Since my last posting I've checked gas mileage at these PSI's, averaging 18.8.

gmcman said:
The consensus here is at least 34,...

Going to try this at fill up tomorrow and compare chalk and mileage for a few weeks.
 

Sparky

Member
Dec 4, 2011
12,927
I've been running 35 front and rear since I got my tires (Firestone Destination A/T, stock size). 30 in the front just seemed off so I bumped it. Wear has been great and the steering is responsive enough. Granted I've never run any chalk tests or anything.
 

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