Chalk test with new Cooper Discoverer ATP's

Really liking my new tires, but after doing the chalk test last night, I'm all the way down to 27 in the front and 26 in the rear . Seems low? I'm wondering if the ATP's are sort of meant to wear the in middle first, as there is much more tread there than near the shoulder of the tire. But I can't think of a reason why a tire company would do that. Thoughts? Just go with the chalk test results? Seems like my fuel mileage will take a hit.

 

My info inside the door jam recommends 26 Psi all the way around for P rated tires. For LT I think its 29 front 26 rear. Check ur door jam, ur probably good.

 

Yeah the middle of mine look more pronounce and out more then the sides.

 

I run the discoverer ATP in 265/75/16 on a 2005 off road access cab and my chalk test results put me at 32 psi front and 28 rear for even wear.

Edited to add, I am not carrying and weight in the truck at all and have 5100's all around, front at .85 (stock spring)

 

The chalk test is a middling tool at best.

Tires deform differently at different speeds and temperatures. It's not major, but it's enough to effect wear patterns. So a good chalk test at, say, 25 mph may not be that great at 70 mph. If you commute 30 miles one way to work each day, on the Interstate, you may wonder why your tire wear is goofy even though your chalk test is perfect.

Generally speaking, the best solution to this is to chalk test for the type of driving (highway, city...pick an average speed and go with it) you do *most often*.

The other option is to wheel the piss out of them, so you destroy them from tread chunking and sidewall cuts long before treadwear puts them out of service. Definitely the pricier option.

 

Intuition would tell me that at higher speeds, for longer drives, the tires would just simply heat up more. Other than this variable, I'm struggling with coming up with other variables (you mention speed, but doesnt that have a direct relationship with temperature?). And all this obviously depends on road surface condition. So it would seem safe to try it out at neighbor hood speeds and error on the side of a little low, so that when your highway driving and tires warm up, they wear perfectly?

Its difficult to do the chalk test with any degree of accuracy for a distance of more than ~.5 mile. Maybe I'll have to be that crazy guy on the side of I-25 chalking my tires while traffic zips narrowly by at 80mph

Thanks for the responses! I think I'm satisfied with where I ended up. Time will tell!

 

Never err on the side of low, you'll get more wear and heat and low mpg erring low. I go max sidewall 44psi with even wear.

 

Tire runout:

http://en.wikipedia.org/wiki/Tire_uniformity#Radial_runout

And yes, increased heat does occur at speed...heat causes gas expansion, meaning the tire will INCREASE inflation from chalk test levels. This is exactly what I was talking about in my previous post (rotational forces also come into play).

 

Am I missing something? It would seem as though there is zero usable info anywhere here VVVVV relevant to the thread

The chalk test is a middling tool at best.

Tires deform differently at different speeds and temperatures. It's not major, but it's enough to effect wear patterns. So a good chalk test at, say, 25 mph may not be that great at 70 mph. If you commute 30 milesonewayto work each day, on the Interstate, you may wonder why your tire wear is goofy even though your chalk test is perfect.

Generally speaking, the best solution to this is to chalk test for the type of driving (highway, city...pick an average speed and go with it) you do *most often*.

The other option is to wheel the piss out of them, so you destroy them from tread chunking and sidewall cuts long before treadwear puts them out of service. Definitelythepricier option.

 

Pricier, but certainly a valid technique.

 

Uh, presumably the idea behind the chalk test is to find the ideal air pressure for uniform tire wear, yes?

What I'm saying is conditions of testing are not necessarily valid to conditions of usage, because conditions of usage cause variance in tire pressure and shape, and thus contact patch and wear patterns.

 

Or go by factory recommended numbers.....

 

Factory recommended numbers apply only to the factory installed tires.

And that's still not where you should be.

Factory recommended inflation is the best compromise between ride quality, fuel economy, and tire life (emphasis on ride quality without sacrificing tire life too badly).


Higher inflation pressures =
Reduced tire temperature = reduced tread wear.
Reduced rolling friction = better fuel economy and reduced tire wear.
Higher speed at which hydroplaning will occur.
NO drawbacks to wet or dry traction on pavement.

Higher inflation pressures =
Harsher ride
Poor floatation on sand/mud


Inflation TO the sidewall max will not wear the center of the tread.
I've been running my tires at or near the sidewall max for 30 years and I have NEVER worn a bald strip down the center of the tire.
BFG TA/KO 285/75-16 on my Duramax, 35,000 miles and wear was perfectly even across the tread face.


"Sidewall max" is not the "burst" pressure..... not even close.
Sidewall max is simply the maximum LOAD... and the tire can carry that load at that temperature.
It is not unsafe to exceed the PRESSURE listed on the sidewall.
It is unsafe to exceed the LOAD listed on the sidewall.

But... I'm not going to tell you that you should inflate beyond that pressure and I'm not going to tell you how far above it you can safely go.

 

well, funny that he did the chalk test and it came out to be spot on with the factory numbers, no?

 

Not funny at all.

It might come up just fine 10psi higher.

The chalk test is not the end-all-be-all determination of the ideal inflation.
Going around a turn, especially at a lower inflation point, the tire will roll on the rim. More pressure is placed on the outside and the inside will lift.

At high speed, the center of the tread will actually lift... and yes, we discussed this in another thread and an "engineer type" tried to shit on my, but I've SEEN the video of a tire at 100mph and it does happen.


Tread pressure is not static... it is constantly changing. The chalk test gives only a very, very small picture of what is happening. It's not totally worthless, but it's also not THAT valuable.
I've driven well over a million miles over the last 35 years, always running at or near the sidewall max, and I have NEVER had a tire wear out first down the center.... the wear has always been on the shoulders.

 

Thanks guys! I think I will bump it up a few psi over what my chalk test revealed