Chalk test questions

First time I have outsize tires, I know 32 is wrong for these 295/70/18 Cooper Discoverer AT3s on TRD PRO rims.

This is at 42 pounds on my Sequoia.

What is the chalk telling me?

Driver front:

Driver rear


Passnger front



Passenger rear

 

Hard to see but looks like the tires are over inflated for the load on them. They may also be just right.

Chalk on the outside means too much air.
Chalk on the inside means too little air.

 

For what it’s worth I ran the same size tire on a ‘14 CM and I found the best handling ride and wear was at 40lbs all around

 

It is hard to see, it looks to me like there is no chalk on the passenger side & a bit on driver side inside.

I layered it on thick on all 4 tires.

Thanks

 

I should reword what I said for clarity.
Chalk in the middle is underinflated
Chalk on the outsides is over inflated.

Given what the other poster said I think you are slightly over on all for corners with exception of the driver front which looks good or very close to it. Overall you are very close. You can also run it through a calculator like this one:

 

I agree, they look a few lbs too high on pressure. That calculator above is a great tool to get in the ballpark on air pressure. Then adjust a few lbs up or down based on how you load and drive your truck.

 

I have found 38-40 as the sweet spot for oversized E rated on a Tundra. It firms up fast over 40 IME

 

How far are you driving after you chalk up the tires? I've been asking myself how much air should I actually be putting in tires. The calculator says 26 PSI, but that seems wrong to me?

 

It should just be a short drive in a straight line on even-ish flat ground. No more than 50ft or so.

 

What I’ve never understood - don’t the forces and dynamics change significantly at speed? How valuable is the info revealed in a chalk test?

 

Easiest thing to do is email Cooper and ask what psi to run.

The chalk test is really a bit outdated but can be somewhat helpful dependent upon tire. The AT3 XLT which those appear to be will be pretty close.
Many tires especially hybrid tires are not meant to have the treads contact the pavement evenly across.

 

They do indeed. At speed the tire will heat and change shape a bit.

The point as I see it though, it to verify proper tread patterns at low speeds, which will equate at high speeds wit the tires natural inflation and deformity.

 

By no means a perfect system but gets you in the ballpark. I've seen it used more on vehicles that are constantly heavily laden. Decent way to predict uneven wear. The tire pressure calculator is equally useful.

 

I drove 40-60 feet. I replaced my front shocks yesterday so am getting a new alignment Saturday. I'll bring it to 40 & do the test again after the alignment. I'll email Cooper now.

Thanks!

 

Set to 40lbs, rechalked, will post after a short drive..

 

When I worked out pressures for the 37s I looked for ~1/4-3/8" of chalk remaining on the edges to let the carcass flex and load up a bit during cornering. This also gives you a visual reference for how many tread blocks are activated for the correct contact patch. If you load up, adjust your pressures to get back to that amount of tread blocks.

For reference, I set my alignment to 0deg for camber and toe. Measuring tread depths a few thousand miles later, I was within 1/32" across the tire width. Pretty dang pleased with the approach.

Just eyeballing, I'd tell you to come down a few pounds on each corner and try 38-40PSI.

 

Chalk test seems to say 40 lbs.

 

No expert here, but I agree. Always seemed silly to me. So I just inflate my 10 ply’s to whatever psi the maker says I need to support the same weight the factory tires did at their factory recommended psi. Besides, chalk dust makes me sneeze. Usually someplace around 40 ish front and 43ish rear has been where I landed so far. Tires are wearing very evenly with 5k rotations.

 

Cooper's response:

Thank you for contacting us. I’ve attached a load & inflation table for the LT295/70r18 tire size that you can use as a reference. In your application, for normal everyday driving a good rule of thumb is to add about 5 psi to your door placard pressure, which based on the information provided would be about 37 psi, there should be no issue with 40 psi if you believe that creates a more even footprint.

 

are you guys doing 40lbs stone cold? If I set to 40 lbs cold in california, 15 minutes on the freeway and Im at like 44 PSI. I have to set at like 36 or 37 cold or it shoots up really fast.

 

Just had mine balanced and rotated, Schwab set all 4 @ 37psi. I have no noticable "strange" wearing after 5000 miles. I am happy with the ride also