Tire chalk test

I have a 17 Tacoma SR5, came factory with 245/75/16 tires. I just lifted the front 3” and the rear 2” and had 285/75/16 Cooper Discoverer STT Pros installed. I have read about the chalk test and tried to do it today to make sure I will have even tread wear. However I lowered the tire pressure all the way down to 20psi and the chalk was still wearing off the middle of the tread but not off the sides. Is there anything else I can do? Or maybe someone with a similar set up what are you running and how is your tread wear?

 

It will never reach the edges, don't go below 28psi cold, and if you haul or tow, don't go below 40-44psi cold.

Especially if you have the stock SR5 rims, they are narrow and the tire curves outwards on 285's. It will simply never contact.

 

The chalk test is an anachronism. Inflate your tires to the manufacturer’s recommended psi for the weight of your truck.

 

So you can read up and learn the whole thing, apply the load tables to your truck weight ect ect, but if you are putting LT tires on a generally not overly heavy Tacoma you will find you will need 35PSI to account for the same load ratings as the standard load tires the factory put on.

This excerpt from the link below says it best:
"WARNING! Please note that size-for-size, LT-metric tires require higher air pressures to carry equivalent loads of P-metric tires and that any failure to adjust air pressure to achieve the vehicle’s load requirements will result in tire fatigue and eventual tire failure due to excessive heat build-up. Due to the higher PSI requirements of LT-metric tires they may not be suitable for replacing O.E. P-metric tires because of the ride harshness that results from higher PSI requirements. "

That said, many people run a little less still.

https://www.toyotires.com/media/pxcjubjs/application_of_load_inflation_tables_20200723.pdf

 

Your stock rims are 7" wide. The tires are approved for rims 7.5" to 9" wide. The tires size measurements were made on an 8" wheel. An 8" or an 8.5" would be ideal unless you can live with the inner tread wearing faster than the outside.

 

Here is a great tool to calculate correct pressure based on factory specs and new tire size and load rating.

 

This is great. Exactly what the charts said, but way easier!

 

Don't forget that the charts are load per tire.

 

I have not been able to get any technical or scientific data in support for the “chalk test” tire inflation method.

What I have found is that whats good for the tire (inflation wise), is not necessarily good for the vehicle and vise versa. The 2001 Ford vs Firestone fiasco proved that, long story.

So it’s no wonder everyone makes their own rules leading to a great deal of grief. In a nutshell, tire inflation is a compromise. You’ll give up something not matter what you choose, to gain something you may want more.

If you look on the sidewall of the tire, it will give you the recommended max load psi tire pressure. Somewhere below the max (around 4-6psi below max) is where you’ll get max tire load, life and mpg. As you go even lower, you’ll lose that, but pick up max vehicle road traction and comfort.

Going back to the mid 90’s-2001 Ford vs Firestone fiasco, Ford needed max traction to help keep their vehicle (explorer) from flipping over on tight road maneuvers, so they recommended lower tire psi which made the tires very unhappy and they just blew it! Literally lol!

I run 38psi on mine, max cold is 44psi recommended on my Coopers Discover ST3 4s and get great gas & tire life and good adhesiveness to the road in the higher speed rainy environment In which I often find myself.
Not much help I know, but it’s based around factual events. Never the less choose wisely because you maybe dammed if you do and darned if you don’t.

Cheers!

 

Using the charts...
You need an inflated capacity of 1,954 lbs fro LT-metric tires...
'Minimum' psi for an LT-metric is 35 psi...
Your tire has a capacity of 2,130 lbs @ 35 psi...

You could extrapolate a value for psi/capacity based on 35-40 psi. About, 31 psi...

 

I'm not sure I have ever heard the word "anachronism" until now. I will now look more intelligent using that word instead of saying that the chalk test is non scientific shade tree gimmick that provides zero meaningful scientific data.

 

https://youtu.be/rcLaXzw-Sds

 

The problem I have with the chalk test is that it doesn’t take into account the ever changing road surface. In other words the surface won’t stay the same as when you ran the test.

Most paved roads have a crown for drainage, which in itself changes the vehicle alignment and weight (shifting) it’s trivial, but overtime (in miles) it all adds up. Then you have hills, inclines and descends, which also change the alignment dynamics and weigh and wear.

These are the real world operating realities that a static “chalk test” might not be able to address.
The door sticker inflation recommendations is a peek into of the automaker’s sweet spot for comfort and optimum traction recommendations, but as we saw in the 2001 tire lawsuit fiasco, they give little to no thought into the tire requirements. That’s their (tire maker) and consumer’s problem.

Granted, tires have improved a lot since the ’00’s and even in the last five years, but the limitations on all tires stand, and so do the warnings.

The tire sidewall is still your friend, stay safe my friends

"WARNING! Please note that size-for-size, LT-metric tires require higher air pressures to carry equivalent loads of P-metric tires and that any failure to adjust air pressure to achieve the vehicle’s load requirements will result in tire fatigue and eventual tire failure due to excessive heat build-up."

 

Thank you all for your insight, I will ran 35psi cold and see how it is wearing. Also believe the stock wheels being 7” wide is probably a big factor, causing the tire to bulge. I am kind of committed to my set up now, but on the next set of tires will look at upgrading my wheels to a 8” or 8.5” width for more even wear. Once again thank you.

 

I agree... The chalk test, as practiced by most is not viable; a more 'dynamic' approach can be...but, it tends to lose it's appeal as 'simple'.

"You can also “calculate” your tire pressure with the chalk method. This involves coloring a section of your tire with chalk to see how much tread is making contact with the ground. Start by finding a flat road surface. Concrete is actually the best choice, but you can also do this on asphalt. Make a mark with soft chalk that goes all the way across your tread. Then, gradually drive your truck forward about 50 feet and then backwards 50 feet.

Analyze the chalk on the tire. If the chalk is only worn off on the center of the tire, reduce the tire pressure slightly and go through the process again. With the adjustment, you should see the chalk wear off more broadly. Keep making tiny adjustments in the tire pressure until the chalk wears off evenly and all the way across the tread.

You will have to complete this process for each of your four tires. Once you’ve found the right street pressure, add 10% to all four tires. Then, measure the tires and add pressure to balance them. As explained above, you need to measure from the wheel to the ground. Start by balancing the profiles of the front tires with each other. Then, balance the front tires again with the rear tires. Always adjust the tires with the smaller profiles by adding air.

The advantages and disadvantages of this method are the same as those involved in the second method above. If you go through the process correctly, you end up with the ideal tire pressure. But, this method is tedious and there’s a reasonable chance that you will make a mistake."

 

Yes, as smartly noted by @Speedfreak the wheel size deviation from the tire wheel/size recommendation is making your setup a lone wolf, or rouge operator. In other words, you maybe in uncharted territory, but I bet someone else has been or is there too lol!

 

From the Toyo chart

My LT235/85/16 have a load capacity of 1700lbs at 35psi. That is 3400lb per axle, 6800lbs for the truck. That is damn close to max load for the our trucks.

The LT265/75/16 that many run has a load capacity of 1910lbs per tire at 35psi. 3820lbs per axle, 7640lbs for the entire truck.

 

I've chalk tested my tires before as well, works great in parking lots with lots of winter salt.

However, keep in mind that tire manufacturers dont make tires based on chalk tests, they spend a lot of time and money engineering their tires and leveraging applicable inflation tables based on load ratings. Hundreds of millions of people, probably billions dont chalk test their tires and they wear fine. IF you have a wear issue its most likely an alignment or inflation issue, no chalk test needed.

 

did you get an alignment after these geometry changes to the trucks suspension?

 

I certainly did.