Trust BFG or Chalk Test on tire pressure?

Is this good enough? Or do I need to have the chalk completely gone? Is there a standard to how much PSI to add for every 100 lb. of load?

 

Rather old thread resurrection

 

Yep, search > new thread.

 

I'd go farther. You're doing right by deflating down.
Chalk is nice but makes no allowance for a laden vehicle or dynamic loading of the tire.
I recommend adding 10% to whatever your final chalk PSI is.
There is no standard for PSI-to-weight. But, it can be calculated if we know your tire size and load rating.

 

You're right. I actually had to add air last night 'cause I needed to haul 10 crates full of books and a big cooler full of frozen meat.

The front PSI is 34 at that "chalk level". When it was at 33, the chalked was rubbed off from about 98% of the whole surface (width).

My tires are: Cooper Discoverer ST Maxx 265/75/16 Load E.

The calculation you mentioned is intriguing, I'm looking forward to seeing it.

 

A 265/75/16/E has a 1,910 lb load rating @ 35 psi; and 2,100 lbs @ 40 psi.

2,100-1,910=190 lbs

40-35=5 psi

190 lbs/5 psi=38 lbs/1 psi

 

I'm curious...

• Where did 1,910 lb at 35 psi come from?
• Where did 2,100 lb at 40 psi come from?
• I'm assuming this formula is what I use to determine how much air to add after a chalk test (with the whole width of chalk marks erased) prior to adding load.
• 38 lb/1 psi is per tire, right?
  • If I have a 200 lb passenger, I would add 1.32 psi per tire, correct?

 

Toyo load inflation pdf.
https://toyotires-1524598101.netdna...ication_of_load_inflation_tables_20170203.pdf

Correct; per tire...

 

Thanks for the resource. I wonder how accurate the chalk test would be in relation to this calculation. Too bad I don't have hundreds of pounds worth of load laying around to test this out.

If I applied your recommendation, won't the chalk marks then be thicker at the edges leaving me with bald center tread in the long run?
I'm assuming this recommendation is for when I need to load something heavy and not bother about worrying whether or not my tires are sufficiently inflated.

 

Correct; payload purposes.
It's optional.
I haul heavy loads on a regular enough basis; I don't want to mess with it all the time. Today it was 800 lbs of wire...

 

If the size of the slow, cold, straight contact patch was the only variable in the universe, then maybe I could trust the chalk test.

 

If you do a proper chalk test, it accounts for some of the variables. Too time consuming and doesn't account for a spontaneous payload, IMO.

Proper chalk test
https://www.4wheelparts.com/a/tire-wheel-package-guide-tire-pressure-checker

 

Good link, thanks!

 

I ran these for a while at 32 cold. BFG told me to run at 50. I have bigger ones now I run at 33. Off-road I run according to trail conditions. I think your wheels are 7 1/2s so you likely can run closer to factory spec.

 

When I got a set of Cooper ST Maxx, I immediately set the air pressure based on a chalk test. It's been 18 months and about 20,000 miles later, wear-and-tear has been pretty good. I also have the tires rotated every 4,000 miles.

On a few occasions where I have heavy load on the bed, I just set all tires to 35 psi. Haven't had a problem.

 

Approx. 62,000 miles on my Cooper ST Maxxs, would you say my tread reading 8.5-11.5/32 is acceptable or can I do better? I've always set my PSI at 26 rear and 32 front, rotated every 5,000 miles (now rotating every 3,500 miles).