tire pressure theorycrafting 285/70/17

[MadCityRich]

So I've just mounted up 285/70/17 Duratracs load range D tires. Currently set at 40 psi. They ride pretty nicely.

I was reviewing the Toyo tire pressure tables and the issues of switching between a P metric pressure recommendation to LT.

http://cache.toyotires.com/sites/default/files/imce/LoadInflationTable.pdf

My door sticker says to do 32 psi on the stock P265/70/16 tires. Using the Toyo table on page A5, they indicate that at 32 psi, the tire has a load rating of 2,326 lbs.

Using the table on page A10, I see that Toyo has LT285/70/17 with 2315 lbs at 40 psi. That's pretty darn close to the stock tire load rating at 32 psi and suggests to me that 40 psi is reasonably appropriate to use on the new tires.

For those that obsess about these things, I'm curious as to whether I'm using these tables appropriately and/or whether 40 psi seems reasonable as a tire pressure on the LT285/70/17 tires.

What says ye?

Naturally, I'll be testing this out to see what issues come up and may adjust based on experience.

Thanks,
MadCityRich
2002 4Runner
285/70/17
Konig CS
199mm brakes
SS 7.2
Poly bushings

 

[PhdNPrerunners]

Sorry this has nothing to do with your post but could you post some pics of your rig?

 

[ALBPM]

40psi is about as high as you would want to run in the front tires. Any higher and they would ride like rocks.

I have 285/75/16 Revo2s and run 39 in the fronts and 37 in the rears. I don't have anything in the back therefore no extra weight over the rear tires. These are the pressures that the tires wear evenly on my Runner.

 

[spectre6000]

You want to run the highest pressure you can without sacrificing safety or handling. You have the benefit of factory recommendations with stock tires, but once you leave that realm you're pretty much on your own. The best way to tell is by looking at the tire's footprint. Too high a pressure and your contact patch turns into a little circle in the middle. Too low and your contact patch lightens in the middle as the sidewall begins to bear the load the air pressure can't handle. Try the paper trick and it will be readily apparent what you're dealing with. Larger tires have more surface area and thus require greater pressure to maintain the same level of performance.

My strategy (aside from the paper trick) is generally to air them up to maximum recommended pressure on the tire with the truck in its "usual" configuration and see where it sits. It will likely be far more pressure than is required unless you have a D rated tire and a very heavy rig. Air down until the tread is good and flat with equal contact across the tread. Ride quality will also be an indicator. Once you get it to a good spot, check where you're at with a good reliable pressure gauge and maintain that pressure. Occasionally keep an eye on the wear. If it starts to wear more in the middle of the tread, air down a little more and maintain the new lower pressure; the converse if it wears more on the sides.

 

[JB.]

For those that obsess about these things, I'm curious as to whether I'm using these tables appropriately and/or whether 40 psi seems reasonable as a tire pressure on the LT285/70/17 tires.

You are, and that's the right pressure from the standpoint of matching the stock load reserve.

Since you obsess about these things, you may enjoy this thread.

http://www.toyota-4runner.org/general-discussions/110299-lt-tires-need-more-air-pressure.html