Another Tire Pressure Question

[steve73]

I've looked and looked and did manage to get part of my question.

32psi is recommended for stock tire

When going from a p-metric to a LT , you add 10-15 psi when the tire dimensions are the same(265/70r17)

What about the tire pressure going from a stock P 265/70r17 to a LT 285/70r17 D rated?

Do I add more/less?


What PSI are you running.

 

[Beakerbox]

Going P to LT isn't an automatic add 10 - 15 pounds. It depends on the load rating of the tire.. I believe the tire dimensions are mostly irrelevant?

AFAIK P rated tires @32 psi = 36/37 psi for C load LT and I believe 44/46 PSI for E load LT. I don't know the "number" for D rated but i'm sure someone on here has posted a PSI since what your going for is a common choice.. Duratrac?

 

[steve73]

Going P to LT isn't an automatic add 10 - 15 pounds. It depends on the load rating of the tire.. I believe the tire dimensions are mostly irrelevant?

AFAIK P rated tires @32 psi = 36/37 psi for C load LT and I believe 44/46 PSI for E load LT. I don't know the "number" for D rated but i'm sure someone on here has posted a PSI since what your going for is a common choice.. Duratrac?

They are Copper STT Discoverer max is 65 psi.

 

[JB.]

Dimension does matter, load range does not, so about 38lbs for the 285/70/17 to match stock load reserve.

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

 

[Beakerbox]

I was just reading that! Very informative explanation! Sorry for the misinformation in response to the OP - unfortunately JB's thread wasn't around when I done my research and searching that topic leads to many different results.

I also found this which was most helpful.
http://www.toyota-4runner.org/general-discussions/110300-ask-tire-engineer.html

 

[steve73]

Thanks JB

 

[steve73]

So 40PSI should do the trick right


I had them at 35 but trying to improve my fuel consumption.

 

[1engineer]

So 40PSI should do the trick right


I had them at 35 but trying to improve my fuel consumption.

It's the lift and the tire weight causing your increased fuel consumption. With the lift you are, for simplicity's sake, punching a bigger hole through the air while at speed. The tire's increased weight (also part of your unsprung weight) is detrimental to efficiency because during city driving you are having to accelerate those heavier tires from a stop at every stoplight and intersection. Tire pressure? Not really gonna help efficiency much but will help load carrying ability.