Does anyone know the best tire pressure to run on a 35x1250x17 bfg km2 for everyday city driving? To keep this thread a little more helpful for everybody, you can just post the tires you run and tire pressures you like best. Thanks.

 

35" Pro Comp Xterrains. 32 PSI on the street and 15-18 PSI on the trails

 

You should just do a chalk test. Everyone is different, and the load ranges and Max PSI are going to be different, so, what works for one tire, amy not be right for another.

 

Another "vote" for chalk test. Really the best method. A quick check can be made with a credit card. Preferably on smooth concrete slide a cc under the edge of the tread. If it goes under you are overinflated, if it doesn't then you are under inflated, if it goes in about a 1/4" you're just right.

Another thing to concider is the '08 TPMS. Mine is not happy unless over 30psi, but my tires like to be at 26...

Bob

 

Why wouldn't you use the max pressure on the side of the tire for the best mileage?

 

Well, mostly because the Max PSI is related to weight capacity....and, if you are not carrying that much weight, the tire tread will be bowed in the middle, and the inner/outer tread patches will be in mid-air.

Now, if the tire's load range is in the right ball park, you COULD run Max PSI, and it would be OK, but, as a general rule of thumb, while max psi will reduce the rolling resistance by dramatically reducing hysteresis losses, it will also reduce traction, control, and handling, and will change your effective spring rate, typically making the tire bounce, cupping the tread, and having other undesireable impacts.

The chalk test is the best way to determine the specific psi you want...and, if applicable, you can play with the PSI from that point, to account for projected higher speeds on a long trip, or extra weight for that trip, etc.....and/or lower psi for aired down work on sand, mud, rocks, etc....

...to help decide what psi works on THOSE terrain.

 

I have 35x12.50x18" Nitto's and I'm running 30 psi but it could stand to be dropped it a few pounds. Again, as a few have stated, the chalk line test is the best method.

 

Someone told me to run about 15% less what is marked as the max psi on the side wall for on the road travel. I can't remember where i heard it but it has worked for me so far

 

This kind of bullshit is what causes so many problems for people.

A well meaning guy mentions a rule of thumb that sounds broadly applicable, but has no basis whatever in fact....and then its repeated until a bunch of unsuspecting newbies get fouled up.

(The BS comment is directed at the guy who you can't remember, not at you btw...)




The "RIGHT" psi has no accurate rule of thumb....there are too many variables.

About the only rule of thumb that comes close, is that the psi on your placard was chosen by the manufacturer for the oem tires....and, that the psi chosen will provide a soft ride and massive, lawyer freindly understeer.

If you do not use the exact same tires, or you prefer tighter handling and a more neutral over/understeer balance...the oem psi on your placard will not work either.




Again - different tires have different MAX PSI, and, Different load carrying capacities at those different psi, etc.

A tire that has a max of 60 psi to support a MAX Load of 1,300 lb, and a tire that has a Max psi of 60 to support a MAX Load of 3,600 lb, will drive nowhere like each other at 15% of their Max psi's....and, in fact, the tire might be dangerously over or under inflated at that psi, on YOUR truck.

For example, lets say your jeep weighs 5,000 loaded up and driving somewhere, so each tire is supporting a 4th of that 5,000 lb, or 1,250 lb.

At 85% of 60 psi, that makes the first tire at 51 psi, and the second tire at 51 psi too (Both have a MAX PSI of 60)

So, the tire that needs 60 psi to hold up 1,300 lb, only has 51 psi, and maybe only able to support 1,100 lb, instead of the 1,250 it needs to.

The tire that needs 60 psi to support 3,600 lb also has 51 psi, enough to support around 3,060 lb.

Tire one will be wishy washy, and might blow out on the hwy.

Tire two will be as bouncy as hell, hydroplane, skitter, etc.

In short - Just figure it out, don't guess....its safer.

The easiest way to figure it out is to chalk it.

Or just keep trying random pressures until you find one that works.