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post #1 of (permalink) Old 09-10-2000, 11:33 AM
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Air pressure

To settle a bet with a buddy, what's the best air pressure to have while running 31-10-15 BFG's on the street?

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post #2 of (permalink) Old 09-10-2000, 11:42 AM
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Re: Air pressure

When I had 31s I ran the same pressure I'm running in the 33s, 23lbs. Any more and you wear the center of the tread.

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post #3 of (permalink) Old 09-10-2000, 11:52 AM
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Re: Air pressure

Sounds about right- I run 25lbs in my 31x10.5s on the Wrangler on road and 8-10lbs off-road

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post #4 of (permalink) Old 09-10-2000, 12:30 PM
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Re: Air pressure

BFG tire dealer said I needed to raise my tire preasure to 40 psi, on the road for safty and handling. I though he was nuts, but the road handling was much better, but a rougher ride and it takes a long time to let the tires down for off road and to air them backup with my little compressor that I carry.

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post #5 of (permalink) Old 09-10-2000, 12:58 PM
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Re: Air pressure

25 PSI? is that for good tire life? i'm running mine at 35 and they used to be at 40? is 25 what u use for the highway too? that seems like it would eat up the tire but i may be wrong!

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post #6 of (permalink) Old 09-10-2000, 01:29 PM
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Re: Air pressure

I always thought that tire pressure depended on the exact weight of the vehicle? Do the chalk across the treads and drive it on a flat surface... If it all wears off evenly then you have the right pressure... At least that's the way I've known it to be? [img]/wwwthreads_images/icons/crazy.gif[/img]

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post #7 of (permalink) Old 09-10-2000, 02:02 PM
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Re: Air pressure

There are a lot of variables that go into an answer to your question. The chalk mark answer probably comes nearest to getting you the answer.

Look at a couple of things. If the tire tread from side to side is distributing equal weight all the way across, then it will have the best traction and most even wear, but there are different things that come into play besides just air pressure. Rim width. If the rim is wide compared to the tire width, the tread itself tends to exert less pressure in the center of the tread width, just as it does when tire pressure is too low, so it might be necessary to raise the air pressure. If the rim is narrow compared to the tire (12.5" on an 8" rim for example), pulling the bead on each side closer together causes the tread to bulge outward in the center of the tread width. So, in this case, to get a flat footprint, the air pressure may need to be lowered.

What if you don't want a flat footprint? What if you have a tire with a good highway tread pattern in the middle third of the tire and good heavy lugs or paddles on each side of that center tread. You might not want the lugs to hit the concrete. Put the tire on a narrow rim with more air pressure. Make the center stick out and keep the lugs off the road. Is this a good idea? I have no idea. Just thought it up on the spur of the moment to further emphasize the changes you can make.

Bias ply and radial ply behave differently too, but there again, the chalk mark will give you some insight.

The above applies to street running. When you get off road, the rules change.

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post #8 of (permalink) Old 09-10-2000, 03:09 PM
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Re: Air pressure

I am running about 26 lbs. with 31 X 11.5's on the road. Was running 35 but made for a much stiffer ride.

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