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Unread 02-26-2012, 03:30 PM   #16
DanZ51
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'Just a perspective: a basic M998 HMMWV (curb weight 5200 lbs) runs 20/26 (F/R) PSI for 37x12.5x16.5" Radials.

Bigger tires need less pressure for a given weight. Although 16PSI maybe a bit wobbly for the street

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Unread 02-26-2012, 03:49 PM   #17
AKGeo
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Quote:
Originally Posted by PredatorNC View Post
Good points made by all, and being a noob to the jeep world, there was a healthy amount of fear thinking that 16 psi was a sweet spot...and that 16 psi was optimistic...there was still chalk there so another 2-4 lbs would have probably made it even.

TYVM! bringing the info on the wheel width! Yes, I am running 15x8's. So literally I would have to run a 12" width for it to lay flatter with more psi correct?

Thanks for being noob kind! lol
10". Your tires are 12.5's but the tread is only 10" wide...the width is also counting the sidewall bulge. Tire manufacturers recommend wheel widths for each size tire, and most 12.5's have a 9 to 10" width recommendation.


It's a trade-off. If you want your tires to last as long as possible, get wider wheels. If you want your tires to perform offroad at lower PSIs without blowing beads, get narrower wheels or beadlocks.
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Unread 02-26-2012, 08:32 PM   #18
Fortune
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I understand the chalk test... What's the spray bottle test?
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Unread 02-26-2012, 09:13 PM   #19
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TJ soft top with 35X12.50 on 15X8. I am probably too high but I am running 30 in the front and 28 in the rear. Might drop them all down 2 psi but they look pretty good right now.
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Unread 02-26-2012, 09:15 PM   #20
Jerry Bransford
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Originally Posted by rkwfxd View Post
TJ soft top with 35X12.50 on 15X8. I am probably too high but I am running 30 in the front and 28 in the rear. Might drop them all down 2 psi but they look pretty good right now.
24-26 is appropriate for that size tire supporting a Wrangler. 28 and 30 is excessive for a 35" tire.
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Unread 02-26-2012, 10:12 PM   #21
Maverickxeo
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I have been trying to find out what I need to run for PSI in my 33x10.50R15 BFG A/T tires, but I cant quite find a good 'balance.' I havent done the chalk test, but I have seen that when Im driving down a dirt road, and come onto the street, the centers of the tires are pretty dirty, but they outsides look relatively clean (basically, they dont seem to be touching all the way). I believe Im running 24PSI right now, on the canyon wheels... Am I set too high for the street?
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Unread 02-26-2012, 10:19 PM   #22
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Quote:
Originally Posted by Maverickxeo View Post
I have been trying to find out what I need to run for PSI in my 33x10.50R15 BFG A/T tires, but I cant quite find a good 'balance.' I havent done the chalk test, but I have seen that when Im driving down a dirt road, and come onto the street, the centers of the tires are pretty dirty, but they outsides look relatively clean (basically, they dont seem to be touching all the way). I believe Im running 24PSI right now, on the canyon wheels... Am I set too high for the street?
Getting the entire tread on the ground is not the goal, that would be underinflated. For a 33x12.50 BFG AT supporting a Wrangler, 26-28 is actually about right.
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Unread 02-27-2012, 03:08 AM   #23
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Quote:
Originally Posted by Fortune View Post
I understand the chalk test... What's the spray bottle test?
On a clean level driveway, with cold tires, use a spray bottle to mist the tire, then roll forward a few feet and look at the tread pattern left on the ground. If it's darker on the inside than the outside of the tread pattern then the tire is over inflated, if it's darker on the edges, then it's under inflated. Same principal as the chalk test but it's faster.
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Unread 02-27-2012, 03:43 AM   #24
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.... and I'm running 30 psi on my Cooper STT 33x12.5r15 ..

Would having a hardtop and a tire carrier makes any difference ??

I guess that I should lower the pressure to 26~28psi....
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Unread 02-27-2012, 09:36 AM   #25
ytowntj
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After running 32x1150 and 33x1050 bfg ats on my TJ Id feel safe recommending 26-27 psi. I ran 28 pounds in my 32s and got TONS of life out of them.
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Unread 02-27-2012, 09:55 AM   #26
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I run 37 in MTR w/Kevlar on Evans Beadlock 17s. PSI for street 26 and off-road 8-10. My jeep is heavy at 5500 lbs loaded.
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Unread 02-27-2012, 10:03 AM   #27
Griff1918
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well, the other way to figure out the psi is a mathmatical equation.
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Unread 02-27-2012, 10:57 AM   #28
Peterpsc
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Quote:
Originally Posted by Griff1918 View Post
well, the other way to figure out the psi is a mathmatical equation.
The formulas I've seen don't work for my jeep. Here's an example of what appears to be a popular formula for tire PSI (cold pressures). It can be found on various forums:

(Axle Weight / 2) / Tire Capacity) x Tire Max PSI = Inflate Pressure

While the formula doesn't work for my jeep it gets real close for my dually.

Which formula are you referencing?
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Unread 02-27-2012, 11:00 AM   #29
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I run 29psi with my KM2 and I have been getting great wear the past 25k miles
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Unread 02-27-2012, 11:02 AM   #30
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26F/24R psi on the road, 8 psi off.
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