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Old 01-19-2008, 01:50 PM   #1
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How Much Pressure On 35x12.5x15 Tires?

hello.

how much pressure sould i have on my 35x12.5x15 cooper STT tires on 8.5x15 rims?

the tire shop put too much air inside in my opinion. itīs about 38 psi. and it rides a bit rough.

would 30 psi be better? or how much would be perfect?

thanks in advance.
nicolas-eric

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Old 01-19-2008, 01:57 PM   #2
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mine are at 33 and they seem good

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Old 01-19-2008, 02:05 PM   #3
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I have MTs on mine and I run 38 on the highway. They roll easier that way. They do feel the bumps more, though. I air them down when I go off road.
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Old 01-19-2008, 02:12 PM   #4
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If you want to do it right, you gotta do the chalk test. you want just low enough pressure to get a good, even footprint.
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Old 01-19-2008, 02:15 PM   #5
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Quote:
Originally Posted by JCS05Rubi View Post
If you want to do it right, you gotta do the chalk test. you want just low enough pressure to get a good, even footprint.
i already did that. the tires have only contact to the ground in the middle.
with the old BFG AT i did the same and it was perfect at only 26 psi.

i asked here here because only 26 psi seems a bit too less to me.
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Old 01-19-2008, 03:17 PM   #6
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26 seems a bit low, i'd say between 30 and 33 would be your best bet...
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Old 01-19-2008, 03:43 PM   #7
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my 33' trXus on 15x8's are at 28# rear (with the HT on) 26# front and rear with out the HT. I get a nice even wear pattern and a soft ride.
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Old 01-19-2008, 05:47 PM   #8
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i don't think 26 seems low.

i think Jerry runs about that or 28 in his 35's.

i don't think 30 would be bad but i might go a little lower.
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Old 01-19-2008, 05:54 PM   #9
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ok thanks.

iīll first try 30 and then after some brake tests in the rain iīll go down to 28.
now with 38 teh STTs donīt brake worse than the old BFG ATs.

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Old 01-19-2008, 07:13 PM   #10
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26-28

30-38 is only good for teeth chattering
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Old 01-19-2008, 08:15 PM   #11
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I run 25psi.
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Old 01-19-2008, 08:19 PM   #12
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i say 26-28
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Old 01-19-2008, 08:21 PM   #13
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I run about 28-29 usually but I like a stiffer ride.

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Old 01-19-2008, 08:25 PM   #14
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just deflated the tires.down to 30 psi.
now it rides smoother, but in curves itīs a bit worse.
braking on wet roads is much better now. even better than with my old BFG ATs.

i think 25 psi wil be loo less. i will try it out with 30 psi for some days.

how low can i go with the pressure off the road?
the old BFG ATs jumped off the rim twice with 17 psi. it was always the right front wheel with engaged lockers in a curve to the left in deep mud.
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Old 01-19-2008, 08:51 PM   #15
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Often people inflate tires according to the recommendation on the sidewall. This is fine if you are at maximum load. However, a jeep TJ weighs about 4000 lbs. stock which means that each tire only has to support about a 1000 lbs. If you look at what the tire can support at maximum pressure you'll find it's a lot more than a 1000 lbs. Adjust your pressure down if you want a smoother ride. If tire life is more important, air them up a bit. Just play around with the pressure until you find whats right for you. I run mine at 30 psi on the road and 8-10 on the trails. I have 35/12.50/15 as well, but my rims are 8 in.
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Old 01-19-2008, 08:56 PM   #16
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8-10 off the road? without bead locks?

then itīs really unbbelievable to me why my BFG ATs fell off the rim twice with 17...
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Old 01-19-2008, 09:00 PM   #17
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I was under the impression under 10 without bead locks is a no no?

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Old 01-19-2008, 09:04 PM   #18
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Quote:
Originally Posted by Levinoss View Post
I was under the impression under 10 without bead locks is a no no?

~Lev
thatīs why i tried it first with 17, but the front tires jumped of the rim nevertheless.

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Old 01-19-2008, 09:19 PM   #19
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thatīs why i tried it first with 17, but the front tires jumped of the rim nevertheless.

Must depend on the tires, I ran on about 14 on my front driver side tire for a good 30 mins around town Friday trying to find a gas station with a air machine. I was hoping like heck nothing would mess up and it didn't thank God.

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Old 01-19-2008, 09:28 PM   #20
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i hope i donīt have to deflate the new STTs that much that the y jump off the rim. a friend used them in deep mud with 30 psi (32s) and could do more than others with MTRs or BFG MTs.

btw. thatīs why i have a viair 400P in my trunk.
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Old 01-19-2008, 09:30 PM   #21
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i hope i donīt have to deflate the new STTs that much that the y jump off the rim. a friend used them in deep mud with 30 psi (32s) and could do more than others with MTRs or BFG MTs.

btw. thatīs why i have a viair 400P in my trunk.
Yea once I few more items for my rig i'll be installing a air pig in mine.

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Old 01-19-2008, 09:34 PM   #22
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is that enough for airing up 4 big offroad tires?

i already have a small ARB compressor, but that one needed 20 minutes to inflate a 35s tire from 15-30. the viar does the same in 3 minutes.
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Old 01-19-2008, 09:39 PM   #23
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I go 28/25psi front/rear and never below 8psi off road.
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Old 01-20-2008, 01:54 AM   #24
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Quote:
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is that enough for airing up 4 big offroad tires?

i already have a small ARB compressor, but that one needed 20 minutes to inflate a 35s tire from 15-30. the viar does the same in 3 minutes.
if you want something that will inflate fast then you need something taht is engine driven not electric. i think quadratec sells them. i will be putting something similar in my jeep when i get the 35's on it.

your other option is to just keep a small pancake compressor in your trunk
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Old 01-20-2008, 05:22 AM   #25
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for my 35 trxus's: street @30 psi works well for mine.
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Old 01-20-2008, 08:48 AM   #26
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Quote:
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I was under the impression under 10 without bead locks is a no no?

~Lev
I ran 8# on the rocks @ Llano, no problems...I was one of many to do the same...
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Old 01-20-2008, 10:28 AM   #27
Knows a couple things...

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I run 7-8 psi on the rocks with my 35x12.50 MT/Rs mounted on non-beadlocked 15x8 AR 23 wheels. Have not lost a bead yet. On the street, I get consistently good even wear at 26-28 psi. I started running 28 just to help with the mpg a little and the MT/Rs seem to like that street pressure, at least they do wear perfectly evenly at that pressure on a 15x8 wheel.
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Old 01-20-2008, 10:30 AM   #28
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i run 26 in my 33-12.5 baha claws... works perfect for me
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Old 01-20-2008, 05:18 PM   #29
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Often people inflate tires according to the recommendation on the sidewall.

I believe the markings on the sidewall are not recommendations. They are a rating for the max inflation for that specific tire.
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Old 01-20-2008, 05:24 PM   #30
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i am a bit cunfused.

why do your MT tires stay on your rims with only 6-8 psi and my ATs jumped from the rims with 17 psi.

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