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Unread 06-04-2013, 03:25 AM   #1
highred
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Tire Pressure Recommendations

I am running Dick Cepek's FC II 33x12.5x15 on my CJ7.

I only drive on the road. No off roading. My tire pressures are 40/45 (front/rear) with a 3.5" CJ to YJ conversion suspension lift. But this is just my guess as to what I think the pressure should be.

What are others running or suggesting for street/highway tire pressure for this set up?

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Unread 06-04-2013, 03:29 AM   #2
billybooster2
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35x12.50x15


35 psi all round. Sometimes 30 ... 45 sounds hi to me and possibly bumpy. Leaves less tread on road...
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Unread 06-04-2013, 03:32 AM   #3
Manhattan
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I'm running my 35/12.50/15 BFG MTs at 22 PSI. I did the chalk test and it wore evenly on all 4. I almost never drive more than 45mph so I'm not at all concerned about heating the sidewalls.
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Unread 06-04-2013, 03:49 AM   #4
keith460
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With 32x11.50's I drive @ 26psi in the front and 24psi in the back. My CJ-7 only weighs 3195lbs with a full tank of gas.
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Unread 06-04-2013, 05:23 AM   #5
jdboy
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My current setup is 31x10.50 Cooper STT's. I ran 25psi front and rear with hard top and hard doors all winter. The ride was very good and tire wear was even all the way around.
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Unread 06-04-2013, 07:38 AM   #6
82JeepCJ7
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I run 33x12.5 on mine. I have 20psi in all the tires. I air down to 10psi on the trail. I pay special attention to the rear, as I have a spool in there and any unevenness can be felt.
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Unread 06-04-2013, 08:03 AM   #7
WindKnot
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I run 31" BFG Mud Terrains and hold 28lbs with even wear.

YOU should do YOUR OWN chalk test for YOUR Jeep. Maximum tire pressures listed on tires have nothing to do with figuring tire pressure for your vehicle. Those numbers just tell you what the maximum you can put in the tire. The same tire will need different pressures on different vehicles depending on weight and ride quality.

Here's everything you'd ever want to know about tires:http://www.4crawler.com/Diesel/Tires.shtml There's a section on proper inflation down the list.
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Unread 06-04-2013, 10:26 AM   #8
LumpyGrits
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22-25psi is all you need and will ride MUCH better.........
Who told you to run 40+psi?
LG
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Unread 06-04-2013, 10:55 AM   #9
lucdog
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Quote:
Originally Posted by LumpyGrits
22-25psi is all you need and will ride MUCH better.........
Who told you to run 40+psi?
LG
This^
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Unread 06-04-2013, 12:02 PM   #10
jurgen24
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45psi, that's probably the max pressure when seating a bead! Not for road use.
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Unread 06-04-2013, 02:55 PM   #11
I6CJ7
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How wide are your wheels?
I have the factory 15x7's (the width makes a difference) with 33x12.50r15 Mtz's
Mine are at 22psi rear and 24psi front and that's cold. Once on the highway they heat up and go up a few pounds. My Mtz's wear perfectly flat and even all the around out to the very edge of the tire.

Narrower wheels can run less pressure because they ate effectively squeezing the tire tighter in the bead and produce a rounder tire profile. Wider wheels, need more pressure to keep the tire tight against the bead and the wider wheel spread the tire giving a flatter profile.
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Unread 06-04-2013, 04:10 PM   #12
lucdog
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Quote:
Originally Posted by I6CJ7
How wide are your wheels?
I have the factory 15x7's (the width makes a difference) with 33x12.50r15 Mtz's
Mine are at 22psi rear and 24psi front and that's cold. Once on the highway they heat up and go up a few pounds. My Mtz's wear perfectly flat and even all the around out to the very edge of the tire.

Narrower wheels can run less pressure because they ate effectively squeezing the tire tighter in the bead and produce a rounder tire profile. Wider wheels, need more pressure to keep the tire tight against the bead and the wider wheel spread the tire giving a flatter profile.
Are you saying that with the same tire, 20 psi with a 15x7 rim is putting more pressure on the bead than on a 15x10 rim. I don't think so.

Bill
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1957 WILLYS pickup, needs work.
1973 J 4000,
1978 CJ7 DD.
1979 CJ7 360, TH400/Quadratrac trail Jeep.
1979 J20
1980 CJ5 trail Jeep.
1983 CJ7 pretty weekend and sometimes to work Driver in the summer, My first rebuild, if the Q-trac and 5 are broke, this one is the one to take. its just as capable as the other 2, except nice paint.
1984 Grand Wagoneer, 1 ton axles, great 360/727, and a big a$& tree fell on it .
1989 YJ the CJ to YJ conversion.
2005 TJ Rubicon.
2011 Grand Cherokee Laredo 4x4, Mrs. LUCDOG's DD.
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Unread 06-04-2013, 04:16 PM   #13
bajaviking
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A narrow wheel is less likely to loose a bead than a wide wheel when running the same airpressure. This is a well known and well proven fact.
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Unread 06-04-2013, 04:42 PM   #14
I6CJ7
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Quote:
Originally Posted by bajaviking View Post
A narrow wheel is less likely to loose a bead than a wide wheel when running the same airpressure. This is a well known and well proven fact.
Yup ^

Its not so much that the air is putting more pressure on it, but the narrow rim clamps the bead better, Like a vise.

Look at a tire when its first put on a wheel but hasn't been seated yet, its loose and sits inside between the beads of the wheel where it wants to, and its sits inches from the edge, especially on a wide 10" rim, not so much on a 7" wide one though. So the narrow wheel keeps the tire more clamped and where it wants to be, instead of the wide wheels pushing the tire outward, then aired down, that tire and the steel belts will want to slip back where they want to be.

Course once you get to super wide tires, over 12.50 then I'd go with wider wheels to support them in the same way.
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Unread 06-04-2013, 04:48 PM   #15
titomars
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I run 33x12.50 GY MTR's on 15x10 rims. For the street I run 28 lbs front and 25 lbs rear. Off road 16 lbs all 4 corners. I maybe rotate my tires once in their life span. So far, 4 years on the ground and mine are wearing pretty evenly. The rears might have a touch less thread left........Barking the tires tends do that.
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