33x12.50 - What PSI do you run?? - JeepForum.com

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post #1 of 22 Old 10-01-2007, 03:48 PM Thread Starter
bman9089
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33x12.50 - What PSI do you run??

Afternoon guys,

I'm wanting to get some advice on PSI to run in the tires. I think I'm sitting at about 33 right now, but want to have the best wear/ride quality possible.

So, what do you think is the best?? What's your PSI on road?









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post #2 of 22 Old 10-01-2007, 03:52 PM
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If you have 8" wide wheels, 24-28 psi will typically get you the most even tread wear.
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post #3 of 22 Old 10-01-2007, 03:56 PM
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Quote:
Originally Posted by bman9089
Afternoon guys,

I'm wanting to get some advice on PSI to run in the tires. I think I'm sitting at about 33 right now, but want to have the best wear/ride quality possible.

So, what do you think is the best?? What's your PSI on road?




Alot will depend on the wieght of your rig, sounds pretty much stock wieght. Then it will depend on the width of your wheels 15x8's or 15x10's. Also depends on how big of hit you wanna tak ein the gas mileage dept.

I'd drop them down to about 25 and see how you like it. 33 is really high.
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post #4 of 22 Old 10-01-2007, 03:57 PM
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I had to reaserch the same thing when I went to 33's. I came to the conclusion that 25-26 is good. You can also do a chalk test.
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post #5 of 22 Old 10-01-2007, 05:18 PM
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bman9089
Quote:
So, what do you think is the best?? What's your PSI on road?
Played with this a little while, finally found 28# worked well for me running the same tires as you. Rolling resistence was less at higher PSI, but looked like it was going to produce a poor tire wear pattern (bad center wear). Too low and it handled for crap on the street (much like driving on marshmellows).
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post #6 of 22 Old 10-01-2007, 05:30 PM
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28PSI, ditto on what the others have said. A bit lower if it snows, which it never does around here.

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post #7 of 22 Old 10-01-2007, 05:43 PM
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Chalk test works best for all tires if you want to extend tire life. Too many factors involved to decide what is best for what your rig weighs, load range, MPG vs ride, weather, tire brand/compound blah blah...

but yeah 28 is a good starting point, and tracking your tire wear and checking PSI often will tell you what is ideal for your particular condition.

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post #8 of 22 Old 10-02-2007, 02:03 PM Thread Starter
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Sounds like mine is sitting a little bit high. I'll air 'em down a bit this afternoon then.

Thanks!



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“Sometimes I wonder whether the world is being run by smart people who are putting us on or by imbeciles who really mean it” -- Mark Twain

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post #9 of 22 Old 10-02-2007, 02:15 PM
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Varies by tire manufacturer too. Depends what the maximum load and pressure of the tyre is. 18 psi is right for my rig on 33 x 12.5 MTRs. Did the maths first and then the chalk test. 20 psi lifted the outside edges of the tread off the road, with no contact till an inch from the edge.

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post #10 of 22 Old 10-02-2007, 02:18 PM
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trXus on 8" wheel TJ SE pretty well loaded. 24psi in the front and rear unless I have the hardtop on then its 26psi in the rears

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post #11 of 22 Old 10-02-2007, 02:23 PM Thread Starter
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Quote:
Originally Posted by Jonny Jeep
Varies by tire manufacturer too. Depends what the maximum load and pressure of the tyre is. 18 psi is right for my rig on 33 x 12.5 MTRs. Did the maths first and then the chalk test. 20 psi lifted the outside edges of the tread off the road, with no contact till an inch from the edge.
Where can I find manufacturer recommended PSI ratings??



"The American Republic will endure, until politicians realize they can bribe the people with their own money." -- Alexis de Tocqueville

“Sometimes I wonder whether the world is being run by smart people who are putting us on or by imbeciles who really mean it” -- Mark Twain

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post #12 of 22 Old 10-02-2007, 02:31 PM
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Quote:
Originally Posted by bman9089
Where can I find manufacturer recommended PSI ratings??
The manufacturer will state the max load rating at a certain PSI right on the sidewall of the tire, for example 3,000 lbs at 50 psi.

So 3,000 lbs x 4 tires = 12,000 lbs total weight carrying capacity of all 4 tires.

A TJ weighs about 4,000 lbs (1/3 of the total 12,000 lb capacity of the tires), so you would inflate the tires to approximately 1/3 of the max psi.
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post #13 of 22 Old 10-02-2007, 04:01 PM
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What's a 'chalk' test? Would you reccomend the same psi for 33 x 10.5's?
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post #14 of 22 Old 10-02-2007, 06:59 PM
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28 in mine

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post #15 of 22 Old 10-02-2007, 10:05 PM Thread Starter
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This afternoon I checked and found out that I had 35psi in every tire!

Good thing I haven't driven but around 1000 miles on my set of tires. I've taken them down to 28 PSI and the on road ride is noticeable better. It makes a huge difference (so much softer!), and makes my OME set up even better!

Thanks guys for the heads up! Much appreciated!




"The American Republic will endure, until politicians realize they can bribe the people with their own money." -- Alexis de Tocqueville

“Sometimes I wonder whether the world is being run by smart people who are putting us on or by imbeciles who really mean it” -- Mark Twain

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