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Old 12-15-2010, 09:19 AM   #1
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Here's a tire question that hasn't already been answered.

Alright tire folks . . . .

I've got a 2010 JKU Mountain, which I believe comes with Rubi tires on the grey 17" wheels. If it's helpful, I've attached a clean, bright pic of the tire itself when it was new.

The sidewalls on the tires list the max cold pressure as 50 PSI. That seems high, but I've attached a closeup pic (sorry it's so dark). It really says "(50 PSI) COLD".

However, the "Tire Placard" (see page 393 of the manual) shows the max pressure should be "37 PSI". The placard does correctly identify my tire size as 255/75/17. That's a pretty big difference. I've attached a pic of that too.

So . . . which is it? Thanks all.

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Old 12-15-2010, 09:25 AM   #2
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Max is just that.... Maximum psi that should be in the tire under full load. Keep in mind those tires are used in lots of other apps than Wranglers.... Much heavier applications. The listing on the door, since it is for your tire size is the recommended psi for your application. Once you change tire size, then that goes out the door as well....
You may find they ride better with a bit less air than the recommended 37lbs... Depending on your application. If you don't have a hard top, and big bumpers etc.... Look at the contact patch.... That's all you really need to do, in any application. If they are contacting edge to edge, you need more air, center only, less air. You want contact across most of the tread, but not all the way to the edge.

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Old 12-15-2010, 09:28 AM   #3
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50psi is what the tire itself is rated for, a tire can be put on anything and therefore just has a maximum. Your jeep however will have it's own recommended psi which is like you said is 37. Never inflate to what is written on the tire itself, follow whats written and recommended on the vehicle. If that same tire was found on a heavy duty pickup then ya you might have it at 50psi but not a jeep it's just too light.
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Old 12-15-2010, 09:45 AM   #4
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Those answers make perfect sense. Thanks.

When my TPMS went off last week, I just pulled into a gas station and inflated to 45 PSI or so per the sidewalls. I didn't even know the placard existed until I saw it in the manual afterwards while looking for something else.

I guess that means that my tires are safe, but will produce a hard ride and eventually wear unevenly if I leave them at 45 PSI indefinitely given the weight of my Jeep. That sound about right?
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Old 12-15-2010, 09:47 AM   #5
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That much pressure will cause a horrible ride and the center of your tire will be higher than the sides meaning less contact with the road making it more dangerous to drive and causing you to wear out your tire unevenly. I run my tires at 32psi
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Old 12-15-2010, 10:20 AM   #6
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Originally Posted by MTH View Post
Those answers make perfect sense. Thanks.

When my TPMS went off last week, I just pulled into a gas station and inflated to 45 PSI or so per the sidewalls. I didn't even know the placard existed until I saw it in the manual afterwards while looking for something else.

I guess that means that my tires are safe, but will produce a hard ride and eventually wear unevenly if I leave them at 45 PSI indefinitely given the weight of my Jeep. That sound about right?
Your PSI is too high, check your door rating and return it back to what is recommended for your tires. Since your tires are stock rubi wheels that came on you Mountain edition, the PSI rating on the door is the recommended air amount for those tires. NEVER use your TPMS as an air indicator or tester. The sensors on this system adjust constantly and are useless and maybe even dangerous to be used as an air gauge. Much better, more reliable, and safer to buy a $3.00 tire gauge and check each your self.
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Old 12-15-2010, 10:24 AM   #7
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my TPMS light came on right after I bought the jeep and filled mine to 35 psi and like the way it rides. i have the same tires you do
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Old 12-15-2010, 10:30 AM   #8
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Heh Heh, I run my Hankooks at 28psi and I don't have any TPMS sys to worry about !!

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Old 12-15-2010, 10:42 AM   #9
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Heh Heh, I run my Hankooks at 28psi and I don't have any TPMS sys to worry about !!

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HUUMMMM, With your AEV Device, your TPMS Light would never kick in, you can run on blades if you wanted to,,lol
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Old 12-15-2010, 10:52 AM   #10
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Heh Heh--BINGO, SLIM !!


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HUUMMMM, With your AEV Device, your TPMS Light would never kick in, you can run on blades if you wanted to,,lol
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Old 12-15-2010, 11:04 AM   #11
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Just checked a picture of the info on your door and I'm pretty sure that the PSI for your tires is 37. I have the same size and run mine at 35-37. Very smooth comfortable ride with even wear.
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Old 12-15-2010, 12:59 PM   #12
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Originally Posted by MTH View Post
Those answers make perfect sense. Thanks.

When my TPMS went off last week, I just pulled into a gas station and inflated to 45 PSI or so per the sidewalls. I didn't even know the placard existed until I saw it in the manual afterwards while looking for something else.

I guess that means that my tires are safe, but will produce a hard ride and eventually wear unevenly if I leave them at 45 PSI indefinitely given the weight of my Jeep. That sound about right?
Your tires may be safe, but you're not. With the pressure that high you would only be riding on the center tread giving you much less contact with the road surface, definitely not safe.
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Old 12-15-2010, 01:23 PM   #13
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Here's a quick trick to evaluate if you've got optimum tire pressure for the largest contact patch in a radial tire.

Measure the width of the tread of your tire at the surface.
Pour a small amount of water on the ground in front of the tire in question. Make sure the puddle is wider than the width of your tire.
Slowly drive through the puddle and stop after about 5' - 10'.
Look at the tread pattern on the drive & measure the width of the tread pattern.
If the width of the print is less than the width of the tire, you have too much air in it.
If the tread pattern is blurry or looks smeared, you have too little air pressure in it.

You can also use this quick tip in the dirt, mud or snow as long as it is not very deep and you can get a reasonably accurate measurement.
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Old 12-15-2010, 01:42 PM   #14
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the center of your tire will be higher than the sides meaning less contact with the road making it more dangerous to drive
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Your tires may be safe, but you're not. With the pressure that high you would only be riding on the center tread giving you much less contact with the road surface, definitely not safe.
I'll deflate this evening.

My primary concern--once I saw the discrepancy (50 PSI v. 37 PSI)--was the tires bursting. Learning that wasn't the case, I figured I could deal with a hard ride and uneven tread wear for the rest of the week. Of course, I hadn't considered the lack of contact with the road, particularly since they're predicting bad weather in my area for the next day or so. Overinflation, while still under the max PSI for the tire, still means I'm effectively driving on rails.

See?? This is why I waste . . . err, excuse me . . . "INVEST" so much time here at WF!
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Old 12-15-2010, 01:42 PM   #15
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Remember when the explorers were rolling over? Kind of same thing, different mfgr recomended tire psi vs tire mfgr recomended psi. Heard there was absolutly nothing wrong with those tires but the bad publicity drug firestone wilderness tires thru the mud
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Old 12-15-2010, 03:50 PM   #16
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I run 37 in my Rubi and it really seems to be the best. Even unintentionally did YaHa's trick today with road salt and the contact patch is perfect. I have off road bumpers and a winch so 37 is the best balance.
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Old 12-15-2010, 11:13 PM   #17
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Lowered down to 37 at a gas station on the way home from work tonight. Thanks all.

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