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-   -   Tire Pressure (http://www.wranglerforum.com/f282/tire-pressure-6676.html)

DocG2828 03-18-2007 03:45 PM

Tire Pressure
 
I have 32x11.5 tires on......what pressure should I keep these at? The sidewall says 50psi....but someone rec'd keeping it at about 35psi like you would a car.....like to get the most mileage out of these and keep the ride nice.

This is for street use....I figure for offroad I'd go lower on the pressure.

Thanks!

Unlimited 03-18-2007 04:26 PM

I have 33x12.5 BFG A/T's. I run 35psi on the street and 15 - 20psi offroad depending where I am. I have 17k miles on the tires and they are showing very little wear.

debruins 03-18-2007 04:40 PM

well int his monts Jp it shows you how to know what tire pressure

first put a chalk mark strgiht across the top of one of the tire

then drive it STRAIGHt for like 30 ft or something than look at the tire and see where it is wearing it should all be gone, if there is chalk on the outside of the tread you need to decrease the pressure if it is in the middle increase and try it again.

in this way the tire will wear evenly and will get the best mpg

Moab Man 03-18-2007 04:57 PM

Quote:

Originally Posted by DocG2828 (Post 63836)
The sidewall says 50psi
Thanks!


That is not a suggestion for tire pressure. It is the max pressure that tire could be inflated to on a heavily loaded vehicle.

The best starting point, when you simply have no idea, is the recommended tire pressure the vehicle lists. Over inflating the tires or too narrow of a rim will cause the center of the tire to wear early. Under inflation the outside will wear prematurely.

The chalk test is the best way to truly get it right so the tire wears squarely across the treadblocks.

GoodLife 03-18-2007 05:00 PM

Quote:

Originally Posted by debruins (Post 63853)
well int his monts Jp it shows you how to know what tire pressure

first put a chalk mark strgiht across the top of one of the tire

then drive it STRAIGHt for like 30 ft or something than look at the tire and see where it is wearing it should all be gone, if there is chalk on the outside of the tread you need to decrease the pressure if it is in the middle increase and try it again.

in this way the tire will wear evenly and will get the best mpg



You beat me to it. I've been meaning to try it out myself. :D

debruins 03-18-2007 06:04 PM

well i havent actually done i yet :(
i guess i should huh makes sense:rolleyes:

jp'rs_peep'rs 03-18-2007 10:00 PM

Do that which works best for my sitsuation.

C.

1BLKJP 03-18-2007 10:08 PM

I actually vary mine everytime I air up after wheeling. I try to stay between 26 and 32 to get a good wear on my tires and I'm running 35's. I air down to about 9 for wheeling.

DocG2828 03-19-2007 09:56 AM

Thanks peeps! I knew the 50 was way too high....but wasn't sure how 35 would be on these. Its at like 46 right now, so its gotta come down. They fill em up full coming from the warehouse it seems.

I'll put them down to about 35 then try the chalk method....thanks again!

gcdcpakmbs 03-19-2007 10:19 AM

50 will get you best gas mileage. However, you'll lose the difference in tire wear if you run them like that. Chalk test is best.

mrbigjeep 03-19-2007 10:22 AM

i run the same size tires and i feel that 35psi is a bit too much. i think 32 would be better. 35psi is way too stiff

affende 03-19-2007 01:51 PM

i run my 33s at 28 on the street ... drop them down to about 10 off road

MouthfulOfGrass 03-19-2007 02:59 PM

Just curious, the chalk test sounds good & makes sense. But, is it realistic ?

You chalk test at very slow speed. What happens when you're driving at highway speed ? Does centrifugal force make the center of a tire tread bow out more if there's not enough pressure to force the sidewalls out to hold the tread surface flat ?
I don't know much about physics, or tires, just was maybe over-thing this. Is the chalk test the most accurate way to determine what my tire pressure should be ? Does anyone know of another way to test ?

Moab Man 03-19-2007 04:43 PM

In my opinion it is the most accurate. And it does make send about the deforming of the tire at speed. I think it works because the actual wear is probably less at speed and around town you have the full slower resting weight grinding on the tires. Just a thought.

DocG2828 03-19-2007 04:48 PM

Hmmmm....centrifugal force. Sensible objection. But I wonder if the centrifugal force is strong enough to not only elongate the tire on the non-surface contact areas....but to also support the weight of the vehicle on the surface contact spots as they touch. If that makes sense. If its stretching out, wouldn't it still stretch out on the part that hits the road...therefore allowing the tire to continue to evenly contact the road? Or at high speeds, the tire is almost stretched and molded to the shape of the road no matter what pressure its at.....or would the weight over power the centrifugal force I wonder.

Where's our physics experts?

I really gotta drop the pressure....I must be having a brain freeze cuz my TJ has been really rough since the install...I've just been attributing it to leaving the Rancho's on 5....but now that I'm connecting two coherent thoughts.....the tires probably aren't helping running around on 45psi!

AzTJ 03-19-2007 04:57 PM

30-32psi on everything I've run on our XJ's with A/T's.... I don't know how many miles we've gotten outta my mothers set, been on there for some time now and they still look pretty good.

debruins 03-19-2007 06:56 PM

well ur phisyics is scrwwey first off not to fluster anybody but centirfugal force is made up, it is the abscence of centripital force, so the ground will provide the force to push the tire towards the center of the circle. At the bottom of the rotatio the tire will flatten out due to the weight of the car and the push towards the center by the earth.
sorry if i am confusing u but at high speeds the tires will actually be flatter!!!

debruins 03-19-2007 06:59 PM

and btw centripital f = about 100# while weight at each tire is like 1000#

of course this is converting to metrics and than back again so i could be absurdly off somewhere.

MouthfulOfGrass 03-20-2007 04:26 PM

Not tryin' to argue, just was throwin' something else out there.
I hear a lot of people goin' "uh-huh, uh-huh, chalk mark, that's the way to go", and was just curious if anyone had some other way to check if the tire air pressure was correct for one's own vehicle.
I personally have always looked at what the tire "maximum" pressure was supposed to be, and gauged the weight difference between what the tire is supposed to carry at max pressure, and what my vehicle total weight actually is, and back off a pound or 3 to compensate the difference.

nicolas-eric 03-20-2007 04:58 PM

i have 32x11.5x15 yokohama geolandar AT on 7.5x15 wheels.
on th eroad i have 32 PSI and off the road down to 18 PSI.

DocG2828 03-20-2007 07:15 PM

Quote:

Originally Posted by MouthfulOfGrass (Post 64484)
Not tryin' to argue, just was throwin' something else out there.
I hear a lot of people goin' "uh-huh, uh-huh, chalk mark, that's the way to go", and was just curious if anyone had some other way to check if the tire air pressure was correct for one's own vehicle.
I personally have always looked at what the tire "maximum" pressure was supposed to be, and gauged the weight difference between what the tire is supposed to carry at max pressure, and what my vehicle total weight actually is, and back off a pound or 3 to compensate the difference.

How dare you go against the grain! :D

MouthfulOfGrass 03-22-2007 02:52 PM

Quote:

Originally Posted by DocG2828 (Post 64537)
How dare you go against the grain! :D

Didn't mean to go against the grain, I'm just trying to learn.

I want what is best, as I'm sure everyone else is. I'm not one to go "with the crowd", if there might be another way to go that proves to be better (or more accurate).


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