Proper PSI

[Tumbleweed13]

I have 35's on my, daily driven, TJ. When I inflate to the recommended 35 psi, the tires are over inflated, and are only wearing, in the middle. To get to , what I think is the proper psi, I put a chalk line across the tread. Then without turning the steering wheel, I drove the jeep forward and back about 40'. Then, after examining the chalk line, this would show me what portion of the tread is touching the ground. I lowered the psi until the contact patch was optimal.

Here's my questions.
What are you doing to find the proper psi?

I ended up at 25 psi for the front and 23 for the rear. Is it dangerous to drive on the street with 20 psi or less, even if it gives you the correct contact patch?

Even at my current psi, the very outer most edges of the tread still don't tough the ground. I have BFG KM2's if that makes a difference.

[Jeeperator]

I am pretty sure that # is the recomended maximum psi if your vehicle weighs the maximum allowed weight your tires can hold. Since the tires total weight far exceed the total weight of your jeep I am pretty sure you are safe to run them lower pressures. I run my 35 km2's about 25-30 psi but I also have 10 inch wheels so that will make a difference also. 8" wheels will require less pressure to wear evenly.

[Tumbleweed13]

Yeah, I'm running an 8" wheel. I feel that I have less of a chance of popping a bead on the trail, with a narrower rim.

[6spdYJ]

33's on 15x7 @22lbs for almost four years with 3300 vehicle weight. No problems.

[OU812]

I emailed BfGoodrich and they sent me the load inflation chart for my specific tire. According to them my 33 10.5 15s needed to be at 20PSI for my axle weight.

[vwtipeii]

Every tire is different. Depending on mods and upgrades (weight distribution per axle/tire) will effect how each tire handles/performs. 25 PSI sounds about right for the highway.

I have SS TSL radials 35" and i run thema bout 25-28 highway and airdown to 6 psi on the trail just to get a bulge.

[nwoods]

I didn't have any chalk, so I just wet my driveway with a hose and backed out over it and looked at the tread pattern on the street. I settled on 28psi with my 35" x 12.5 KM2's on 16" x 8" rims in my slightly heavy LJ. Still trying to figure out good trail pressure. I think the 8PSI I've been running is a little low for these guys.

[Jerry Bransford]

35 psi is WAY excessive for 35" tires. If you inflated them to 35 because of the air pressure molded onto the tire's sidewall, that is only the tire's maximum safe air pressure to be used only when the tire is carrying its maximum safe wait. The Jeep is probably only half of that weight.

For a 35" tire carrying a Wrangler, 24-26 is about right. 28 is more appropriate for perhaps a 33" tire.

[Tumbleweed13]

Still trying to figure out good trail pressure. I think the 8PSI I've been running is a little low for these guys.

I use 9 to 10 psi, on the trail. I get great traction and I've never had a popped bead.

[neilbyrd]

I run 15 psi on my 40" irok radials with beadlocks on the street and it's just right with my light m38a1.

[Tumbleweed13]

I run 15 psi on my 40" irok radials with beadlocks on the street and it's just right with my light m38a1.

15 psi on the street. Thats crazy, but those iroks have thick side walls. How ofter does that jeep see the street? You must be at 4psi on the trail.

[neilbyrd]

I drive it on the weekends around town all the time. And I just finished the 3 year build, about 3 months ago, so it hasn't been an the trails all that much. I haven't needed to air it down yet.

[Mitch]

15 x 33 on 8" rims. 28 lbs on the road and 12 lbs in the dirt and rocks. Never a problem.

[LW93Jeep]

I know Ford/Firestone had their fair share of tire issues we all know about. If I remember, they wanted 26psi in the tire. Wasn't enough PSI to cool the tire at highway speeds.

With that in mind, I keep mine at 30psi. You can google it or someone can post up. If I remember, there is a way to properly check your tire by getting the tire wet and checking the foot print?

Good luck, most had good luck with their explorers. But, those who didn't, didn't.

[Russ Chung]

Joe,

The "chalk test" that you did is usually a pretty reliable indicator of the pressure that would give you the best tread wear pattern. However, you said that you are running 15x8 rims, which is somewhat narrower than the rim width that BFG recommends for 35s (10 inch rim width). As a result, you had to lower the pressure to 23/25 psi in order to get the entire tread to contact the pavement. The tradeoff is that you have more flex in the sidewall because of the lower pressure. The sidewall flex causes more heat to build up in your tires at highway speeds, and reduces your gas mileage. I think that you would be safe at 23/25 psi on pavement, but no lower. I personally would use the chalk test as a guide, but increase the tire pressure to 28/30 psi while on pavement. This will cause the center of the tread to wear more, but your offroad use when aired down will cause the edges of the tread to wear more, so the overall result will even out.

Russ