Tire PSI (again)
 

Through the search I found a lot of posts on the recommended PSI for the stock tires...what about 275/35-18s? Unfortunately I was running the max (which is 55 I believe??) before doing some reserach about max and recommended pressure.

First off, welcome to MB. This seems to be a gray area, and it seems you hear alot of different ideas and reasonings. Assuming the tire and wheel size is relatively close to the stock- or factory tire, I would pay more attention to the sticker in the door jamb. Just because it says on the sidewall "Max Pressure- 44 psi" or whatever, doesn't mean they NEED 44 psi.

You could contact the tire manufacturer. I'm sure they'd offer their suggestion. Personally, i'd get 'em close pressure-wise, then pay attention to how they drive at first, then pay attention to wear.

*EDIT* I have 235-50-18's BFG G-Force's on mine. Says mx pressure 44 psi, and I run 34 psi in them. I have only put 600 miles on it since I got it, but they are wearing fine.

Thanks for the quick response. My tire has a max of 55 but I am now running 42. I have had a problem with vibration with the new tires/rims (purchased them from AM last summer) and I was hoping it was due to me over-inflating them which may have caused uneven wear?? I have had the rims balanced 3 different times, have gotten a front end alignment, and have had two of the four rims replaced. Unfortunately I still have vibration which comes and goes as I drive. I purchased new tires for my stock rims for winter and those drive fine without any problems so it is definately something with the tires. Is it possible that there was a defect in the tire from the beginning or do you think it will correct itself once the tires start to wear correctly? Thanks for your help.

42 is still a but much, i have some 17x19 tires and i have mine at around 32-34 front to rear. The usual pressure for most tires that i have seen is 30-36.

I am not sure what kind of "uneven wear" you have, but an over-inflated tire will wear in the center of the tread. As for new tire defects, I think it's pretty uncommon, but it is possible. A ply can seperate too, but it sounds like you have been chasing the problem for quite awhile. If that were the case, it would have probably blown, or have an obvious bulge. When you had the wheels balanced, are any of them way out? Maybe 3 oz. or more? You could check wheel run-out too, but that again would probably be detected when balancing. And can a tire correct itself? If you keep 'em rotated to where the problem never gets bad, yes...but if they are bad, I wouldn't bet money on it.

Deathdiesel - 42 is too much even for larger 275/35-18s tires? I just assumed if the stock recommended psi is between 30-36 that the 18s would be slightly higher due to the larger tire :confused:

BlueOvalFanatic - I definately have been chasing this problem for over a year now...it is getting really frustrating. If it is the tires then there is nothing I can do but live with it I guess. Sometimes it vibrates so bad on the freeway that my jaw rattles...other times it rides perfectly smooth. I guess that is the part that confused me...you think it would do it all the time or not at all. When I have had them balanced they never told me if they were out of balance...they just charged me the fee and rebalanced them. Unfortunately it never helped. I don't see any bulges on the tires...they are still pretty new with only about 10-15k miles on them.

Just because you have a larger wheel, does not change the amount of psi that is needed. What size wheels are these on 18x9 I assume. I would run the stock 32psi setting and see how it wears.
Wheel and tire size over stock sizes will change what psi you might need to run to get them to wear evenly. Such as my 275's on stock 17x8 rear wheels, needs 22psi max to wear even.

Yes, they are 18X9s. There is so little rubber between the rim and the road with these rims/tires that it made me nervous to go as low as 32psi. I will definately lower it though and give it a try.

Please explain why a larger tire would not require more air to keep it properly inflated? I am totally confused lol.

Thanks for your help.

Just because its for a larger rim does not change the psi that is required for the tire. Running to high a psi will wear the middle out faster, or to low will make the sides wear out to fast. IN fact your total tire height is still the same as stock.

Dude, I've never run any more than about 34psi in any of my tires on any of my past vehicles.. I've had everything from 14/6" to 17/10.5".

55 is WAY too high, hell, 44 is still too high. I don't think I'd ever run anything over about 36-38psi unless it was some kind of a truck on 35's.

I keep my tires all around 32-34 psi...
And speaking of vibration, my car vibrates really rough at around 55-60mph..it gets a bit softer round 70-80...but I rarely drive that fast anymore, unless Im on the interstate. Ive had my tires balanced and rotated so many times, and an alignment didnt help...however....I dont have a tire weight on my front/driver side tire. But I dont think that could be it either, cause its been doing for a year now.

A wheel weight being thrown off can seriously disrupt the balance of a tire, depending on how off balance it was in the first place. Other than that, it could be several things, like tie-rod ends with some slack in them or something like that. The driver side tie-rod end in my stratus is just barely out of spec and it shakes like a mofo at about 70-85mph.

My problem, unfortunately is in the tires/rims. I purchased tires for my stock rims for the winter and I do not have any vibration problems at all.

I think reason why bigger tires dont need higher amount of air is because its pounds per sqaure inch which means thats how many pounds of force is pushing out against the insides of the tire, not the amount of air thats in it. Not sure if you knew that or not but its the best way i could think of explaining it. :P

tie rods.
Ill have to check into that. Never thought about that..
But yeah....I realized my wheel weight was off when I found one lodge into the rear driver side fender well. But...I dont think it came off my car cause all my other weights are smaller than the one I found, and I think they weigh more. But...finding that one did make me realize that not only was someone else wheel weight lodged under my car, but that I was missing one as well. Funny how things work out.

That makes sense.....thanks for the explaination.

I used to keep my 315's at about 30. But that's cause that car was fun as hell to just light em up, reverse to a stop sign, and launch... Sumi's suck lol, I went through 3 sets in 15k miles.. But damn it was fun... I miss my old car, dammit.