Herkypilot

I'm having a problem with uneven tire wear. I'm sure there's a tire guru on this site that can answer this. My 8 has 8,700 miles on it with the stock 18" Potenzas and I've had two different dealerships check the alignment and balance. I've checked the tire pressure routinely and kept all four at 32 psi. The wear is feathering on both the inside and outside of the tires. The center of the tire tread looks normal. I've had them rotated and balanced a few times to try to fix this so its hard to tell if the cause is from the front or back. I've put about 1,500 miles on the tires since the last balance check and it doesn't seem to be getting any better. My driving is pretty conservative with occasional aggressive handling.

Another question. When tires are properly balanced, are all the old weights removed, then the tire is spin-balanced and new weights added, or is it acceptable to just leave the old weights on and add weights as necessary to balance the tire? I've had my tires balanced (checked) 3 different times and all my wheels still have the original factory weights on them with a few added weights to bring them into correct balance. Sound OK to you all?

Thanks

8pex

The wear on the inside and outside edges are usually associated w/ underinflation and/or hard cornering. It sounds like you are ok on inflation, so maybe hard cornering. Regardless, tires will take the path of least resistance once an irregular condition is present, so the condition of you tires will probably not improve even after you shave a few /32 off of them.
Unless you have thrown some of the tape weights on your wheels, they should still be balanced and have not had any added/subtracted.
Stay up on the rotation/inflation and you should be good.

Go48

I would just add that for future balancing, search out a facility that has the Hunter GSP9700 balancing machine. This machine is one of the best and it can check many aspects of the tire-wheel configuration that other machines can't. Try the web site below for the location of facilities in your area and for detailed information on this machine:

http://www.gsp9700.com]

EDIT: Apparently that site is down or no longer valid. Try this link for info on the machine: http://www.craigautometrics.com/huntergsp9700.htm

wintergrn

Follwing links from hunter.com, I ended up here:

http://209.176.154.132/pub/search/FindGSP9700.cfm

which looks like it's the right place. Might be a temporary DNS problem with www.gsp9700.com. Either way, it turns out that my dealership has a GSP9700... thanks for the pointer.

Herkypilot

Thanks for the timely replies and the links. I seem to not have good experiences with most car tires for some reason, despite my attempts at good maintenance practices. :o


Herkypilot

schrottie

uneven wear:
are you sure its not the front wheels that show these signs of wear? it would be very unusual for the back-tires to become slicks both inside and outside.

balancing:
Leaving the old weights in place doesn't make a perfect balance impossible but normally a decent dealer would remove the old ones. This will look less cluttered and you don't end up with lot's of masses counteracting other masses.

just my .02EUR

beachdog

Some additional clarity on the weights... there are two types of weights on the 8's wheels. The glued-on flat weights on the inner radius (typically opposite the valve stem) are there to counteract the primary imbalance caused by the tire pressure monitor. Leave those weights on unless you want to spend money to buy new ones to put right back on where those were taken off. As long as the TPMS is there the counterbalance will still be needed.

The rim weights on the inside rim should be removed before balancing. The amount of rim weights should always be minimized. If you need more than two small weights a couple of degrees apart you need to start over.

As far as edge wear that you described, that is generally underinflation. Have you ever had your tire pressure guage calibrated? Do you use the guage on the compressor?

I have a huge collection of cheap, inaccurate guages. When compared to a racing guage they are all anywhere from 1 - 4 pounds low. The guages on my compressors before calibrating were also 4 pounds low. If you haven't already tried this, get ahold of a racing guage and then check your tire pressure. (my wife just had the tires on her car rotated and balanced and the shop adjusted the pressure for her - every tire was exactly 7 pounds under inflated - a combination of inaccurate guage and someone that didn't know the correct pressure)

Once you're sure about the pressure, about the only option that you are going to have with those tires is to run them slightly overinflated. I have kept mine at 32.5 since the beginning and the wear is very even. You might need to go to 33 or 34 to even things out till the time to replace them.

Herkypilot

Beachdog - Thanks for the info. I really didn't think about the TPMS - makes sense. i haven't checked my gauge, but its worth a try. I already increased my tire pressure about two pounds each thinking the same thing that you stated. These tires are too damn expensive to be going through them so quickly. Do you recommend any particular type gauge (digital vs the pencil type w/sliding measure)? I'll have to spend a few bucks to get an accurate one.


Herkypilot

zoom44

you say its not getting any better but has the rate of wear decrease? what i mean is are the getting worse slower now?

Herkypilot

After about 1500 miles, they appeared about the same. I just recently increased the tire pressure by two pounds per tire to see if my gauge was just inaccurate. I suspected what beachdog said, underinflation due to my pressure gauge reading low. Since all four tires have the same indication, I suspect that this is the problem.

Thanks

Mr M

Underinflated tires sounds like the cause to me to.
Depending on your driving patterns, you may need a couple of extra psi in the tires to help them keep their profile. Not too much though, otherwise you reduce the contact patch with the road and that will affect your braking ability/grip.

Try checking the pressures with another gauge too.

beachdog

I use a dial type guage (it's pretty old and I spent at least $30-40 for it) I have recently obtained a couple of digital guages. They are very consistent and only off by about 1/2 lb. I like the digitals because there is no interpretation. Spent $15 on one of the digitals and $20 on the other.

schrottie

One more note on tire-pressure on the RX8:
Most manufactures suggest a pressuse of only 29-31 psi (~2.0 bar).
The 8 is relatively lightweight and has relatively 'roomy' tires that will carry the car even with these low pressures.