Horrible Rear Tire Wear
 

Guys, please help the newb.

I got my 2005 Boxster S used and fitted with the wrong sized rear tires. They were low price (~110$) Cooper Zeon 2XS size: 265/30/19.

I recently replaced with N1 Bridgestones with the proper spec: 265/35/19. However I was extremely alarmed at how my old rear tires looked when they were changed out (pictures bellow).

They're only about 3 month old tires. Granted I've been driving them very very hard (full throttle often in 1st gear). I'm not surprised they were chewed so quick, I'm surprised about the uneven wear. Should I check my car?

Also side question: one of my rear wheels (19 inch Lobsters) is a bit bent and I have a little bit of vibration felt through the steering wheel only. Is it repairable? or should I look for a used wheel?

1). Is the car lowered?
2). Get your alignment checked

not a very caring person drove on those tires. imo. how old were they [production date] ?

The wear on your tires are not related to age but mileage. These cars have substantial camber and that's how they wear. Get an alignment any time you do more than one tire. You can get your rim fixed with an aftermarket shop. Your local dealer probably knows who to use. I'd do that before buying a wheel. It will be balanced also.

1) I didn't lower it myself. It is used but the indy checked and didn't tell me of any lowering and it certainly doesn't look like it's lowered at all visibly. The only lowering visible is the rear tires not being spec (265/30 while spec is 265/35)

2) I had my alignment checked recently. I guess it wouldn't be a bad idea to do it again.

Unfortunatly, I didn't check the date on them and they're gone now.

And yeah, that "not a very caring person" might me embarrassingly the newb me :).

This is sort of what I expected. It's a rear wheel drive with the rear wheels driven through a CV joint. When it squats at a powerful launch I would imagine camber would very significant.

It's not so much the launching. Your tires will look the same with or without launching. Obviously it will wear faster but that wear is just excessive miles. Just keep an eye on the inner edges of your tires and fix any alignment issues quickly. You'll be all good.

Excessive miles? According to the post those tires are only 3 months old.

Based on [unhappy] experience, I'm going to say that you have a severe toe problem, probably toed way out. (In addition to lots of neg. camber.) Handling is probably pretty squirrely too.

The short response is get the alignment checked/set.

Proper prep for an alignment: Full tank of fuel. Car empty of junk (dead weight). Spare/jack/toolkit (if any) stowed properly.

FYI, some alignment techs like to use ballast to stand in for driver weight when aligning the car. Porsche doesn't list this as a requirement (unlike the full fuel tank, etc. I mentioned above). I've had my cars aligned both ways and couldn't tell the difference.

Be sure you ask the steering wheel be centered and ask that you get a before and after printout.

The longer response is the alignment has to be suspect, though real aggressive driving probably contributes to the wear.

Toe is the main culprit. I've driven hundreds of thousands of miles with plenty of negative camber on both of my Porsches and rear tire wear is even across the tread even as the tire mileage reaches 20K miles and beyond.

Aggressive driving contributes some to the tire wear in the pictures. What happens is if you use too much throttle around a turn the inside tire spins. (Helped by lack of an LSD.) If you watch a Porsche corner you can see the inside rear tire tread face is not alway parallel to the pavement surface. If the tire spins the inside edge makes the most contact and thus should wear more.

Another side effect is in the USA most turns taken are right hand so the right rear tire is most often the inside tire and it spins more than the left so the right rear tire wears more than the left rear tire.

Now even after a "proper" alignment this may still have the rear tires wearing on the inside edges, though probably not as severe. Where this comes from is there are differences of opinion regarding how much rear toe is optimum.

In some cases some alignment techs believe lots (relatively speaking) rear toe is best for some reason. Others are willing to use less toe.

I prefer less toe myself. Tire life is very good (I help tire life by avoiding excessive throttle around turns to keep tire spinning to a minimum) and even with my big heavy powerful Turbo getting over 20K miles from its rear tires is doable time and time again.

And road feel and handling are not affected when compared to the same car with more toe which results in much shorter tire life. In one case tire life was just 8K miles.

OH, bear in mind if the car was lowered the stock suspension may not have enough range of adjustment to allow the tech to bring the car into proper alignment. To address this you may have to swap out stock parts with aftermarket parts that have more adjustment range or start out with a different geometry to compensate for the effects of lowering has on alignment.

[QUOTE=Macster;11462919]

Toe is the main culprit. I've driven hundreds of thousands of miles with plenty of negative camber on both of my Porsches and rear tire wear is even across the tread even as the tire mileage reaches 20K miles and beyond.

Aggressive driving contributes some to the tire wear in the pictures. What happens is if you use too much throttle around a turn the inside tire spins. (Helped by lack of an LSD.) If you watch a Porsche corner you can see the inside rear tire tread face is not alway parallel to the pavement surface. If the tire spins the inside edge makes the most contact and thus should wear more.

/QUOTE]


Thanks! that was a very detailed response. Not to take any thunder from other posters who contributed. I just seem to have learned more from this post in particular.

Do you think it's possible that my shock absorbers are worn out and need replacement? or that has nothing at all to do with alignment?

One thing that really got my attention is the mention of wheel spin on tight corners. I did that every so often in my car. I basically turn in sharper than I need to, and then stab the throttle suggestively and slide the car sideways. Don't give me a hard time about my driving. Non of my driving was dangerous despite what it might sound like and, in short, I really hated those rear tires. They made the whole car look so wrong. And I was eager to shorten their life span. I'm just shocked the lifespan was only about 4000 miles. Then again, I do have prior experience with crappy tires wearing out very rapidly. And it wasn't a Porsche.

Oh other weird things I want to mention:

As I said the rear wheels were fitted with wrong spec tires (265/30) and when I first got the car, there was this strange rattling sound coming from the exhaust that only occurs when I'm rolling it in 1st gear. The car also wheel hops on 1st gear full throttle (rear wheels starts jumping up and down violently). Finally, every time I stepped out of the vehicle, I can smell tire burn, even if I weren't driving very aggressively.

After replacing the rears with stock tires (265/35), the rattle is gone. I couldn't induce it tonight no matter how many times I stopped/rolled. Added to that, I put in 1st gear, turn off traction, and absolutely nailed it to the floor; no wheel spin, no wheel hope, no nothing. Just straight sling shoot acceleration. And there is no smell of the usual burning rubber after exiting the car.

Shock absorbers can wear out, or more likely just go bad, at any time.

My techs tell me when I ask them about replacing the shocks on my Boxster (now with 280K miles) that if the shocks aren't leaking or showing signs of trouble and the car doesn't pogo or porpoise when it encounters a dip or crest in the road to leave the shocks alone.

You can test the shocks in some fashion by with the car parked on flat ground pushing down on a corner and then releasing and repeating this to try to get the car moving up and down. When you have the car going up and down stop and see how quickly the car stops moving. If it stops in a cycle or two that's a good sign the shock at that corner is ok.

However, I've tried this with my Boxster (and Turbo) and the cars are so stiffly sprung about all I can really test is the front shocks on the Boxster or the Turbo. I have to stand in the front trunk and use my body to get the front of the car moving up and down then stop. The car stops moving almost as soon as I do. Shocks are ok.

The rear end of both cars is so stiff I can't really use this technique and I'm not about to stand in the rear trunk of the Boxster nor try to stand/balance myself somehow at the rear of the Turbo.

I note in the pics of the rear tires the tires show some signs of uneven wear around their circumference. This could be cupping and cupping is a sign of worn shocks. The shock can't control the tire/wheel and the thing bounces up and down after a bump and this up and down action causes the tire to, well, cup.

But alignment can cause this too. If the toe is wrong the tire gets pulled out of alignment but eventually it is pulled too far and will return to where it wants to be when the tire/wheel gets light from a bump. This sideways action can also cause the wear patterns visible.

When you go in for new tires have the tech check the shocks, look them over for any signs of leaking. He can look at the old tires and from their appearance make some assessment of the condition of the shocks.

Unless it is obvious the shocks are bad I'd have a proper alignment done and drive the car and see how it feels after. Check the tread faces for any odd wear patterns/signs, like feathering or the early signs of cupping that could be from worn or bad shocks.

Running the wrong tires on my Porsches is something with which I have no experience.

In your case, with the right tires on the car the symptoms/behavior are now gone I think provides you with a clue that the wrong tires were somehow at fault.

Over the years I have smelled the tires when getting out of the car. They are right there, they are big and they are often hot. So that you smell hot tire odor is not surprising.

But I note the wrong spec rear tires were obviously wearing at a fast rate and this comes from friction and friction produces heat so the rear tires could have been running hotter than normal which could explain the lack of tire smell now with new tires which track truer and run cooler. I suspect though you'll smell the tires some times as even properly aligned and the right spec tires will get plenty hot enough to smell.

The lack of hopping and what have you could be explained by the car's suspension geometry is now closer to optimum with the right tires fitted.

I have to stress these cars are high performance sports cars. We tend to forget this but not too many years ago a car capable of 0 to 60mph in under 6 seconds, and with a top speed in excess of 150mph was at the top of the performance car list.

Tires play a critical role for these cars and coupled with this is proper alignment to ensure the tires have optimum contact with the pavement and maintain this under all conditions.

Your experience I think underlines the critical role proper tires have in the car's behavior and performance.