Mixing tires on 99 Boxster
 

My 99 Boxster is in need of new rear tires. Right now there are Bridgestone S03's all around. The front tires have almost half tread left and it seems like a waste to get rid of them. I was looking at putting new S02's on the rear and keep the S03's in front.

Has anyone done this and do you see any problem. My feeling is that since the S02's will wear quicker than the S03's, when the rears wear out, I will change out all 4. My thinking is that the S02's will provide better performance than the S03's.

Hi,

It's never recommended to mix/match tires. Especially true on a Performance Car w/ Performance Tires.

That said, you won't automatically collide with the next object you encounter, but I would definitely not take the car anywhere near it's limit with that setup.

If one simply must mix/match tires, at least keep the same tire on either side of the axle. One concern I might have are the different characteristics of the 2 Bridgestones - that they may oppose each other or heat up more, etc. I'd shoot the Tech Dept. at Bridgestone an email just to make sure you're not attempting something truly unsafe. Also, be sure to have a 4-wheel alignment done when you mount the new rubber. Good Luck...

Happy Motoring!... Jim'99

In a related story.... I bought my Boxster with Pilot Sports tires on the front and Toyo Proxes on the rear. I's my first Boxster, so I don't know what to compare it to. There does not seem to be a problem, other than the car does not handle ruts in pavement well. On a rutted freeway I need to keep both hands on the wheel. Should I cough up for new tires?

Mixing tires also sets-up the car for a more pronounced harmonic imbalance. Meaning road noise and potential vibrations.

Hi Kls:

1) What are your tire pressures?
2) What are your tread depths as measured in mm or 32's?
3) You should always have both hands on the wheel :) , as this is the preferred driving position.

My owners manual says not to mix tires.

I chose to ignore that and just replaced the rears when I had a flat tire. I definitely would not mix tires on the same axle, but I haven't encountered any problems with the Toyo Proxes on the rear and Yokohomas on the front. The tread patterns are similar so that might help.

I've been using the car as a daily driver with some spirited driving on mountain roads. Before I do any high speed driving such as drivers education on a track, I plan to have matched tires all around.

"Hi Kls:

1) What are your tire pressures?
2) What are your tread depths as measured in mm or 32's?
3) You should always have both hands on the wheel , as this is the preferred driving position."


I'm running 29 lbs in front and 36 rear. The rear tires, at their worst, have 4/32 of tread and the front 6/32.

Kls, you need new rear tires...soon. When new, our tires are about 10/32's. Tires are considered "worn out" at about the 3/32nd mark.

"Kls, you need new rear tires...soon. When new, our tires are about 10/32's. Tires are considered "worn out" at about the 3/32nd mark."


Thanks bmussatti, it shall be done. Would you match the Michelins on the front, or just get a new set? Also, does the tire pressure sound OK?

Kls, Michelins are great tires...$$$$...but good. I would just replace the rears with a set that matches the fronts. Your tire pressures appear fine.

What are your thoughts on replacing the rear tires with new SO3's to match the front. Are there any concerns with the differing tread depths? That way, they would all match just not be the same age. The age of the front tires is 4 years also.

Hi,

If it were me, I think that's the best plan if not doing a complete set. One thing to bear in mind too is that many tires, especially Performance Tires often do not wear linearly, that is the Tire may have only gone from 10/32s to 7/32s in 10k mi., but be all in by 15k mi. - just something to be aware of and keep an eye out for...

Happy Motoring!... Jim'99

I'm assuming that mixing tires between front and rear axles is an easy way to seriously make your car oversteer/understeer-happy at the limit? Especially with a higher stickiness performance tire?

Its pretty common that the rear tires will wear faster than the fronts, I'm curious how much wear alone decreases a tire's stickiness. Could wear alone make as much difference as a different tire between the axles?

-David

Hi,

You're correct. The handling can be affected, the effect can be magnified at speed or high g maneuvering. You're also correct that Tires lose grip as a product of age. The compounds used in Modern Tires will harden with age resulting in greater slippage, irrespective of Tread Depth...

Happy Motoring!... Jim'99

um... yes and no

A DOT Competition tire like the Toyo RA-1 actually improves its DRY grip as the tread blocks wear down. Conversely, its wet weather performance diminishes due to smaller areas to dissipate the water.

While it is not recommended to run two different types of tires on a car, one should at minimum make sure the front wheels match each other and the rear wheels match each other.

It would also help to make sure the tires were of like compound and construction. ie.. a tire with a Treadwear rating of 300 and heat rating of AA will wear differently than a tires whose ratings are 100 and A, respectively.

Be smart about it. Boxsters (and Porsches in general) were not CHEAP to buy OR Maintain.

Also, expect rears to wear out about in about 1/2 of the time it takes to wear out the fronts. After all, that is where the weight and power go to!

Hehe, if my rears are going that much faster than my front tires than I'm not braking deep enough into the corners ;)

-David

Hi,

Sorry but you're talking apples and oranges. All tires will lose grip as they age and the compounds making them up harden, Toyo RA-1s included.

Does a slick have more grip than a treaded tire? Usually, because it has a larger contact patch. But, two equal slicks will demonstrate different grip if one is new and the other several years old. The new one will stick better than the aged one...

Happy Motoring!... Jim'99