So had a blowout yesterday. I've got a 996 C4S (so it's all wheel drive). The rears have about 60-70% tread life left. Is replacing only the left rear a BAD IDEA or should I replace both of them? Basically, would this affect the differential? Thanks.

 

Absolutely. Change the pair. Doing otherwise will have a dramatic affect on handling and road adhesion - not sure if it would affect the differential.

This isn't a Honda Civic, and you likely don't drive it like a Civic - anything that affects your tires ability to stay connected to the road is a safety issue.

 

If you are truly at 70% you may consider getting your new one shaved to match the remaining tire. You may have to call around and see if there is a shop that could do a tire as wide as yours. Seems like there should be.

 

sounds like I should just buy the pair guys. Thanks for the second and third opinions.

 

Check out tirerack:

tirerack shave to match service

A difference of >4% circumference can damage the AWD system.

 

+1 on shaving.

If you go this route, drive the first few trips on the "new" tire sedately to get some heat cycles into the new tire before you drive the car at 100% (like during a track day). The tires will behave differently until you've heat cycled the new one.

 

Excellent Excellent Excellent feedback gentlemen. Much appreciated.

 

I would not replace both if I had 70% left on the other side. I would start with a reputable used tire place to see if they can match tread life with the other side. When I bought my car the dealer (Straightline Automotive ps they're a joke) had the rear tires all messed up with size and brand, lol. I just rocked it like that until last week when I had a blowout on I10 thanks to our lovely road contruction.
I would went to Tire 59 on Southwest Freeway (gone their several times with great results) to see if they had anything that would match the tread life on the other side, but no such luck so I ended up replacing both with new tires.

As far as handling, unless your on the track or something, mine did not bother me one bit. I definetly do not think its a safety matter, IMO. It

 

Really? You'd put used tires on your Porsche?

 

I knew that was coming, lol.

When I'm in a situation where I still have one good one, or want to get them all on the same change rotation absolutely. Theres a spot in Htown that has great tires for a fraction of the price (Tire 59). I have used them on my vette, lexus, boxster, and was going to use them on this porsche except the one that had in stock to match was defective so I just bought 2 new ones. Which got at 285 30 18 $250 installed for the Rear Set Brand New so not too shabby.

Honestly, I've had great luck out of those guys (never dealt with anyone else), some of their tires are practically brand new for 1/4 of the price. Used tires, new tires, all the same to me as long as they are sound (not defective in anyway). Once I kept them all on same tire changing rotation I like to buy complete sets of 4 at a time.

These are the only used "Rubbers" that I recommend though, lol......

 

IMHO: You must go for the pair, the only reason to buy one tire only would be a flat or if only one was somehow more worn.

You must keep both front tires similar and both rears.
Even if one tire gets a flat and has 60-70% wear, ya gotta replace both or suffer the consequences.........................

 

It's not just about matching tread depth - that's just one dimension.

Rubber compound. Different tires are harder or softer rubber. That will affect how one tire sticks vs. the other tire. It will also affects how tires wear - so even if you get your tire shaved, it will wear differently anyway.

Tread pattern. The pattern affects several aspects of handling, notably, how your tire moves water. In wet weather different tread patterns will result in different levels of hydro-plane. Also not good.

If you are going to replace a single tire - get the same brand, same model, then get it shaved to match.

 

I guess I forgot to mention that I agree its important to match brand, model, etc...