Need Advice on an Autocross Tire

[KMG]

Hello, I'm buying a set of track tires for my stock 07 Z4MR using the stock size wheels. I'm looking at Continental Extreme Contact Force because reviews say they grip well when cold like they will be when Autocrossing. 245/40/18 in front and 275/35/18 rears. Anyone have advice on a better size or tire?
Thanks

[Coi]

When I used to autocross my Miata a couple years ago the Bridgestone RE71R and Yokohama Advan A052 were setting the best times. I haven't taken my Z4. Based on reviews it does seem the Continentals may be competitive with those.

Seems like the A052 isn't available in 275/35R18 so would have to go to 265. Seems like RE71R are available in the size you're considering.

You're running pretty wide tires for the width of the stock wheels, so that will get you more grip but at the cost of steering precision. I'm guessing you're looking to run street class so wider aftermarket wheels are off the table. My advice would be to max camber as much as possible to prevent the tire excessively rolling onto the sidewall or getting pinched by the rim. During events, watch the condition of the sidewalls and don't put your tire pressures too low.

If you're worried about fitment or the tires rolling onto the sidewall, could go with 235 front and 265 rear. These 200tw sort of tires do tend to be more square in profile and have wider tread than street tires so watch for clearance to the strut. Can run spacers and extended wheel bolts if they rub. Your clearance to the fender with the stock wheel offset should be fine.

[KMG]

Thanks for the reply. I'd like to increase my engine RPMs when autocrossing by lowering the diameter of the tires so was considering 17" wheels (+- 1" allowed in BS class. Can't change width). I found a used set of 17x8 and 17 x9 BMW style 32 wheel. Do you know if it will clear my M's brakes? Thanks

[kaybat]

Re71's are no longer available(a shame)

[Coi]

Originally Posted by KMG

Thanks for the reply. I'd like to increase my engine RPMs when autocrossing by lowering the diameter of the tires so was considering 17" wheels (+- 1" allowed in BS class. Can't change width). I found a used set of 17x8 and 17 x9 BMW style 32 wheel. Do you know if it will clear my M's brakes? Thanks

There is a member of this forum called "3002 tii" who had 18" Style 32 wheels on their Z4M. I don't know about the 17" ones though. I know some 17" Apex wheels clear the front brakes but not much besides that.

You'll probably need to use one of those free online tire-size calculators to figure out what tire sizes lower your effective gearing but are still the same OD front to rear. Unless you go with very low profile tires on the 17 in wheels the most you'll only gain about 2-3% acceleration over tire with same outer diameter as stock. Will also look really strange because the tires won't fill out the wheel well, if that matters to you.

[Coi]

Originally Posted by kaybat

Re71's are no longer available(a shame)

Yeah, I heard the RE71R ended production but I think they're still legal for auto x street class for a little while. Tirerack doesn't have them anymore but it seems like America's Tire/Discount Tire and Simple Tire still have them in stock in many sizes.

[deemo319]

Don Wright would be a great reference on this subject.