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Originally Posted by Shabodah
Moving from a 215 to a 315 seems like a bad idea without changing the gearing or torque output significantly. Furthermore, I'm not sure how far said tire would stick out of the wheel wells and how bad it would rub. What all tires have you been running in the past?
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I've been running Hoosier A6 225/40 x 17s and 225/45 x 17s. 295/35 x 17 Hoosier A6s are about the same diameter as the 225/45s (less than an inch taller than the stock 215/45 x 17 Dunlop). 315/35 x 17 are 1" taller (go to Tirerack and check-out the diameters for the tires). The biggest problem with the Redline is sliding (or spinning) the tires in the corners and/or under power (I have a qaife).
Summary Stats:
TIRE BRAND/MODEL SIZE DIAMETER TREAD WIDTH
Dunlop SP 9000 215/45 x 17 24.6" (stock) 7.9" (stock)
Hoosier A6 225/40 x 17 23.8" (-0.8") 8.9" (+1.0")
Hoosier A6 225/45 x 17 24.7" (+0.1") 8.8" (+0.9")
Hoosier A6 295/35 x 17 25.3" (+0.7") 10.8" (+2.9")
Hoosier A6 315/35 x 17 25.6" (+1.0") 11.6" (+3.7")
Both the 295/35 and the 315/35 are about 1% larger than stock -- not a big deal with as much torque as the Redline puts out. But differences in adhesion with almost 4" of additional tire with a 315 are HUGE!
The tires will likely sit outside the body width -- which is the biggest reason I have no plans of using lowered springs. Maintaining speed in the corners is the biggest potential gain I can make on an autocross track -- there's plenty of power, particularly if I can carry 1st up to 7000 RPM. Actually reducing the torque (1% taller tires) improves performance because there's less likelyhood of spinning the fronts coming out of a corner. Higner entry speed, higher cornering speed, and less tire spin on exit = faster times. I don't expect any rub, but it it happens, I'll deal with it. There are lots of suspention tricks to stiffen the suspention or increase roll stiffness (the reason for the added reas swaybar). BTW, the rear wheels are being shimmed out to 1.5 degrees of negative camber tomorrow -- and the front camber is being upped to 2.0 degrees of negative. Did I mention that I usually drive this only to autocross events, not normally on the street, it's usually garaged.
There are a number of very fast DSP & FSP cars racing in this region with tires as much as 2-3" outside the body -- BMWs mostly -- and some very low HP cars (Rabbits and Scirrocos -- <110 horses) with huge rubber and very high corning speeds.
Scott