Quote:
Originally Posted by mlee
I was having issues getting squirly (unstable) on the rear end and putting the smaller tires on increased that quite a bit.
Most will probably be fine with 35's but 40 seemed to be the perfect fit for these cars. However they cost a little more.
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That makes sense and it's encouraging that you didn't get any ECM intervention with the 26.4" tires. I'm not sure what size rims you have but I'm guessing 18x11. Assuming you went with 305/35R18x11, your new tires would be 8/10 inch shorter. That would explain the tendency to spin the wheels - they'd effectively increase your gear ratio, putting more torque (higher wheel RPM) to the pavement for roughly the same size contact patch. The 305/40R18x11 would work the opposite way, providing less torque and keeping the tires from spinning so much.
Code:
Size Dia (height) Difference from stock
305/30R20x11 27.2" (691mm) stock
305/35R18x11 26.4" (670.7mm) -0.8" (-20.3mm)
305/40R18x11 27.6" (701.2mm) +0.4" (+10.4mm)
I'm trying to do the opposite, increase the effective gear ratio to increase power to the pavement, but I'm going with a wider tread to increase the contact patch and minimize wheel spin. I know from my MT P345/35R18 DRs and 18x12 (43mm offset) rims that the wider tread will fit so my only concern going to a 26" tire is whether the automated systems will muck with my engine timing as some have suggested. If the 12" tread spins I'll just add fuel for weight and/or heat them up more.
Code:
Brand Size Dia (height) Difference from stock
Goodyear 305/30R20x11 27.2" (691mm) stock
Mickey Thompson 345/35R18x12 27.5" (698.7mm) +0.3" (+7.7mm)
Mickey Thompson 325/35R18x11 27.0" (684.7mm) -0.2" (-6.3mm)
Hoosier 335/30R18x12 25.9" (658.2mm) -1.3" (-32.8mm)
I'd really like to get the Hoosier slicks (bottom row). If it's likely the 26" tires will cause problems I'll have to go with the slightly shorter but narrower MT 325/35R18x11.
Now if I can find another M6 ZL1 driver that's used 26" tires without ECM intervention I'll feel more comfortable pulling the trigger.
--Cal