Tire Sizes for Street and Autocross SC

[RobertR506]

This Spring I’ll be getting new Summer tires for my 2017 MX-5 ND1 AT, most likely Conti ECS and 17x7 wheels. Which, do you think, would work better for spirited street driving and an occasional autocross SC, 205/45, 215/45, or 225/45? Also, what offset should I have for each size? Would there be any advantage going to a 16x7 wheel with 225/50s. I noticed that you have 225/45s on your SC car. Thanks.

[Brian]

My wife's supercharged RF indeed has 16x8 and 225/50. That's to soften the street ride with the race valved Ohlins on that car.

For street use 215/15 on light 17x7 works great, plenty of performance and yet some curb rash protection for the wheels. The 225/45 on 17x7 is what we must use for SCCA autocross, feels a bit sloppy on just 7 inch wide wheel but if softer ride was the goal then that would get you that result, typically customers going 17x8 for 225/45. You can indeed push offset out a bit with the more conservative tire size choices, how much depends on variables like which tire, which size, how much negative camber.