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      10-12-2017, 08:03 AM   #1
jbh
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17 or 18 inch wheels for autox

I'm back in a Z4M again, a black roadster this time. Picked it up last month. I was planning to run kosei k1 wheels with 255/40-17 re71r tires for autocross. Any other options on lightweight wheels that are close to that price? I could also run 18 inch wheels but tire and wheel price rises dramatically. Only other thing I plan to do is alignment and install my turner shim kit. Will still daily drive on stock wheels and tires.

Any idea what this smaller wheel will do to my top speed in second gear at deadline? Maybe 66mph with 18's and 62mph with 17's? I see that as the main disadvantage of a smaller wheel.

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      10-12-2017, 03:02 PM   #2
dc_wright
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What organization do you run AutoX with? That will have some bearing on what you do.
The BMWCCA points system will treat you pretty fairly, but most everyone else uses SCCA classes and installing the shims moves you from Street to Street Prepared. The wheel diameter change is OK so long as you stick with stock widths and keep within +/- 7 mm of OEM offset.
Do the 17's actually clear the front calipers on the M?
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      10-12-2017, 07:35 PM   #3
jbh
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Quote:
Originally Posted by dc_wright View Post
What organization do you run AutoX with? That will have some bearing on what you do.
The BMWCCA points system will treat you pretty fairly, but most everyone else uses SCCA classes and installing the shims moves you from Street to Street Prepared. The wheel diameter change is OK so long as you stick with stock widths and keep within +/- 7 mm of OEM offset.
Do the 17's actually clear the front calipers on the M?
There are a couple local clubs that just have general classifications which I will be fine with. There are two other clubs that run the SCCA rules that one has an unlimited class I can always get myself into. I’m just really out to have fun, I won’t do any national or even regional SCCA events. I have owned competitive STR and STU cars before. But I get to race about 6-8 times per year now so I’m just out to have fun and try to beat the one M coupe in my area, plus a few other locals I usually run close to. This is not the car to get real serious with. But it is a very fun dual purpose car. I found with the other competitive cars I had, once I changed out the suspension I really hated driving it anywhere but the Autocross course. So this car is staying with the stock suspension.
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      10-12-2017, 08:28 PM   #4
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Quote:
Originally Posted by jbh View Post
There are a couple local clubs that just have general classifications which I will be fine with. There are two other clubs that run the SCCA rules that one has an unlimited class I can always get myself into. I’m just really out to have fun, I won’t do any national or even regional SCCA events. I have owned competitive STR and STU cars before. But I get to race about 6-8 times per year now so I’m just out to have fun and try to beat the one M coupe in my area, plus a few other locals I usually run close to. This is not the car to get real serious with. But it is a very fun dual purpose car. I found with the other competitive cars I had, once I changed out the suspension I really hated driving it anywhere but the Autocross course. So this car is staying with the stock suspension.
Roger! Didn't know what your experience level was. I've seen too many people do what seemed like an innocuous mod only to find it's moved them up three classes and they're getting absolutely smoked from a run time standpoint.
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