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Old 11-20-2009, 10:58 PM   #1
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Default Wheel offset and handling/scrub radius

I searched offset and scrub radius here and didn't really find much.
I'm looking at some wheels locally that are 20 offset. I'm sitting on shitty daisies right now. I know changing offset affects scrub radius and what not and could affect handling, I just don't know in what way exactly. Would anyone advise not to run a 20 offset, and if so, why?
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Old 11-20-2009, 11:51 PM   #2
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Quote:
Originally Posted by MartinezA92 View Post
I searched offset and scrub radius here and didn't really find much.
I'm looking at some wheels locally that are 20 offset. I'm sitting on shitty daisies right now. I know changing offset affects scrub radius and what not and could affect handling, I just don't know in what way exactly. Would anyone advise not to run a 20 offset, and if so, why?
Its really complicated, but think of scrub as a literal tire scrubbing. When you have 0-scrub, then you turn right, the left side of the tire gets cleaned. If you had a scrub even to the inside edge of the tire, the complete tire is "scrubbed" or cleaned. This gets more complicated when you consider steering-axis-inclination.

There's an incredibly sensitive balance between spring-rate, damper force, camber, and offset. Scrub-radius changes have huge affects on handlobraesing and there's a reason Emilio made his wheels 36 or 40mm offset and has specific camber recommendations. This is the reason why my car won't turn worth a **** on the 99 wheels, and with the 6ULs it feels like a totally different car.

I suspect that if you went with a 20mm offset you'd have to run very-little camber to get "effective" scrub, and then when you loaded up the tire on turn-in there would be so little camber that contact patch would drop so low that you'll wish you had a 36mm offset. The Miata has pretty good suspension geometry, I wouldn't change it unless you have a badass calculator and an accelerometer because every concept in suspension is dynamic and you're screwed if you put that ricer crap on your car.
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Old 11-21-2009, 01:55 PM   #3
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Interesting. This past autocross season I ran 13x8s 0 offset with 225/45/13 Hoosier A6s at local events, and 13x9 32 offset with the same tire for National events. I set the car up around the 9s, and every time after when I ran the 8s it felt like CRAP. I thought wheel width/ tire age was to blame, but I guess the offset could have been the primary culprit.

When I'm running the 9s I have to run a 1/4" spacer to clear the rear control arms and front brake calipers (the previous 32et accounts for this). I did this to keep the rear of the car as narrow as possible for increased slalom/transitional speed. IYO should I run a larger spacer to increase my track a bit in the front, or even front and rear? Do you think my grip would go up (specifically front end grip, I just set the rear to work around a max'd out front)?
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Old 11-21-2009, 10:37 PM   #4
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Ehh, I thought so, I'm gonna pass til I find normal offset. Which is 36 right?
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