Street Prepared Class - Wheel Calc. Question

Discussion related to classification of cars in the NEHA series.

Street Prepared Class - Wheel Calc. Question

Postby skimobile » Tue Apr 30, 2013 9:15 pm

I'm doing the calculations to determine the SP class of my car.
The question I have involves calculated adjustments for wheel size and width of my current wheel setup vs factory available option size for my year/model;
(e.g., the 2003 Subaru WRX had a factory BBS wheel option of 17"x 7").
The wheels I"m currently running are 18" x 8".
Would this calc. adjustment net out to:
a) A "zero" adjustment, based on a -2% for 1" LARGER rim dia. and +2% for using a 1" wider rim, or
b) 4% total adjustment based on deviation, regardless of whether it's up or down, from factory option sizing. I would think that INCREASING the wheel diameter would result in a negative performance advantage (size/weight).
Please let me know your thoughts.
Thanks!
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Re: Street Prepared Class - Wheel Calc. Question

Postby Rabbit Farmer » Wed May 01, 2013 12:03 pm

b) 4% total adjustment based on deviation, regardless of whether it's up or down, from factory option sizing. I would think that INCREASING the wheel diameter would result in a negative performance advantage (size/weight).


I think it is b....

Any change from stock could have a performance advantage.... taller = faster speed on the straights, but slower acceleration.

I remember asking this question last year either in the forums (I will look around) or at the NEHA banquet.

Steve
Go Fast VW & Audi parts at FastAddiction.com
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Re: Street Prepared Class - Wheel Calc. Question

Postby walterclark » Wed May 01, 2013 2:26 pm

My understanding is the SP class allowances permit updating and backdating within a model without penalty. If true this would permit 18x8 wheels on your WRX with no adjustment if they were available from the factory on any WRX.
The older I get the better I was.
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Re: Street Prepared Class - Wheel Calc. Question

Postby skimobile » Wed May 01, 2013 5:45 pm

I will check into that, thanks : )
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