I had a Miata a few years ago, and I don't know if it was because of the type of suspension it had, but people really wanted to match the factory offset when going aftermarket on wheels due to "scrub radius." Read about it here: http://www.miata.net/garage/offset.htm

Any thoughts? Jim from TireRack? Should this be a concern for us Fitties too?

 

The problem with matching factory offset is there aren't many 15" rims with +55mm offset.

We could probably get rota to make a special order of Slipstreams that match the stock wheels in 14" or 15" or even 16" if the order and demand were big enough say 20 or 30 sets of wheels all in the same finish.

Or maybe tirerack.com will work with us to make special lighter weight not too expensive stock sized performance rims. How about it Jim????

The more you can keep the wheels close to stock the better for performance as it keeps with the overall design.

One option is to use the stock rims and just change the tires to higher performance ones that suit the duty. Use these for autocross or driving school and use the aftermarket wheels with different offset for normal street driving with street tires- hopefully this is less demanding so this works adequately.

 

Plus you really do not need to match the factory offset if the wheels are wider. If you keep the offset the same and you make the wheels wider the wheel is going to go in toward your brakes more. Lowering the offset would actually improve handling by widening the track of the car.
If I can help let me know.

 

So it sounds like given the rim diameter and width you could choose an offset that is near the limit of how much it can fit yet be a bit wide compared to stock.

So in the case of a stock FIT 15x7" rim about +38mm to +42mm offset.
For 16x7" or 17x7" about +45 offset.

 

scrub radius is the distance between the center of the contact patch and the steering axis, this measurement will afffect the tendency for the car to straiten out itself, this is much more important for a fwd car since scrub radius is directly related to torque steer, keeping this scrub radius as small as possible will make handling better (all things equal, which means no rubbing and what not)

right now i'm trying to find a set of 15 or 16 inch wheels which are 5-6 inches wide (whatever is optimum for a 195 or 205 width tire) with proper offsets which is really hard >.< (expecially considering how picky i am with styling and weight)

if anyone knows of a rim which is in this size and under 15 lbs (max is 17, cant take nething heavier then that) and preferably shot peened (i know forged is too much to ask for at a price of $1XX per rim) then PLEASE either post or PM me !!!

 

oh shit, i forgot to mention that you can only go so wide before the clearance between the strut and wheel becomes nothing which forces you to go less in the offset section, which increases scrub radius (most likely, unless the people who designed ur suspension were smoking something)

for the fit i believe (i have no scientific reason to back this up as it's just a gut feeling) that it's useless to go above 205 in width expecially with grippy tyres, this means anything wider then a 7 inch wheel is going to be too much (personally i wont go over 6.5 as they can comfortably fit a 205 tire onto em)