My autocross Miata came with two sets of wheels from the previous owner. One is a set of racing steelies that fit under the stock fenders. I put a set of R888Rs on them and that is what is currently on the car. The other is a set of super lightweight aluminum (?) Keizer racing wheels with slicks. These are considerably wider and have a lower offset, and as such poke out about 1.5" beyond the fenders, but since the wheels are only 13" they don't rub. I like the idea of being able to switch back and forth between the less- and more-extreme setups, but I think the little tires poking out so much just looks kinda awkward, and if I added permanent flares the street tires will look strangely recessed.
I've been mulling an idea along these lines: get a set of cheap fender flares, bolt on style. Epoxy a bunch of strong magnets to the recessions where the bolts are supposed to go. Epoxy another set of magnets to the back side of the fender to match up with the ones on the flare, effectively sandwiching the fender and fender flare together between two banks of magnets. This car only sees autocross speeds, so I'm not worried about them flying off at 100 mph. Am I crazy? Has anyone else tried something like this before?
I would say not a terrible idea, just be prepared that some fenders may get destroyed in testing it out. Offroaders like to attach flares with plastic bolts so that they don't damage the bodywork when they get torn off (also plastic can't rust 
).
You could also consider the well-tested stancebro solution of attaching them with O-rings strung between spools (which they use to let things move around when they scrape), but that's not so pretty.
In reply to AMiataCalledSteve :
Tape them on with clear shipping tape. When time to take them off use a heat gun. ( or your wife's hair dryer if you're brave enough).
The car already has a bunch of snaps for the tonneau it appears. Wy not just continue the theme and make snap on fender flares?
NickD
MegaDork
9/21/22 3:20 p.m.
I could see a tech inspector potentially getting squeamish about the idea of a fender flare flying off and clocking a course worker.
Two words: Dzus fasteners.
If you use some of those high strength rare earth magnets I don't think you'd need to add any to the back side of the fenders, just epoxy them to the flares. Harbor Freight is a cheap source for them.
With enough strong magnets the biggest danger may be getting your finger in between the fender and car when you are putting them on
Cardboard or heavy paper flares. nobody gets hurt.
