I'm kind of embarassed not to know the answer to this, but....
I'm thinking of grafting Miata front and rear subframes to an older car. - Problem is, the older car has a track that is 4.5 inches narrower. The fenders of said car will take another inch or so prior to tire rub, but that still leaves me about 1.25 of offset difference. I don't want to add flares (Well I do, actually, but that might spoil the surprise
) so it would seem that finding rims with the requisite negative offset would make things fit visually.
How will this affect the handling and suspension geometry?
You'll get more weight transfer due to the narrower track. I can't remember if the roll centers will change, I think they will. You'll also mess with the scrub radius, which will affect steering kickback. Hitting a bump on the left wheel might pull the car to the right if I have it figured correctly in my brain.
That's going to be a fair bit of offset - you're looking for a wheel with around a +77mm offset. I'm not sure where you'd find that.
oldtin
Reader
3/26/10 11:05 a.m.
Effects on scrub radius comes to mind - but whether it's good, bad or indifferent would kinda depend on a bunch of factors. There's some suspension freeware on the locostusa site that could help sort it out.
I have rims on my S2000 with a 77+ offset, but they're 10' wide 
10 foot wide wheels? I'd like to see that. 
stuart in mn wrote:
10 foot wide wheels? I'd like to see that.
I think that he was thinking of his steam-roller!
TJ
Dork
3/26/10 3:01 p.m.
Honda fit wheels are 4x100 same as the Miata and are +55 offset. They might work. Not sure about the center bore size.
I ran into a similar problem with my stillborn rotary Opel GT project.
Miata rear subframes are easily narrowed. Chop the requisite measurement out of the middle, shorten the diff mount 'ears' and have the axle shafts resplined. Bing, you are done.
Front: you can do basically the same thing but you need to shorten the steering rack the same amount as you are narrowing the subframe.
This sounds harder but is nowhere near as much trouble as trying to do something with the weird scrub radius of really deeply positive offset wheels. Roll centers will be affected at really high body roll angles but not enough to be of concern.
