Narrow Miata Suspension Assemblies?

Project is a MGB with front and rear Miata suspension running a 302 ford.

Miata track is 3.5" wider per side. Manageable with flared fenders.

Trying to figure out the repercusions of the geometric mayhem that will result from narrowing the track on a Miata front and rear suspension assemblies? I am guessing that the roll axis for/aft is going to be affected?

Doing this would avoid the need for fender flares on an MGB, but I am not clear on what it would do to the handling. Steering rack would be an obious issue.

Also not clear if the rears half shafts that are available for Miata V8 swaps can be shortened to suit. Could be a tipping point towards a 8" solid rear axle with a 3 link.

I narrowed a miata rear suspension and used all four hubs on my MG Midget. I didn't use the miata front or rear subframes. Made my own rear subframe and re-used the miata a-arms with the same geometry as mazda did. Front I welded up new a-arms, narrowed my steering rack, etc.. The rear axles are harder than chinese algebra. It took some doing to re-spline them.

I'm going on a decade of having this under my car, three iterations of front suspension, two of the rear, and going on a third rear and fourth front. Granted, I started this when I was younger and less smart on the stuff, but it can be a pain to build a ship in a bottle. I'd be strongly inclined to get a big brake kit for the front, and get a ford 8.8 for the rear and be done with it unless you are very good at this stuff, and enjoy an endless tuning project.

Since I've got a Miata engine in an MGB/GT, I wrote about it for GRM, and it's gotten picked up by search engines, I get e-mails and phone calls from people fairly often who are trying to put the whole Miata suspension in like your suggesting. I've never seen one finished and I've gotten follow-up e-mails and calls from people who gave up and wanted advice on the best way to unscrew up the car they cut up. I'd stay away from it.

Narrowing it isn't really the description for the job. You've got to basically redesign everything. As alluded to above, there are already alternatives and that would save a lot of time, effort, and risk.

I think Keith Tanner used parts of the Miata suspension in his LS1 B/GT--he'll probably have some very good advice!

--Carl

I'm pretty sure Keith used the donor Miata bits without modifying them, changing the MG's frame rails instead, and the track is still wider than stock. You can find his build diary online; his suspension work starts at http://slowcarfast.com/MG/diary.php?start=121

I did indeed use the Miata bits without modification in the front of the MG. Instead of mounting the subframe up front, I built new frame rails and used the Miata pickup points. Oddly, after essentially building a new car from the firewall forward, I decided it would be too much work to put the rear subframe in the back and went to a more traditional three-link setup.

Narrowing the assemblies will move your roll centers - not just static, but I think it will make them more mobile. That might lose some of the Miata's predictability, although I'm not completely sure about it. You would pick up more weight transfer with all that implies for handling and grip. The Miata rack can be shortened by 5.5" by sectioning the rack and the housing so that's not a major problem.

One thing to remember about flaring the body to fit over the Miata track - make sure you've got enough flare to cover fatter tires as well. Just about every rubber upgrade will push the edges of the tires out further. On my car with Rabbit flares, I'm stuck with a pretty narrow tire unless I dig up some really high offset wheels because the flares are only enough to compensate for the stock Miata width.

If you're buying axles for a V8 conversion to use, chances are you can get them made to whatever length you need as they're all custom parts anyhow.

Hey Keith, you must be getting tired of me asking these questions all over the net, but , like with my day job,I find that with a larger sample rate comes clarity.

You nailed it on the dynamic aspect of changing the roll center. It would become an unknown and one that could not be controlled after the fact. I do not for a second underestimate the amount of enginering effort that went into creating the Miata suspension geometry and realize that I would change it at my own peril.

The reasons for using the Miata suspension in the first place is because I still think it is a benchmark vehicle in the handling/feel department. In my opinion, the early Miata handles better than my FRS so that says something. I am trying not to mess with this attribute.

The answer then is to leave track alone and work around it. My flars will be m

Still deciding on integrating the Miata sub-frames or putting the pick-up points on to the tube frame.

No worries, I figure other people might learn from reading it even if I know you already have the info

If you use the Miata front subframe, you're going to have to modify it to work with the 302. So it's hard to come up with a real benefit there, given that the amount of work to mount the subframe isn't too much different than the amount of work to mount the control arms on your tube frame. As you might have seen on my build, there's a happy alignment of dimensions on the MG. Run a pair of frame rails along the inside (I think it's the inside) edge of the existing ones and they're almost the perfect width for attaching the front lower arms.