GRM Exclusive Reveal: Exocet Spec-A

Meierznutz wrote: Keith, what are you running and where are they hitting? Very interested in knowing if I should sell off the 15x8 +15's I have....

On the shop car, we have +30 15x7 with a 205/50-15 and a 10mm spacer. There's rubber all over the frame. It hits at the leading edge of the tire on the lower arcing tube. I think it might be bushing deflection under power (stock 1999 engine) or it could be under cornering.

The XXXocet had 235s on a +36 15x9 with 26mm worth of spacers. They touched the frame during a gentle drive as we broke in the rings.

Warren has said that you need even more negative offset to clear the fender mounts, but I've never seen them so I can't comment.

I consider this a bit of a design flaw. The car is supposed to use a Miata donor, but it requires a very specific and unusual wheel set. I only know of one decent set of wheels offhand that has the right dimensions, along with a bunch of stance models. I think Warren inherited this from the original uk design.

ashneyder wrote: Has anyone considered or tried these Konig Dial Ins (15x8, +25 offset)? If I go with these, will I need to get any spacers?

Since we are back to wheel/offset discussion, can someone answer my questions above? I like these wheels. Will they work well with an Exocet? What kind of spacers do I need to get to clear the frame and fenders (front vs back)?

Try reading the post right before yours. I guess I did leave the final calculations as an exercise to the reader.

Short version: they'll probably rub like hell unless you have at least a +25 spacer.

We have the XXXocet set up right now with 205s on effectively a +4 15x7. We'll see how that works.

Thanks Keith. Is rubbing a concern only in the back, or will the fronts need spacers as well?

In reply to Keith Tanner:

Warren. What is the latest news with the fenders anyway? Guessing these are going thru a big redesign too?

The fronts have lots of room. Depends on what happens with fender stays, of course.

I just realized that I DO have a set of fender stays for the UK design fenders. Are they any different on the US ones?

I like those tail lights!

Speaking of which, I need to call you/FM to place an order for some parts.

Keith, how close are you to selling an exocet lighting kit?

I need to evaluate some options. I've been working on this.

Here's a link that gives some example wheels and their offset requirements.

As for why you need an offset on wide wheels: yes, Keith is right, it is a bit of a legacy thing. There's a lot of things going on at that part of the frame, and the length of the UK tank cover dictated the position of that intersection in question. The fundamental design of the UK original forces a tradeoff between cabin width and wheel clearance, and the way they got their wheel clearance was by only connecting the roll hoop to the transverse tube in front of the fuel tank or the top arc tube (depending on the chassis version, as there have been many iterations). The US version's roll hoop passes through the upper arc tube and lands on the lower arc tube, greatly increasing strength in a crash and overall chassis stiffness. I also widened the passenger cabin by about an inch on each side, and the tradeoff was rear tire clearance. The UK version still requires the same offsets to run fenders, and almost as much offset without.

I felt the increase in safety, stiffness, and passenger cabin space was well-worth having to run a low offset on wide wheels. Thinking forward, there is also an opportunity to use custom control arms in the future that eliminate that offset requirement while giving a few other advantages.

Two guesses as to which design is the US version.

Keith, that car does strange things to me.... who needs bodywork to cover that? Just wanted to say thanks for making me drool more!

Warren, I bet it's the second pic??? Nice job!

Carry on....

Here is a good question for you. How much work would it be to go from a Miata Exocet to and LS Exocet?

Not that much. Well, you'll pull out the entire rollerskate and wiring harness and replace it with another one. But you don't need to do much to the frame, so it's just a matter of disassembling and reassembling and rewiring. The fact that the Exocet is so naked makes life a lot easier.

To grossly oversimplify things.

Here's what the AIM dash on the XXXocet says when you turn on the key.

God I want a hooning video of the xxxocet. Its berkeleying EVIL.

Ive never ridden in anything that would even approach that.

Stupid question: why couldn't you run 17x10 wheels with 315's on all 4 corners? The only way ive ever measured offset is in inches, but cragar makes the soft8 in. 4.5 backspaceing.

Not in a 4x100 bolt pattern, I'll bet. And a 315/35-17 is nearly 26" in diameter, which is about 3" bigger than nominal for a Miata based platform.

It'll be at the track tomorrow with a GoPro.

I can't stop staring at these pics... so beautiful

Driving around that motor in a 4500lb car is exciting. You can spin 285's with just throttle up to any street legal speed. I can't quite wrap my head around attempting to drive the xxxocet. Eagerly awaiting the video.

Warren v wrote: Here's a link that gives some example wheels and their offset requirements.

I don't completely agree with that spreadsheet. Our yellow car was running an effective +20mm offset on 15x7 wheels with 205/50-15 tires (+30 wheel, 10mm spacer). There's rubber all over the side of the frame. The spreadsheet shows a +19 being acceptable with a 6UL 15x7.

The XXXocet definitely needs to be treated with respect.

In reply to Keith Tanner:

Hmm. Those numbers were based on our results with poly bushings, therefore they might need to be more conservative. Do you have a rear subframe brace installed?

I don't believe we do. Stock bushings, 87k on them.

I confirmed today that 16" front Lotus wheels with 175 55 tires clear the rear of an Exocet.

For those greatly confused I'm entering a Drag, Drift, Autocross triple venue without a rear E-Brake.

Do they clear when driving? There's a surprising amount of movement. I'd want an inch of air between the rubber and the frame at rest.

I wonder if Mazda put variable durometer rubber bushings in the lower control arm as a way to control toe under lateral load...that might also help explain why Miatas are so prone to wheel hop...

I've got an inch, please don't take out of context.