ps I've spent a LOT of time thinking about this, so no, I don't always have answers off the top of my head like I happen to today. 
ps I've spent a LOT of time thinking about this, so no, I don't always have answers off the top of my head like I happen to today.
There some promising options on the list, but listed for fa. I have no idea what fa means.
I think that's formula atlantic:
Dusterbd13-michael said:I have -3 camber front, -1 rear, zero toe all around. Fully seam welded and braced chassis. Gm 3400v6 from a Buick rendezvous swapped in. Subframe connectors 4 point roll bar. Butterfly brace. 1 1/4 front bar, none rear. Hard s bilstiens and 450/350 springs. Stock nb miata 15s (15×6 i think)
So you're really wheel limited with those 6" wide pizza cutters. And your front spring rate is lower than I'd think is ideal.
Is it still running a miata trans behind that GM motor? In my ecotec NB I discovered a real problem with the low redline limiting 2nd gear to 51 mph. If you're topping out 2nd a lot it'll kill your times as well, while shifting to 3rd may not be as helpful unless the course is huge.
Im running a gm world class t5 and 4:10 torsen. On the ONE event ive had it out to, i found it hit the rev limiter way too quick in second, but third never seemed to be too low in the revs. I did hit limiter in third once though. Now that its running better, im interested in seeing how the gearing wirks. I agree its too soft eith wheels too narrow. However, its what i have to work with. I have been unable to source cheaper/equivalent price parts of more suitable nature yet.
Whew, yeah you're gonna spend some time developing that beast.
And I know you don't want to hear this but my worst finishes in the past 5 years of autocrossing were in my Monster Miata. It was largely the suspension. Slightly heavier than factory but not serious enough and KYB shocks just didn't control the poor thing as it wallowed around the course. Running 15x8 wheels with 595-RR tires.
And I don't know if it's in the cards but I ended up with a LSD from a Thunderbird SC with a 2.73 ratio. It gave me a 2nd gear (same trans as you) worth almost 80 mph.
I looked at the ford diff. I MAY be able to do it in budget, but durability of the homemade half shafts would be questionable at best. We decided to stick with miata stuff for simplicity sake.
The hard s bilstiens and spring rates seem pretty well matched so far based on street testing and the single autocross. Honestly, with as poorly as it was running, and as bad of a driver as i am, theres no telling how well it actually works.
A Facebook marketplace ad just pipped up for a full set of 205/55/14 hoosier r7 slicks. For $200.
This, in challenge budget world, would cut 75 from my budget. But only if i mount them on my 14x5.5 or 6 steelies.
Would they have more or less gtip than the sm7 in this application? My guess is the setup would be heavier, more sidewall flex, and similar heat up issues and grip to the sm7. Is my gut right? Because that would make them not worth it.
In reply to Dusterbd13-michael :
I'd be surprised if the SM7 isn't the R7 compound. I bet that is pretty much the exact same tire.
Robbie said:In reply to Dusterbd13-michael :
I'd be surprised if the SM7 isn't the R7 compound. I bet that is pretty much the exact same tire.
Even if they aren't, I know they both need heat in them to stick, which is the problem.
Thats what i thought!
Well see how the sm7 do with hotter ambient temps. Deadskunk, justjim, and others have run pretty strong challengeprograms on them. And i probably should be worried about other things more.
I have some 225 45 15 rs4 and also some 245 40 15 rs4 tires.
You can have the 225. The 245 would be either borrow or buy.
The 225 would work well with an 8 or 9 inch wheel.
In reply to wvumtnbkr :
Thanks! Unfortunately, im pretty much stuck with 6-7 wide wheels due to budget constraints. Which sucks. Same with the low spring rates. I doubt cramming a 225 on a 7 inch wheel would work well.
Michael, you're over-thinking again. I ran SM7s on my Miata at the 2017 Challenge. They got plenty hot on that abrasive asphalt. We had to reduce the tire pressures by 3 psi twice in 6 runs (started at 30si stone cold) because they were overheating pretty quickly. After the 5th run I could not put my hand on the tread face. The only car faster than mine was the Georgia Tech Insight, and I would expect your car is every bit as capable as mine. I'd bet yours is faster head to head.
Edit: My spring rates were 450/325, wheels were 15x7, front sway bar was 26mm, no rear bar. I have no feel if my home-brewed aero helped , or not.
The challenge is normally a little different than a local event. You have a better chance of being able to hot lap tires and keep heat in tires.
Just keep checking FB marketplace and craigslist eventually something will appear. Try a few different search words.
Do tire blankets not work in this application?
Call me when you get this post day or night
Pardon me, I'd like to revive this topic for a minute.
Used tires for the challenge. I have a set of stock miatas 15x6 wheels and a set of aftermarket 15x6.5 as wheel options. My used tire options are 205 SM7 or 225 A7. Which combo would work the best?
Im running sm7 on stock miata wheels for the challenge
Probably the A7s would be better, unless it rains
In reply to bigben :
225 A7s on the wider wheels. More rubber and a softer compound will win out.
DeadSkunk (Warren) said:In reply to bigben :
225 A7s on the wider wheels. More rubber and a softer compound will win out.
It'll look like a sportbike rear wheel with that much of a squeezed fit, but that is the best wheel & tire combination out of what you have.
Those 225 A7s would be even better on a wider wheel, 8.5~9" would be ideal.
In reply to Robbie :
I think Dusterbd was asking for a translation of the abbreviations on the Hoosier spec list....not SCCA classing.
Compund ALWAYS beats fitment.
A 225 Hoosier A7 even being a bit floppy on a too-narrow rim will be WAY faster than a R7/SM7.
Us idiots seriously autocrossing Miatas run 225's on 7.5's and 7's all the time. They work fine. In stock classes people run 225's on 6" wheels too, with light weight and camber it's perfectly normal.
Patrick's former 245 Hoosier S80 on 6.5" wheel.
Based on this a 225 might not look so bad.
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