Real world example. Dusterdb13's Miata ran SM7s last year for autocross. Budget reasons mean that allowed him to run dedicated drag tires for you guessed it the drags.
So what would GRM do? Exempt brand new autocross tires? I looked at A7s but ones that fit are out of stock at tire rack. Could probably/maybe get them before Challenge but not before I go up to NC and get to sit down with Michael. Then I talked with Go_Gators to see if I could grab something local and he tells me the smaller cars aren't running A7s anymore. They're running 200tw tires.
So two questions. Run the SM7s to be able to run dedicated drag tires or grab some 200tw tires and run them only? If so what 200tw tires to kick all the shinny at the Challenge?
Autocross tires suck at drag launches. If you air them way down, they suck less. In my 96 PGT, yes I know lemons to grapes, 13psi gave best 60ft.
It's really a trade off of whether the A7s or 200tws will hurt you in the drags more than the SM7s will hurt you in the autocross
Yes they suck at launches. First year of the Q45 we ran autocross tires only. Spun them hard all the way through first gear. Next year we went to drag tires and IIRC gained 2/10s of a second in the drags. Was it worth it? Yes because I did other changes for autocross. Here we can't do those changes. Can I make up 2/10's in the drags with better autocross tires? Will something get me ore than 2/10s in the autocross? Do I want to spend $1k for 1/10th of a second no.
In reply to Stampie (FS) :
FWIW A7's still look to be worth about 2-seconds over 200tw, based on SS vs. SSR results at national events this year. I'm not sure why smaller cars wouldn't be running A7s, but I don't see why they wouldn't be faster than similarly sized 200tw tires.
In reply to Pete Gossett (Forum Supporter) :
What about A7s vs SM7s soaked in dressing?
In reply to Stampie (FS) :
I think fresh 200tw tires will likely be better than SM7s.
Drag tires on the back and A7s on the front? Would that handle like absolute dog-doo?
I'm a fan of SM7s. I ran them on my Miata in 2017 and they stuck far better than I expected. We were almost overheating them, too. It comes down to which type of tires can you find to give you the most budget assistance. I got the SM7s free and spent a few bucks on a pair of short drag slicks which were then budget exempt. The drag slicks helped the launch , even though the car is only making 175ish horsepower.
For my next car I've found some cheap drag slicks and will use my tire exemption for some A7s instead. The power to weight ratio will double the Miata , so decent drag tires will certainly help. It's all about budget, so what can you find in drag and autocross/road race tires for the least budget hit?
In reply to Stampie (FS) :
Nope. I just remember some article from a magazine where they did autocross on drag radials, but can't remember the results. I think they had all 4 the same though. Which, if you think about it, would give you double the drag launches if you rotate them enough. Probably makes more sense for a dedicated drag racer doing an occasional autocross, than for a challenge car.
dps214
HalfDork
10/12/20 10:57 p.m.
Pete Gossett (Forum Supporter) said:
In reply to Stampie (FS) :
FWIW A7's still look to be worth about 2-seconds over 200tw, based on SS vs. SSR results at national events this year. I'm not sure why smaller cars wouldn't be running A7s, but I don't see why they wouldn't be faster than similarly sized 200tw tires.
That's not a great comparison. Not the same cars at the pointy end of each class, and pretty much all of ss is running up against some type of tire availability limit meaning they're running less than optimal sizes. Also ss is typically hit or miss with competition level and has been more "miss" than usual this year where ssr had had at least one national champion at pretty much every event. I'm definitely not saying a7s aren't faster, but all else equal including size, I'd say it's more along the lines of one second on a 60s course. I agree that I wouldn't expect sm7s to be as good as good 200tws, especially in cold weather and on lighter cars.
Autocross tires (whether slicks or 200TW) are MUCH more effective at drags than the opposite, at typical Challenge-car levels of performance. Your Q45 has lots of torque and front weight bias. This Miata, while more powerful than a normal Miata, isn't exactly a V8 torque monster and weight distribution is better. I doubt your drag times will be severely limited by tire.
I had a similar predicament with Datsaniti, but ran a 13.1 on nitrous on A7's at the Challenge. Simlar weight as your Miata. Similar power. Similar balanced weight distribution. May have spun a tiny bit off the line, but that car's best ever ET was 12.9 on drag radials a month later after I got the balls to spray off the line. So we're talking about 0.2 seconds here.
One thing's for sure - do NOT autocross on drag radials. Last summer I tested it out. DR's out back, massive oversteer. DR's up front, massive understeer. Either way was extremely difficult to predict, and either way was several seconds slower than old, worn 200TW tires of the same size.
scrounge some 15x8's and the run some Nankang AR-1's in 225/45R15... $135, and 100tw?
Call Berget tire. Seriously. Tell him the size you need and what you are doing. He'll hook you up with used slicks shipped right to your door. His number should be in the back of your closest GRM issue.
In reply to sleepyhead the buffalo :
aw, berkeley... I said I'd keep my mouth shut... didn't I. 
I've had very good results on track and autox from 200TW tires, Nitto NT05s, specifically. I've had a set for 3+ years now, and they still offer amazing grip (especially when turbo boost is not involved). The price was good, too.
