It has been pretty well established that R compounds are terrible for drag racing, and that drag slicks are horrible at autocross. Since you only get four budget exempt tires, has anybody found something that works for both? Maybe there's a 200TW that launches acceptably? Or a DOT drag radial that can sort of corner? Just thinking out loud and wondering what people's experience has been, with the challenge fresh on all our minds.
R compounds work fine up to about 200hp. So the answer is build a 1000lb car with 200hp.
In reply to ¯\_(ツ)_/¯ :
There was a lot of testing in the Datsun build.
After reading this I'd think you want two cheap used tires out of the 6 2- A7 or drag slicks. Tires make up a lot of time at both events.
I still wouldn't pull the trigger on new unless I knew it was going to go 12's or below in the 1/4.
No.
AutoX and Drags are about as far apart as you can get wrt car setup and tires. This is a big part of what makes Challenge, well, challenging. We went into this year's Challenge with a goal of being top3 in Dynamic. We tried not to focus on chasing tenths in either discipline for fear of ignoring half or even full seconds in the other. Proper tires for each segment was the biggest setup swing we made. A7's for autoX. M/T slicks for drags.
We are definitely still in the fat part of the drag race learning curve, but the lack of drama launching the car means we will be able to start adding power as we get more runs in and bring the rest of the setup on par with the slicks.
Avon's worked well. Need to clarify if they are legal though.
Watch FB Marketplace for bargains and decide which set of tires will be really good and exempt, then get "acceptable" cheap tires and put them in the budget. For most cars I would think that means exempt autocross tires and cheap drag slicks, but the last time I entered a car I did the reverse. Smaller, lighter cars can autocross well on that lot surface with SM7 or R7 take offs. We were overheating SM7s on my Miata to the point that Alan McCrispin asked if I had brought a sprayer. I also found a cheap ($50) set of Mickey Thompson drag slicks in a 22x8x15 size that very few cars can run because they're so short. I would strive to show up with drag and autocross tires unless you decide to run a 200TW tire.
In reply to KyAllroad :
Why wouldn't they be legal?
Non Drag tires dig into the rubber on the starting line and ruin the launch area. A drag tire is compliant when forces are applied rotationally, flattens out and grips the track then springs the car out as the tire unwraps. An A-x tire has stiff sidewalls and digs the rubber out. It doesn't take long for the street and A-x tires to wreck the lanes for everyone. Once the bald spots are created, everyone slows down.
Datsaniti was 2500 lbs and 260 hp + nitrous. On fresh A7's, it went 13.1 with a 2.0 60' and I don't think they held me back at all. Leading up to the 2019 Challenge, I tried autocrossing with drag radials, both in back and front. Both were pretty awful.
From what I've seen *at Challenge car performance levels* an autocross tire will drag race better than a drag tire will autocross. Or put in Challenge terms, you will get a higher dynamic score on 4 autocross tires. Obviously for a very serious drag car like what the Nelsons bring, that may not hold true. Likewise a car setup too well for autocross (really stiff rear, low CG) may not launch no matter what tire you have. See nocones LPM360 and F-Dat.
So it's not just a tire calculation. You have to set up the whole car to be good at both.
The answer is not old heat cycled out Hoosier R7s. They scary. Would not recommend.
I'm going to try softer suspension and A7s at some test and tunes at a local strip to see if that's better. But several Drag tires are available local on rims for $100 so that may have to happen.
Don't discount the other performance advantage drag slicks bring: Access to the drag tire only lane for the first hour of drag racing. Autocross slicks don't count, so you're missing out on the best-prepped track if you don't bring the right tires for the job.
I actually had a conversation with Alan about this over the weekend. When I brought the Stude with the 6 cylinder I had no intention of winning anything. I was there to hang out and do car things with my car friends. That meant I didn't feel like changing tires. So we ran street radials in the front and drag radials in the back. Alan said it handled decent and perhaps with some autocross rubber in the front (and a front sway bar/alignment), it may be able to handle better. We ended up finishing 5th overall that year if I remember right.
In reply to maschinenbau :
Mathematically, your reasoning is accurate. A 13.1 car should 1.76 second 60'. A loss in the 60' typically translate to a 2.5-3 times improvement in quarter mile time. So a 0.24 second loss would easily be a 0.6-0.7 drag improvement, far less then the 2-3 seconds you see on the A-x. Unfortunately the unintended consequence is every racer who follows is running on the track that is compromised as the rubber gets pulled up/off.
In reply to wheels777 :
Perhaps the deteriorating track condition is another advantage for autocross tires? I would imagine you see less performance drop-off on A7's compared to a proper drag tire as the track wears out. There is probably some trade-off between getting 2 runs of perfect track in the first hour vs spending a whole night perfecting a launch on autocross tires. Then factor in the temp drop as the sun goes down, but before the dew point, etc... Challenge is a complicated formula, and that's why it's so fun to me.
In reply to maschinenbau :
Brad is 2100lbs on the start line and put down 215rwhp. My only pass at Challenge was also my only pass in the car and my first ever with slicks on any car. With a SWAG at tire psi, no idea what rpm to launch at, and no tach to read anyhow, I pulled a 1.6sec 60ft.
Anecdotally, *at Challenge car performance levels* I think the A7's may have kept you out of the 12's in 2019.
Is it worth chasing the tenths for the typical Challenger? Probably not, but the right tire makes it so much simpler to get the most out of whatever is available
In reply to maschinenbau :
It does.
Each team has to figure out their strategy and/or goals. A discipline win and/or an event win may not align. I am grateful the drag lane is available. I would prefer it was available longer (1.25 to 1.5 hours gets us 3 shots at it). We know the ground rules before we get there.
Our HP in the first pass was 130 less then our last pass. Unfortunately we had to lower the power in the bottom segment and apply it all on the top. It's the challenge of the Challenge.
I will point out that this year a FWD car posted a 13.3 drag time (and 2nd dynamic overall - so FAST autox too) and they ran the entire event on 200TW.
dunno what their 60ft was, but many folks are starting to see that 200TWs are approaching A7 performance in autox (and with the semi recent SCCA rules change on street tire classes, I bet they continue to close the gap).
We struggled with our 60ft this year. Last year (heavier car) we got a 1.8 on our fastest run of 13.6. This year we managed a 13.4 but it was with a 2.14 60ft. I think our best 60ft this year was 2.09, and that was on the run I tried nitrous for the first time and it wasn't setup right.
Out of all the non-drag specific tires the Toyo R888 are the best that we have found on the higher power FWD cars. They give up a lot on the hit (to slicks or a bias cheater) but don't do too bad down track where we can roast pretty much any tire if we try. Get about 1.9x 60' out of them, full drag slick would be low 1.7 and true, sticky street tires can be as low as 2.0x but usually 2.1x due to spin (and not wasting the clutch slipping it for the 60)
wheels777 said:In reply to maschinenbau :
Mathematically, your reasoning is accurate. A 13.1 car should 1.76 second 60'. A loss in the 60' typically translate to a 2.5-3 times improvement in quarter mile time. So a 0.24 second loss would easily be a 0.6-0.7 drag improvement, far less then the 2-3 seconds you see on the A-x. Unfortunately the unintended consequence is every racer who follows is running on the track that is compromised as the rubber gets pulled up/off.
I've built three challenge cars that ran 13.1 ish. Never had a 60 foot that low, nice to know I was leaving that much on the table. thanks for letting me know how bad I am at drag ;)
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