Grassroots Challenge Autocross Speeds?

Hey guys I was wondering what kind of speeds/ rpm ranges people were at most of the time during the autocross at the challenge. I'm trying to figure out the rear end gearing for my challege car and this would help out alot! Also, did anyone run a trackmate or anything like that at any of the challenges?

Thanks alot!

Speeds varied depending on the car. Historically, the autocrosses tend to keep speeds relatively low, maybe 60ish? for the fast guys.

On the other hand, if the only thing that screws you up is improper gearing for the autocross, I'd say your car is better sorted than 100% of the competiiton.

Bryce

I'd say gear the autocross for a max of 70 if you're just going by overall speed.

If you're not planning on switching rear ends, though, I'd make sure and leave a gear or three for the drag race.

Also doesn't it depend kinda on the course. I was under the impression that this last event was a faster course then the one before.

Yup. The minimum turning radius is what's going to make the difference in gear selection, though.

unevolved wrote: I'd say gear the autocross for a max of 70 if you're just going by overall speed. If you're not planning on switching rear ends, though, I'd make sure and leave a gear or three for the drag race.

Unless the autocrosses have gotten a lot more open at the challenge, 70 seems overkill. My old car would do 63 in 2nd, and though I hit the rev limiter regularly on National courses, I never would on any of the challenge courses I've seen.

yea i'm with Dave. our ex-challenge e30 has a shorter 4:10 gear in it and is often between 2nd and 3rd on hoosiers locally (bigger more open track) but has never been out of 2nd gear at the challenge.

The course we set up last year was good for third in a few of the cars I drove along the 'back straight'.

DILYSI Dave wrote: Unless the autocrosses have gotten a lot more open at the challenge, 70 seems overkill. My old car would do 63 in 2nd, and though I hit the rev limiter regularly on National courses, I never would on any of the challenge courses I've seen.

Never been to the Challenge, but in general, this seems right on. Mid 60s is what I shoot for. An E Stock MR2 won't get that fast, but I very rarely shift to third.

I try to design the track for the top of 2nd gear but the short tire cars tend to get into 3rd on the long section. The boosted Hondas just about always have to shift to 3rd at least 2 times. I about wet myself when I hit 3rd in Andy's Bug last year on the back straight...Never thought it would stop but it did (except for the time the brake peddle came loose) and made the turn at speed. I had to use 3rd in the Condor's cars the last several years and in the Hong Hondas.

admc58 wrote: I try to design the track for the top of 2nd gear but the short tire cars tend to get into 3rd on the long section. The boosted Hondas just about always have to shift to 3rd at least 2 times. I about wet myself when I hit 3rd in Andy's Bug last year on the back straight...Never thought it would stop but it did (except for the time the brake peddle came loose) and made the turn at speed. I had to use 3rd in the Condor's cars the last several years and in the Hong Hondas.

Is there a mandated minimum radius you shoot for?

There are always box 90s at low 2nd gear speeds. I don't measure anything, I just do it by feel generally by driving something about where I think I want the course to go and then lay cones around the tire marks. I'll generally drive a mid-speed car/truck when laying out the courses.

Power application off corners is IMPORTANT...If I had a chalk board I would underline that. ;-)

OK, I gotcha. The only reason I ask is that's how we determined our drive ratio for FSAE. We knew the couse will have a minimum radius of 29.5' OD, so if we decide we want to never use first (with the standard shift pattern on a sequential motorcycle box, it makes it a lot more likely to accidentally get in neutral), we decide that at 5000RPM (or something) we're making the minimum amount of torque we'd feel comfortable accelerating with. Then it's just V^2/R assuming an optimal acceleration of 1.5G, and we've got our idea drive ratio.

Hopefully that method could be useful to some people on here. I know some other organizations list a minimum turn radius.

Have you asked Per if you're allowed to use math in the $20xx?

The Man said: 1.If the rules do not say you can do something, you cannot do it.

I'm pretty sure you can't.

Bryce

Seriously. That's far more thought than i put into my real race car.

Nashco wrote: Have you asked Per if you're allowed to use math in the $20xx?

The Man said: 1.If the rules do not say you can do something, you cannot do it.

I'm pretty sure you can't. Bryce

Damn. That makes your '09 Fiero effort all the more impressive, then.

I used 3.73 gears with a 25.5" tire and just barely hit the rev limiter at the end of the back straight in second gear. Redline only comes at 6,000 rpm for me though.

92CelicaHalfTrac wrote: Seriously. That's far more thought than i put into my real race car.

Meh. I wish we could've fit 15" wheels and tires in the budget. The 13's killed us...like, potentially "the difference between 2nd and 1st place" - type killed us. Like Alan said, 3rd gear was a must.

92CelicaHalfTrac wrote: Seriously. That's far more thought than i put into my real race car.

"real" race car?

what are you trying to say about our cars

floating second and maybe grabbing third seems pretty common for me at a challenge autocross as well as most of our local events

evildky wrote:

92CelicaHalfTrac wrote: Seriously. That's far more thought than i put into my real race car.

"real" race car? what are you trying to say about our cars floating second and maybe grabbing third seems pretty common for me at a challenge autocross as well as most of our local events

Well, i meant compared to my Challenge car. I'm sure half the Challengers would eat my "real" race car alive when/if it gets finished.

poopshovel wrote:

92CelicaHalfTrac wrote: Seriously. That's far more thought than i put into my real race car.

Meh. I wish we could've fit 15" wheels and tires in the budget. The 13's killed us...like, potentially "the difference between 2nd and 1st place" - type killed us. Like Alan said, 3rd gear was a must.

SPSH...forget the budget, I wish I could have fit 15" wheels and tires on my car!

Bryce

Bryce said: SPSH...forget the budget, I wish I could have fit 15" wheels and tires on my car!

15's would look like dubs on your car.

The only math involved in our rear end calculations involve how much money it's going to take out of the budget to get whatever 5 speed and whatever diff we can find onto the car. lol

yew guyz must thank yer speshul cuz youns can use maths and stuff ta mayke yer rayce car fastur.

The only math involved in my rear end calculations...

...never mind.