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      03-05-2012, 03:38 PM   #1
Trev
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Autocrossers How do you Launch?

So come to try the Z4 for the first time on RS3's. On cold tires anything more than 1500rpm will spin any prayer of a good launch into the weeds.

So let's discuss how to get a good launch given the parameters autocrossers face.

We're not able to pre-warm by burning out in hot pits.
We have to have sufficient rear tyre pressure to withstand lateral loads. Which means 20-25psi is to low.

So what's the hot ticket setup & technique???
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      03-05-2012, 03:59 PM   #2
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Leave 3' of space between the bumper and the timing beacon. Launch hard.
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      03-05-2012, 06:45 PM   #3
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3k RPM, your tires will grip second run if they don't on first...

I shoot for 38 PSI hot, with even tire temps.
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      03-05-2012, 07:21 PM   #4
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In my only event so far with my Z4 M Coupe, I launched at about 3k RPM to get initial some heat into the rears. This is about what I did in my E36 STU car.

If your course design follows Roger Johnson's guide, there may be a sharp turn (pg 5) after the start so you won't have much of a launch before you need to brake. This first element is not only fair to slower cars, I would think it also saves your driveline a bit. I find if I drive within the limits, I can get things warmed up for the next run. If I spin, I try to quickly recover and keep going at 9/10ths to build up heat without seriously over-driving.

So on the only 4 runs I've had last fall, which were on OE Continentals, I had fun with understeer (full depth fronts) and glorious throttle oversteer usually on the same corner . While I'd gotten used to the E36 for 11 years, I quickly learned how the E86 talks back - slightly more sharply, but the car still makes my skills look better than they are .

I'll be running in a very lightly prepared road tire BSP with 265 Star Specs with AST 4150s and camber on order. Wheel studs coming in tomorrow (only had 2.75 turns of engagement with OE bolts and 5mm front spacers and my long bolts are too long) so I'll at least be able to try out the Star Specs sans ASTs in time for our first tune up event.

Happy runs to all!
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      03-19-2012, 08:11 PM   #5
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So far our courses have all been run in damp to full wet, heck yesterday was snowing.

So here's a technique for Ultra performance summer tires in 30-40F temperatures.
A, If you have a choice DON'T use Ultra performance tires at temp's below 50F.
B, Wind up 1800-2000rpm
C, Bring clutch up smoothly, approx 1-1.5 seconds from clutch stop to fully up.
D, Once your rolling & NOT wheel spinning, Feed in power until your Either at full throttle Or at shift point.
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      03-19-2012, 08:24 PM   #6
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I launch around 2000 on hot tires.

To be honest, there is never a "set" number on what you aim for...as I learned this last year. I tried to launch the same RPM on airport tarmac and bogged it hard.

What I do, when I have cold tires, is launch at 2500 RPM. My first run is always a throw-away...if it's my fastest of the day there is a huge problem. I will get to my RPM up to around 2500 (sometimes I go even more), and dump the clutch hard. I never ride the clutch out. I go full WOT.

This, obviously will spin the tires, and usually most of the time it'll grip hard. If I feel the car spinning too much, I'll let off the gas a bit til I feel it grip and get back on the gas ASAP. That'll get heat into the tires and I'm usually good to go after 2 runs when my tires are at temps.

When I'm launching correctly, I get alittle squeal and get grip fast. Everywhere I've been, you have to line up at the cone...there is no extra room to launch. I try to get power down asap
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      03-20-2012, 04:03 PM   #7
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i was launching at around 3k and slipping the clutch on the way out. I assume your not just dropping the clutch, but i figured i would mention it anyway, with the track setup i was on it started on a turn so 1st was a total waste. I short shifted to second as soon as i got the car moving at a good pace.
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      04-03-2012, 06:27 AM   #8
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A couple of thoughts:

1. I notice you live in Portland Oregon, report wet conditions and cold temps. Honestly, while Hankook RS3's are great in the dry/hot of the summer, they are notorious for being poor in the wet and questionable in cold since they need heat. I'd suggest recruiting a co-driver to help warm your tires for early in the season but that's just me. I personally run a second set, Toyo R1R right now and will be Michelin Super Sports when the R1R's are spent, in cold and wet conditions because they perform much better than the RS3's.

2. Launch is a personal matter. I launch by sidestepping at 1500 rpm in cold/cool temps or low grip surfaces to as high as 2500 rpm on hot high grip surfaces. I used to "slip" the clutch and even with the removal of the CDV, there were times when the clutch glazed ruining the run.

3. While I am not against spinning the tires to gain heat on the first run, there is a finite benefit to this.

4. I've tested tire pressures on RS3's from as high as 36 to as low as 25. My sweet spot is 33F/31R both cold and bled down hot but can vary this by a pound either direction. The only issue I'd warn is going too low, the RS3 will grip but does cup and wears prematurely.
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      04-19-2012, 09:04 PM   #9
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Quote:
Originally Posted by z3papa View Post
2. Launch is a personal matter. I launch by sidestepping at 1500 rpm in cold/cool temps or low grip surfaces to as high as 2500 rpm on hot high grip surfaces. I used to "slip" the clutch and even with the removal of the CDV, there were times when the clutch glazed ruining the run.
I'm not an expert on SCCA Solo Rules, but I don't believe removal of the CDV is permitted in Stock or Street Prepared categories.
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