Took the new-to-me car out to a PCA autocross last weekend and had a blast. I did two runs with traction control on and one run with it off.

With it off, and a pretty aggressive launch, the rear tires spin and I get some hopping of the back tires, which I would expect.

With traction control on, I didn't have wheel slip, but something else was going on. I ended up smelling hot brakes or clutch. How does the PSM work on a hard launch (on a manual transmission)? Does it throttle back the engine power or apply the brakes to keep the tires from slipping? Given the smell, my hunch is that it's activating the brakes.

2010 Carrera S Cabrio 6-speed

 

i always thought it was clutch given that the clutch is hydro - same as brakes/ABS. i figured it worked with a similar principle - the ECU slows or stops clutch disengagment if it senses wheel slip.

 

Clutch slip is what it felt (and smelled) like to me but I'm not sure. Seems like an awfully good way to burn up a clutch if the engine slips it under heavy load to keep the wheels from spinning. I'd much rather it burn up brake pads!

 

I thought, like on most performance cars, traction and stability control are first executed by applying brakes. If the situation is severe, then it will dial back throttle. I've never seen an instance where the clutch was manipulated... though I'm no expert on Porsches.

 

you can not launch a manual car with traction control On.
it will just Bog off the line, every time.

it sounds like you got a so-so launch with your traction Off.
The RR layout in the 911 helps the car shoot straight off the line. There should not be Bog or any delay.

 

Yeah, it's definitely NOT done with the clutch. That doesn't mean that you didn't screw up the launch and slip the clutch too much. But if you did, it wasn't TC's fault.

TC is usually done by the computer dialing back the power of the engine (i.e., pulling spark similar to the rev limiter, and/or modulating throttle on drive-by-wire cars like modern 911s). Stability management is usually done by modulating the brakes at various corners of the car.

This article talks about it a bit, too:
http://www.engadget.com/2011/02/23/t...che-911-video/


After your run, you were probably smelling brakes from 1) using your brakes aggressively on the course, and 2) PSM using the brakes for stability management (not launch control). For autocrosses, always turn off your PSM. You'll likely end up being 1-2 seconds faster, and autocross is all about learning car-control anyway.

Happy driving!

 

You smelled many $$ worth of your clutch going up in smoke.