Autocross question: parking brake and running, put in gear and off?

Sportscar magazine got even more useless IMHO when they dropped anything local. It always seems to be 95% not related to anything I'm interested in, plus a 1/2 page article of rallycross (tires or something).

Doesn't stop me from reading it on a 1/2hr lunch break. Skimming thru today I caught an article on brakes, and caught two things that seemed prudent.

1) not setting the parking brake after driving. 2) not sitting on the brake pedal after a run to discuss your run/debrief/etc.

Mostly the parking brake thing...usually after a run I pull into grid, shut it off (if it's taking awhile to cycle thru), parking brake and pop the hood (that little turbo makes the black hood like a skillet)

Would the parking brake thing really be a concern after a 40-60 second run? Or more towards Club Racing/etc? What say the GRM?

No it's not a problem for an autocross run. If you come off the track from doing some laps and you can smell your brakes, that's when you shouldn't use the parking brake.

Just depends on your driving and the course setup. I avoid using the parking brake on hot rotors. I usually just shut down the car and leave it in gear to hold my place.

Also depends on the parking brake setup. If it's a drum-in-disc setup, use the parking brake all you want. If it's built into the rear caliper, then it'll depend on the course/run/style of driving. I'm lucky to have the mini-drum in disk setup. When I started left foot braking I could smell the pads coming off a longer run.

Probably doesnt matter too much, but if you want some peace of mind, you can keep a piece of wood or something to block the wheel with once you park it, allowing you to keep the car running and not use the brakes.

They probably mention it, as I do when instructing students, to get you into the habit of not using it in the case you might start doing track days.

I don't use the parking brake after autoX runs. Other (more experienced) Miata pilots told me not to so I got in the habit of shutting it off, leaving it in gear, and popping the hood as quickly as practical after each run. Warm engine, warm brakes, and hot tires FTW. I just have a hard time getting them in that order.

I've seen a car come to a stop in a stop box and then blow a big cloud of smoke out of all four wheels after sitting with the brakes on for two seconds. A very visual illustration of how much heat you can put into brakes in 60 seconds.

I try not to even come to a full stop with hot brakes. Parking brake? Verboten.

At the HPDE this past weekend they specifically taught the no parking brake thing in class and it was reiterated by my instructor. In addition, they suggested rolling the car a couple feet after it had been parked for a few minutes because the pads hold in enough heat to warp a rotor even if they're not clamped down with the parking brake.

Of course, we're talking about open track there - my street/track brakes were so hot the were squealing like crazy when I'd come off track. All the years I autocrossed I set the parking brake every time and never had a problem. I just don't think they're hot enough to hurt unless you've got some seriously thin little rotors.

In reply to HunterJP:

That seems like a good idea. Track night in America, and PDX's, are hopefully on my list this year.

Keith Tanner wrote: I've seen a car come to a stop in a stop box and then blow a big cloud of smoke out of all four wheels after sitting with the brakes on for two seconds. A very visual illustration of how much heat you can put into brakes in 60 seconds. I try not to even come to a full stop with hot brakes. Parking brake? Verboten.

Yeah, it's definitely possible to damage the brakes this way. When I stripped 3rd gear at Laguna Seca one year, I had to stop the car in the runoff and sit there waiting for the tow truck. This required keeping my foot on the brake to stop it rolling backwards down the hill (parking brake wasn't working at the time), and of course there was no cool down lap after the transmission failure so everything was hot. When I got it home, there was a big crack running across one of the 11" front Wilwoods.

To kind of piggyback on this thread a bit (my apologies Jerry), if I wanted to reduce the likelihood of damage in this scenario, would increasing the thermal mass (thicker rotor), and improving cooling (via ducts) help? Obviously the ducts would only work while moving, but perhaps they'd keep the temps down a bit during a run making it less likely during a pause on grid? Am I off base with this line of thinking?

Also, depends on the power the car makes. Brakes can only dissipate kinetic energy that the engine has put into the car. Is a Fiat500 going to overheat the brakes on a 40 second run? On street tires? Unlikely.

Is a 350hp SM Miata running 1.6 brakes running 275/35 hoosiers capable of doing that? A whole lot more likely.

After an autocross run I move slowly through grid (as everyone should) and its usually at least a minute from my last hard braking zone to when I get back to my grid spot. Everything is usually cool enough by then.

Just to pick a nit on that point ProDarwin. Some new cars use an "E-diff" to control wheelspin, this applies brake drag on the spinning (inside) wheel during hard driving. We have a couple locally who drive a Fiat 500 Abarth and it's brakes get positively roasted doing back to back runs.

I suspect there are other cars that do this as well, it's just the Fiat that stands out in my mind.

Fortunately most cars do the majority of their braking with their front brakes and parking brakes are on the rear axle so there is that.....

Auto cross should not cause a problem.

On track days, I always tried to use minimum braking on the cool down/last lap. Never had a brake problem. The only time I used the parking brake was on the trailer.

Hmm. So after everyone's input, it appears the answer is either yes, no, or maybe. I think I'll err on the side of caution. If I can remember, of course.

If you've got a drum in disc e-brake you're good to go. If you don't, the answer is mayebe. lol

Jerry wrote: Hmm. So after everyone's input, it appears the answer is either yes, no, or maybe. I think I'll err on the side of caution. If I can remember, of course.

I think it sums up as either "I can't imagine there would be a problem" and "yes, I've definitely seen it cause a problem". I.e., supposition vs experience.

KyAllroad wrote: Just to pick a nit on that point ProDarwin. Some new cars use an "E-diff" to control wheelspin, this applies brake drag on the spinning (inside) wheel during hard driving. We have a couple locally who drive a Fiat 500 Abarth and it's brakes get positively roasted doing back to back runs.

Interesting. Didn't know the e-diff could load the brakes that much.

I've never had it be an issue with autocross. I've always run light cars though.

Anything with a longer run time though it is definitely on my mind and I keep wheel chocks around