I've been reading several postings on this forum about brake torque for better start and wheel spins on a steptronic (auto). Does anyone know if brake torque does any harm to the auto tranny? If no harm, what is a good rpm range on a mild to hot day with dry weather for an optimal launch and/or wheel spin?

 

Brake torque should not do any harm to your tranny at all, but it might harm your torque converter.

 

shouldnt harm it. When brake torqueing dont rev above a point where your engine produces maximum torque... 3400rpm max

or on the 545i max being about 3700rpm (since it has a slower power delivery than the 550i)

 

I have about 25-30 launches on my 6er STEP using brake torque technique. NO indications of any issues. If you are looking FOR wheel spin, then DSC off and slowly increase revs to 2300-3000 range. This may result in best 1/4 mile ET and speed. On the otherhand, if you are looking for best 0-60 times, or 0-60 ft. 0-330 ft times, I recommend quickly depressing and releasing gas pedel all the way to floor while brake torquing and then reapply gas fully. Revs will only go to about 1100-1300 and remain there for launch, even though you have it floored (DSC still off). I find this gets excellent 0-60 times nad still get decent 1/4 ET and MPG. I do not like wheel spin unless just for the occasional test.

Znod may have other recommendations in his 545 testing. I do not think anybody has joined up testing with 550 yet. I thought you might be joining us soon, yes?

 

I'd never heard of doing this - I guess cause we don't go much for sporty automatics in the UK, but I've been trying it over the last few weeks.

The other day - I think I cracked it - brake torqued to about 1500rpm and floored it ...


I got wheelspin with DSC on !!!!!

It impressed me - I've never been able to beat the electronic safety net before

 

I do this on my Z3 all the time - no issues so far...

 

The shop foreman at my dealer tested my car for failure of DTS/DTC to fully disengage. He used monster brake torquing. He said that brake torquing should not hurt unless done repeatedly over a very short period of time. Heat build up apparently will not occur otherwise. I seldomly try to brake torque above 1K RPM. To break the wheels loose, try 1.2k. Since 20.01.00, I get little wheel spin. I sometimes get some pretty good spin on a coldish day brake torquing to 1.2k. There is no acceleration advantage, and, there is a highly likely acceleration disadvantage, to wheel spin, per se, for our cars given my test results.

 

I have my car now for about eight months and have not "wiped its shoes" except on wet pavement and slight cornering. I've done some "launches" but do not feel the brute V8 power from 0-60 mph. The car is fun weaving in and out of traffic and merging onto freeways, but the straight line feels muted. Maybe I'm just used to it power, but don't flame me if I said that it feels a couple of knotched faster than my Camry V6.

 

What exactly is brake torque? Hold down both brake pedal and gas pedal?

 

Yes. And a watch the rpm go to a certain level, release the brake but continue to pedal to the metal. This is only for Steptronic (auto tranny).