BMW 1-Series Forum (F20) 135i - 1Addicts.com > Second Generation 1 Series Forum > 2012 BMW 1-Series Sporthatch (F20) Discussion > Launch control broken
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      12-14-2015, 09:37 PM   #1
dishy
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Launch control broken

When I activate and use launch control, the rear wheels just spin up and the car doesn't accelerate. I get quicker acceleration if I don't use launch control. It's my understanding that the car is supposed to limit wheelspin to get the best traction and put the most power through to the road. This doesn't seem to be happening. I know launch control is activating because it flashes up "Launch Control Active" on the dash board.

When I'm stationary, to activate launch control I move the gear lever over to manual mode and S1 comes up on the dash. I then press the traction control button once. Left foot hard on the brake and right foot hard on the accellerator. RPM goes to around 2000rpm and the launch control active shows on the dash. I then release the brake.
At this point the car starts to move but then both rear wheels break free and spin. You can feel that the acceleration force drops off.

Am I doing anything wrong here?

Any thoughts?
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      12-15-2015, 02:20 AM   #2
ovekvam
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There is probably less traction than the car anticipates, then.
With some tyre types, the best launch is actually achieved with a small amount of wheelspin.
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      12-15-2015, 03:29 AM   #3
dishy
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Quote:
Originally Posted by ovekvam View Post
There is probably less traction than the car anticipates, then.
With some tyre types, the best launch is actually achieved with a small amount of wheelspin.
From memory the best traction is with around 20% slip, think it's like 18% or something.. But I'm not certain.
But there must be way more than this, as you don't get pulled into your seat like you do when I floor it and shift up manually.

Thanks for the advice RE traction. On both times I tried it was on the same part of the road (same lights). I'll try somewhere else and see what happens.

I've only used it 2 times on separate days.

So there's nothing wrong with what I'm doing then? When the wheels spin up, I back off the throttle as it's an automatic reaction from me. Not sure if I should have consciously kept my foot planted.
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      12-15-2015, 03:47 AM   #4
ovekvam
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If you want to rely on the car to regulate the traction control, you are better off with the throttle pedal floored. If you accelerate without traction control (DSC Off), you need to modulate the throttle yourself. But in this case, you will have the electronic (fake) differential brake to help you gain traction.

The amount of slip that will give you the best acceleration varies with tyre type and ground conditions. If there is snow of gravel, you will need more wheelspin. Soft winter tyres will also like more wheelspin than low profile R-compounds.

The car will have to guess how hard it can launch, and it doesn't know how grippy tyres you have and how slippery it is.

Last edited by ovekvam; 12-15-2015 at 04:39 AM.
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      12-15-2015, 04:11 AM   #5
dishy
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Thanks mate
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      12-15-2015, 07:17 AM   #6
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You also need to be aware that there is only a certain number of Launches allowed to be performed by the driver (controlled by BMW in the Engine's management systems).
It is also dependent upon which engine is being used.
It is something to do with the warrantee.
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      12-18-2015, 03:14 AM   #7
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Quote:
Originally Posted by AusF20/F48 View Post
You also need to be aware that there is only a certain number of Launches allowed to be performed by the driver (controlled by BMW in the Engine's management systems).
It is also dependent upon which engine is being used.
It is something to do with the warrantee.
Elaborate please. References if you can. Never heard or read anything to this affect, and doesn't seem true or correct.

The manual states you must not do repeated launches and need to wait a certain amount of time before repeating a launch, to let temps cool down to norm. Due to the stresses and strains on the gearbox, extra heat generated etc.

Basically, all launch control is, is the engine limiting engine RPM to 2000, and the brake on the wheels wheels stopping the gearbox from moving through the drive train. The result is constant slip on the torque converter unless I am mistaken. It's really not good for the oil in the gearbox, and you must not hold the car on the launch for more than x amount of seconds (is it 5 seconds or 10 or something).

Cheers,
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      12-18-2015, 06:42 AM   #8
Ben_M135i
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If you have PSS tyres, I found once they were a little worn the straight line grip was quite reduced. Still plenty of wear left, but not as grippy.
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      12-18-2015, 08:05 AM   #9
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Quote:
Originally Posted by dishy View Post
Elaborate please. References if you can. Never heard or read anything to this affect, and doesn't seem true or correct.

The manual states you must not do repeated launches and need to wait a certain amount of time before repeating a launch, to let temps cool down to norm. Due to the stresses and strains on the gearbox, extra heat generated etc.

Basically, all launch control is, is the engine limiting engine RPM to 2000, and the brake on the wheels wheels stopping the gearbox from moving through the drive train. The result is constant slip on the torque converter unless I am mistaken. It's really not good for the oil in the gearbox, and you must not hold the car on the launch for more than x amount of seconds (is it 5 seconds or 10 or something).

Cheers,
I've been researching the BMW data, specifically it's launch control feature. To clear up some confusion
The launch control, we are discussing just holds back the transfer of power by over powering the torque converter using the brakes (this can be done in any automatic). They call this launch control because the car is limited to around 2000 rpm, similar to that of a manual clutch release

BMW OBC records the number of attempts made and the time lapsed between attempts.
BMWs reckoning is that 'Launch control' should only be performed once, with time and distance between attempts. If a LC was performed 3 or more times in succession, it could put undue ware on 'components' which then could void or negate the warranty claim if the use of the launch control was deemed excessive and lead to a failure of a component. It would not void the cars general warrantee or duration - only that claim.
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      12-21-2015, 03:21 AM   #10
dishy
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Yep I agree with you. Not sure where the confusion was
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