Hi all. This question is kind of targeting Acta Non Verba but anyone with any specific knowledge would be great. Does using launch control stress the trans heavily or is it designed from the start for this feature? I have watched the Porsche guys use launch control over and over again but for some reason I am hesitant to try it on the GTC.

Katie

 

Of course it does. The harder you are on the car the more wear it will have and that goes for launch control. Race Start slips the clutch for an optimal ratio between clutch slip vs wheel spin during a launch. This obviously puts additional wear on the clutch. The transmission is generally engineered to handle it, but you will see accelerated wear from using Race Start compared to a transmission that was never subjected to Race Start. As far as I know AMG doesn't put a limit on how many Race Starts it allows before the clutch has to be replaced and AMGs require regular transmission fluid changes to get all those wear particles out and prolong the lifetime of the transmission. But for example Audi famously only allowed 200 launches with their dual clutch. It had an internal counter and once it reached 200 the party was over.

Just as an aside, Race Start basically simulates how an F1 car takes off, the difference being in an F1 car the driver controls the clutch manually via two paddles. They set the desired clutch bite point before the race, then when the light turns green they let go of the first clutch paddle as fast as possible which dumps the clutch to the preset bite point while still holding the second clutch paddle. Then as they accelerate they slowly release the second paddle until the clutch is fully engaged. After that F1 cars don't use the clutch anymore to change gears. It's only used again to come to a stop and start off again from a pit stop. F1 clutches get super hot during these takeoffs.

Our AMGs are not F1 cars, but it's the same idea. Race Start drops the clutch to the bite point and lets it slip there and then gradually keeps engaging it until full engagement. The clutch obviously gets hot during these launches and wears. Being wet clutches helps to cool them and reduce wear and there are protections in the transmission so that if it gets too hot it won't allow further Race Starts until the transmission has cooled down enough. But again, this all puts accelerate wear on it.

 

Super Swiss:

I understand what you’re saying that a Race start is far more abusive to the car as a whole, but given that each clutch pack doesn’t consist of a single ‘clutch’ anymore, I do wonder exactly how much wear and tear takes place within the individual clutches via a Race Start. In fact I sort of wonder if the rear diff; half shafts, etc. might let go prior to the DCT clutches wearing out. Thankfully our German engineering cousins placed safety constraints which limit the use of the Race Start when certain parameters are reached as you mentioned.

 

Yea I got ya Swiss. I guess I was trying to gather how much wear is imposed on the system and if it was designed from the beginning for that exact wear. I can use an example. A farm tractor pulling a trailer is working far less than the same tractor pulling a plow that uses the max output of the tractor. But a farmer might say that the tractor does not seem to show any extra wear from using the plow.
I think Acta Non Verba is the person to get a serious technical point of view on this one.

 

F1 clutches also have multiple discs. Multi plate clutches primarily allow them to be much smaller in diameter compared to a single plate clutch. Doesn't necessarily reduce wear. It just spreads the wear over multiple smaller plates. What's more of a factor is that the clutches are wet clutches vs. dry clutches in F1 and the single plate clutches in manual transmission cars, so that reduces wear and helps with cooling as I said. The oil is actually part of the friction mechanism in a wet clutch. It's not purely friction material. The electronic locking differential also uses a multi plate wet clutch which is often only partially engaged when cornering. During Race Start the diff clutch is actually fully engaged for a complete lock, so it has pretty much no wear during a launch. Clutches only wear when they have to slip and for the diff that's during cornering. Yes, shafts could snap, but they are rated for the appropriate torque and there is no frictional wear.

 

Hi Katie,

Sorry I missed your thread. I’m up in Park City for a few days and didn’t see it.

superswiss has good answers. He always does and I agree with him.

A couple of Mechanical Engineering “truisms”:


anything mechanical will wear out and eventually fail with use. Sometimes even when not used.

As use approaches 100% of design capacity the “wear” timeline accelerates (shortens).

On a performance option like launch control by its very nature, will shorten the useful life of the machine.

The question you’re asking is “ how much” will its life be shortened?

MB design engineering probably knows the answer to that question through alpha/beta testing. From that they develop a mean time between failure MBTF, but that is never published to the public.

The fact they offered it SHOULD mean the car is capable of using the option more than one time. Your question is more on the lines of HOW MANY TIMES?

Since no one here can answer that specifically only generalizations can be offered.

I suggest you’ll be safe trying it out knowing that it might also be your incredibly unlucky day (saying that lightheartedly).

Finally the MTBF SHOULD exceed the warranty. After that MB doesn’t mind if you break it!…lol. And, the good news is there is little “public complaints “ this is a weak system that breaks

Hope that helps, now back to my beer at the Stein Lodge…hahaaa.

Acta

 

I don't see anywhere in the warranty where its voided after a certain number of launches.

For what it's worth, it's a pretty tame launch compared to a Porsche launch. Drop the car in race mode and I would be it's pretty close to the same out of the hole - the rev limiter kind of makes it a bit of a yawner - which suggests to me that its designed to (within reason) not affect the car in a super aggressive way. Now that said, use it to excess and I would expect to pay a price for that. My guess is that it gets boring before it creates a mechanical problem.

 

Hi,

In addition to the good statements by Acta and Superswiss,

A race start now and again shouldn't do much damage to the clutch discs. But she will surely die a hero's death a few miles sooner.

What I see critically are e.g. 10 race starts in a row.

The temperature build-up in the friction and steel discs is then very high. A closed clutch is a heavy, fat block without a large surface = cooling surface. And the heat comes from "inside".
This makes cooling more difficult and delays it. The differential oil temperature (cooling medium) and the real inner clutch temperature can deviate significantly at the same time.

Heat, well above operating specification, always leads to greater wear.

My personal opinion on many race starts in a row:

There are protective mechanisms that at some point no longer allow a race to start.
Usually it runs over the transmission oil temperature. If the temperature here is too high, the clutch core is already "glowing". :-)

Best regards

Stenzel

 

This. The launch control in my GTC is almost useless for anything other than going through rear tires faster. We have a drag strip nearby and my times are slower with launch control.