[dinonz]

Originally Posted by Andy0323

That's a very nonsensical assumption. I'm sure all drivers who launch their cars regardless of drivetrain layout love their cars.

Awd launches puts less drivetrain stress than 2wd launches due to torque transfer/splitting to 4 wheels opposed to 2.

Evos are an exception due to very small gearlands from the transverse tranny layout. That's why the 5 speed is the choice for tuners. Still, hell of a lot of fun.

Well, my uncle's AWD is an EVO and he still will not treat it like that. But I guess you know more than his rally team though... so it's ok.

[Steve33]

Originally Posted by Andy0323

Awd launches puts less drivetrain stress than 2wd launches due to torque transfer/splitting to 4 wheels opposed to 2.

You are backwards

AWD puts more stress on the drivetrain for that exact reason. It'll find the weakest link and break that part... then the next weakest, and the next, etc. Can't wait for the "Destroyed my drivetrain, will the dealership know I've been dumping my clutch?" thread.

This may be the reason he's had 10 MT's... because they keep breaking

[avantix]

Originally Posted by Steve33

You are backwards

AWD puts more stress on the drivetrain for that exact reason. It'll find the weakest link and break that part... then the next weakest, and the next, etc. Can't wait for the "Destroyed my drivetrain, will the dealership know I've been dumping my clutch?" thread.

This may be the reason he's had 10 MT's... because they keep breaking

A wise man once told me to never argue with an idiot. He'll bring you down to his level and beat you with experience.

[Andy0323]

Originally Posted by dinonz

Well, my uncle's AWD is an EVO and he still will not treat it like that. But I guess you know more than his rally team though... so it's ok.

LOL. I don't, but there should be an objective and logical reason why launching an awd causes more drivetrain stress than a 2wd, which is what I don't get (see example below). Why don't you ask your uncle or his chief mechanic for some insight instead of blurting "oh my uncle is a rally driver and he says not to do it"? I'd rather learn than read asinine comments that do not contribute anything towards the sake of this thread. Cool uncle though.

Originally Posted by Steve33

You are backwards

AWD puts more stress on the drivetrain for that exact reason. It'll find the weakest link and break that part... then the next weakest, and the next, etc. Can't wait for the "Destroyed my drivetrain, will the dealership know I've been dumping my clutch?" thread.

This may be the reason he's had 10 MT's... because they keep breaking

That doesn't explain why awd launches puts forth more drivetrain stress than a 2wd launch. Any drivetrain regardless of layout can break via the chain reaction of the weakest links. Are you insinuating that awd drivetrain parts have weaker pieces than 2wd? I don't think that's always the case.

As mentioned above, I want to learn, so objective and logical reasoning is key here. Let's use a 335i and 335ix as an example. Lets say both cars have 300 ft/lbs of torque, use the same drivetrain pieces (similar transmissions but same gear sizes/lands, same halfshafts, same driveshaft, same bearings, same differentials, etc etc). Now the awd version will have additional halfshafts at the front, but lets say they are the same pieces as the rear halfshafts in material and tensile strength.

For the sake of simplicity, let's ignore drivetrain loss. As each car launches, the 335i's torque splits into 2 (150 ft/lbs per rear wheel), and the 335ix's torque splits into 4 (75 ft/lbs per wheel). Now assuming that all drivetrain parts have similar tensile strength/torque threshold, I don't see why and how 75 ft/lbs per wheel puts forth more stress than 150 ft/lbs per rear wheel?

If the car is tuned to, say.... 600 ft/lbs, the 335i splits 300 ft/lbs per wheel, while the 335ix splits 150 ft/lbs per wheel. How is launching the car with 150 ft/lbs per wheel worse than 300 ft/lbs per wheel?

Lastly, as a stress test for the 600 ft/lbs monster, if each halfshaft has a tensile strength/torque threshold to withstand 300 ft/lbs, wouldn't the 335i's drivetrain be in worse condition (from torque stress) than the 335ix?

BTW... are you dinonz uncle?

And happy 4th (shit... too late), oh well.

[dinonz]

Originally Posted by Andy0323

LOL. I don't, but there should be an objective and logical reason why launching an awd causes more drivetrain stress than a 2wd, which is what I don't get (see example below). Why don't you ask your uncle or his chief mechanic for some insight instead of blurting "oh my uncle is a rally driver and he says not to do it"? I'd rather learn than read asinine comments that do not contribute anything towards the sake of this thread. Cool uncle though.

Basically Andy, it comes down to stiction. In a 2WD (lets assume square setup in identical cars other than 2WD vs 4WD/AWD for this) you have half the stiction because you have half the contact area of driving wheels on the road. When you get to 6000 RPM and dump the clutch, once the clutch has full engaged you pretty much have maximum torque being transmitted through the drivetrain. What generally happens in a 2WD is this torque overcomes the stiction, the tyres break traction and the torque is released as it were through tyre spin.

If you do the same in a 4WD/AWD the torque might not be enough to overcome the stiction of the tyres, so all that torque is transmitted to the ground as forward motion. The problem is that at the moment of dropping the clutch, you have an engine at 6000 RPM and wheels at 0 RPM and neither one wants to change that rapidly, so somewhere in the middle something has to give. Severe stress will be placed on all parts of the drivetrain as it gets twisted, and 99% chance the part that "gives" will be the clutch which will probably slip a bit to take up the strain, but only once the transmission and every CV/Universal joint have been wound up as tight as they can take without breaking. Until one day they do break.

As they say, a chain is only as good as it's weakest link, and the weakest link in a 2WD is the tyre contact with the road. On a 4WD/AWD though, that's not the case, thus something else somewhere in the chain will eventually give up.

That better Andy? It's difficult to explain on a forum - be easier with a white-board, but that's the general idea.

[Steve33]

Originally Posted by Andy0323

That doesn't explain why awd launches puts forth more drivetrain stress than a 2wd launch. Any drivetrain regardless of layout can break via the chain reaction of the weakest links. Are you insinuating that awd drivetrain parts have weaker pieces than 2wd? I don't think that's always the case.

As mentioned above, I want to learn, so objective and logical reasoning is key here.

BTW... are you dinonz uncle?

This reply below is perfect. I don't know him

Originally Posted by dinonz

Basically Andy, it comes down to stiction. In a 2WD (lets assume square setup in identical cars other than 2WD vs 4WD/AWD for this) you have half the stiction because you have half the contact area of driving wheels on the road. When you get to 6000 RPM and dump the clutch, once the clutch has full engaged you pretty much have maximum torque being transmitted through the drivetrain. What generally happens in a 2WD is this torque overcomes the stiction, the tyres break traction and the torque is released as it were through tyre spin.

If you do the same in a 4WD/AWD the torque might not be enough to overcome the stiction of the tyres, so all that torque is transmitted to the ground as forward motion. The problem is that at the moment of dropping the clutch, you have an engine at 6000 RPM and wheels at 0 RPM and neither one wants to change that rapidly, so somewhere in the middle something has to give. Severe stress will be placed on all parts of the drivetrain as it gets twisted, and 99% chance the part that "gives" will be the clutch which will probably slip a bit to take up the strain, but only once the transmission and every CV/Universal joint have been wound up as tight as they can take without breaking. Until one day they do break.

As they say, a chain is only as good as it's weakest link, and the weakest link in a 2WD is the tyre contact with the road. On a 4WD/AWD though, that's not the case, thus something else somewhere in the chain will eventually give up.

That better Andy? It's difficult to explain on a forum - be easier with a white-board, but that's the general idea.

+1

[Teemo Panda]

I would suggest doing this to your dealers Loaner car when you get your car into service :P

[avantix]

Dinonz......that's exactly what I was looking for. Very well explained sir and it makes sense. I was also under the impression that since the torque was dispersed over 4 wheels instead of just 2 there would be less strain on drivetrain.

[Andy0323]

Originally Posted by dinonz

Basically Andy, it comes down to stiction. In a 2WD (lets assume square setup in identical cars other than 2WD vs 4WD/AWD for this) you have half the stiction because you have half the contact area of driving wheels on the road. When you get to 6000 RPM and dump the clutch, once the clutch has full engaged you pretty much have maximum torque being transmitted through the drivetrain. What generally happens in a 2WD is this torque overcomes the stiction, the tyres break traction and the torque is released as it were through tyre spin.

If you do the same in a 4WD/AWD the torque might not be enough to overcome the stiction of the tyres, so all that torque is transmitted to the ground as forward motion. The problem is that at the moment of dropping the clutch, you have an engine at 6000 RPM and wheels at 0 RPM and neither one wants to change that rapidly, so somewhere in the middle something has to give. Severe stress will be placed on all parts of the drivetrain as it gets twisted, and 99% chance the part that "gives" will be the clutch which will probably slip a bit to take up the strain, but only once the transmission and every CV/Universal joint have been wound up as tight as they can take without breaking. Until one day they do break.

As they say, a chain is only as good as it's weakest link, and the weakest link in a 2WD is the tyre contact with the road. On a 4WD/AWD though, that's not the case, thus something else somewhere in the chain will eventually give up.

That better Andy? It's difficult to explain on a forum - be easier with a white-board, but that's the general idea.

That makes sense. Thanks for the insight. Here's a beer for you.

[Presario]

Originally Posted by dinonz

Basically Andy, it comes down to stiction. In a 2WD (lets assume square setup in identical cars other than 2WD vs 4WD/AWD for this) you have half the stiction because you have half the contact area of driving wheels on the road. When you get to 6000 RPM and dump the clutch, once the clutch has full engaged you pretty much have maximum torque being transmitted through the drivetrain. What generally happens in a 2WD is this torque overcomes the stiction, the tyres break traction and the torque is released as it were through tyre spin.

If you do the same in a 4WD/AWD the torque might not be enough to overcome the stiction of the tyres, so all that torque is transmitted to the ground as forward motion. The problem is that at the moment of dropping the clutch, you have an engine at 6000 RPM and wheels at 0 RPM and neither one wants to change that rapidly, so somewhere in the middle something has to give. Severe stress will be placed on all parts of the drivetrain as it gets twisted, and 99% chance the part that "gives" will be the clutch which will probably slip a bit to take up the strain, but only once the transmission and every CV/Universal joint have been wound up as tight as they can take without breaking. Until one day they do break.

As they say, a chain is only as good as it's weakest link, and the weakest link in a 2WD is the tyre contact with the road. On a 4WD/AWD though, that's not the case, thus something else somewhere in the chain will eventually give up.

That better Andy? It's difficult to explain on a forum - be easier with a white-board, but that's the general idea.

One of the best explanations I've read about the topic. Thanks Dinonz!

[avantix]

Originally Posted by Presario

One of the best explanations I've read about the topic. Thanks Dinonz!

+1

[Steve33]

This is from an AWD that had been doing launches...

[Agamemnon]

A picture is worth a thousand words. The above post is the best argument on this thread!

[ppatel223]

Originally Posted by avantix

So I'm really enjoying the xdrive experience in that I don't just sit there burning through first and second gears like my old RWD 335i. I routinely drop the clutch at 6k rpm and boy does this car take off like a bat out of hell. Question is will it likely break anything in the long run?

Think of it this way. Take a hammer, place the hammer on your head gently, this should not hurt. Now apply some pressure on hammer against your head, should hurt little. But now, swing a hammer at your head at about 20 mph, you should get concussion or some bleeding. If you are still with me, apply this analogy to your car.

[Seagull]

Originally Posted by ppatel223

Think of it this way. Take a hammer, place the hammer on your head gently, this should not hurt. Now apply some pressure on hammer against your head, should hurt little. But now, swing a hammer at your head at about 20 mph, you should get concussion or some bleeding. If you are still with me, apply this analogy to your car.

Depends if there's anything of worth in there LOL.

[t335xi]

Definitely face palm. Op is being a bit of a ass too..Don't ask for advice if you don't want a real answer.