Higher RPM vs Weight to start car from stop in 1st gear

[daleadbull]

^ I think the trouble with no-gas launch might be because your car is AWD. Mine is too and in order to no gas launch, you need to slip the clutch more. More grip means more force needs to overcome it. I usually pause for a second at clutch engagement in order to get it hooked up.

Nobody is overcoming grip with a no-gas launch in any car, unless it's got a 1000hp alcohol fueled dragster engine with a messed up high idle and bald street tires on snow.

There's more drivetrain loss with AWD, wasting some energy, but that would just mean your no-gas launch would be a little slower; it shouldn't cause anything described as "stutters like a mechanical bull". The buggy ECU program sounds like a plausible explanation.

No one's talking about breaking all four tires loose with a no-gas launch. lol

I was talking more in the lines of grip in the sense of friction. Launching in general takes more slipping the clutch in an AWD vehicle, do you agree with that?

If so, then no-gas launches should be no different right? I think the stuttering is due to releasing the clutch too early while its still hooking up, again much easier to do in an AWD vehicle since you need to slip the clutch longer to get fully engaged.

*This is just me speaking from my experience, feel free to disprove me and educate me.

[Chiba]

^ I think the trouble with no-gas launch might be because your car is AWD. Mine is too and in order to no gas launch, you need to slip the clutch more. More grip means more force needs to overcome it. I usually pause for a second at clutch engagement in order to get it hooked up.

Nobody is overcoming grip with a no-gas launch in any car, unless it's got a 1000hp alcohol fueled dragster engine with a messed up high idle and bald street tires on snow.

There's more drivetrain loss with AWD, wasting some energy, but that would just mean your no-gas launch would be a little slower; it shouldn't cause anything described as "stutters like a mechanical bull". The buggy ECU program sounds like a plausible explanation.

No one's talking about breaking all four tires loose with a no-gas launch. lol

I was talking more in the lines of grip in the sense of friction. Launching in general takes more slipping the clutch in an AWD vehicle, do you agree with that?

If so, then no-gas launches should be no different right? I think the stuttering is due to releasing the clutch too early while its still hooking up, again much easier to do in an AWD vehicle since you need to slip the clutch longer to get fully engaged.

*This is just me speaking from my experience, feel free to disprove me and educate me.

Definitely a fair reasoning

Let me try it this weekend using a much much longer slip, at a safe location, and see what happens. However I still suspect the ECU program isn't helping either.

[theholycow]

I was talking more in the lines of grip in the sense of friction. Launching in general takes more slipping the clutch in an AWD vehicle, do you agree with that?

If so, then no-gas launches should be no different right? I think the stuttering is due to releasing the clutch too early while its still hooking up, again much easier to do in an AWD vehicle since you need to slip the clutch longer to get fully engaged.

*This is just me speaking from my experience, feel free to disprove me and educate me.

In an automotive context, traction means whether the tire is gripping or slipping. In a no-gas launch, the tire is gripping 100% regardless of 2WD or AWD, period. Using the word "traction" to describe clutch engagement, if that's what you're doing, is confusing, doubly so when you start talking about the difference between 2WD and AWD which is entirely about tire traction. If you need a label for that, use "clutch friction", as in the oft-used term "friction point".

There is no reason why launching AWD at the same speed as 2WD should take more slipping of the clutch. The extra drag's wasted energy isn't that severe. If it was, AWD vehicles would use twice the fuel and go half the speed of 2WD vehicles and AWD wouldn't exist, we'd have part-time 4WD systems in its place. Instead, the little bit of extra drag is almost nothing, worth maybe 10% in a badly engineered system.

The only context in which launching AWD could call for a different amount of slipping is when you're doing a drag racing launch where you get to launch harder than 2WD can -- and in that case you might be doing LESS slipping with AWD since you aren't worried about breaking traction. That is the polar opposite of no-gas launching.

[daleadbull]

Definitely a fair reasoning

Let me try it this weekend using a much much longer slip, at a safe location, and see what happens. However I still suspect the ECU program isn't helping either.

I don't want you to go out there and slip the clutch for 30 seconds trying to do a no-gas launch. lol

It shouldn't take more than 2 or 3 seconds. Pause at the engagement point and don't just immediately release the clutch when the car starts moving. Hold it until you feel the car's engine sound smooths out and you have enough momentum then smoothly let off the clutch.

If this doesn't help the jerky starts then it might be the ECU but your car has more than enough torque to do no-gas launches all day!

[theholycow]

I don't want you to go out there and slip the clutch for 30 seconds trying to do a no-gas launch. lol

It shouldn't take more than 2 or 3 seconds. Pause at the engagement point and don't just immediately release the clutch when the car starts moving. Hold it until you feel the car's engine sound smooths out and you have enough momentum then smoothly let off the clutch.

Well said!

I had a problem with launching that I couldn't get over for a while. On previous vehicles it all just felt natural, but when I got my 2008 VW I just couldn't get a decent launch and I stalled a lot. Eventually I realized that once the car was moving along decently I figured my left foot's job was done and I dumped the rest of the clutch. I thought I could use a continuous movement and just vary the speed. In fact, in that car once the car started moving I had to pause my left foot and then move my left foot very slowly while it continued to grab more and more. That was true of no-gas launches and regular ones too.

[daleadbull]

In an automotive context, traction means whether the tire is gripping or slipping. In a no-gas launch, the tire is gripping 100% regardless of 2WD or AWD, period. Using the word "traction" to describe clutch engagement, if that's what you're doing, is confusing, doubly so when you start talking about the difference between 2WD and AWD which is entirely about tire traction. If you need a label for that, use "clutch friction", as in the oft-used term "friction point".

There is no reason why launching AWD at the same speed as 2WD should take more slipping of the clutch. The extra drag's wasted energy isn't that severe. If it was, AWD vehicles would use twice the fuel and go half the speed of 2WD vehicles and AWD wouldn't exist, we'd have part-time 4WD systems in its place. Instead, the little bit of extra drag is almost nothing, worth maybe 10% in a badly engineered system.

The only context in which launching AWD could call for a different amount of slipping is when you're doing a drag racing launch where you get to launch harder than 2WD can -- and in that case you might be doing LESS slipping with AWD since you aren't worried about breaking traction. That is the polar opposite of no-gas launching.

First off, I don't want to come off like I'm arguing cus you're obviously more experienced than I am. This is more of a discussion anyway, what forums are meant for.

I wasn't talking about "clutch friction", that shouldn't matter. If you put the same clutch in an AWD, FWD or RWD car, it should function the same. I am however talking about the tire friction with the ground. In full-time AWD vehicles, the torque is split among all four wheels right? So wouldn't it be fair to assume the car needs to overcome more static friction in order to get moving. In 2WD, all the power is going to 2 wheels thus less torque being needed to overcome that static friction but the threshold is lower too so easier to break traction by transmitting too much torque to the wheels and spinning the tires. There are obviously more factors at work here like drivetrain loss and the overall weight of an AWD car.

Also, in the case of hard launches. You said: "LESS slipping with AWD since you aren't worried about breaking traction". I don't think that's quite right in practice. If you simply side-step or dump the clutch at high rpms in a AWD car you are more likely to bog because unless your car is an absolute monster or your tires are bald, you won't spin the tires and the drivetrain will end up taking up the slack. This is why a lot of people don't like launching their AWD cars even though technically they are the best at launching because you need to "abuse" the clutch to do it.

Just wondering, have you owned any AWD cars?

[Chiba]

Lol! I don't think anyone gets high from sniffing clutch burn.

[six]

I wasn't talking about "clutch friction", that shouldn't matter. If you put the same clutch in an AWD, FWD or RWD car, it should function the same. I am however talking about the tire friction with the ground. In full-time AWD vehicles, the torque is split among all four wheels right? So wouldn't it be fair to assume the car needs to overcome more static friction in order to get moving. In 2WD, all the power is going to 2 wheels thus less torque being needed to overcome that static friction but the threshold is lower too so easier to break traction by transmitting too much torque to the wheels and spinning the tires. There are obviously more factors at work here like drivetrain loss and the overall weight of an AWD car.

As long as your car has 4 wheels and 4 tires of the same size, on the same kind of material (the ground), static friction remains the same no matter what kind of drivetrain is in the car. You don't need to "overcome" static friction with a car; it's actually your friend. It's what allows your car to have any traction at all. Overcoming static friction would be moving the car while all four wheels are locked.

When you're accelerating, you are overcoming the inertia of the car, not static friction, and inertia (from a standstill) stays the same for any two cars that weigh the same, no matter what kind of drivetrain it has. And besides, with most AWD systems, most (or all) of the power goes to only two wheels most of the time anyway, unless one or both of those wheels lose traction somehow.

[ClutchFork]

Lol! I don't think anyone gets high from sniffing clutch burn.

Ummm, yum. Clutch Burn! Well described by the Beach Boys in "Shut Down":

Superstock Dart is windin' out in low
But my fuel injected Stingray's really startin' to go
To get the traction I'm ridin' the clutch
My pressure plate's burnin' that machine's too much

[theholycow]

First off, I don't want to come off like I'm arguing cus you're obviously more experienced than I am. This is more of a discussion anyway, what forums are meant for.

Agreed. It's always a worry that the wrong emotion will be conveyed in a forum, and I think I may be particularly bad at avoiding that problem. This is intended entirely as logical discourse, and I am glad that you feel the same.

I am however talking about the tire friction with the ground. In full-time AWD vehicles, the torque is split among all four wheels right? So wouldn't it be fair to assume the car needs to overcome more static friction in order to get moving.

If my understanding of static friction is correct, it is not in play unless you want to break traction.

Are you talking about rolling resistance?
http://en.wikipedia.org/wiki/Rolling_resistance
You've got 4 wheels worth of rolling resistance no matter how many of them are used for propulsion. The un-driven tires still have the same amount of RR.

In 2WD, all the power is going to 2 wheels thus less torque being needed to overcome that static friction but the threshold is lower too so easier to break traction by transmitting too much torque to the wheels and spinning the tires.

I totally agree with that, but I don't see how it's relevant to no-gas launching. You won't be breaking traction and spinning them either way.

Also, in the case of hard launches. You said: "LESS slipping with AWD since you aren't worried about breaking traction". I don't think that's quite right in practice. If you simply side-step or dump the clutch at high rpms in a AWD car you are more likely to bog because unless your car is an absolute monster or your tires are bald, you won't spin the tires and the drivetrain will end up taking up the slack. This is why a lot of people don't like launching their AWD cars even though technically they are the best at launching because you need to "abuse" the clutch to do it.

No doubt, a harder launch with less slipping is more abusive. I originally wrote that post with an added piece but decided to remove it:
LESS slipping with AWD since you aren't worried about breaking traction (OTOH you might choose more slipping because you're worried about breaking the car).

Just wondering, have you owned any AWD cars?

No, and I don't claim to know personally about the hard launches that can only be done with AWD; on that subject I know what has been posted to Standardshift. Shadow has posted about how he would rev it up to redline, pop the clutch, and make use of all 4 tires, abusing the car horribly but getting one hell of a launch. See the last paragraph in this post for one example:
http://www.standardshift.com/forum/view ... 00#p354900

[daleadbull]

Good discussion in this thread.

I don't know if static friction was the right term to use. I should know though cus I do have an engineering degree but I'm not in the field anymore.

I don't know if its inertia or what, but I've heard and experienced that AWD cars need more clutch slip in order to get going and are easier to stall. I think the torque needs to be gradually applied because if not then the 4 wheel grip is hard for the engine to overcome thus leading to a stall. This I am almost positive of, but I'm not quite sure what this phenomenon is called. Do you guys know what this is or do you disagree with this?

[Shadow]

No, 400 lbs of passengers in a 3500 lb car really isn't very significant.

Actually 400 lbs is a significant amount of weight in a 3500 lb car. That's about 11.5% of the cars weight.

When it comes to getting a car moving from a stop, it is insignificant. I wouldn't have to adjust my driving at all with an extra 400 lbs in the car.

[Shadow]

First off, I don't want to come off like I'm arguing cus you're obviously more experienced than I am. This is more of a discussion anyway, what forums are meant for.

I wasn't talking about "clutch friction", that shouldn't matter. If you put the same clutch in an AWD, FWD or RWD car, it should function the same. I am however talking about the tire friction with the ground. In full-time AWD vehicles, the torque is split among all four wheels right? So wouldn't it be fair to assume the car needs to overcome more static friction in order to get moving. In 2WD, all the power is going to 2 wheels thus less torque being needed to overcome that static friction but the threshold is lower too so easier to break traction by transmitting too much torque to the wheels and spinning the tires. There are obviously more factors at work here like drivetrain loss and the overall weight of an AWD car.

Here's the thing....the number of drive wheels doesn't really matter with a no-gas launch. No matter what, there are still four tires in contact with the ground, so friction isn't a factor. I think what you're trying to describe is really parasitic driveline losses (or drag) that result from an AWD drivetrain.

Also, in the case of hard launches. You said: "LESS slipping with AWD since you aren't worried about breaking traction". I don't think that's quite right in practice. If you simply side-step or dump the clutch at high rpms in a AWD car you are more likely to bog because unless your car is an absolute monster or your tires are bald, you won't spin the tires and the drivetrain will end up taking up the slack. This is why a lot of people don't like launching their AWD cars even though technically they are the best at launching because you need to "abuse" the clutch to do it.

Just wondering, have you owned any AWD cars?

If you want the best possible launch with an AWD car, you want little or no wheel spin, but you also want little clutch slip as well. Think about it....the less time spent slipping (clutch or tires) means faster forward motion.

Yes, a hard AWD launch can be brutal to the car, but if you are asking how to get the best launch possible, I'll tell you how I did it with my very first AWD car, which was a 1990 Eagle Talon Tsi. I raced that car at the track on a regular basis, so I have plenty of experience launching the car. Anyway, I'd rev the engine to 6000 rpm and hold it there. Then I'd sidestep the clutch (meaning that I'd slide my left foot off the side of the pedal, letting it pop up as quickly as possible) while flooring the gas pedal. Brutal, yes....but the car would jump off the line like a scalded cat. The tires would only chirp, no real spin, and the clutch had minimal slip. It only slipped as much as necessary to transfer power and do its job. In other words, I wasn't slipping it.....it only slipped as much as it had to from fully disengaged to fully engaged. BTW, I'd regularly get 1.7 short times with my launch method, which was pretty good for a moderately powered car on regular street radials.

[ClutchDisc]

No, 400 lbs of passengers in a 3500 lb car really isn't very significant.

Actually 400 lbs is a significant amount of weight in a 3500 lb car. That's about 11.5% of the cars weight.

When it comes to getting a car moving from a stop, it is insignificant. I wouldn't have to adjust my driving at all with an extra 400 lbs in the car.

Maybe 400 lbs is insignificant for your car, but I'm sure there are plenty of cars out there that an extra 400 lbs would make a difference.

[Chiba]

This thread is evolving and becoming very interesting because it's gives a better understanding of manual driving in an AWD compared to FWD or RWD.

EDIT: There is an on going discussion if you need a slightly longer clutch slipping from a stop to get an AWD going due to a comparatively higher energy loss. This depends on the driver. It's great information for both new and experienced drivers.

To summarize the weight portion of the discussion: Extra weight, relative to the weight of the car, will likely affect how to start from a stop (not conclusive in the discussion yet). Edited: Best to slip the clutch just that longer and a little more gas to get it going. My preference for now is to think as if I'm on an incline to get into that "a little longer" mindset - until I feel comfortable.

Yes, a hard AWD launch can be brutal to the car, but if you are asking how to get the best launch possible, I'll tell you how I did it with my very first AWD car, which was a 1990 Eagle Talon Tsi. I raced that car at the track on a regular basis, so I have plenty of experience launching the car. Anyway, I'd rev the engine to 6000 rpm and hold it there. Then I'd sidestep the clutch (meaning that I'd slide my left foot off the side of the pedal, letting it pop up as quickly as possible) while flooring the gas pedal. Brutal, yes....but the car would jump off the line like a scalded cat. The tires would only chirp, no real spin, and the clutch had minimal slip. It only slipped as much as necessary to transfer power and do its job. In other words, I wasn't slipping it.....it only slipped as much as it had to from fully disengaged to fully engaged. BTW, I'd regularly get 1.7 short times with my launch method, which was pretty good for a moderately powered car on regular street radials.

Good to know how to hard launch a manual AWD. Just in case people want to try it after reading: - please remember to drive responsibly and attempt at your own risk!