why 4wd car starts slower than rwd car

[mathematica]

It is mentioned several times on TG that, in a drag race, a 4wd car will start slower than a rwd car. Why? I didn't get it at all. 4WD means you can have more grip at the begining, and thus should be able to put more power down to the ground in 1st gear? A two wheel drive super can will only spin the wheel but struggle to put the power down in 1st gear. What's wrong?

[ja404]

Eh, a number of reasons. One being the extra rotational inertia needed to move 4 wheels instead of 2. Another main reason is if there's a center diff and the rears start to lose traction the diff sends power to the front the car bogs down in the process because it loses momentum. AWD basically has too much traction, if the wheels were allowed to spin more, you'd get a better launch. The only hope is to turn off traction control, rev to 6k and dump the clutch and hope you get enough wheelspin in all four wheels to overcome any power transfer, I guess.

[GraemeH]

There's too much grip. If you rev it hard and drop the clutch, the engine bogs down to near idle revs instantly because there isn't (usually) enough power to overcome the grip of all 4 tyres with rotational force. So generally (at least, if you pay your own maintinence and didn't want to bust your drivetrain), you'd get the car rolling and the clutch fully up first then floor it.

[thedguy]

It's because Europeans don't know how to drag race. They look at 4wd as a disadvantage because you'll destroy the clutch. Americans (and Aussies) see it as a traction advantage. Plus they do things like save weight by putting in weaker axles (Lamborghini Superleggera is a perfect example).

Perfect proof is the fact that Americans think Subaru transaxles (non-sti's) are weak because repeated clutch drops at 6000rpms will blow them up. You launch one at high revs and drop the hammer and it'll rocket out of the hole. In America 4wds are impossible to beat 0-60, in Europe not the case. The few American (performance) vehicles with AWD came with automatics because they could cope better with hard launches like this.

I've talked to a couple of people who've drag raced GT-R skylines and they are damn near made for the job of drag racing. Their 4wd system keeps things from blowing up (as it allows the rear tires to give a bit, rather than the clutch or weakness in the transmission) before the front wheels take control and pull the car out of the hole. There is still a limit to how much power they can take, especially as you start adding on bigger tires and/or slicks.

What I find funny is the Audi guys don't have trouble breaking parts with hard launches, so I don't know why Europeans seem to fear breaking parts on 4wd's when doing hard standing starts.

[dMa]

like thedguy said, it overloads the clutch. To avoid this, there cant be any spin on the wheels which makes the launch slower because the tires are not going at max speed.

[maximus]

Of course you know much about European drag racing thedguy?

[Ford Prefect]

drag racing is gay unless you´re driving one of those 1000+ hp ethanol monsters...

which is why most of the drag racing going on in germany is done by teenagers who have been watching too many fast n furious films...

[Mach1]

Originally Posted by Ford Prefect

drag racing is gay unless you´re driving one of those 1000+ hp ethanol monsters...

which is why most of the drag racing going on in germany is done by teenagers who have been watching too many fast n furious films...

You drive a little girl's car and you think drag racing is gay!

[watto]

Originally Posted by thedguy

It's because Europeans don't know how to drag race. give a shit about drag racing.

Originally Posted by Mach1

You drive a little girl's car and you think drag racing is gay!

Oh man, just leave. Leave.

[Ford Prefect]

Originally Posted by Mach1

You drive a little girl's car and you think drag racing is gay!

[thedguy]

Originally Posted by dMa

like thedguy said, it overloads the clutch. To avoid this, there cant be any spin on the wheels which makes the launch slower because the tires are not going at max speed.

A little bit of wheel spin actually helps actually. It means the tires take the load and the shock from the sudden burst of power. This is why the Skyline GT-R's system is so good. It allows that little bit of give in the tires to release the energy from the shock, then it grabs and goes. It's also one of the fastest launching cars on the planet, besting even the Evo's and STi's.

Originally Posted by maximus

Of course you know much about European drag racing thedguy?

Yep, I'm all knowing about how much Europeans don't like it.

In general, Europeans don't like it (exception seems to be the Swedes and Fins), most seem to think that it's just to easy. "All you have to do is shift fast" is what I hear a lot say... nevermind the fact that a drag race is usually won or lost in the first 60 feet.

[jayhawk]

Originally Posted by thedguy

Perfect proof is the fact that Americans thing Subaru transaxles (non-sti's) are weak because repeated clutch drops at 6000rpms will blow them up. You launch one at high revs and drop the hammer and it'll rocket out of the hole. In America 4wds are impossible to beat 0-60, in Europe not the case. The few American (performance) vehicles with AWD came with automatics because they could cope better with hard launches like this.

The problem with Subaru five speeds is the transmission, specifically first gear; the diff's are rock solid.

Key to launching a Subie is to get it to about 4,000 rpms, slip the clutch until it revs down to 3,00 then ease, not step off, the pedal. And your right, it is like a rocket...first and second gear are a blur, I am constantly amazed how efficient the power is put down with my car, all 225 measly horses.

[Karoug]

A guy I know used to be the Swedish champion in a Audi S4...

[ahpadt]

Originally Posted by Ford Prefect

x2

[andyhui01]

Originally Posted by jayhawk

Key to launching a Subie is to get it to about 4,000 rpms, slip the clutch until it revs down to 3,00 then ease, not step off, the pedal. And your right, it is like a rocket...first and second gear are a blur, I am constantly amazed how efficient the power is put down with my car, all 225 measly horses.

Or if you get free gearboxes... dump it at 6k and the car will just fly off... I've been in a mate doing that, he doesn't know much about cars and it was pretty fun so I didn't bother telling him...

[MadCow809]

Originally Posted by mathematica

It is mentioned several times on TG that, in a drag race, a 4wd car will start slower than a rwd car. Why? I didn't get it at all. 4WD means you can have more grip at the begining, and thus should be able to put more power down to the ground in 1st gear? A two wheel drive super can will only spin the wheel but struggle to put the power down in 1st gear. What's wrong?

if you are into drag races and know the concept behind it then its rather easy to explain....

for example, lets say WRX v.s M3 on a drag strip. Side step the clutch, hard launch the STi and you will get a clean start off the line, you get a descent time of around 13.5 to 14.0sec with a trap speed of 160~163kph or so. Now the M3's turn, without the advantage of AWD, the car launches with some wheel spin, it cross the finish line in around 13.4sec with a trap speed of 170kph. Now the question comes, the times are similar, but why are the trap speeds so different?

Launching a RWD car creates wheel spin, this revs the engine and spins the wheel, as the wheels catches traction you rocket off with an advantage of more speed, but that doesnt mean you will get a faster 1/4 mile time, you just carry more speed across the finish line, hence the higher trap speed.

AWD on the other hand doesnt wheel spin as much, sometimes they just rocket off, this is why the have a slower trap speed but a generally a good 1/4 mile time. Another example would be the old Subaru legacys from the mid90s. With 160bhp or less, wheel spin is almost impossible, but launching on a wet patch, you can spin the wheel, carry more momentum and trap with a higher speed.

Just one of those things you learn at drags.

[Ottobon]

most of the reasons have been mentioned, the biggest factor is that many cars have too weak of holding pressures on the clutch/torque converter, so even if the rest of the drive train could take a 5 or 6k launch the clutch will just spin itself up. Not so much "too much grip" as "too much grip for the weakest part" (which is usually the clutch's pressure plate or the torque converter on a automatic)

To add to that, i've actually driven many 2wd cars that spin their clutches if you launch at too high of revs, the 2zz drivetrain in the Lotus Elise is such a example of this, assuming they haven't fixed the weak pressure plate on the newer models.

With all that said I can almost guarantee that on a slippery surface the AWD cars launch will always be faster.

[MadCow809]

Originally Posted by Ottobon

With all that said I can almost guarantee that on a slippery surface the AWD cars launch will always be faster.

i concur, read my above post.

[epp_b]

Thedguy has some good points. But, mostly, it's because it's very expensive to make a 4WD car capable enough to handle dry, clutch-dropping launches without the drivetrain exploding. If you launch a 4WD in the wet, it will create wheel-spin at all four corners, which will beat RWD every time.

On one of Clarkson's DVDs (can't remember which one off-hand), he drags a 1000HP 4WD R33 Skyline using a full-bore start. All four wheels spin. The thing costs ₤150,000. The Bugatti Veyron, which is 4WD, can also spin all four wheels, but only because of the expensive components and brilliant engineering.

You drive a little girl's car and you think drag racing is gay!

No, no, it's a metrosexual car

[edkwon]

Originally Posted by thedguy

I've talked to a couple of people who've drag raced GT-R skylines and they are damn near made for the job of drag racing. Their 4wd system keeps things from blowing up (as it allows the rear tires to give a bit, rather than the clutch or weakness in the transmission) before the front wheels take control and pull the car out of the hole. There is still a limit to how much power they can take, especially as you start adding on bigger tires and/or slicks.

im not sure how this european vs americans being able to drag race is remotely relevant to the OPs question, its kind of off topic.

anyways, im replying to your choice of using the GTR as an example, and its not a very good choice, as the GTRs AWD system is nothing like the full time split 50/50 of most manual T subarus. i know yoy know tha the GTRs ATTESA system is primarily RWD that sends some power to the front wheels, so drag racing those is similar to launcing a RWD car, the rears will light up first, then some power is delivered to the front before it takes off