best launch RPM?
Discussion
I'm sprinting this weekend, & i'm looking for some launch advice.
last time i did it i kept the revs at around 3.5k & slipped the clutch in - resulting in loads of wheelspin & a best time ( over 3 runs ) of 14.8.
Any one have any tips re RPM? is it best to gently get it rolling, then boot it? Or is high rpm/dropped clutch the way to go?
the car is a 97 4.2 with std suspension & 18" spiders with 255 s/03's on the back.
Need to get the times down & beat the sti imprezza's!
Darren.
last time i did it i kept the revs at around 3.5k & slipped the clutch in - resulting in loads of wheelspin & a best time ( over 3 runs ) of 14.8.
Any one have any tips re RPM? is it best to gently get it rolling, then boot it? Or is high rpm/dropped clutch the way to go?
the car is a 97 4.2 with std suspension & 18" spiders with 255 s/03's on the back.
Need to get the times down & beat the sti imprezza's!
Darren.
is watching you and then floor it. I've found that the very best launches are when you get no wheel spin at all, so called granny starts. You can get a 64' time in the low 2.3s on cold tyres. Get any wheel spin and this can go up to 3s or even more. Avoiding wheelspin is critical.
Here's my best technique. You're allowed to use this for drag racing, but if you ever compete against me in speed competitions you'll have to promise not to use it. OK?
Assumine you are launching in 1st? Find the lowest RPM that the engine will just barely spin the wheels in first gear. I mean with sustained torque not by dumping the clutch. This is your optimum launch rpm. I expect it'll be somewhere round 3000 rpm. You also need to find three points on the clutch. The first point is where the clutch just starts to bite. The second point is where the clutch is transmitting about 75% of the torque you need to spin the wheels in 1st. The third point is where the clutch is slipping but transmitting enough torque to just about spin the wheels in 1st.
Hold the revs a little over your launch rpm, bring the clutch up to the biting point and hold the car on the handbrake, when you actually launch bring the clutch up to 75% as fast as you can and drop the handbrake as soon as it starts to roll, then bring the clutch up to 100% over about half a second, holding the revs more or less constant. They will waver (unless you are exceptionally good at this) but that doesn't matter as long as they stay somewhere near your launch rpm. So, at this point half a second has gone by, the clutch is slipping, tyres are gripping (maybe with a slight squeal), revs and throttle are constant, the car is fully loaded up and pulling like a train. Typically, the launch revs will be about 3000 rpm which corresponds to about 20 mph (this will vary depending what car you have). If you get the launch right it will take the car a little over a second to get to this speed - at which point the clutch stops slipping, you may feel a little kick as it engages and the revs start to climb, you can now engage the clutch fully. Now focus on the throttle. You want to hold the tyres on the limit of grip without actually spinning them. The more power and the less grip you have the harder this is. You may be tempted to try to control the wheelspin directly but this is near enough impossible - average human reactions simply aren't quick enough. Far better way is to concentrate on the rpm - you want to roll on the power so the rpm winds up steadily so you hit the red line in about a second and a bit. Slower if it's slippery, faster if its grippy, the aim is to get as close as possible to the way the revs climb when you get the launch absolutely perfect. In the heat of the moment you may not get it spot on, and you may under/overestimate the grip, so this may result in a bit of wheelspin or it might not. Either way, you will have stayed pretty close to the limit of grip. Once you hit the shift point it's just a matter of chucking gears at it and bringing the clutch up smoothly each time so you don't snatch the tyres loose.
Hope this helps, let us know how you get on?
Here's my best technique. You're allowed to use this for drag racing, but if you ever compete against me in speed competitions you'll have to promise not to use it. OK?
Assumine you are launching in 1st? Find the lowest RPM that the engine will just barely spin the wheels in first gear. I mean with sustained torque not by dumping the clutch. This is your optimum launch rpm. I expect it'll be somewhere round 3000 rpm. You also need to find three points on the clutch. The first point is where the clutch just starts to bite. The second point is where the clutch is transmitting about 75% of the torque you need to spin the wheels in 1st. The third point is where the clutch is slipping but transmitting enough torque to just about spin the wheels in 1st.
Hold the revs a little over your launch rpm, bring the clutch up to the biting point and hold the car on the handbrake, when you actually launch bring the clutch up to 75% as fast as you can and drop the handbrake as soon as it starts to roll, then bring the clutch up to 100% over about half a second, holding the revs more or less constant. They will waver (unless you are exceptionally good at this) but that doesn't matter as long as they stay somewhere near your launch rpm. So, at this point half a second has gone by, the clutch is slipping, tyres are gripping (maybe with a slight squeal), revs and throttle are constant, the car is fully loaded up and pulling like a train. Typically, the launch revs will be about 3000 rpm which corresponds to about 20 mph (this will vary depending what car you have). If you get the launch right it will take the car a little over a second to get to this speed - at which point the clutch stops slipping, you may feel a little kick as it engages and the revs start to climb, you can now engage the clutch fully. Now focus on the throttle. You want to hold the tyres on the limit of grip without actually spinning them. The more power and the less grip you have the harder this is. You may be tempted to try to control the wheelspin directly but this is near enough impossible - average human reactions simply aren't quick enough. Far better way is to concentrate on the rpm - you want to roll on the power so the rpm winds up steadily so you hit the red line in about a second and a bit. Slower if it's slippery, faster if its grippy, the aim is to get as close as possible to the way the revs climb when you get the launch absolutely perfect. In the heat of the moment you may not get it spot on, and you may under/overestimate the grip, so this may result in a bit of wheelspin or it might not. Either way, you will have stayed pretty close to the limit of grip. Once you hit the shift point it's just a matter of chucking gears at it and bringing the clutch up smoothly each time so you don't snatch the tyres loose.
Hope this helps, let us know how you get on?
darreni said:
I'm sprinting this weekend, & i'm looking for some launch advice.
last time i did it i kept the revs at around 3.5k & slipped the clutch in - resulting in loads of wheelspin & a best time ( over 3 runs ) of 14.8.
That seems a bit slow. I was managing a 13.4 even with loads of wheelspin and waiting for the lights to change green before even starting to pull away. I was in a 4.5 but I don't think that should matter too much as its top end where the extra cc's kick in.
I found that having no wheel spin was impossible, best just to try and reduce it by only using 1/4ish throttle on the off and then once it gets rolling boot it.
The waiting for green bit is irrelevant. Your quarter mile time is from from when you break the timing beam to when you cross the 1/4 mile - i.e. reaction time is excluded, though obviously matters if you're racing to cross the 1/4 mile line!
The important thing is to have hot rears. If you're allowed, do a nice long first (or even 2nd gear) burnout, ideally in some ammonia if they put it down (for some drag days they have this). Make sure your engine and transmission is nicely warmed up before you do this if you have any mechanical sympathy whatsoever!
Then, granny start as Peter said, feeding in the throttle. Some wheelspin on shifting into 2nd and 3rd is probably inevitable if you're going for it though.
Corners are better for the car and more fun for the driver though :-)
The 4.5 generally has more low down torque, so a bit harder to get moving, but similar power to the 4.2. There's more difference in driver, condition of the tyres, state of the tarmac, air temperature etc.
danny
>> Edited by dannylt on Tuesday 2nd September 15:15
The important thing is to have hot rears. If you're allowed, do a nice long first (or even 2nd gear) burnout, ideally in some ammonia if they put it down (for some drag days they have this). Make sure your engine and transmission is nicely warmed up before you do this if you have any mechanical sympathy whatsoever!
Then, granny start as Peter said, feeding in the throttle. Some wheelspin on shifting into 2nd and 3rd is probably inevitable if you're going for it though.
Corners are better for the car and more fun for the driver though :-)
The 4.5 generally has more low down torque, so a bit harder to get moving, but similar power to the 4.2. There's more difference in driver, condition of the tyres, state of the tarmac, air temperature etc.
danny
>> Edited by dannylt on Tuesday 2nd September 15:15
15 psi? really?
I'll give it a go.
the only thing is this is not a straight drag run, its a club sprint with a nice open bend in the middle & a crest / dip over the finish ( though i accept that is no excuse for my previous crap times), so i dont want any handling suprises mid run!
Darren.
I'll give it a go.
the only thing is this is not a straight drag run, its a club sprint with a nice open bend in the middle & a crest / dip over the finish ( though i accept that is no excuse for my previous crap times), so i dont want any handling suprises mid run!
Darren.
now how do you measure 10% wheelspin?
I was sorry to see this thread had ended last September. I found it doing a search of "quarter mile" after I spent too long spinning on the start line at Crail and needed advice.
It's been really useful though I wondered if anyone had any comments on fade2grey's question re. staring in 2nd.
Cheers.
It's been really useful though I wondered if anyone had any comments on fade2grey's question re. staring in 2nd.
Cheers.
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