launching from standstill...what techinique?
Discussion
hi people,
just wondering the quickest way to get a car off the line with a little mechanical sympathy?
my 944 T seems to want me to keep the rev's up and feed the clutch in but i'm worried about knackering the clutch (1k+ for a replacement
)
am i just being wet or should i give mr clutch a rest?
ta
just wondering the quickest way to get a car off the line with a little mechanical sympathy?
my 944 T seems to want me to keep the rev's up and feed the clutch in but i'm worried about knackering the clutch (1k+ for a replacement
) am i just being wet or should i give mr clutch a rest?
ta
A "Granny Start" is the answer. Get rolling gently first and then accelerate firmly up to the point where the rear wheels are slipping at peak grip (5-10%). This is easy in both my n/a road cars - they take full throttle in 1st gear without an issue on a dry road. In your 944T watch out for when the turbo starts coming in though.
Even successful racers use the "granny start", as it's way easier than a conventional racing start, and less hard to cock up.
Naturally, in a car like the 944 Turbo this technique isn't ideal because the turbo won't be on the boil when you pull away. Any technique that involves being in the boost zone upon launch isn't going to be very mechanically sympathetic though!
Even successful racers use the "granny start", as it's way easier than a conventional racing start, and less hard to cock up.
Naturally, in a car like the 944 Turbo this technique isn't ideal because the turbo won't be on the boil when you pull away. Any technique that involves being in the boost zone upon launch isn't going to be very mechanically sympathetic though!
Edited by RobM77 on Friday 15th August 00:35
As Rob has said - the clutch release is the time limiting step. Pull away as gently as possible focussing on getting the clutch fully engaged as quickly as possible, rather than on getting as much speed on. Once the clutch is fully engaged then feel free to find out whether the engine has more torque than the tyres have grip...
More sympathetic, and remarkably quick, less likely to stall etc etc.
More sympathetic, and remarkably quick, less likely to stall etc etc.
I expect it's a similar technique to my Sierra. Big T4 turbo make zero boost at low rpm / low load so there's a few options:
1. Big rpm to spin up the turbine. Dump the clutch and spin up the wheels then moderate the throttle to minimise wheelspin. This technique is what the Gp.A guys used and it's practially impossible and busts diffs if you've got a bit of power.
2. Same as above but slip the clutch a bit to safe the diff and tyres. OK but knackers the clutch.
3. The odd prod on the throttle to wake up the turbine, but not spin it right up, medium throttle and minimal clutch slip. As soon as the car is rolling, dump the rest of the clutch and nail the throttle. Get ready to short shift to second as the rear wheels spin up. Safest for all driveline components...!!!
1. Big rpm to spin up the turbine. Dump the clutch and spin up the wheels then moderate the throttle to minimise wheelspin. This technique is what the Gp.A guys used and it's practially impossible and busts diffs if you've got a bit of power.
2. Same as above but slip the clutch a bit to safe the diff and tyres. OK but knackers the clutch.
3. The odd prod on the throttle to wake up the turbine, but not spin it right up, medium throttle and minimal clutch slip. As soon as the car is rolling, dump the rest of the clutch and nail the throttle. Get ready to short shift to second as the rear wheels spin up. Safest for all driveline components...!!!
I think it depends on the car, and how much torque you have. In my 1.6 hyundai getz, to go at all quick off a standing start i need to rev it and let the clutch up with full throttle to keep the revs around peak power (about 5500). I can bearly make the wheels spin on a dry road even doing this. Problem with a granny start is that it's just horribly slow at 2000-4000rpm. If you got a hefty diesel or something its probably just as fast to granny start anyway.
Scho said:
just wondering the quickest way to get a car off the line with a little mechanical sympathy?
It's going to vary hugely depending how much power you have relative to grip, whether you need boost to generate enough torque to exploit all the grip, and whether you have fwd/rwd/4wd.GreenV8S said:
Scho said:
just wondering the quickest way to get a car off the line with a little mechanical sympathy?
It's going to vary hugely depending how much power you have relative to grip, whether you need boost to generate enough torque to exploit all the grip, and whether you have fwd/rwd/4wd.250bhp
rwd.
Edited by Scho on Friday 15th August 18:52
I can see the relevance of this if we're talking about a track based activity, but do we really bother about this when driving on public roads? According to what I hear, quick starts are apt to generate disapproval if witnessed by a police officer, so it might be worth bearing that in mind.
Best wishes all,
Dave.
Best wishes all,
Dave.
7db said:
Very relevant to the road -- there's usually a massive clear space with no cars in it just ahead of the junction. It's the safest place to be.
Of course, being first into the junction isn't.
But do we really feel we're appreciably safer by rushing into that open space ahead of the pack. I honestly doubt if it makes sufficient difference to justify this eagerness to make quick starts. You tell me; I'm listening.Of course, being first into the junction isn't.
BTW, if one of your 'opponents' turns out to be a tailgater, you might wish you hadn't got there first.
Best wishes all,
Dave.
I won't debate the issue of whether it is sensible to practice fast getaways on the road. And the balance between speed and mechanical sympathy is one that only you can make.
Assuming you do want to get off the line as fast as possible, the first question is whether the engine produces enough power to spin the wheels. I mean by sustained power, not dumping the clutch. If it can't, the fastest getaway is probably going to include holding the engine at very high revs to keep as much kinetic energy in the engine as possible, dump the clutch and allow the wheels to spin, trading off lost grip from wheel spin against the extra drive you will get as the tyres pull the engine speed down. This approach is brutal and not compatible with any mechanical sympathy, but it's the fastest way off the line if the vehicle has more traction than power.
On the other hand if you have enough torque available to spin the wheels in the chosen launch gear, then it gets a lot more interesting. Hopefully with 250 bhp this is the situation you will find yourself in. Here the challenge is to make the best possible use of the available traction and that means keeping the tyres right at the point of sliding but not actually spinning up. The method I use works like this:
Decide which gear it will launch in. Unless you have massive torque available this will be first gear.
Find out the minimum revs that the engine produces enough torque to spin the wheels - I mean purely based on sustained engine power not by dumping the clutch. If you're turbo charged then this needs to be under the conditions that you will be launching i.e. no boost.
This will be the rpm that you use off the line, possibly plus a small margin if you have trouble balancing the throttle against the clutch. For example in the V8S with a huge torquey engine and 50:50 weight distribution this corresponds to about 2000 rpm on cold tyres in the dry.
Hold the engine at your selected launch rpm with the clutch just at the biting point and the handbrake held on.
At the point you decide to launch, engage the clutch far enough to just start to squeal the tyres, and apply enough throttle to stop the revs dipping. This is a very sudden transition and needs practice to judge how much throttle and clutch to apply.
As the car starts to accelerate it will settle back on the suspension and transfer weight to the rear. If you have rwd this means the traction increases so you can engage the clutch further; for fwd it means you have to feather the clutch slightly as it settles.
Now you hold still, balancing the clutch at the point of squealing the tyres and keeping the engine revs constant on the throttle, until the road speed gets high enough to match the engine revs. You will recognise this because the engine revs will suddenly start to climb. Now you fully engage the clutch and roll the throttle open to keep the tyres at the limit. The next part happens very quickly as the engine heads for the red line. At this point I don't bother trying to manage the wheel spin (my reactions aren't fast enough) instead I know roughly how quickly the revs need to rise when it's on the limit of grip and I concentrate on spinning them up that quickly. It's rarely perfect but does mean that regardless of conditions you stay quite close to the optimum.
The whole process typically takes about two seconds in the dry and double that in the wet.
This technique is really only applicable for motorsport (sprinting is my game) but the nice part about it for road use is that the first part is very similar to a granny start so you can pootle gently off the line and change to a competitive start at the drop of a hat - as long as you choose to practice your granny starts at the right rpm.
Assuming you do want to get off the line as fast as possible, the first question is whether the engine produces enough power to spin the wheels. I mean by sustained power, not dumping the clutch. If it can't, the fastest getaway is probably going to include holding the engine at very high revs to keep as much kinetic energy in the engine as possible, dump the clutch and allow the wheels to spin, trading off lost grip from wheel spin against the extra drive you will get as the tyres pull the engine speed down. This approach is brutal and not compatible with any mechanical sympathy, but it's the fastest way off the line if the vehicle has more traction than power.
On the other hand if you have enough torque available to spin the wheels in the chosen launch gear, then it gets a lot more interesting. Hopefully with 250 bhp this is the situation you will find yourself in. Here the challenge is to make the best possible use of the available traction and that means keeping the tyres right at the point of sliding but not actually spinning up. The method I use works like this:
Decide which gear it will launch in. Unless you have massive torque available this will be first gear.
Find out the minimum revs that the engine produces enough torque to spin the wheels - I mean purely based on sustained engine power not by dumping the clutch. If you're turbo charged then this needs to be under the conditions that you will be launching i.e. no boost.
This will be the rpm that you use off the line, possibly plus a small margin if you have trouble balancing the throttle against the clutch. For example in the V8S with a huge torquey engine and 50:50 weight distribution this corresponds to about 2000 rpm on cold tyres in the dry.
Hold the engine at your selected launch rpm with the clutch just at the biting point and the handbrake held on.
At the point you decide to launch, engage the clutch far enough to just start to squeal the tyres, and apply enough throttle to stop the revs dipping. This is a very sudden transition and needs practice to judge how much throttle and clutch to apply.
As the car starts to accelerate it will settle back on the suspension and transfer weight to the rear. If you have rwd this means the traction increases so you can engage the clutch further; for fwd it means you have to feather the clutch slightly as it settles.
Now you hold still, balancing the clutch at the point of squealing the tyres and keeping the engine revs constant on the throttle, until the road speed gets high enough to match the engine revs. You will recognise this because the engine revs will suddenly start to climb. Now you fully engage the clutch and roll the throttle open to keep the tyres at the limit. The next part happens very quickly as the engine heads for the red line. At this point I don't bother trying to manage the wheel spin (my reactions aren't fast enough) instead I know roughly how quickly the revs need to rise when it's on the limit of grip and I concentrate on spinning them up that quickly. It's rarely perfect but does mean that regardless of conditions you stay quite close to the optimum.
The whole process typically takes about two seconds in the dry and double that in the wet.
This technique is really only applicable for motorsport (sprinting is my game) but the nice part about it for road use is that the first part is very similar to a granny start so you can pootle gently off the line and change to a competitive start at the drop of a hat - as long as you choose to practice your granny starts at the right rpm.
Edited by GreenV8S on Tuesday 19th August 22:44
7db said:
I'm not sure I have an opponent in this matter.
The nice thing about getting into space is that there's more space to deal with anyone else who needs dealing with.
It's the space that's important -- sometimes there's more of that going second then there is trying to go joint first.
Yes OK, the word opponent was bunged in there a bit carelessly. I should have said fellow road users.The nice thing about getting into space is that there's more space to deal with anyone else who needs dealing with.
It's the space that's important -- sometimes there's more of that going second then there is trying to go joint first.
Having thought about it a bit more, I'm still not sure that it will always be best to try to be leading the pack. For example, suppose you're on the front row of the grid
at the lights, and alongside you is a boy racer type. In that case I think I'd prefer to let him get away first rather than have him snapping at my heels a bit further down the road.Perhaps that's what you're recognising in your last line quoted above?
Best wishes all,
Dave.
p1esk said:
7db said:
I'm not sure I have an opponent in this matter.
The nice thing about getting into space is that there's more space to deal with anyone else who needs dealing with.
It's the space that's important -- sometimes there's more of that going second then there is trying to go joint first.
Yes OK, the word opponent was bunged in there a bit carelessly. I should have said fellow road users.The nice thing about getting into space is that there's more space to deal with anyone else who needs dealing with.
It's the space that's important -- sometimes there's more of that going second then there is trying to go joint first.
Having thought about it a bit more, I'm still not sure that it will always be best to try to be leading the pack. For example, suppose you're on the front row of the grid
at the lights, and alongside you is a boy racer type. In that case I think I'd prefer to let him get away first rather than have him snapping at my heels a bit further down the road.Perhaps that's what you're recognising in your last line quoted above?
Best wishes all,
Dave.
You do have to be careful with this approach though. As someone pointed out earlier, the Boys in Blue often don't take kindly to quick starts. I was once pulled over for a lecture even though I hadn't broken any laws. Waiting at a red light in a 40 limit, 2 lanes at the lights merging quickly into 1 lane. I was in a very accelerative car, the person next to me wasn't, there was a queue of cars behind each of us. I decided the safest option was to set off very briskly to avoid us trying to occupy the same piece of road at the same time. Due to a slightly uneven road surface, one of my rear tyres broke traction (LSD so no stability issue) generating a small amount of tyre squeal. As soon as I hit the speed limit I backed off, well clear of the car that had been next to me. BiB who had been several cars back in the queue hit his lights and pulled me over for a lecture (but no laws broken so he couldn't charge me with anything). Being a smart boy, I didn't argue the point. I do wonder if the BiB would have stopped me if I'd performed the same manoeuvre in a Mondeo rather than in a nick-me-red Corvette...
p1esk said:
For example, suppose you're on the front row of the grid at the lights, and alongside you is a boy racer type
Give it lots of beans on red, shoot the guy a look, grimace, revs up on amber, and then drop it and pull away like a granny. You'll be in lots of space as he shoots off. at the lights, and alongside you is a boy racer typeUnless he's in another seven and you're stopped at lights at the entrance to a tunnel...
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