Double declutching & heeling and toeing
Discussion
Right, just overheard an arguement in the office about Double declutching & heeling and toeing. Didn't want to interject as I was not 100% sure...
re: Double declutching
Is it worthwhile in a road car?
Does it reduce stress on any compnents?
Does it give a smoother gear change?
re: heeling and toeing
Is it worthwhile in a road car? (do the revs really fall that quickly with a modern flywheel?)
Does it reduce stress on the gearbox?
Any other comments / notes / thoughts / observations?
Ta muchly
re: Double declutching
Is it worthwhile in a road car?
Does it reduce stress on any compnents?
Does it give a smoother gear change?
re: heeling and toeing
Is it worthwhile in a road car? (do the revs really fall that quickly with a modern flywheel?)
Does it reduce stress on the gearbox?
Any other comments / notes / thoughts / observations?
Ta muchly
in a rear wheel drive car (eg a lotus) esp on a wet road or a bend brake situation - ie running uop to a round about - I use heel toe technique to keep the car balanced - especially when pressing on. result in better car control - and less chance of upsetting the ride. I find it very useful andI admit I practise on the road as much as possible to help me on the track.
Since synchromesh double de clutching is in my view not worthwhile - no it won't stress any componets and it is mechanically sympathtic - but its time consuming.
just my 2p
Since synchromesh double de clutching is in my view not worthwhile - no it won't stress any componets and it is mechanically sympathtic - but its time consuming.
just my 2p
Agree with Scruff400, in a modern car with working synchromesh, it just ensures a smooth downchange. Heel and toeing ditto when you are braking. On a bike its more important to blip the throttle on a down change since a sudden downchange can lock the rear wheel briefly, very tricky if you are on a slippery surface. (Hence the use of slipper clutches on competition bikes.) This becomes less of a problem in a car but I would be grateful for input from car track day/ competition experts. Presumably the aim is to get all gear changing out of the way before the corner, but progress doesn't always let that happen.
Double declutching is a waste of time with a synchro car.
Heel & toe is always a good technique, even in my discovery!
In the absence of heel & toe and in a large engined car such as a TVR, if you change down while braking (which you have to do at, for example, a hairpin such as that at Mallory), you will hear the rear wheels chirp as they get addditional braking. This unbalances the car and causes additonal wear on the clutch as the tranmission forces the engine revs up.
Well worth learning. It requires properly set-up throttle and brake pedals, and isn't necessarily heel and toe - most people just use the side of the foot.
with practice it comes naturally, and makes everything very smooth, just in the way boosting the throttle does as you change down to overtake.
R
Heel & toe is always a good technique, even in my discovery!
In the absence of heel & toe and in a large engined car such as a TVR, if you change down while braking (which you have to do at, for example, a hairpin such as that at Mallory), you will hear the rear wheels chirp as they get addditional braking. This unbalances the car and causes additonal wear on the clutch as the tranmission forces the engine revs up.
Well worth learning. It requires properly set-up throttle and brake pedals, and isn't necessarily heel and toe - most people just use the side of the foot.
with practice it comes naturally, and makes everything very smooth, just in the way boosting the throttle does as you change down to overtake.
R
Heel and Toe is very worthwhile on road or track to aid progress (doesn't upset car when near the limit) and to preserve machinery.
Double de-clutch hasn't been necessary in cars since the fifties regardless of syncromesh or not. I've got a race car with no syncromesh - Double de-clutch achieves nothing, whereas with a bit of practice on the heel and toe and gears can be changed clutchless.
In fact nearly all cars can be changed clutchless with heel and toe - try it on the way home tonight - but it's much harder to match the revs when you're not going flat out
Double de-clutch hasn't been necessary in cars since the fifties regardless of syncromesh or not. I've got a race car with no syncromesh - Double de-clutch achieves nothing, whereas with a bit of practice on the heel and toe and gears can be changed clutchless.
In fact nearly all cars can be changed clutchless with heel and toe - try it on the way home tonight - but it's much harder to match the revs when you're not going flat out
quote:
My left foot is far too 'heavy' to master this.
Thats exactly what i find whenever i have 'tried' a bit of left foot braking!
What are the advantages of left foot braking - i've been told its useful in turbocharged cars to keep the car on-boost - is this true?
Moonie
>> Edited by theboymoon on Thursday 12th September 12:37
Double declutching still has it's uses. I used to drive an old Mitsubishi Shogun 2.5 TDi which was vary underpowered. When going up hills in 3rd gear the thing would steadily slow down to a point where 2nd was needed. If you changed without double de-clutching then you'd knock another 3-4 mph of your already dropping speed. If you double declutch you have the car out of gear for a fraction of a second longer, but loose less speed and the momentum of the car is not sapped and turned into engine speed.
I think heavy engined cars (with high compresion ratios?) benefit most as their engines have the most resistance to spin up to speed.
I think heavy engined cars (with high compresion ratios?) benefit most as their engines have the most resistance to spin up to speed.
Left foot braking is useful (mainly on a circuit of course!) where you're approaching a bend which requires you to slow, but not enough so you'll have to change down a gear.
The main benefit is that you're right foot is there, poised to mash the throttle at the earliest possible opportunity, since all the braking is done with the left. IMO I found this fairly easy to get used to (but then I might be doing it all wrong), and not entirely dissimilar to karting.
Having trouble mastering double de-clutching on our hydrostatic 2.5 tonne forklift though!
The main benefit is that you're right foot is there, poised to mash the throttle at the earliest possible opportunity, since all the braking is done with the left. IMO I found this fairly easy to get used to (but then I might be doing it all wrong), and not entirely dissimilar to karting.
Having trouble mastering double de-clutching on our hydrostatic 2.5 tonne forklift though!
quote
i've been told its useful in turbocharged cars to keep the car on-boost - is this true?
I guess so. I think it works well (if you can do it) on 'normal' cars too. You keep the revs up and the engine driving hard so that when you lift off the brakes, the car surges forward.
I think you foot 'learns' the amount of pressure required for the different controls but my left foot will to go back to university for 3 or 4 years before I can do it smoothly.
i've been told its useful in turbocharged cars to keep the car on-boost - is this true?
I guess so. I think it works well (if you can do it) on 'normal' cars too. You keep the revs up and the engine driving hard so that when you lift off the brakes, the car surges forward.
I think you foot 'learns' the amount of pressure required for the different controls but my left foot will to go back to university for 3 or 4 years before I can do it smoothly.
quote:
quote:
My left foot is far too 'heavy' to master this.
Thats exactly what i find whenever i have 'tried' a bit of left foot braking!
What are the advantages of left foot braking - i've been told its useful in turbocharged cars to keep the car on-boost - is this true?
Moonie
>> Edited by theboymoon on Thursday 12th September 12:37
Left foot braking as in brakes (left foot) and throttle (right foot) simultaneously is handy on turbos to load the engine without accelerating the car - very hard on the brakes though. Also useful on front wheel drive cars to provoke oversteer. Left foot braking combined with a throttle lift can also be used to give a quick 'dab' of brakes into a corner to loose a few mph (braking keeps the car more balanced than just easing off the power) while getting back on the power instantly (no need to move your right foot across the pedals). Basically, unless you're rallying in a 4wd/fwd car it's probably a waste of time.
Heel-n-toe on the other hand is something that people in rwd cars should do as a matter of course, IMO.
Above all sound right to me. Done properly synchromesh are not worked as hard, but that means you have to select neutral first (with clutch in up position), before blipping. Depends on what you are downchanging for. If its to use the engine for braking then don't do it. Use the brakes. Best use of heel and toe just before a corner, to balance the car after braking and selecting more accelerative gear for exit. That said, if you're not amazing, you could just brake for the corner, and rather than heel and toe, and then select the right gear at the right time. It can be more effective for novice racers. But sometimes you need to blip as the engine character also dictates your driving style to an extent.
Disclaimer: I learnt heel and toe from autocar magazine two years ago and I may actually be talking shit!
Disclaimer: I learnt heel and toe from autocar magazine two years ago and I may actually be talking shit!
OK, don't read this post if you don't want to hear the mechanics of why h&t is useful. 
Fundamentally the issue is one of traction and stability. The concept of traction circles/ellipses is probably familar to a few people but basically the boundary of the ellipse marks the point of maximum tyre/road friction in any given direction. So, under perfect acceleration and braking the opposite points of the ellipse would be reached in the North-South direction. Under perfect cornering (with no brake or throttle applied) the East and West points of the ellipse would be reached, depending on the direction of cornering. For any combination of acceleration/braking and cornering some intermediate point, e.g. North-North-West would be reached. The point of all this is if you are braking 'perfectly' (i.e. you are on the edge of the ellipse) and you change down a gear without h&t the reduction in engine rpm relative to the wheels will act to brake the wheels further. This takes you outside the traction ellipse, which means maximum traction has been exceed, hence you can very easily lose the back of the car (with rear wheel drive). Even when not braking 'perfectly' the additional sudden braking caused by the downchange can unsettle the car, meaning that the suspension is not working at full effectiveness when you go into the corner - this can reduce cornering speed, precision of vehicle position control and ultimately cause a loss of traction.
By blipping the throttle between gearchanges and matching the relative engine speed to the wheel speed the additional braking effect is avoided and hence you stay within the traction ellipse and keep the car stable.
Hope that helps. Not easy to explain without a diagram but hopefully it's pretty comprehensible?
roadsweeper.
Fundamentally the issue is one of traction and stability. The concept of traction circles/ellipses is probably familar to a few people but basically the boundary of the ellipse marks the point of maximum tyre/road friction in any given direction. So, under perfect acceleration and braking the opposite points of the ellipse would be reached in the North-South direction. Under perfect cornering (with no brake or throttle applied) the East and West points of the ellipse would be reached, depending on the direction of cornering. For any combination of acceleration/braking and cornering some intermediate point, e.g. North-North-West would be reached. The point of all this is if you are braking 'perfectly' (i.e. you are on the edge of the ellipse) and you change down a gear without h&t the reduction in engine rpm relative to the wheels will act to brake the wheels further. This takes you outside the traction ellipse, which means maximum traction has been exceed, hence you can very easily lose the back of the car (with rear wheel drive). Even when not braking 'perfectly' the additional sudden braking caused by the downchange can unsettle the car, meaning that the suspension is not working at full effectiveness when you go into the corner - this can reduce cornering speed, precision of vehicle position control and ultimately cause a loss of traction.
By blipping the throttle between gearchanges and matching the relative engine speed to the wheel speed the additional braking effect is avoided and hence you stay within the traction ellipse and keep the car stable.
Hope that helps. Not easy to explain without a diagram but hopefully it's pretty comprehensible?
roadsweeper.
Oh, meant to say, there's nothing wrong with practicing h&t on the road when it's quiet, as long as you give yourself some extra braking distance (say when approacghing roundabouts, junctions, etc.)
Personally, I've been practicing it for a while now in the Chimaera and still need a lot more practice. I can recommend adjusting the brake and throttle pedal to make it easier though - try and get the throttle pedal to be just below the brake pedal when the brake pedal is fully depressed as a good starting point, and then adjust for personal preference from there.
I never bother with double-declutching.
I can left-foot brake, though I am a bit out of practice, as noted by my instructor when I left-foot braked a Ferrari and nearly locked it up! It is normal that your left foot will be 'heavy' but practice sorts this out. My experience came from driving an automatic for three years - I left foot braked it all the time, partly because it reduced the shame I felt when admitting to people what I drove (I could always add, "...but it's great for left-foot braking!")
Personally, I've been practicing it for a while now in the Chimaera and still need a lot more practice. I can recommend adjusting the brake and throttle pedal to make it easier though - try and get the throttle pedal to be just below the brake pedal when the brake pedal is fully depressed as a good starting point, and then adjust for personal preference from there.
I never bother with double-declutching.
I can left-foot brake, though I am a bit out of practice, as noted by my instructor when I left-foot braked a Ferrari and nearly locked it up! It is normal that your left foot will be 'heavy' but practice sorts this out. My experience came from driving an automatic for three years - I left foot braked it all the time, partly because it reduced the shame I felt when admitting to people what I drove (I could always add, "...but it's great for left-foot braking!")
Gassing Station | General Gassing [Archive] | Top of Page | What's New | My Stuff