Changing down without going through the gears
Discussion
In the instruction session on a recent trackday, the instructor *really* didn't like my using roadcraft-y corner approach - take the right line, brake to appropriate speed, select correct gear, turn in, etc.
He was insistent that shifting down through the gearbox during a braking phase was better. He wasn't really able to articulate why though. He asked "on a track do you change UP from second to fifth? You don't - so why change down that way?". My response had there actually been a pause to give one would have been that if there was ever a point when I'd reached the maximum speed I wanted to get from the car, I suppose I might - but that's unlikely on circuit. Bleeding off all the speed you want to from the car happens more often though.
He did make the much more persuasive point (if true) that pro race drivers shift down through the box using the gearbox and transmission as part of braking the car. He didn't think this would make the braking less controlled when I asked. Clearly, a race car doesn't have the same mechanical car consideration issues that a road car does, and if shifting directly from 5th to 2nd was viable on circuit, every race driver wouldn't do it differently...
But what's the advantage? The car's brakes are more than able to lock the wheels, so how does using the engine and transmission to slow the car suddenly (presumably these race drivers aren't rev matching on these gearchanges?) help with entry to a corner?
Posted to both advanced driving and track days...
Cheers for your thoughts in advance,
Tol
He was insistent that shifting down through the gearbox during a braking phase was better. He wasn't really able to articulate why though. He asked "on a track do you change UP from second to fifth? You don't - so why change down that way?". My response had there actually been a pause to give one would have been that if there was ever a point when I'd reached the maximum speed I wanted to get from the car, I suppose I might - but that's unlikely on circuit. Bleeding off all the speed you want to from the car happens more often though.
He did make the much more persuasive point (if true) that pro race drivers shift down through the box using the gearbox and transmission as part of braking the car. He didn't think this would make the braking less controlled when I asked. Clearly, a race car doesn't have the same mechanical car consideration issues that a road car does, and if shifting directly from 5th to 2nd was viable on circuit, every race driver wouldn't do it differently...
But what's the advantage? The car's brakes are more than able to lock the wheels, so how does using the engine and transmission to slow the car suddenly (presumably these race drivers aren't rev matching on these gearchanges?) help with entry to a corner?
Posted to both advanced driving and track days...
Cheers for your thoughts in advance,
Tol
The only technical answer that I know is that engine braking allows you to vary the brake bias between the driven wheels (since these are the only ones engine braked) and the whole set which your pedal affects.
Not sure I've ever been good enough to notice or use the difference.
3 gear-changes = 3 chances to screw up rev matching...although each one is a smaller step so possibly easier to do.
Not sure I've ever been good enough to notice or use the difference.
3 gear-changes = 3 chances to screw up rev matching...although each one is a smaller step so possibly easier to do.
Your technique (as I understand it - change to the gear you need for the corner, without selecting every intermediate gear on the way down) was good enough for Prost, who used it with some success.
That said, changing down through the box is a recognised technique which harnesses engine braking to help you slow more quickly and improve stability under braking.
From personal experience, driving a GT3 fairly enthusiastically, I think it's enabled me to brake later in wet conditions. But I'm not sure that I'm good enough to be sure that it's effective for me, let alone to rely on it to set a later braking marker.
That said, changing down through the box is a recognised technique which harnesses engine braking to help you slow more quickly and improve stability under braking.
From personal experience, driving a GT3 fairly enthusiastically, I think it's enabled me to brake later in wet conditions. But I'm not sure that I'm good enough to be sure that it's effective for me, let alone to rely on it to set a later braking marker.
Edited by WilliBetz on Monday 11th August 11:36
youngsyr said:
Won't something like a Caterham lock the back wheels if you ram the gear lever into 2nd from 5th in a heavy braking zone and lift the clutch (assuming you haven't dropped the revs enough)?
Obviously not ideal when you're approaching the turn in point!
Bear in mind you do the braking *first*. So you slow to 20mph, then put the gearbox from 5th to 2nd - and with a traditional roadcraft approach you use the gas pedal to raise the engine revs while the clutch is engaged so that there's the minimal engine braking possible. That's certainly what I've always strived for on the road.Obviously not ideal when you're approaching the turn in point!
I thought the point for discussion was whether to change down via all the intermediate gears (eg. 5->4->3->2), or to simply select the gear required for the corner (eg. 5->2).
Whichever technique you choose, on circuit you'll be wasting time if you follow the roadcraft mantra of "speed for the hazard, then gear for the speed".
And, whichever technique you choose, selecting a gear at too high a road speed for that gear is likely to prove expensive.
Whichever technique you choose, on circuit you'll be wasting time if you follow the roadcraft mantra of "speed for the hazard, then gear for the speed".
And, whichever technique you choose, selecting a gear at too high a road speed for that gear is likely to prove expensive.
WilliBetz said:
I thought the point for discussion was whether to change down via all the intermediate gears (eg. 5->4->3->2), or to simply select the gear required for the corner (eg. 5->2).
That was the original question, spot on.I wanted to disagree with the suggestion that a 5->2 gearchange would involve locking the rear wheels as a matter of course on a lighter vehicle though.
Tol
Assuming you approach the corner at high revs in 5th gear, its a long way down to a usable rev range in 2nd. Plus the very real chance of a lock up if you incorrectly rev match when you do finally release the clutch. Which is more than likely as you`ll have lost all feel for the engine.
That means coasting in effect, which is no good either on or off track.
Most competetive cars have sequential gearboxes these days which I guess says it all.
That means coasting in effect, which is no good either on or off track.
Most competetive cars have sequential gearboxes these days which I guess says it all.
Edited by crisisjez on Monday 11th August 15:14
crisisjez said:
Assuming you approach the corner at high revs in 5th gear, its a long way down to a usable rev range in 2nd. Plus the very real chance of a lock up if you incorrectly rev match when you do finally release the clutch. Which is more than likely as you`ll have lost all feel for the engine.
That means coasting in effect, which is no good either on or off track.
Most competetive cars have sequential gearboxes these days which I guess says it all.
It is just a question of timing. I do not find it hard, nor have I ever had a problem, shifting from 5th to 2nd on the approach to, say, the tight left hander at Bedford after the back straight. As someone who has blockshifted for years on the road, I do not find it hard to judge the right time in the braking phase to take the lower gear (with H&T obviously), and to raise the revs to match - e.g. up to 8,000 rpm in my GT3, prior to re-engaging the clutch with a good rev match.That means coasting in effect, which is no good either on or off track.
Most competetive cars have sequential gearboxes these days which I guess says it all.
Edited by crisisjez on Monday 11th August 15:14
There is no "coasting" inherent in this technique - just a single change down late in the braking phase (i.e. once sufficient speed has been lost for the lower gear (selected for the upcoming corner) to be engaged).
I do accept, however, that without practice or training, there is more risk inherent in a blockshift (of engine overrev).
Like Willibetz, I believe there is a potential advantage to be gained in terms of overall stopping distance by shifting down through the box, but when on track for recreational purposes, I prefer to blockshift.
That said, when done well, as in this clip, shifting down through the box is pretty neat (if a bit busy!)
.http://www.youtube.com/watch?v=-UjnbIuJNuI
Kind regards
Steve
stefan1 said:
There is no "coasting" inherent in this technique - just a single change down late in the braking phase (i.e. once sufficient speed has been lost for the lower gear (selected for the upcoming corner) to be engaged)
One of the issues that I've been working on recently is not having this *too* late in the braking phase -- so that one is not managing the feather off the brakes at the same time as the feather off the clutch -- ie all the clutchwork is done with a firm brake pedal anchor.But then I think your point was to leave it just late enough to let the gear engage without the layshaft exploding.
As ever, Goldilocks changing is required...
Edited by 7db on Monday 11th August 15:55
crisisjez said:
Would it not then allow an old style NA engine to come `off cam` as the revs fall on entry.
I am not sure what you mean, but I think the answer is "no". Whilst braking, and staying in a higher gear prior to a block downshift, the revs will fall quite low, but since one is braking not accelerating that is not an issue (in terms of whether the engine is on cam or not).You then take, in one shift, the correct (lower) gear for the corner, and whether you sequentially shift or blockshift makes no difference to that choice.
If the gear chosen is too high then perhaps the engine will not be "on cam", in which case the answer is select a lower gear - achievable with either block or sequential shifting - it is just the last gear you take.
Kind regards
Steve
Edited by stefan1 on Monday 11th August 16:44
Edited by stefan1 on Monday 11th August 16:44
youngsyr said:
Won't something like a Caterham lock the back wheels if you ram the gear lever into 2nd from 5th in a heavy braking zone and lift the clutch (assuming you haven't dropped the revs enough)?
Obviously not ideal when you're approaching the turn in point!
Obviously not ideal when you're approaching the turn in point!
If you're on or near the threshold of braking then not heel and toeing will lock the rear wheels immediately on any rear wheel drive car (and front drivers if you're especially violent or it's wet). Caterhams, being particularly light, would probably suffer the worst though, yes. I race a Caterham, but I have to say never tried it, and I don't want to!! 
I can start by saying that both changing down sequentially and block downchanging are used on track by racing drivers across the board (listen to videos of Senna entering hairpins in the stick shift days to hear block downchanges). Changing down sequentially is much more often used though because it results in smaller blips of the throttle, which are easier to get right. At the end of the braking zone you're thinking about the turn in and who's around you, so this is the last place you want to be concentrating on blipping the throttle - better to do it instinctively and subconciously on the way down through each gear. The argument for block selecting a gear at the end of braking is that you can concentrate on threshold braking without your right foot constantly twisting. Dave Minter (ex chief Lotus chassis engineer who also instructs at Hethel) once told me that he ran an exercise where he got people to try braking whilst changing down and then just braking without gearchanges, and they were able to brake much more effectively when they weren't changing down as they went, ergo he advocates block changing. Clearly there's advantages and disadvantages to both methods, so it's up to the individual to make the decision. It also depends on how quickly your car decelerates, and the situation you're in.
One other point: The roadcraft method of selecting the gear once the braking's done doesn't apply to track driving because a) it lengthens your braking zone considerably b) the car's totally unbalanced for the corner because it's rising back off its springs when you turn in (don't forget you've just braked much harder than you ever would on the road). The correct approach is to nurse the car into the corner as you come off the brakes, in a smooth blended fashion so as to neutralise the car's balance.
If you know anyone with the ARDS "Go Racing" video, then Steve Deeks of Silverstone Racing school demonstrates all of these techniques beautifully and simply in about five minutes.
One other point: The roadcraft method of selecting the gear once the braking's done doesn't apply to track driving because a) it lengthens your braking zone considerably b) the car's totally unbalanced for the corner because it's rising back off its springs when you turn in (don't forget you've just braked much harder than you ever would on the road). The correct approach is to nurse the car into the corner as you come off the brakes, in a smooth blended fashion so as to neutralise the car's balance.
If you know anyone with the ARDS "Go Racing" video, then Steve Deeks of Silverstone Racing school demonstrates all of these techniques beautifully and simply in about five minutes.
RobM77 said:
One other point: The roadcraft method of selecting the gear once the braking's done...
Agreed - although roadcraft isn't rigid about this. A common phrase during roadcraft commentary drives is: "I'm going to overlap brake and gearchange because..." (usually because there's close-following traffic, and despite an indication, if your brake lights go off, it can confuse them into thinking you're no longer about to turn off, prompting a rear-quarter shunt when you do actually turn).Tol
Edited by Anatol on Tuesday 12th August 08:02
RobM77 said:
One other point: The roadcraft method of selecting the gear once the braking's done doesn't apply to track driving because a) it lengthens your braking zone considerably b) the car's totally unbalanced for the corner because it's rising back off its springs when you turn in (don't forget you've just braked much harder than you ever would on the road). The correct approach is to nurse the car into the corner as you come off the brakes, in a smooth blended fashion so as to neutralise the car's balance.
The roadcraft method doesn't result in a longer braking zone, it results in firmer braking than would be normal on road & a braking zone that starts & ends further from the hazard. The car isn't totally unbalanced because it's not rising on the springs at turn in, you've finished the braking at such a distance from the hazard that it's returned to a neutral position on a slight throttle at turn in. It's not the fastest method, but they don't care about that, it just makes it easier for a greater number of people because it is less dependent on great judgment of entry speed & blending several tasks well. In short it's more forgiving. Edited by vonhosen on Tuesday 12th August 09:22
Anatol said:
RobM77 said:
One other point: The roadcraft method of selecting the gear once the braking's done...
Agreed - although roadcraft isn't rigid about this. A common phrase during roadcraft commentary drives is: "I'm going to overlap brake and gearchange because..." (usually because there's close-following traffic, and despite an indication, if your brake lights go off, it can confuse them into thinking you're no longer about to turn off, prompting a rear-quarter shunt when you do actually turn).Tol
vonhosen said:
RobM77 said:
One other point: The roadcraft method of selecting the gear once the braking's done doesn't apply to track driving because a) it lengthens your braking zone considerably b) the car's totally unbalanced for the corner because it's rising back off its springs when you turn in (don't forget you've just braked much harder than you ever would on the road). The correct approach is to nurse the car into the corner as you come off the brakes, in a smooth blended fashion so as to neutralise the car's balance.
The roadcraft method doesn't result in a longer braking zone, it results in firmer braking than would be normal on road. The car isn't totally unbalanced because it's not rising on the springs at turn in, you've finished the braking at such a distance from the hazard that it's returned to a neutral position on a slight throttle at turn in. It's not the fastest method, but they don't care about that, it just makes it easier for a greater number of people because it is less dependent on great judgment of entry speed & blending several tasks well. In short it's more forgiving. 
However, my point was that when track driving you're always threshold braking, so if you have to add a period of time between the end of braking and your turn in, then your braking point must be moved back accordingly because you can't brake any harder. This would shave maybe as much as a second per corner off your lap time. Even the little Brands Indy circuit has four corners that you brake for ... I'm not even sure you'd qualify, even if you were an ace through the bends. In racing you're after tenths - losing whole seconds would be utterly disastrous!My second point was that when you're on the limit, you can't turn into a bend in this manner. Most cars, even racing cars, have a final handling state of understeer, but because this is reached normally only in flat out bends a balance is easy to achieve at this very high speed (well over 100mph) through subtle weight transfer management on the throttle. In a slower bend that you've braked for you have to blend braking into steering to balance the car, otherwise you'd be ploughing through with terminal understeer.
Back to the road for a second though - what you're saying basically is that if you can't won't or don't heel and toe you end up braking earlier and harder to allow for this period where you change gear? Personally, I'd rather brake more gently to keep the car further from the limit. It also allows my foot to be over the brake prior to the hazard or corner. If you're actualy slowing for roadworks or some other hazard, I'd say that covering the brake as much as possible is a priority, especially when you're close to the hazard. I'm really not sure I understand the IAM's motives for not using heel and toe at all
Edited by RobM77 on Tuesday 12th August 09:35
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