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
Anatol said:
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.
This bit is key in my opinion. There are pros and cons to block shifting, and their relative importance varies between cars, between drivers and even from corner to corner. It seems to me that your instructor was just trying to get you to copy the technique that he found most comfortable and didn't really understand why it worked or whether it would always be most appropriate technique.He was insistent that shifting down through the gearbox during a braking phase was better. He wasn't really able to articulate why though.
Edited by GreenV8S on Saturday 9th August 13:07
Racing drivers use engine braking to help slow the car. Brake bias is invariably in favour of the front and it's the front that locks first. ( if the brake bias favours the rear and the rear locks first the car is very unstable under braking). Changing down as early as possible keeps the revs up and increases engine braking which in a rear wheel drive car shifts some of the brake bias to the rear without decreasing the braking force to the front thus increasing overall braking force. It's marginal though but in racing 1/100s of seconds count. You'll need to heel and toe since sudden increas in rear braking by a sudden increase in engine braking ( sometimes enough to lock the rear wheels) by having mismatched engine and wheel speeds will cause instability.
Edited by tony.t on Saturday 9th August 13:02
GreenV8S said:
Anatol said:
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.
This bit is key in my opinion.He was insistent that shifting down through the gearbox during a braking phase was better. He wasn't really able to articulate why though.
tony.t said:
Racing drivers use engine braking to help slow the car. ................................... Changing down as early as possible keeps the revs up and increases engine braking
A racing driver I know has his idle speed set to about 3000rpm in order to prevent too much engine braking effect just in case he gets a down change or a heal & toe wrong.Edited by tony.t on Saturday 9th August 13:02
Elderly said:
tony.t said:
Racing drivers use engine braking to help slow the car. ................................... Changing down as early as possible keeps the revs up and increases engine braking
A racing driver I know has his idle speed set to about 3000rpm in order to prevent too much engine braking effect just in case he gets a down change or a heal & toe wrong.Edited by tony.t on Saturday 9th August 13:02
elderly - is this driver at the sharp end of the pack??
Maybe it wasn't your use of roadcraft that the instructor disliked but your appropriate speed for the corner? The appropriate corner entry speed is going to be higher on a racetrack because you have more road width (track) to work with. By changing down earlier (than you would on the road) you have more time to set up for the corner which allows you achieve a higher speed through it. My guess is he thought you were losing too much speed going into the corner.
I received almost the same piece advice from a track instructor. My down changes at the end of the braking zone were conflicting with the turn-in point. Anything less than a perfect downshift and I'd missed the turn-in and consequently messed up the corner. Even with a perfect downshift ny turn-in was 'snatchy' and the revs were often too low resulting in very poor corner speed. By following instructions to shift down a fraction earlier (I doubt if it's more than a second earlier in reality) my cornering technique was transformed because I was now concentrating on the corner and not the forthcoming downshift. It meant that I could now concentrate on coming off the brakes smoothly and turning in smoothly. And by having higher revs through the corner meant I had the power available to feed in at the apex. The result is that I can now corner faster with a car that is a lot more balanced.
I received almost the same piece advice from a track instructor. My down changes at the end of the braking zone were conflicting with the turn-in point. Anything less than a perfect downshift and I'd missed the turn-in and consequently messed up the corner. Even with a perfect downshift ny turn-in was 'snatchy' and the revs were often too low resulting in very poor corner speed. By following instructions to shift down a fraction earlier (I doubt if it's more than a second earlier in reality) my cornering technique was transformed because I was now concentrating on the corner and not the forthcoming downshift. It meant that I could now concentrate on coming off the brakes smoothly and turning in smoothly. And by having higher revs through the corner meant I had the power available to feed in at the apex. The result is that I can now corner faster with a car that is a lot more balanced.
By seperating the downchanges from the braking, it means you have to brake earlier because there needs to be a gap, after you've finshed braking and before you turn in for the corner to allow you to change gear and so consequently will be slower over the whole lap. By changing down whilst braking, your already in the correct gear for the corner and can turn in straight away as soon as the car is at the right speed. Also, if you tried to seperate the braking and down changes and your trail braking into the corner after the turn in point, you'll have no time for the down changes, being stuck trying to do them somewhere mid corner when you should be back on the power.
It doesnt make the car stop any faster (as in reduce the distance needed to bring about the same decrease in speed), because your already trying to stop the car as quickly as possible by using the brakes to keep the wheels just on the threshold of locking up. Only if the brakes were not able to make the wheels lock no matter how hard you jumped on the brake pedal, for example if you had much more grip than braking power, would the effect of engine braking stop the car faster. Rev matching on the down changes by heel and toeing prevents the wheels form locking which you have to do using both methods, either block changing or going down through the gears.
Choice between the two is just a matter of preference. Some people feel that changing down through the gears keeps the car more stable. In one of his books Alain Prost says that he blocked changed in the dry and changed down through the gears in the wet beacuse he felt the car was more stable that way.
It doesnt make the car stop any faster (as in reduce the distance needed to bring about the same decrease in speed), because your already trying to stop the car as quickly as possible by using the brakes to keep the wheels just on the threshold of locking up. Only if the brakes were not able to make the wheels lock no matter how hard you jumped on the brake pedal, for example if you had much more grip than braking power, would the effect of engine braking stop the car faster. Rev matching on the down changes by heel and toeing prevents the wheels form locking which you have to do using both methods, either block changing or going down through the gears.
Choice between the two is just a matter of preference. Some people feel that changing down through the gears keeps the car more stable. In one of his books Alain Prost says that he blocked changed in the dry and changed down through the gears in the wet beacuse he felt the car was more stable that way.
If you are driving a rear wheel drive with high torque, it can be very easy when all the weight is shifted to the front under braking to lock the rear wheels when changing down several gears and getting the timing just slightly wrong, this will put you in an instant spin, by changing down through the gears the effect is reduced but can still happen.
Edited by AC Motors on Monday 11th August 15:06
weight transfer has a lot to do with it.
If you are smooth going down through the box, using H&T for example, there is no *extra* weight transfer happening, as the inertia of the engine doesn't have to be overcome.
Crucially, you are ready to get on the gas to balance the car in a crucial part of the corner (i.e. turn in to apex) w/o upsetting the weight transfer, and/or waiting for the engine to speed up to the correct speed.
Going into the bend on the limit of adhesion on a slick normally means as soon as you have turned in, the weight transfer must be very gradual to avoid overcoming the grip on either end of the car.
If you are smooth going down through the box, using H&T for example, there is no *extra* weight transfer happening, as the inertia of the engine doesn't have to be overcome.
Crucially, you are ready to get on the gas to balance the car in a crucial part of the corner (i.e. turn in to apex) w/o upsetting the weight transfer, and/or waiting for the engine to speed up to the correct speed.
Going into the bend on the limit of adhesion on a slick normally means as soon as you have turned in, the weight transfer must be very gradual to avoid overcoming the grip on either end of the car.
All interesting stuff...
There was an article in Track & Race Cars recently by Roberto Giordanelli in which he was adamant that block changing is the best approach on the basis that the brakes are there to slow the car down and the engine is there to speed it up. His opinion was also that just one heel & toe down-change per corner leaves less room for error.
I had exactly the same experience as the OP about 5 years ago & since then have always been a change-down-through-the-gears but I might give block changing a go next time I'm out on track...
There was an article in Track & Race Cars recently by Roberto Giordanelli in which he was adamant that block changing is the best approach on the basis that the brakes are there to slow the car down and the engine is there to speed it up. His opinion was also that just one heel & toe down-change per corner leaves less room for error.
I had exactly the same experience as the OP about 5 years ago & since then have always been a change-down-through-the-gears but I might give block changing a go next time I'm out on track...
I block change on track and on rallies, not all the time depends on the corner, tickover speed is raised to 1200, H/T on track /tarmac always, sometimes H/T on gravel but not always.
Don't believe there is a right answer and all these sequential boxes make it a mute point for pro racers.
Cannot understand why the instructor was so adamant, block changing has been a preference for ages as it allows absolutely massive late braking without messing it up with gear changes, then you can quickly select the right gear turn in under brakes and gas it, all fluid motions.
going from 5th to 2nd which is the biggest change i come across would be a pain if i went through all the other gears, however someone mentioned that if the brakes are marginal then you may do it to help them out - no problem for me its the tyres that give up first.
Don't believe there is a right answer and all these sequential boxes make it a mute point for pro racers.
Cannot understand why the instructor was so adamant, block changing has been a preference for ages as it allows absolutely massive late braking without messing it up with gear changes, then you can quickly select the right gear turn in under brakes and gas it, all fluid motions.
going from 5th to 2nd which is the biggest change i come across would be a pain if i went through all the other gears, however someone mentioned that if the brakes are marginal then you may do it to help them out - no problem for me its the tyres that give up first.
Pork_n_Beem said:
going from 5th to 2nd which is the biggest change i come across would be a pain if i went through all the other gears
The other school of thought is that it's safer to make several small mistakes rather than one big one i.e. if the heel-n-toe isn't done perfectly disrupting the balance of the car. Personally I don't always do it one way or the other, it depends how busy I am and whether I want more or less engine braking at the time.
t.Did you have a chap walking in front with a red flag whilst separating your braking and shifting phases?
Block shift vs non block shift depends on car, driver, corner etc. Do what makes you quickest most consistently. Down-shifting outside of the braking phase is disastrous on track (and I can't see any argument to do it on the road either). Presumably you are just coasting as you shift? If so how are you managing the balance of the car into the corner, which is just about the most crucial thing and can't be done if coasting. By coming off the brakes early to shift you are unloading the front of the car hampering turn in and corner entry speed.
Block shift vs non block shift depends on car, driver, corner etc. Do what makes you quickest most consistently. Down-shifting outside of the braking phase is disastrous on track (and I can't see any argument to do it on the road either). Presumably you are just coasting as you shift? If so how are you managing the balance of the car into the corner, which is just about the most crucial thing and can't be done if coasting. By coming off the brakes early to shift you are unloading the front of the car hampering turn in and corner entry speed.
interesting read! although i got taught to block shift, i have never done so- i always go down through the gears as i feel able to not only balance the car more easily, but also be in full control should i need to make an evasive manouvre
one of the more amusing things ive ever seen is people block changing (or indeed changing down through the gears) whilst all the time having the clutch depressed...(i kid you not)
anyway, i digress...
one of the more amusing things ive ever seen is people block changing (or indeed changing down through the gears) whilst all the time having the clutch depressed...(i kid you not)
anyway, i digress...
brakes are for braking, gears are for going. Engine braking is a bad thing and most race drivers heel and toe all down shifts through the box to prevent you from locking the rear wheels whist the weight of the car is transfered to the front. This is how i would imagine 99.9% of decent race drivers do it, myself included.
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