Downshifting whilst Braking
Discussion
Hello all,
Just a quick introduction from myself, have been on quite a few other enthusiast sites, a regular visitor to pistonheads and the last autosport show. Have read up and always wanted to participate in advanced driving courses and advanced police driver training, hence a few questions to improve my knowledge.
(Please forgive me if i don't know all the correct terms and definitions)
For example,
If on a pursuit and need to brake hard for the hazard such a roundabout, blind corner etc is there any harm in applying consistent pressure on the brakes, after a few seconds as speed is down matching revs and pressing down on clutch downshifting ie from 4th to 3rd and whilst braking to brush of more speed lift up clutch on the biting point ( for further brake assist)pre hazard. Then engage gear with the clutch pedal fully up as it is clear to continue on with the hazard and accelerate away out of the exit point.
Just wanted to know your views on this approach and any pro's and con's with it?
Thank you
Just a quick introduction from myself, have been on quite a few other enthusiast sites, a regular visitor to pistonheads and the last autosport show. Have read up and always wanted to participate in advanced driving courses and advanced police driver training, hence a few questions to improve my knowledge.
(Please forgive me if i don't know all the correct terms and definitions)
For example,
If on a pursuit and need to brake hard for the hazard such a roundabout, blind corner etc is there any harm in applying consistent pressure on the brakes, after a few seconds as speed is down matching revs and pressing down on clutch downshifting ie from 4th to 3rd and whilst braking to brush of more speed lift up clutch on the biting point ( for further brake assist)pre hazard. Then engage gear with the clutch pedal fully up as it is clear to continue on with the hazard and accelerate away out of the exit point.
Just wanted to know your views on this approach and any pro's and con's with it?
Thank you
Edited by GuvGTI on Tuesday 12th February 02:18
You mean heel/toe ?
Heel/toe is a perfectly valid driving technique, it is not taught on Police driving courses although it is acceptable for it to be used on them in certain circumstances. That's because it's an overlap of brakes/gears & the Police system by default discourages overlaps unless they are a pre-sold necessity on the grounds of safety.
Heel/toe is a perfectly valid driving technique, it is not taught on Police driving courses although it is acceptable for it to be used on them in certain circumstances. That's because it's an overlap of brakes/gears & the Police system by default discourages overlaps unless they are a pre-sold necessity on the grounds of safety.
Ok thanks for the quick reply,
another way or alternative to the example given would be, whilst braking not blipping the throttle during gear change, just braking hard in straight line engage clutch whilst braking, downshifting at the appropriate speed and lifting up of the clutch at a slower rate during biting point to engage (if im correct on terms) engine braking? to slow the car down faster than if to stamp on the brakes.
Just wondered if this was an ok procedure and making sense? and again any pro's or con's with this.
Thanks
another way or alternative to the example given would be, whilst braking not blipping the throttle during gear change, just braking hard in straight line engage clutch whilst braking, downshifting at the appropriate speed and lifting up of the clutch at a slower rate during biting point to engage (if im correct on terms) engine braking? to slow the car down faster than if to stamp on the brakes.
Just wondered if this was an ok procedure and making sense? and again any pro's or con's with this.
Thanks
Edited by GuvGTI on Wednesday 13th February 23:51
If I'm reading this correctly, you want to use the gears to slow you down quickly by changing to a lower gear whilst also braking but not rev matching? If so, see below. If not, just ignore 
If you don't match the revs on the downchange, you're going to ruin the clutch PDQ. If the speed/gear differential is too great and the clutch comes up quickly, you risk locking the drive wheels. Not advisable. The whole idea is to leave a big enough safety margin, just in case. If you leave braking so late that you need the engine braking and brakes to slow in time, there is no margin for error.
As Von says, H/T is one way to go, or don't overlap the gear/braking.
If you don't match the revs on the downchange, you're going to ruin the clutch PDQ. If the speed/gear differential is too great and the clutch comes up quickly, you risk locking the drive wheels. Not advisable. The whole idea is to leave a big enough safety margin, just in case. If you leave braking so late that you need the engine braking and brakes to slow in time, there is no margin for error.
As Von says, H/T is one way to go, or don't overlap the gear/braking.
GuvGTI said:
Ok thanks for the quick reply,
another way or alternative to the example given would be, whilst breaking not blipping the throttle during gear change, just braking hard in straight line engage clutch whilst braking, downshifting at the appropriate speed and lifting up of the clutch at a slower rate during biting point to engage (if im correct on terms) engine braking? to slow the car down faster than if to stamp on the brakes.
Just wondered if this was an ok procedure and making sense? and again any pro's or con's with this.
Thanks
Clearly you can "smooth out" a gear change under braking by lifting the clutch up slowly. You will still get "clutch drag" braking but it will be slower and less destabilising than simply braking hard, changing down at the same time and letting the clutch up with a bang whilst still braking.another way or alternative to the example given would be, whilst breaking not blipping the throttle during gear change, just braking hard in straight line engage clutch whilst braking, downshifting at the appropriate speed and lifting up of the clutch at a slower rate during biting point to engage (if im correct on terms) engine braking? to slow the car down faster than if to stamp on the brakes.
Just wondered if this was an ok procedure and making sense? and again any pro's or con's with this.
Thanks
On an IAM/Rospa course (which uses the Police System of Car Control as its basis) you would be taught to avoid braking whilst changing gear - as completely as possible. This
- avoids any destabilising effects of clutch-drag/engine braking
- keeps your hands on the steering wheel whilst braking allowing a fast reaction to any slipping of the wheels etc
One can compromise as VH talks about using heel and toe. This eliminates clutch-drag braking by matching engine revs with the throttle to the newly selected gear - the heel/toe bit is that the right foot brakes AND (by twisting the foot) the right foot also "blips" or presses the throttle to raise engine revs actually during the braking.
Disadvantages of this are
- you need a bit of twinkletoes practice to do it right
- you take your hand of the steering wheel whilst braking
It is notable that manufacturers of race cars and now road cars have developed computerised flappy paddle gear-changing. These systems eliminate the problems of brake/gear overlap by matching revs for you (using a computer) and you keep your hands on the steering wheel at all times. They must have done all that for a good reason, eh?
What I think you're talking about is what I'd call "clutch braking" i.e. engaging a lower gear without matching revs and then use the clutch to bring the engine speed up (and slow the car at the same time).
Depending on the car's handling characteristics and the amount of braking being applied this could have a negligible effect on the car's stability, or a catastrophic one. For example in a typical TVR it is a recipe for a quick trip backwards into the hedge. In a less powerful FWD car the consequences could be negligible.
Assuming the safety/handling implications are acceptable, the next issue is wear and tear on the car. If you are talking about small rev changes (i.e. changing down at relatively low revs) and doing this occasionally rather than every gear change, I don't think wear would be an issue. At the same time, the amount of braking that will result won't be significant. Hence, if you're doing this in situations where you expect a significant amount of engine braking it's probably not doing the clutch any great favours. It's not likely to be doing a *lot* of harm (compared to an aggressive standing start, for example) but still best avoided. Engine to go, brakes to slow. Brakes are a heck of a lot easier and cheaper to replace and have the advantage of distributing the effort amongs all wheels to maximise grip and stability.
Depending on the car's handling characteristics and the amount of braking being applied this could have a negligible effect on the car's stability, or a catastrophic one. For example in a typical TVR it is a recipe for a quick trip backwards into the hedge. In a less powerful FWD car the consequences could be negligible.
Assuming the safety/handling implications are acceptable, the next issue is wear and tear on the car. If you are talking about small rev changes (i.e. changing down at relatively low revs) and doing this occasionally rather than every gear change, I don't think wear would be an issue. At the same time, the amount of braking that will result won't be significant. Hence, if you're doing this in situations where you expect a significant amount of engine braking it's probably not doing the clutch any great favours. It's not likely to be doing a *lot* of harm (compared to an aggressive standing start, for example) but still best avoided. Engine to go, brakes to slow. Brakes are a heck of a lot easier and cheaper to replace and have the advantage of distributing the effort amongs all wheels to maximise grip and stability.
Gromit37 said:
If you don't match the revs on the downchange, you're going to ruin the clutch PDQ.
I think that is overstating the case somewhat. The majority of people overlap braking and gearchange without ruining their clutch PDQ. It might wear it at a faster rate, but it's unlikely to be a significant effect.Bert
Ive been reading roadcraft and I find brake gear overlap one of the hardest things to change in my driving style.
My grandfather helped me to lean to drive and (in FWD cars) would always rely on engine braking to slow the car. He would often drive barely using the brakes at all. I think this was standard practice when he was first driving as the brakes on his early cars (1940's and largely homemade) were pretty poor.
After learning this habbit from him and my mother I find it hard to stop doing it, even though it isnt necicary in a modern car.
I find that to impliment the system correctly im braking much earlyer than i usually would to leave time for downshifting (this is probably a good thing).
I still find it hard to be smooth as im not very good at blipping the throttle to match the revs at the moment.
Im waiting for my IAM pack to arrive, watching an observer do it will (hopefuly) make things easer.
My grandfather helped me to lean to drive and (in FWD cars) would always rely on engine braking to slow the car. He would often drive barely using the brakes at all. I think this was standard practice when he was first driving as the brakes on his early cars (1940's and largely homemade) were pretty poor.
After learning this habbit from him and my mother I find it hard to stop doing it, even though it isnt necicary in a modern car.
I find that to impliment the system correctly im braking much earlyer than i usually would to leave time for downshifting (this is probably a good thing).
I still find it hard to be smooth as im not very good at blipping the throttle to match the revs at the moment.
Im waiting for my IAM pack to arrive, watching an observer do it will (hopefuly) make things easer.
some great replies there lads from everyone and/or ladies thanks for the reassurance.
v/h thanks for the clarification.
Don thanks for the write up there was informative and clear.
Greenv8s i think youve got it as close i can describe and i much agree. The weight balance and transfer in a rwd car to a fwd would be differnt. I was referring to fwd cars. If the term is clutch brake or engine brake. Clutch brake: A device for slowing down the clutch discs (and thus the gears themselves) so that shifting is smoother and quieter. source http://www.motorera.com/dictionary/CL.HTM
It seems to work in automatics also with a manual (-) downshift whilst braking. I have noticed if brakes aren't great, the effect of downshifting whilst lifting up the clutch to the biting point slows the car down, aswell as apply frictional brake.
So to clarify, this isn't good to a degree and Heel Toe effect of blipping the throttle to match the revs aids a smoother gear change ( slows downs better or is this still down to frictional brakes?)?
The other approach is not to do this at all, to apply frictional brakes only to reduce speed to a safe speed for the hazard, and downshift seperatley?
SO to understand and generalise you guys only use the brakes to slow, so more frictional wear?
v/h thanks for the clarification.
Don thanks for the write up there was informative and clear.
Greenv8s i think youve got it as close i can describe and i much agree. The weight balance and transfer in a rwd car to a fwd would be differnt. I was referring to fwd cars. If the term is clutch brake or engine brake. Clutch brake: A device for slowing down the clutch discs (and thus the gears themselves) so that shifting is smoother and quieter. source http://www.motorera.com/dictionary/CL.HTM
It seems to work in automatics also with a manual (-) downshift whilst braking. I have noticed if brakes aren't great, the effect of downshifting whilst lifting up the clutch to the biting point slows the car down, aswell as apply frictional brake.
So to clarify, this isn't good to a degree and Heel Toe effect of blipping the throttle to match the revs aids a smoother gear change ( slows downs better or is this still down to frictional brakes?)?
The other approach is not to do this at all, to apply frictional brakes only to reduce speed to a safe speed for the hazard, and downshift seperatley?
SO to understand and generalise you guys only use the brakes to slow, so more frictional wear?
BertBert said:
Gromit37 said:
If you don't match the revs on the downchange, you're going to ruin the clutch PDQ.
I think that is overstating the case somewhat. The majority of people overlap braking and gearchange without ruining their clutch PDQ. It might wear it at a faster rate, but it's unlikely to be a significant effect.Bert
Ian
Edited by Gromit37 on Wednesday 13th February 10:04
The gearbox isn't being used for braking, it is the engine compression that is doing the braking transfered through the clutch and gearbox. The gearbox is designed to take full power acceleration in lower gears, so the strain, such as there is, when on overrun, acts in the opposite direction to the drive force and uses gearfaces that are not usually used in the application of power i.e. most of the time, but are capable of taking severe strain.
I think you guys are getting your terms confused.
Your not going to cause any wear on your gearbox by engine braking, but you will wear out the clutch faster. As your slowing the car by dragging the clutch.
Although you will save wear on your brakes.
How much extra wear is difficult to say, compared to a driver who perfectly rev matches every change I would expect it to be significantly worse.
If your rev matching every change then I would expect a clutch to last a very long time, as your only going to slip the clutch starting from a standing start.
Do you IAM guys ever have to replace your clutch?
Ive tried some heel toe braking today and Im getting better at doing it in my Prelude, but the peugeot diesel van I drive for work is useless as I have to press the pedal a long way to get the revs up.
Your not going to cause any wear on your gearbox by engine braking, but you will wear out the clutch faster. As your slowing the car by dragging the clutch.
Although you will save wear on your brakes.
How much extra wear is difficult to say, compared to a driver who perfectly rev matches every change I would expect it to be significantly worse.
If your rev matching every change then I would expect a clutch to last a very long time, as your only going to slip the clutch starting from a standing start.
Do you IAM guys ever have to replace your clutch?
Ive tried some heel toe braking today and Im getting better at doing it in my Prelude, but the peugeot diesel van I drive for work is useless as I have to press the pedal a long way to get the revs up.
Edited by Holst on Wednesday 13th February 16:42
Gromit37 said:
Sorry, but I disagree. Surely the amount of wear depends on the differential between the two clutch plates and how regularly it is done? Using the gearbox for *braking*, as the OP implied will wear out a gearbox far more quickly than using it correctly. Unless you know how to bend the laws of physics?
Ian
It'll wear out more quickly I'm sure, but that isn't the same as "ruining it PDQ". I think that many (most) people drag the clutch on downshifts because they don't know any better...and modern clutches seem to cope ok.Ian
Mind you, it puts my teeth on edge when people do it.
Holst said:
Do you IAM guys ever have to replace your clutch?
Out of interest I have never needed to change a clutch in any of my cars. The Vectra (which I share with my Mrs) looks like it will need a new one at about 80,000 miles. My mate who has one still has it on the original clutch at 170,000. My Mrs wore out the clutch in her Chimaera in 50,000 miles. To be fair - clutches go in TVRs as some of 'em clearly weren't up to the job. Part of it is her driving style - she clutch rides at junctions despite years of me nagging her not to.Interestingly neither of my Boxsters have needed a new clutch - despite the time when the Box and the Tamora were compared by Fifth Gear/Driven/Some show or other the clutches on both their Boxsters gave way. Again - to be fair my current car has only done 26,000 miles so it jolly well shouldn't need a new clutch! In that time, mind, its had two sets of discs and pads.
Track days do tend to wear 'em out...well I was a habitual overlapper until about 7 years ago and I have never worn out a clutch in my 27 years of driving. Unless you are being seriously abusive on the down change, you won't get noticable extra wear. The majority of the engine braking is done by the engine with the clutch engaged. The drivetrain of a normal production car is built to take pretty high stress levels. Sidestep the clutch from a standing start in 1st with your foot full on the gas in your scooby-do. That'll ruin the clutch PDQ!
I find the mechanical sympathy argument argument of Advanced Driving to be pretty weak in terms of the benefits of AD. Safety is the overwhelmingly beneficial outcome. Any arguments of less-wear are secondary.
Bert
PS whilst I am in the mood, doesn't anyone else find the dogma "gears are for going, brakes are for slowing" an insult to the intelligence? The fact that it's a rhyming couplet doesn't make it a winning argument based on a strong and well argued proposition for me My version is "gears used in conjunction with raising the engine revs are for going, brakes are for slowing apart from all the circumstances where using the engine is more appropriate"!
I find the mechanical sympathy argument argument of Advanced Driving to be pretty weak in terms of the benefits of AD. Safety is the overwhelmingly beneficial outcome. Any arguments of less-wear are secondary.
Bert
PS whilst I am in the mood, doesn't anyone else find the dogma "gears are for going, brakes are for slowing" an insult to the intelligence? The fact that it's a rhyming couplet doesn't make it a winning argument based on a strong and well argued proposition for me
My version is "gears used in conjunction with raising the engine revs are for going, brakes are for slowing apart from all the circumstances where using the engine is more appropriate"!BertBert said:
brakes are for slowing apart from all the circumstances where using the engine is more appropriate"!
Some of those circumstances are? I am not sure whether you are disagreeing with the general approach for road driving of slowing to an appropriate speed before changing gear, or only with trying to describe this approach using a simplistic form of words.BertBert said:
well I was a habitual overlapper until about 7 years ago and I have never worn out a clutch in my 27 years of driving. Unless you are being seriously abusive on the down change, you won't get noticable extra wear. The majority of the engine braking is done by the engine with the clutch engaged. The drivetrain of a normal production car is built to take pretty high stress levels. Sidestep the clutch from a standing start in 1st with your foot full on the gas in your scooby-do. That'll ruin the clutch PDQ!
I find the mechanical sympathy argument argument of Advanced Driving to be pretty weak in terms of the benefits of AD. Safety is the overwhelmingly beneficial outcome. Any arguments of less-wear are secondary.
Bert
PS whilst I am in the mood, doesn't anyone else find the dogma "gears are for going, brakes are for slowing" an insult to the intelligence? The fact that it's a rhyming couplet doesn't make it a winning argument based on a strong and well argued proposition for me My version is "gears used in conjunction with raising the engine revs are for going, brakes are for slowing apart from all the circumstances where using the engine is more appropriate"!
I agree with you. I'm not overly keen on this 'gears to go, brakes to slow' business if anybody's going to get too dogmatic about it. It's a fair approach in general terms, especially with the braking systems on modern cars, but I don't think it would be sensible to get too fixated with it.I find the mechanical sympathy argument argument of Advanced Driving to be pretty weak in terms of the benefits of AD. Safety is the overwhelmingly beneficial outcome. Any arguments of less-wear are secondary.
Bert
PS whilst I am in the mood, doesn't anyone else find the dogma "gears are for going, brakes are for slowing" an insult to the intelligence? The fact that it's a rhyming couplet doesn't make it a winning argument based on a strong and well argued proposition for me
My version is "gears used in conjunction with raising the engine revs are for going, brakes are for slowing apart from all the circumstances where using the engine is more appropriate"!One thing that did surprise me (and I must say I was a bit shocked at the time) was to hear that HGV drivers are now taught to use only the brakes when descending hills. Living in a part of the country that has its full share of steep hills, one of which has a history of runaway HGV accidents, I feels that's a most unwise technique to advocate, and I hope that is not actually what is being taught.
Best wishes all,
Dave.
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