how effective is it??

[MrKipling43]

^^ yeah, I know what you mean. If I'm not 'pressing-on' I tend to be more gentle. Having said that, I find it easier (and smoother) to make the shift quickly.

[willibetz]

MrKipling43 said:

One thing I've found is that in order to get a heel-toe downshift smooth, you have to be quite aggresive with the clutch - if you're too slow the revs drop too far and it messes the whole thing up. It's quite an odd technique in that respect.

Don't really understand that. There's no need or advantage to rushing a heel-and-toe gearchange, and no reason (in my experience) to be hard on the clutch when taking the change. You can even combine the technique with double declutching.

[MrKipling43]

That's the point of heel-toe, though. You can be as quick as you want to be without being hard on the clutch if you match the revs correctly.

[willibetz]

Sorry - I still don't understand.

The point of a heel-and-toe change is to enable a lower gear to be taken while braking, while placing no undue stress on the gearbox / drive train.

The speed of the gearchange is limited by the synchros, but there's typically no reason to rush the gearchange anyway (unless, I suppose, you've a car where the braking distance is so short that it restricts the time available for the gearchange or changes required - not something I've experienced!)

[MrKipling43]

willibetz said:

Sorry - I still don't understand.

The point of a heel-and-toe change is to enable a lower gear to be taken while braking, while placing no undue stress on the gearbox / drive train.

The speed of the gearchange is limited by the synchros, but there's typically no reason to rush the gearchange anyway (unless, I suppose, you've a car where the braking distance is so short that it restricts the time available for the gearchange or changes required - not something I've experienced!)

If you match the engine speed correctly the 'box doesn't need the synchro rings - in a car with ratios that are short like mine (low powered, low capacity supermini) - you have to shift quickly to get through the gears.

[willibetz]

MrKipling43 said:

If you match the engine speed correctly the 'box doesn't need the synchro rings - in a car with ratios that are short like mine (low powered, low capacity supermini) - you have to shift quickly to get through the gears.

If you match the engine speed correctly, you don't need the clutch either. More normally, the minimum time for any sympathetic gearchange is constrained by the time taken for the synchros to do their bit. I have to confess that I don't know whether that time varies significantly - does it take significantly longer for the synchro to work if the driver has made a poor job of synchronising the speeds?

In a car that I presume has the engine and gearbox at the front, do you perceive any advantage in going down through the gears as opposed to block changing?

[gridgway]

willibetz said:

Sorry - I still don't understand.

The point of a heel-and-toe change is to enable a lower gear to be taken while braking, while placing no undue stress on the gearbox / drive train.

That's the mechanical sympathy point, but the safety point is to keep the braking force being determined by the brake pedal pressure alone, not "engine braking". Well actually that's the point of raising the revs. It can of course be done in the usual non-ovelapping sense without any heel n toeing.

The (lack of) synchro thing requires dd-clutching. In fact dd-clutching with a blip doesnt do a good job of raising the revs to match to road speed. The blip tends to come too early as it has to be there to get through the gate into gear.

I did a lot of my early driving on a car with poor synchros (BMW 2002 - ace car!) so did a lot of dd-clutching by habit. When I came to track driving (in a caterham), I noticed being out with other drivers that their rev matching was much better than mine. That's because they did the blip (not dd-clutching, just H&T) later which I had to re-learn.

Graham

[willibetz]

gridgway said:

willibetz said:

Sorry - I still don't understand.

The point of a heel-and-toe change is to enable a lower gear to be taken while braking, while placing no undue stress on the gearbox / drive train.

That's the mechanical sympathy point, but the safety point is to keep the braking force being determined by the brake pedal pressure alone, not "engine braking". Well actually that's the point of raising the revs. It can of course be done in the usual non-ovelapping sense without any heel n toeing.

Graham

Graham,

I agree that the linked causes of mechanical sympathy and safety are both served by well executed h&t downchanges. However, in some cases it can be beneficial to make use of intermediate gears (and therefore engine braking) when downchanging. For instance, driving a Porsche sportscar, the technique can provide more effective braking of the rear wheels. Other cars won't benefit in the same way, and I don't expect the approach to be useful for FWD superminis or road applications.

But I'm still surprised by the perceived necessity to rush the downchange. My track experience is that there's sufficient time to enjoy a sustained rev ddc combined with h&t. Some may prefer to reduce the time braking with one hand free of the wheel, but I can't remember driving a car so lacking in stability under brakes that I couldn't take the time to change gear in an unhurried manner.

WilliBetz

[boxsey]

Reading this thread has prompted a few thoughts for me . While I was aware that during road driving; brake, clutch down, change gear, blip, clutch up is good practice for keeping the car stable, many of you appear to be suggesting that it is good advice for extending the life of the clutch?

If so, has anyone got an idea of what is going on with an auto box? I mean, in an auto you brake and the gears change at the same time and there's no throttle blip under normal driving . Therefore, the auto is breaking all the rules! Is it because the Torque converter is much more robust than a clutch because it's almost friction-less, so engine to road speed is less of an issue? But surely it's still breaking the rule that you shouldn't brake and change gear at the same time which could unsettle the car?

While anyone's thinking about this I should say that mine's a tiptronic which I tend to drive in its manual mode most of the time. This allows me to throttle blip on down changes (needs a bit of nifty timing to get it right). And although I'm not 100% certain, it appears to raise the revs itself under heavy braking when I take it on a track.

[gridgway]

willibetz said:

But I'm still surprised by the perceived necessity to rush the downchange.
WilliBetz

WillBetz, I agree entirely about there being no rush per se. However, there is a timing constraint to make H&T easier. Doing a H&T gearchange with a rythm is necessary as its very hard to be varying brake pedal pressure as well as timing the raise in revs and take a long time over it.

It's easiest to do when you have a firm brake pedal, when you are not varying the brake pressure and by a single blip in that period. So you effectively have to time going through gate with the gearlever, doing a single blip and raising the clutch at a point of constant braking. That's all best done in a snappy (not necc rushed) fashion.

However, if one is doing proper Advanced Driving you will still be rev matching, but effectively you have a good deal of time after braking to dip the clutch, select the gear, raise the engine revs and release the clutch. The time constraint here is to make sure you are not coasting with the clutch dipped and the gearchange not completed.

Graham

[waremark]

boxsey said:

If so, has anyone got an idea of what is going on with an auto box? I mean, in an auto you brake and the gears change at the same time and there's no throttle blip under normal driving . Therefore, the auto is breaking all the rules! Is it because the Torque converter is much more robust than a clutch because it's almost friction-less, so engine to road speed is less of an issue? But surely it's still breaking the rule that you shouldn't brake and change gear at the same time which could unsettle the car?

I think that because the torque converter uses a fluid connection rather than a mechanical one to connect the engine to the drive, no wear is caused by failing to match engine to road speed.

So far as blipping is concerned, I don't know what your gearbox does. The latest ZF's such as the six speed in the DB9 apparently blip the throttle on downchanges, but this is still a rare feature. I agree that it is good practise to try to blip the throttle 'manually' for the smoothest downchange even in an auto, but I do not find that I can get the timing right reliably enough to make this worth doing, and I really cannot make it work at all when changing down under braking.

I often downchange in an auto under braking and I cannot remember it ever causing lockup, although that is theoretically possible. You would not normally downchange at particularly high revs as you would not achieve much engine braking anyway, and would just want to have a suitable gear engaged before arriving at the next hazard.

[boxsey]

waremark said:

So far as blipping is concerned, I don't know what your gearbox does. The latest ZF's such as the six speed in the DB9 apparently blip the throttle on downchanges, but this is still a rare feature. I agree that it is good practise to try to blip the throttle 'manually' for the smoothest downchange even in an auto, but I do not find that I can get the timing right reliably enough to make this worth doing, and I really cannot make it work at all when changing down under braking.

I often downchange in an auto under braking and I cannot remember it ever causing lockup, although that is theoretically possible. You would not normally downchange at particularly high revs as you would not achieve much engine braking anyway, and would just want to have a suitable gear engaged before arriving at the next hazard.

By pure coincedence, I can now clarify the point about automatic throttle blipping. An extensive article in last month's Porsche Post on the Sportmatic and Tiptronic gear boxes (I read last night) informs that this has only just been introduced on the 997 turbo. Therefore we with older tiptronics have to blip the throttle ourselves when driving in tip mode. The same article also informs that tip down changes can appear to be 'laggy' because the ECU will wait for the revs to be suitable for the down shift. Personally I find this lag can be perceptably reduced by throttle blipping as I push the button.

I too find that throttle blipping and hard braking at the same time is very difficult with a tip box so I just downshift as I brake (the downshifts being done when I sense they are appropriate for the road speed). However, I am reliably informed that you can use throttle blipping with heel and toe just like you would in a manual car. The same article also mentions that Walter Rohrl advocates the use of left foot braking and throttle blipping with a tiptronic. But we're not all up to his standard!

[skinny]

rev matching is good for the clutch, double de-clutch with rev match is good for the clutch and synchros.

in reality, the difference in actual wear is probably very little but it's still quite satisfying

i'm not sure i'd necessarily advise starting off trying to do either tho as when you're a new driver, there are probably other things you should be thinking about... i mean, not doing them is hardly bad practise is it, and it's easy enough to pick up later when you have the experience to think about what you're doing a little more

Edited by skinny on Wednesday 13th December 16:57