Gears 2 go brakes 2 slow

UK PROFESSIONAL DRIVERS FORUMS THE UK PROFESSIONAL DRIVERS FORUM (INTERACTIVE)
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Carryfast:

peterm:
I agree with what Albion said about synchro’ boxes. Double de clutching on a synchro’ box uses the synchro’s twice, so you end up with the baulk rings wearing out faster.

The simple fact is the load and stress on synchros is directly proportional to the mismatch between input and output sides of the box.Double de clutching reduces that mismatch effectively to the point of zero hence less load on the synchro and a faster lighter shift.To the point where as I’ve said a double de clutched downshift ‘could’ get a gear which a single clutched one wouldn’t.Simply because synchros aren’t as fast in synchronising any mismatch,let alone an accelerating mismatch if/when a loaded de clutched truck starts to accelerate down a decent hill.As opposed to removing that mismatch by well executed lightening fast double de clutched shift.The flaw in the double de clutched changes,supposedly causing extra wear on synchros,argument, is that it totally misses the point that the shifting into neutral part of the operation is totally seperate to the engagement of the gear part and the object of double de clutching is that it removes the problem that synchros are there to solve.IE there is no mismatch there for the synchros to deal with once nor twice anyway because that was removed while the box was in neutral and the engine speed/input shaft speed matched to the road speed/output shaft speed. :bulb:

viewtopic.php?f=5&t=24294&hilit=+double+clutch&start=90#p833327

He’s right.

Double de-clutching even on a synchro box, if done correctly, will reduce the wear on the synchros as they down’t have to work so hard to match the speeds.

Just rebuilding a T9 gearbox at the moment and I can’t see anything in it that wouldn’t mean that double de-clutching wouldn’t help - even though it is strictly unnecessary as the gearbox and synchro life is probably greater than that of the car anyway.

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Move what goalposts? Read my first post again please. As I said right from the start brakes to slow is used by car trainers and I was under the impression from what you were saying in a previous thread the same was being done for truck training.
It has now become obvious from other posters that is not the case.
You seem to be stuck in a time warp. You need to progress and realise there might be a reason for changing things 30 years later.

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Racing drivers do not slow using gears, they are flat out until the last possible moment and then hard on the brakes, then they select the gear for the corner and accelerate.

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newmercman:
Racing drivers do not slow using gears, they are flat out until the last possible moment and then hard on the brakes, then they select the gear for the corner and accelerate.

Yes but their carbon fibre brakes are almost non existent until they are hot. Whereas the truck racers need to have water cooled discs to keep the temperatures under control.

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cav551:

newmercman:
Racing drivers do not slow using gears, they are flat out until the last possible moment and then hard on the brakes, then they select the gear for the corner and accelerate.

Yes but their carbon fibre brakes are almost non existent until they are hot. Whereas the truck racers need to have water cooled discs to keep the temperatures under control.

I know they’re completely different to on highway brakes, which is to be expected as they have a different kind of job to do, their purpose is to scrub off a lot of speed in a short space of time. Lots of heat is generated, which requires different materials and extra cooling.

Which kind of proves the point about brakes to slow, gears to go. Applications that use lots of braking use different friction material and have extra cooling.

Expecting consistent performance from standard braking systems, no matter how much they’ve improved in the last few years is asking for trouble really.

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I think motor racing is more about being in the right gear at the apex with the engine spinning at the right revs for maximum acceleration away from the corner than slowing the car down with the gears. In the case of a sequential gearbox the driver hasn’t got any alternative than to drop down through however many gears on the approach. Certainly anyone who tries block changing (if even possible) into eg 2nd on the exit is going to get lapped pretty quickly. I really don’t think Lewis Hamilton is sequential downshifting on corners to slow the car down; he does that by taking his foot of the gas which immediately produces tremendous drag from the downforce and then almost simultaneously using the brakes. His use of the brakes recharges the battery for the energy recovery system.

And yes they do often overheat the brakes in motor racing at all levels.

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I agree Cav, for any situation, there is the correct gear. It is not the act of changing the gear down that you should use for braking effect, but being in the right one at the right time. Whether that is exiting a corner in a race car with maximum acceleration, or easing a truck down a steep descent so the engine is neither over revving or at risk of running away due to excessive foot brake use because it is in too high a gear and descending too fast.

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Carryfast, sequential downshifting causes weigh transfer to the front of the car, and can also cause a drive axle to lock on slippery surfaces, the same can happen in a truck. The driver is just making expedient changes so he is in the correct gear for the exit. He is just changing gear to match his speed, not to brake.

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Racing cars do not have auxiliary engine braking systems, so sequentially down shifting them is done for different reasons and in a different manner than how it would be done in a lorry.

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Janos:
I agree Cav, for any situation, there is the correct gear. It is not the act of changing the gear down that you should use for braking effect, but being in the right one at the right time. Whether that is exiting a corner in a race car with maximum acceleration, or easing a truck down a steep descent so the engine is neither over revving or at risk of running away due to excessive foot brake use because it is in too high a gear and descending too fast.

Exactly the point I was trying to make about entering roundabouts. Using the gears to slow; and slowing to use the gears (ie to be in the correct gear for any given situation) are two separate, but related issues.

Block changing is everything. Sequential changing for the sake of it is nonsense. Entering any hazard in the appropriate gear means planning ahead, block-changing if necessary and slowing in time to be in that appropriate gear - and if that means using the gears to slow down, so be it. Robert

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Geoffrey old chap, you seem to be having a case of tunnel vision.

There is no one size fits all way to reduce speed, this is true for racing and driving cars or lorries on the roads.

I’ve done plenty of track days and can heel and toe with the best of them, sometimes I would use this method to downshift and help with braking, other times it would be flat to the boards until the last minute, hard on the brakes, pick the right gear and floor it again, every corner is different.

On the road I’ve used braking only to come to a halt or slow down and I’ve slowed down using engine braking in conjunction with an exhaust brake, a compression brake and a retarder. Again, every situation is different.

I’ve come down mountains in a very low gear in a lorry with no auxiliary braking system, been down them with an exhaust brake, a compression brake and a retarder, I’ve also been down passes so steep that I’ve come down on the brakes from top to bottom as no auxiliary system would hold the lorry back.

The thing is I’ve done it every way and not just one way, this is why the gears to go, brakes to slow method is wrong, it teaches that there is one correct way to do things and there definitely isn’t, not even on the same corner, junction or mountain pass, there are far too many variables, weight, weather, traffic, the type of auxiliary or foundation brakes fitted to the vehicle and a million other things dictate which method is best at the time.

This is why both methods should be taught.

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I’m in the ‘lost the will to live’ club. :cry: :cry: