0000000000
Quote:
Originally Posted by mantis
Rev-Matching technique: Double Clutching
Correct me if I'm wrong, which probably am.
When you downshift to gain more power your engine will be spinning at a higher speed (higher RPM). Synchronizers will be spinning harder to to synch the speeds. It is a good practice rev-match.
Rev-matching is manually bringing up the RPM before engaging the lower gear you are shifting into. So when you ditch your clutch, your synchros will not have much to do, and they wont wear out.
This is how it is executed: (let's say you are going on 5th gear cruising at 50 mph, and you want to pass someone, so you want to go to 3rd gear)
1. Depress clutch
2. put gear in neutral
3. Undepress the clutch
4. blip your gas to bump it up 1500-2500 RPM's more (Do not take the #'s literally here, i dont know im just guessing, but you'll get that down by practice/experience)
5. Depress clutch again
6. put shifter in 3rd gear
7. Undepress the clutch
The beauty of this technique is it has to be done in less than 1 second (sure with experience and practice)
This is an exercise to get your foot used to the concept if you have never done it. This is basically a short version of it for practice, to get you to the real double-clutching
1. Depress clutch
2. put gear in neutral
3. blip gas
4. engage 3rd gear
5. undepress the clutch
(note: the 5 steps i just listed are not enough, they do not synchronize tranny's internal parts spinning speed - you need to blip gas while clutch is undepressed to synch the speed of flywheel *i think*)
practice that ^^ a few times when in open road, and when safe. Then double clutching will be real easy.
|
First let me express my initial amazement at this thread.
I'd seen another thread where someone mentioned someone who put the car in neutral when going round bends and I postulated that this individual was in the running for a Darwin award.
Then I thought about it a bit and reckoned that the lack of knowledge on how to use a manual transmission might be due to what I understand to be the case that on your side of the pond automatic transmissions are the norm so many of you learn to drive using an auto box. So I'm not here to heap abuse and or ridicule on anyone.
So, the first method of downshifting you describe where the gearbox is moved into neutral and the clutch is reengaged, is what is known as double declutching - you attribute this to the second method.
You do not need to double declutch with a full synchromesh gearbox at all. This technique was used before synchro gearboxes were invented and I see no benefit in practicing it unless you need to drive a Heavy Goods Vehicle.
If you want to downshift use the second method i.e.
1 Clutch down i.e. disengaging the engine from the gearbox
2. Shift gear using a blip of the throttle to match the revs required for the same speed in a lower gear. You do not need to put the gear in neutral - just move it straight through neutral into the desired gear
3. Clutch up i.e. reengaging the engine and the gearbox.
Blipping the throttle is not necessary with a synchro gearbox but is good practice since as you have noted it means that when you reengage the clutch the engine is spinning at the same or a similar speed to the gearbox. This means that as the clutch is reengaged you don't have put a sudden load on either component, thus saving unnecessary wear on both the engine and gearbox. The basic idea is be smooth.
Other points.
Never leave the car in neutral when on the move. Always have the car in gear. Make sure that it is the appropriate gear for your speed and the road conditions. Neither hold a gear to the redline every time before changing up, nor hold the car in too high a gear as you slow down. The car needs to be able to respond at all times to deal with the unexpected.
When you come to a halt at say some stop lights and you can see that they won't change in less than a few seconds, engage the handbrake and put the car in neutral. Keeping the clutch depressed wears out the thrust bearing unnecessarily.
You should note that with a synchro box it is possible (but not recommended) to change gear without using the clutch at all. It is quite simple with upshifts, not so simple with downshifts, but the principle is true either way that if the engine revs are matched to the speed at which the gearbox is spinning the gears will engage without the use of the clutch.
Hear endeth the lesson.
May your manual gearboxes give you as much pleasure as mine does!....