A Conversation for Advanced Driving Techniques
Recumbentman Started conversation Jul 29, 2003
Your advice on double declutching seems to be contradicted, or at least left ambiguous, in the bit about driving without a clutch, where you say:
"Changing down gear is similar except that you don't rev up beforehand and you leave the engine longer out of gear so that it can slow down and match to the lower speed."
Going to a lower gear would normally require boosting the engine up to a higher rev between gears. The "it" that can slow down if you just "leave the engine longer out of gear" would be the car, not the engine. If you let the car's road speed slow down, the engine's idling speed will have a better chance of meshing at the lower gear.
Gnomon - time to move on Posted Jul 29, 2003
You're right! I've driven without using the clutch and the way I described it is the way it felt, but thinking about it, it must be car that is slowing down, not the engine. I'll have to do some experiments, then get the entry changed.
as-is-fab Posted Oct 2, 2009
a couple of points regarding double de-clutching, and modern car [and bigger] gearboxes.
 nearly all modern manual gearboxes have synchromesh fitted, which, as we know, obviated the need for double de-clutching to change gears.
By using the clutch twice during a gearchange [and we are all allowed mis-timed gearchanges now and again] the synchro-mesh cones are subjected to twice the wear and tear than otherwise would occur with the accepted, normal gearchange. Increased wear also occurs on the clutch thrust bearing
 Rather than doubling the clutch, I suggest simply [on a downshift]using the throttle to raise the engine revs to where the driver thinks they should be for the intended gear ,at that speed.
In a car, which will likely have a lightweight engine, this will merely be a quick blip of the throttle.
On the topic of clutchless gearchanges, I would add, that when changing gear, try to do so at lower engine revs/road speed for the chosen gear, ie changing up earlier rather than later.
The bi problem will be , with a modern gearbox, that there is considerable resistance to clutchless gearchanges, probably caused by the presence of the synchromesh, but I may be wrong on that one....certainly, a 'crash' gearbox is far easier to change without the clutch...as is a high mileage, worn gearbox.
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