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I'd personally recommend against downshifting the way Jesse described. Sure, it will slow your car down, but it does so by wearing the clutch. As the saying goes, it's cheaper to replace the brakes than the clutch.
It is possible (and fun) to downshift without wearing the clutch or transmission. However, to avoid clutch wear, you have to match revs before letting out the clutch, and to avoid synchro wear, you have to double clutch. You should rev match at the very least when downshifting, and if you downshift often, you should learn to double-clutch.
Rev matching:
To downshift, lift off the gas, depress the clutch, shift, and then give it enough gas to speed the engine up to where you think it will be after you let the clutch out. This takes some practice and experience. When you have sped up the engine, let out the clutch, and you will notice that the engagement is much smoother, and the car does not slow down as quickly. You're saving your clutch.
Double clutching:
Synchros are like little clutches inside your gearbox. There are really three parts of your drivetrain that can move independently: the engine, the transmission input shaft, and the transmission output shaft (which is connected to the wheels). The engine and transmission input are connected by the clutch; the transmission input and output are connected (through a series of gears) by one of the synchros, depending on which gear you are in. Rev matching, above, got the engine to the appropriate speed to match the transmission output. When you move the gear lever, you engage the synchros, and they do the work to speed up the transmission input shaft. Synchros won't wear as fast as a clutch, but double-clutching will make them last longer. So here's how it's done:
Lift off the gas. Clutch in, shift to neutral. Now, let the clutch back out. Use the gas as if you were rev matching; this time, instead of just speeding up the engine, you are also spinning up the transmission input shaft. Now, quickly depress the clutch, shift into your new gear, and let out the clutch. If you're slow letting the clutch back out, give it some more gas to maintain the engine speed (you're rev matching here).
If done correctly, when you shift into the new gear, the gear shift lever will feel like it is falling into place, without the usual resistance (resistance = synchro wear). Takes a lot of practice to do it smoothly, but if you're going to downshift a lot, it will save you money in the long run. Besides, it's fun!
A note on shifting into first...the advice you give is actually based on some old technology that is no longer a factor. Cars and trucks didn't used to have synchro meshes on first gear, so there was nothing to make the speed of the input shaft match the output shaft unless you could double-clutch perfectly (which none of us can do 100% of the time). If you tried to shift into first while moving, you'd just grind your gears.
Cars now have synchro meshes on first, so that's no longer an issue. You can shift into first while moving slowly. However, it's still a bad idea to downshift into first if the revs will be above 1500 or so. Because the gear ratio difference between first and second is proportionally greater than any of the others, all of the wear (clutch and synchro) mentioned above is greater when shifting into first than between any other gear. With proper rev matching and double clutching, there should be very little wear, even when downshifting into first. However, because of that big difference in gearing, this is also the most difficult gear switch to do smoothly. I personally don't downshift into first because I'm just not good enough at driving stick :)
By the way, Jesse, nice cloth shift boot. I've got the same one :)
Matt
'99 9³
posted by 65.106.18...
, Tue, 18 May 2004 15:40:34
, Wed, 19 May 2004 11:23:57, Wed, 19 May 2004 13:07:57, Tue, 18 May 2004 10:35:48
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