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okay i just read a thread on downshifting with an auto. and now im a lil confused about downshifting with my 5speed. a guy said we're not supposed to just let go of the clutch when we downshift. we hafta rev match it? how do u rev match...etc? does he mean...1)step on clutch and keep it held down 2) shift down 3)gas 4)let go of clutch? i thought we're not supposed to rev when the clutch is down...i don't really know much about driving stickshift. some1 please give some insight..thanks

 
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When upshifting, you don't want to rev when the clutch is disengaged (foot on the cluch) because it just wastes gas. When downshifting, you want to rev the engine a little bit to match the input shaft RPM to the output shaft RPM in the lower gear.

For example, if you are doing 70 mph in 5th gear (input and output shafts both at 3000 RPM) and you downshift to 4th, your output shaft is going to jump from 3000 RPM to around 4000 RPM or more. However, your input shaft is still stuck at 3000 RPM, so when you engage the clutch (foot off the cluch) you'll hear a nasty grinding noise in the engine when the input shaft (< 3000 RPM since the RPM dropped when you momentarily disengaged the clutch while shifting) tries to engage with the output shaft (4000 RPM).

To correct this, you should rev match (gas it up a bit when you have the clutch disengaged) so that the RPM of the input and output shafts are about the same. Then when you engage the clutch the downshift should be a lot smoother.

You should also use rev matching when your car is coasting in neutral and you need to suddenly shift out of neutral. Like if you happen to be coasting in neutral at 50 mph and you suddenly need to shift it into gear.

So remember to rev match when you anticipate a jump in RPMs due to a gear change (your engine will thank you for it).

 
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How do you know how much to rev it up to?

 
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thank you soo much...i understand better now. doesn't that serve the same purpose as double clutching? why do you need to shift to neutral when u double clutch when u can just rev with the clutch in?

 
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Doesn't the synchro mesh eliminate the need for rev matching? When I downshift I can do it very smoothly without the need to rev match. For example I know what speed is done in each gear. 1st 0-20Km/h 2nd 20-40km/h 3rd 40-60km/h 4th 60-80km/h 5th 80km/h>. So if doing 70km/h and I want to downshift from 4th to 3rd I'll wait for the speed to drop to that range( 40-60km/h) and then downshift.

 
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that's exactly how i drive (not rev matching) and everything works out ok for me.

 
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yeah, I wait for speed to go down, I dont rev match... like lets say I'm going at 60 and in 5th... I'm coming to a stop sign, I break slowly and ease into about 40 and shift to 4th, but as I release the clutch slowly I break some more to bring the speed down to about 30 for a smooth downshift and some engine breaking.

this makes me ues the clutch more and I'll probably wear it out more.. but thats how i do it. I'm not sure if thats the correct way to downshift though.

oh yeah I'm talking about downshifting to a stop... not downshift for acceleration.

downshifting for acceleratoin, I think, u shouldn't bother to rev match... it'll make it smoother, but unless u do it fast, it defeats the purpose of downshifting to speed up... I just downshift into the appropriate gear that wont let me hit redline, and fly. (or as fast as a civic can fly, anyway)