Downshifting on decel: Why and how you should do it
08-07-2007, 11:17 AM
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Downshifting on decel: Why and how you should do it I just sent this PM to plainred02Z per his thread. He suggested I post this, so here it is:
The main reason to downshift while slowing down is safety. You want to spend most of your time "in gear," (not coasting in neutral) so you are in better control of your car. For instance, if you are slowing down for a red light and you look in the mirror and the guy behind you isn't paying attention, you are better off being in gear (not neutral) so you can avoid being rear-ended.
Same thing if you are slowing down to make a turn. Try to get into the proper gear with the clutch out before you enter the turn. That way you don't risk breaking the rear tires free in the middle of the turn, and you are ready to tip into the power after the turn.
With all of that said: I always try to double clutch my downshifts to reduce wear on the clutch and trans. It also makes the smoothest downshifts to keep your passengers happy Practice rev-matching first, then learn to double-clutch.
Rev-match: Say you are in 4th gear at 45 mph and 2,000rpm and you want to go to 3rd. When you go into 3rd at 45 mph, the engine will jump to 2600 rpm (for 3.42 axle). When you push in the clutch, give the engine some gas to spin it up to 2600, then let out the clutch. You'll notice the downshift is smoother, and you won't get that surge hitting the back wheels. This also saves wear and tear on the clutch because the flywheel and clutch disk are spinning at the same speed when you let the clutch out. Less slipping = less wear. Practice with small steps at first (5th to 4th, 4th to 3rd) then try bigger jumps (5th to 3rd, 4th to 2nd)
Double-clutch: Once you are comfortable with rev-matching, try double-clutching. This has an extra step and seems like a lot of foot work at first. When you need a downshift:
1. Push in the clutch
2. Pull the shifter into neutral
3. Let up the clutch
4. Give the car gas to spin the engine to the right speed for the lower gear
5. Push in the clutch
6. Put the shifter in the lower gear
7. Let up the clutch
With practice, you'll be double clutching quickly without thinking about it. The difference from rev-matching is you are revving the engine up with the stick in neutral and the clutch pedal UP.
That probably seems like a lot of work. The benefit is that it saves wear/tear on the trans synchros. Just like the rev-match saves wear on the clutch, the double-clutch puts the input and output shafts of the trans at the proper speeds to mesh without slipping the synchros. Again less slip = less wear.
For big downshifts (say 5th or 4th down to 2nd) your engine rpms will jump up ALOT (more than a 2000 rpm jump). The synchros in the trans have to scrub against each other until the gear sets are at the same speed to let you into gear. That's where the double clutch really helps. By revving with the clutch pedal UP and the stick in neutral, you are speeding up the trans input shaft so the synchros don't have to wear out trying to speed it up. For smaller jumps, rev-matching is fine.
Practice rev matching until your brain and ear can automatically tell how much you need to rev up the engine for the lower gear. Then try double-clutching once you are more comfortable with your car. I drove a manual for 10 years just rev matching before I learned to double clutch, so don't feel rushed. For smaller jumps, I still just rev-match.
good luck!
The main reason to downshift while slowing down is safety. You want to spend most of your time "in gear," (not coasting in neutral) so you are in better control of your car. For instance, if you are slowing down for a red light and you look in the mirror and the guy behind you isn't paying attention, you are better off being in gear (not neutral) so you can avoid being rear-ended.
Same thing if you are slowing down to make a turn. Try to get into the proper gear with the clutch out before you enter the turn. That way you don't risk breaking the rear tires free in the middle of the turn, and you are ready to tip into the power after the turn.
With all of that said: I always try to double clutch my downshifts to reduce wear on the clutch and trans. It also makes the smoothest downshifts to keep your passengers happy Practice rev-matching first, then learn to double-clutch.
Rev-match: Say you are in 4th gear at 45 mph and 2,000rpm and you want to go to 3rd. When you go into 3rd at 45 mph, the engine will jump to 2600 rpm (for 3.42 axle). When you push in the clutch, give the engine some gas to spin it up to 2600, then let out the clutch. You'll notice the downshift is smoother, and you won't get that surge hitting the back wheels. This also saves wear and tear on the clutch because the flywheel and clutch disk are spinning at the same speed when you let the clutch out. Less slipping = less wear. Practice with small steps at first (5th to 4th, 4th to 3rd) then try bigger jumps (5th to 3rd, 4th to 2nd)
Double-clutch: Once you are comfortable with rev-matching, try double-clutching. This has an extra step and seems like a lot of foot work at first. When you need a downshift:
1. Push in the clutch
2. Pull the shifter into neutral
3. Let up the clutch
4. Give the car gas to spin the engine to the right speed for the lower gear
5. Push in the clutch
6. Put the shifter in the lower gear
7. Let up the clutch
With practice, you'll be double clutching quickly without thinking about it. The difference from rev-matching is you are revving the engine up with the stick in neutral and the clutch pedal UP.
That probably seems like a lot of work. The benefit is that it saves wear/tear on the trans synchros. Just like the rev-match saves wear on the clutch, the double-clutch puts the input and output shafts of the trans at the proper speeds to mesh without slipping the synchros. Again less slip = less wear.
For big downshifts (say 5th or 4th down to 2nd) your engine rpms will jump up ALOT (more than a 2000 rpm jump). The synchros in the trans have to scrub against each other until the gear sets are at the same speed to let you into gear. That's where the double clutch really helps. By revving with the clutch pedal UP and the stick in neutral, you are speeding up the trans input shaft so the synchros don't have to wear out trying to speed it up. For smaller jumps, rev-matching is fine.
Practice rev matching until your brain and ear can automatically tell how much you need to rev up the engine for the lower gear. Then try double-clutching once you are more comfortable with your car. I drove a manual for 10 years just rev matching before I learned to double clutch, so don't feel rushed. For smaller jumps, I still just rev-match.
good luck!
08-07-2007, 02:07 PM
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Originally Posted by MrDude_1
you dont need to double clutch the stock transmission.
To each his own, you don't need to use the clutch at all for rolling shifts if you don't want to! A good right foot and a fast hand will get the job done with no clutch wear!
My point in the original post was "why" you should downshift and the best way to do it with regard to trans longevity and smooth driving practice.
I know a few "old dudes" with manual trans, compact car, daily drivers. They've racked up very high mileage on stock clutch and trans parts. One reason is they learned to drive smooth on non-synchro'd vehicles. When you apply those skills to a sync'd car, you make the car happy. I punish my car enough at wide open throttle, I try to be a little nicer at part throttle.
08-07-2007, 02:31 PM
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Originally Posted by aggie-chase
I guess these methods are all well and good- for people who like to slow down that is! 
