Rev Matching
05-16-2011, 07:20 AM
#21
Le Mans Master
05-16-2011, 07:33 AM
#23
Racer
Member Since: Sep 2010
Location: West Point NY
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Man, I feel lost. What are we talking about? When I down shift, I give the throttle a little nudge to make the rpm go up to compensate for the lower gear so the car doesn' buck and surge and all when I get the clutch out in the new gear. Is that what we are talking about? Doesn't everyone do this--seems like it would be a very jerky downshift otherwise? If that's not what the discussion is about, what IS it about?
I hate to sound stupid, but would someone very courteously insult my intelligence for a minute and help me understand this thread better? I thought I new how to drive a manual, but I admit, it was largely self-taught. Maybe I've been doing something wrong?
I hate to sound stupid, but would someone very courteously insult my intelligence for a minute and help me understand this thread better? I thought I new how to drive a manual, but I admit, it was largely self-taught. Maybe I've been doing something wrong?
05-16-2011, 08:06 AM
#27
Team Owner
Man, I feel lost. What are we talking about? When I down shift, I give the throttle a little nudge to make the rpm go up to compensate for the lower gear so the car doesn' buck and surge and all when I get the clutch out in the new gear. Is that what we are talking about? Doesn't everyone do this--seems like it would be a very jerky downshift otherwise? If that's not what the discussion is about, what IS it about?
I hate to sound stupid, but would someone very courteously insult my intelligence for a minute and help me understand this thread better? I thought I new how to drive a manual, but I admit, it was largely self-taught. Maybe I've been doing something wrong?
I hate to sound stupid, but would someone very courteously insult my intelligence for a minute and help me understand this thread better? I thought I new how to drive a manual, but I admit, it was largely self-taught. Maybe I've been doing something wrong?
In a Corvette you really can't use your heel and toe, but that is what the racers call it. You can use the left side of your foot on the brake while using the right side of your foot to blip the throttle as you downshift for the curve. That is what I do. I suspect that some of the folks that say they "rev match" are not really doing this while they are braking at the same time.
05-16-2011, 10:38 AM
#28
Melting Slicks
I've always rev-matched when downshifting.
It's the way I was taught (I'm 48 now), and it's completely natural to me.
I've tried double-clutching on downshifts, but it's really pointless for me.
I rev-match so smoothly I don't see any reason to do anything else.
Plus, not rev-matching is extremely hard on the clutch & transmission.....is it not?
It's the way I was taught (I'm 48 now), and it's completely natural to me.
I've tried double-clutching on downshifts, but it's really pointless for me.
I rev-match so smoothly I don't see any reason to do anything else.
Plus, not rev-matching is extremely hard on the clutch & transmission.....is it not?
05-16-2011, 11:16 AM
#29
Melting Slicks
Member Since: Sep 2008
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Blip rev match all the time in my A6. But I'm also 100% paddles. My vette is also on a mild boil and ready to pounce.
Would love to track on road course but I have the vert.
David
05-16-2011, 11:27 AM
#31
Melting Slicks
I only heel-toe when cornering. I usually don't engine brake when coming up to lights. I'll clutch and cover the brakes while approaching a stop or traffic and row down through the gears. If traffic starts moving before I get to 1st I'll blip it and release the clutch.
05-16-2011, 11:41 AM
#32
Burning Brakes
If you are double-clutching in a C6... you need to stop. No need to do this at all. Fast & the Furious got everyone caught on to that and its stupid really, especially for these cars.
Just rev matching and heel-toe rev matching are two different things to me. I view rev matching to be just blip the throttle and put it in the next lower gear of choice. Not using the brakes. I would do this alot in normal driving since there was typically never a need to be at the threshold braking point. Heel-Toe is where you are at threshold braking, rolling the right foot over or using the back of your right foot to blip the throttle all while still using the brake. This is what many racers use on the track.
Now that I've become smoother with heel-toe downshifting, I catch myself doing it on the streets when needed. Just a habit now.
Just rev matching and heel-toe rev matching are two different things to me. I view rev matching to be just blip the throttle and put it in the next lower gear of choice. Not using the brakes. I would do this alot in normal driving since there was typically never a need to be at the threshold braking point. Heel-Toe is where you are at threshold braking, rolling the right foot over or using the back of your right foot to blip the throttle all while still using the brake. This is what many racers use on the track.
Now that I've become smoother with heel-toe downshifting, I catch myself doing it on the streets when needed. Just a habit now.
05-16-2011, 12:39 PM
#34
If you are double-clutching in a C6... you need to stop. No need to do this at all. Fast & the Furious got everyone caught on to that and its stupid really, especially for these cars.
Just rev matching and heel-toe rev matching are two different things to me. I view rev matching to be just blip the throttle and put it in the next lower gear of choice. Not using the brakes. I would do this alot in normal driving since there was typically never a need to be at the threshold braking point. Heel-Toe is where you are at threshold braking, rolling the right foot over or using the back of your right foot to blip the throttle all while still using the brake. This is what many racers use on the track.
Now that I've become smoother with heel-toe downshifting, I catch myself doing it on the streets when needed. Just a habit now.
Just rev matching and heel-toe rev matching are two different things to me. I view rev matching to be just blip the throttle and put it in the next lower gear of choice. Not using the brakes. I would do this alot in normal driving since there was typically never a need to be at the threshold braking point. Heel-Toe is where you are at threshold braking, rolling the right foot over or using the back of your right foot to blip the throttle all while still using the brake. This is what many racers use on the track.
Now that I've become smoother with heel-toe downshifting, I catch myself doing it on the streets when needed. Just a habit now.
05-16-2011, 01:14 PM
#36
Burning Brakes
I take pride in providing my prized Corvette a smooth, jerk free experience when either accelerating or decelerating through the gears, and one cannot accomplish that without rather exacting rev matching. I also brake well in advance and at a uniform rate and then coast at the very end of a making a stop for the same reason. On the other hand, I can speed shift faster than you can blink if need be. I really enjoy driving a standard transmission smoother or faster than can be accomplished with an automatic, and telling the car when to shift, and into what gear, rather than visa versa. I think driving well, be it cruising or racing, is an art form, and something that should give one a real sense of accomplishment.
Only needed to change two words.
05-16-2011, 05:11 PM
#38
Burning Brakes
That's a bit harsh, and not completely correct. See, you're probably young enough that "The Fast & the Furious" is foremost in your mind. But good examples of double-clutching abounded before that waste of celluoid. Try watching the Bullitt - Steve McQueen Famous Car Chase on YouTube. Start at ~6.30 in the video, and listen as McQueen double-clutches the Mustang. I'm listening to him drive at this moment, he's the master.
Last edited by fnbrowning; 05-16-2011 at 05:20 PM.
05-16-2011, 05:13 PM
#39
Burning Brakes
I had to wait till I got home to find this document:
The basis of misunderstanding about double-clutching, rev-matching and heel-and-toe is a lack of understanding of the basic way the engine/clutch/transmission combination works. So take a deep breath and follow along.
What do synchros do? They are used to make the the layshaft match the gear that you are going to. To do the job in a car without synchromesh, you have to make the layshaft go the speed of the new gear yourself.
(Note, I have always just called the gears on the layshaft "the layshaft" so it is easier to visualize. This is a schematic description, not an analysis of which gear slides where on which shaft, or how synchros work, or what oil to use for them. So if you don't agree with the schematic concept I outline here, tell me where I went wrong, and we will look at it. Technical statements about gear movements on shafts or the like will be sent to the bit bucket. I know that modern transmissions are constant-mesh but it really does not change the concept.)
You have three rotating parts in series (1,2,3) with two ways to connect and disconnect them from each other (A B):
1 A 2 B 3
engine -> clutch -> layshaft -> gear selector -> various transmission gears
1) The engine speed is controlled by the throttle alone when the clutch is disengaged ("in"). It is equal to the layshaft speed when the clutch is engaged.
A) The clutch disconnects the engine from the layshaft when you step on the pedal.
2) The layshaft speed is equal to the engine speed when the clutch is engaged. The layshaft speed is related to the road speed when a gear is selected. Therefore, when the clutch is engaged AND a gear is selected, the engine speed is related rigidly to the road speed. (Nobody spins the wheels in this schematic outline!) When the clutch is disengaged AND the selector is in Neutral, the layshaft coasts down freely, regardless of either engine or road speed.
B) The gear selector disconnects the layshaft from the transmission gears when you select "Neutral", and connects the layshaft to a specific transmission gear when you select one.
3) The various transmission gears are being pushed around by the road speeding under your car via the differential and driveshafts. All of them All of them are spinning at different speeds in rigidly defined relationship to each other. If your tires are not slipping, the speed of the system is rigidly proportional to your road speed.
If you have working synchromesh: You are loafing along in Third gear and want to change to Second gear. When you put in the clutch and change the gear selector from Third to Neutral, the layshaft is going a particular speed that matched Third gear at the present road speed. If you do not change your road speed (your brakes are broke, say), the layshaft is going too slowly to match Second gear. As you approach the Second gear selection, the synchros will speed the layshaft up to the same speed as Second gear is now rotating. How do they do that? Ask a mechanic. They just DO it. I have a rough intuitive grasp of how they work, but it does not matter here.
If you have no synchromesh (Crash Box City): You are loafing along in Third gear and want to change to Second gear. When you put in the clutch and change the gear selector from Third to Neutral, the layshaft is going a particular speed that matched Third gear at the present road speed. If you do not change your road speed (your brakes are broke, say), the layshaft is going too slowly to match Second gear. (Sound familiar so far?) As you approach the Second gear selection, the gears go GRAUNCH.
What should you have done? This:
Push in clutch Layshaft equals Third gear speed
Select Neutral Layshaft coasts
Let out clutch Layshaft equals engine speed
Blip throttle Engine and layshaft speed up to Second gear speed and a
little
Push in clutch Layshaft coasts
Select Second No GRAUNCH if you have the speeds right. Ideally,
layshaft has coasted down to exactly Second gear speed
Let out clutch System is all locked up in Second.
This is double-clutching. It INCORPORATES rev-matching, or there is no point in doing it. Therefore, in my opinion, there is no reason to have to say "rev-matching" to describe this process. The rev-matching is the tricky part. How high do you rev it? Experience is the only teacher.
Does double-clutching do any good if you have a synchromesh box? Yes, it makes the synchros work less hard than they were designed to, so they will last longer. The synchros will make up for any errors.
Can you rev-match the layshaft without double-clutching? Yes. Don't use the clutch at all:
Ease the throttle Takes the load out of the system
Select Neutral Layshaft equals engine speed
Blip throttle Engine and layshaft speed up to Second gear speed
Select Second No GRAUNCH if you have the speeds right
This works exactly the same in a synchromesh box as a crash box. Since the layshaft is always connected to the engine, synchros will NOT help you. In fact, I think errors in this method can wreak your synchros. Normally, synchros only have to deal with the rotating mass of the layshaft. Now you are asking them to deal with your whole engine. They ain't gonna like it. You have to be perfect. This is what Rick Mears and many other disgustingly able drivers do. I couldn't do it on a bet.
Can you rev-match the layshaft to the transmission gears by throttle - blipping with regular single clutching? No. The layshaft is not connected to the engine while the clutch is in. Those that recommend throttle-blipping rev-matching are right that it gives a smooth transition when they let the clutch out, but it does absolutely nothing to match the layshaft and does not save your synchros any work at all.
What do synchros do? They are used to make the the layshaft match the gear that you are going to. To do the job in a car without synchromesh, you have to make the layshaft go the speed of the new gear yourself.
(Note, I have always just called the gears on the layshaft "the layshaft" so it is easier to visualize. This is a schematic description, not an analysis of which gear slides where on which shaft, or how synchros work, or what oil to use for them. So if you don't agree with the schematic concept I outline here, tell me where I went wrong, and we will look at it. Technical statements about gear movements on shafts or the like will be sent to the bit bucket. I know that modern transmissions are constant-mesh but it really does not change the concept.)
You have three rotating parts in series (1,2,3) with two ways to connect and disconnect them from each other (A B):
1 A 2 B 3
engine -> clutch -> layshaft -> gear selector -> various transmission gears
1) The engine speed is controlled by the throttle alone when the clutch is disengaged ("in"). It is equal to the layshaft speed when the clutch is engaged.
A) The clutch disconnects the engine from the layshaft when you step on the pedal.
2) The layshaft speed is equal to the engine speed when the clutch is engaged. The layshaft speed is related to the road speed when a gear is selected. Therefore, when the clutch is engaged AND a gear is selected, the engine speed is related rigidly to the road speed. (Nobody spins the wheels in this schematic outline!) When the clutch is disengaged AND the selector is in Neutral, the layshaft coasts down freely, regardless of either engine or road speed.
B) The gear selector disconnects the layshaft from the transmission gears when you select "Neutral", and connects the layshaft to a specific transmission gear when you select one.
3) The various transmission gears are being pushed around by the road speeding under your car via the differential and driveshafts. All of them All of them are spinning at different speeds in rigidly defined relationship to each other. If your tires are not slipping, the speed of the system is rigidly proportional to your road speed.
If you have working synchromesh: You are loafing along in Third gear and want to change to Second gear. When you put in the clutch and change the gear selector from Third to Neutral, the layshaft is going a particular speed that matched Third gear at the present road speed. If you do not change your road speed (your brakes are broke, say), the layshaft is going too slowly to match Second gear. As you approach the Second gear selection, the synchros will speed the layshaft up to the same speed as Second gear is now rotating. How do they do that? Ask a mechanic. They just DO it. I have a rough intuitive grasp of how they work, but it does not matter here.
If you have no synchromesh (Crash Box City): You are loafing along in Third gear and want to change to Second gear. When you put in the clutch and change the gear selector from Third to Neutral, the layshaft is going a particular speed that matched Third gear at the present road speed. If you do not change your road speed (your brakes are broke, say), the layshaft is going too slowly to match Second gear. (Sound familiar so far?) As you approach the Second gear selection, the gears go GRAUNCH.
What should you have done? This:
Push in clutch Layshaft equals Third gear speed
Select Neutral Layshaft coasts
Let out clutch Layshaft equals engine speed
Blip throttle Engine and layshaft speed up to Second gear speed and a
little
Push in clutch Layshaft coasts
Select Second No GRAUNCH if you have the speeds right. Ideally,
layshaft has coasted down to exactly Second gear speed
Let out clutch System is all locked up in Second.
This is double-clutching. It INCORPORATES rev-matching, or there is no point in doing it. Therefore, in my opinion, there is no reason to have to say "rev-matching" to describe this process. The rev-matching is the tricky part. How high do you rev it? Experience is the only teacher.
Does double-clutching do any good if you have a synchromesh box? Yes, it makes the synchros work less hard than they were designed to, so they will last longer. The synchros will make up for any errors.
Can you rev-match the layshaft without double-clutching? Yes. Don't use the clutch at all:
Ease the throttle Takes the load out of the system
Select Neutral Layshaft equals engine speed
Blip throttle Engine and layshaft speed up to Second gear speed
Select Second No GRAUNCH if you have the speeds right
This works exactly the same in a synchromesh box as a crash box. Since the layshaft is always connected to the engine, synchros will NOT help you. In fact, I think errors in this method can wreak your synchros. Normally, synchros only have to deal with the rotating mass of the layshaft. Now you are asking them to deal with your whole engine. They ain't gonna like it. You have to be perfect. This is what Rick Mears and many other disgustingly able drivers do. I couldn't do it on a bet.
Can you rev-match the layshaft to the transmission gears by throttle - blipping with regular single clutching? No. The layshaft is not connected to the engine while the clutch is in. Those that recommend throttle-blipping rev-matching are right that it gives a smooth transition when they let the clutch out, but it does absolutely nothing to match the layshaft and does not save your synchros any work at all.
05-16-2011, 05:22 PM
#40
Pro
Member Since: Nov 2007
Location: Silicon Valley California
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St. Jude Donor '09-'11
I rev match whenever I can. But since I cannot heel/toe, I don't rev match if I must keep my right foot on the brake through the downshift. If there's time to let off the brake and do the rev match and then do what's needed after that, I'll rev match. If not, I just carefully let the clutch in.
Double clutching is pointless in a transmission like this. Yes, I can still remember Vin Diesel in "The fast and the furious" criticizing the new guy for "granny shifting" and not "double clutching", but what kind of crap transmission were they supposed to be using where you needed to do that? It was a funny scene in my mind, like science fiction movies or "computer" movies where a bit of jargon is rattled off that is meaningless if you know the field in question.
Double clutching is pointless in a transmission like this. Yes, I can still remember Vin Diesel in "The fast and the furious" criticizing the new guy for "granny shifting" and not "double clutching", but what kind of crap transmission were they supposed to be using where you needed to do that? It was a funny scene in my mind, like science fiction movies or "computer" movies where a bit of jargon is rattled off that is meaningless if you know the field in question.