What are the effects of downshifting on the clutch?
I was thinking about this today, and thought there might be a difference in up shifting and downshifting according to the clutch use.
So question is, how does downshifting affect the clutch and engine? and is there a difference is clutch engagement between up and down shifting?.....and i'm talking technical here, not the obvious "engine braking" ;) all in reference to a 5sp transmission......... |
i think your putting way to much thought into it. :p I see it as the forces that are put to the clutch when upshifting are then reversed when down shifting. insted of the engine providing the power the trany is. heck i dunno. im confused now.. time to take a nap.;)
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IMO i think the clutch goes threw the same. no matter up or downshifting.
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Re: What are the effects of downshifting on the clutch?
Originally posted by mazdaspeedwest I was thinking about this today, and thought there might be a difference in up shifting and downshifting according to the clutch use. So question is, how does downshifting affect the clutch and engine? and is there a difference is clutch engagement between up and down shifting?.....and i'm talking technical here, not the obvious "engine braking" ;) all in reference to a 5sp transmission......... Upshifting, if you're mashing the pedal, and then shift without letting off the gas, you could run the risk of overheating the clutch with one launch. The disc would slip until the engine slowed down to match the tranny, creating heat. Stock disks will start to slip pretty fast, and then you're left to feather the throttle to gain speed. Letting out the clutch too quickly will give a jolt to the disc, but the stock discs have a spring loaded plate. So that absorbs a lot of the punishment. Oh. If your clutch does overheat, and it slips too much, you risk glazing your clutch and possibly warping your flywheel. The same principles apply to downshifting. If you don't rev match, you're just heating up your clutch, and eventually it'll start to slip. Letting out the clutch too fast with out rev matching, forces one end to match speeds of the other, and in this case, it's usually the engine that has to match the speed of the car/tranny, which isn't good on the engine (and this doesn't apply to engine braking when the engine is forced to slow down to slow the car. I'm talking about sudden need to slow down). Like I said, the springs on the stock disc absorbs a lot of the punishment, but that doesn't mean that nothing else will be affected by harsh use. |
told you i didnt know. but thought i would give it a shot. ;)
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Re: Re: What are the effects of downshifting on the clutch?
Originally posted by zenilder Well, there's not too much to it. Just so long as you rev match when you downshift, things should be okay. if thats what ur refering to,....i think ur shifting wrong.:rolleyes: |
Re: Re: What are the effects of downshifting on the clutch?
Originally posted by zenilder Well, there's not too much to it. Just so long as you rev match when you downshift, things should be okay. Upshifting, if you're mashing the pedal, and then shift without letting off the gas, you could run the risk of overheating the clutch with one launch. The disc would slip until the engine slowed down to match the tranny, creating heat. Stock disks will start to slip pretty fast, and then you're left to feather the throttle to gain speed. Letting out the clutch to quickly will give a jolt to the disc, but the stock discs have a spring loaded plate. So that absorbs a lot of the punishment. Oh. If your clutch does overheat, and it slips too much, you risk glazing your clutch and possibly warping your flywheel. The same principles apply to downshifting. If you don't rev match, you're just heating up your clutch, and eventually it'll start to slip. Letting out the clutch too fast with out rev matching, forces one end to match speeds of the other, and in this case, it's usually the engine that has to match the speed of the car/tranny, which isn't good on the engine (and this doesn't apply to engine braking when the engine is forced to slow down to slow the car. I'm talking about sudden need to slow down). Like I said, the springs on the stock disc absorbs a lot of the punishment, but that doesn't mean that nothing else will be affected by harsh use. |
Re: Re: Re: What are the effects of downshifting on the clutch?
Originally posted by Maz94Protege ??? REV MATCH....huh??? you dont ( or not supposed to rev to down shift) if thats what ur refering to,....i think ur shifting wrong.:rolleyes: when you enter a corner under braking (heel on the brake pedal) you rev (toe on the gas pedal) the engine to match the downshifted gear's RPM, this way you'll be in the power band when exiting the corner and the car will not slow down due to engine braking, but rather spit you out of the corner faster. very dificult to do correctly i might add, takes alot of practice. |
Re: Re: Re: Re: What are the effects of downshifting on the clutch?
Originally posted by mazdaspeedwest rev matching is more of a racing technique. also refered to as heel-toe. when you enter a corner under braking (heel on the brake pedal) you rev (toe on the gas pedal) the engine to match the downshifted gear's RPM, this way you'll be in the power band when exiting the corner and the car will not slow down due to engine braking, but rather spit you out of the corner faster. very dificult to do correctly i might add, takes alot of practice. |
I really don't see where there is a problem with this at all....can't see where it does any harm.... I have over 135K on my little truck...and the clutch don't slip a bit...and I use the engine to break ALL the time....its how I drive.
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Originally posted by Sir Nuke I really don't see where there is a problem with this at all....can't see where it does any harm.... I have over 135K on my little truck...and the clutch don't slip a bit...and I use the engine to break ALL the time....its how I drive. So don't stress it if you do your normal daily driving. If you push your car hard everyday, then you might worry about it. |
Re: Re: Re: Re: Re: What are the effects of downshifting on the clutch?
Originally posted by Maz94Protege oooo aight gotcha...thanks for the clearing up!:D |
Re: Re: Re: Re: What are the effects of downshifting on the clutch?
Originally posted by mazdaspeedwest rev matching is more of a racing technique. also refered to as heel-toe. when you enter a corner under braking (heel on the brake pedal) you rev (toe on the gas pedal) the engine to match the downshifted gear's RPM, this way you'll be in the power band when exiting the corner and the car will not slow down due to engine braking, but rather spit you out of the corner faster. very dificult to do correctly i might add, takes alot of practice. |
Originally posted by Sir Nuke ...and I use the engine to break ALL the time....its how to drive. If you doubt that engine breaking works, make a point to get close to an 18-wheeler in traffic. When things start slowing down and you hear rhhhhhaaaaaaaaarrrrrrr gaaaaaa gaaagg ggaaa gaa ga gaaahhhhhhh..... you'll realize that people who drive all goddamn day long know that engine breaking is a fact of life. |
Re: Re: Re: Re: Re: What are the effects of downshifting on the clutch?
Originally posted by turboge Hmm... I usually use my toe portion on the brake pedal and stab the bottom of the gas pedal with my heal. I couldn't see my feet turning the other way to put the toe on the gas pedal, and the heel on the brakes.. contortion!? |
How does that go now?
Originally posted by Brubeck you hear rhhhhhaaaaaaaaarrrrrrr gaaaaaa gaaagg ggaaa gaa ga gaaahhhhhhh..... |
your toe is more sensative, and you can use that sensitivity to keep your tires from locking up. the gas does not require this sensitivity, only proper timing. my problem is that my heel gets stuck on the side of the centre console:p
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ya thats more like what i do too, i've been practicing in our lovely Cali traffic..... aftermarket pedals help too, as the gas pedal will have a tab on the brake pedal side. This helps me perfectly, since when i come home at night the system is at FULL VOLUME (stress relief) and the RPMs will dip at a dead stop. So i have my foot half on each pedal and can keep the RPMs at 1000 to keep from dipping....ya i know, time for a bigger alternator, but eh, won't make me go faster so it's not a priority :D :D :D :D
It's kind of a roll over effect too, hard to explain, but hey do what ever works for you. |
Umm is it just me or is the point being missed in this thread?
Well its my belief that engine breaking doesn't really do anything to the clutch the only thing engine breaking will really affect are the syncho's in the gearbox. And this wont happen unless you're doing some heniously different revs from one gear to another. my $0.02 |
Re: Re: Re: Re: Re: What are the effects of downshifting on the clutch?
Originally posted by turboge Hmm... I usually use my toe portion on the brake pedal and stab the bottom of the gas pedal with my heal. I couldn't see my feet turning the other way to put the toe on the gas pedal, and the heel on the brakes.. contortion!? Here's a good on-line article on it. |
That's a nice site.
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I should have a couple video's with a little heel/toe shifting up on the web shortly. I just pulled them off my camera along with a quick little run through the mountains in the Spec V.
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Clearing up a few things here.
Engine braking does so little that it's not very useful for slowing a car. It was done in the past because brakes were not very good (rear mechanical drums, hand-lever operated), engines were huge and full of friction. Nowadays, brakes on cars are so good that downshifting to slow a car is pointless. Also, most of the braking is from friction, not compression. And what isn't friction is actually vacuum braking, as the pistons try to pull air past the closed throttle plate. Now, downshifting for performance driving, or when entering a corner, is something different. Here, it's done so that you are in the correct gear when you exit a corner. The point of heel-toe downshifting, or rev-matching downshifts, is that it reduces the upset to the car (don't believe me, try downshifting a RWD car without rev-matching and watch the lightly loaded rear wheels lock up. It will also reduce wear on the synchros. And, diesels engines produce almost no compression/vacuum braking, because they have no throttle plate. That noise you hear diesels making is from a device called a Jake Brake (generically). This acts on the valves to produce nearly 100% of the engine's output in braking force (A typical 400hp diesel engine might have 350-400hp of braking with a Jake Brake). Diesel pickups often use an aftermarket exhaust brake (a valve in the exhaust system that can be closed off) to perform a similar function. Semis also use things like hydraulic retarders to slow them down, but these generate enormous amounts of heat. |
Diesels also use an exhaust brake, or is that the Jake Brake your refering to?
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Originally posted by mazdaspeedwest Diesels also use an exhaust brake, or is that the Jake Brake your refering to? For how it works, try How stuff works |
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