MT Rev matching question
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From: Florida
MT Rev matching question
It's been about 20 years since my last manual and I'm loving my MT Carrera T.
Decades ago, I was taught to downshift to slow down and save brake pad wear. But is the theory also that downshifting (without rev matching) puts unnecessary wear in other respects?
I love the rev matching in Sport and Sport Plus modes but find myself braking a lot more than while in Normal mode, especially in day-to-day commuting.
P.S. I do not track the car (yet).
Decades ago, I was taught to downshift to slow down and save brake pad wear. But is the theory also that downshifting (without rev matching) puts unnecessary wear in other respects?
I love the rev matching in Sport and Sport Plus modes but find myself braking a lot more than while in Normal mode, especially in day-to-day commuting.
P.S. I do not track the car (yet).
Racer
Joined: Jan 2020
Posts: 265
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From: TN
I was taught the same thing, I find myself doing it for multiple reasons: It sounds cool, auto blip makes you feel like a hero, ready to go in gear if traffic eases or a situation arises where you need to accelerate (e.g. avoid a rear ending), and yes it saves brake wear (and DUST!). I feel like with auto blip the clutch engagement is so smooth, that clutch wear is minimal. I actually can’t recall reading about anyone needing a replacement clutch on a 992 (but maybe someone will chime in).
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From: Doylestown, PA
You need to unlearn some of that stuff you were taught decades ago. You shouldn't be dumping the clutch with mismatched revs.
I was taught to heel and toe, matching the revs myself. I still find myself doing it out of habit, even though the auto rev matching renders the skill more/less unnecessary.
I was taught to heel and toe, matching the revs myself. I still find myself doing it out of habit, even though the auto rev matching renders the skill more/less unnecessary.
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Rev matching is better for the transmission.
Heel toe is useful when daily driving, not just for performance driving. You keep the car in the power band and the drive is smoother.
Obviously auto-blip gets you there, but it's a little boring for street driving, IMO. On a track, auto-blip all the way.
In actuality, it's also not really "heel-toe" for me. On one car it's "toe - side of foot" and on the other it's "ball of foot - side of foot"
Heel toe is useful when daily driving, not just for performance driving. You keep the car in the power band and the drive is smoother.
Obviously auto-blip gets you there, but it's a little boring for street driving, IMO. On a track, auto-blip all the way.
In actuality, it's also not really "heel-toe" for me. On one car it's "toe - side of foot" and on the other it's "ball of foot - side of foot"
Three Wheelin'
Joined: Jan 2021
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It's been about 20 years since my last manual and I'm loving my MT Carrera T.
Decades ago, I was taught to downshift to slow down and save brake pad wear. But is the theory also that downshifting (without rev matching) puts unnecessary wear in other respects?
I love the rev matching in Sport and Sport Plus modes but find myself braking a lot more than while in Normal mode, especially in day-to-day commuting.
Decades ago, I was taught to downshift to slow down and save brake pad wear. But is the theory also that downshifting (without rev matching) puts unnecessary wear in other respects?
I love the rev matching in Sport and Sport Plus modes but find myself braking a lot more than while in Normal mode, especially in day-to-day commuting.
Once I figured out how to rev match the downshifts, the car no longer would lurch on the downshift and the car still would engine brake, though not as immediate as it would if you didn't bother rev matching. The trade off is the car feels vastly smoother. In fact, if you rev match perfectly, you wouldn't feel the shift at all, but you would definitely still get the benefit of engine braking.
You don't want to engine brake w/o rev matching b/c you are mechanically forcing your engine to instantly jump 1000+ RPMs. It sound bad when you do this b/c you are probably doing some harm to the engine. If you rev match your downshift, it places minimal wear on the engine b/c you are not forcing it to a higher RPM. Instead you are freely revving the engine to a higher RPM, with the clutch completely disengaged, before you go into the lower gear. Clearly rev matching and the resulting engine braking is not an issue at all as most (all?) modern manual cars rev match the downshifts.
Race Car
Joined: Aug 2020
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IT DEPENDS ON YOUR RPM RANGE. Downshifting above 6k rpm can be a very bad thing for the reasons stated by others above. However, downshifting at 2k rpm to keep your engine rpm in its torque/power band and to prevent lugging the engine is a good thing and recommended by automotive engineers. This is particularly true during engine break in as the slow and easy varied rpm between 2k - 4k will help seat your piston rings. I always use rev match for downshifting and I never downshift above 3k unless I am on track. However, I constantly downshift at 2k rpm to not lug the engine like a PDK. But, I would not be concerned about brake pad wear. New brake pads are cheaper than clutches and gear sets.
Last edited by Fullyield; Jul 7, 2024 at 07:41 AM.
Rennlist Member
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From: Buffalo, NY
You need to unlearn some of that stuff you were taught decades ago. You shouldn't be dumping the clutch with mismatched revs.
I was taught to heel and toe, matching the revs myself. I still find myself doing it out of habit, even though the auto rev matching renders the skill more/less unnecessary.
I was taught to heel and toe, matching the revs myself. I still find myself doing it out of habit, even though the auto rev matching renders the skill more/less unnecessary.
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Drifting
Joined: May 2021
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I have been downshifting to slow down for the last 40 years and have never had to replace a clutch. For me the question is which is cheaper after 70K miles--- replacing brake pads or having my clutch only have 30K useful miles left instead of 50K useful miles left?
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Instructor
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From: Canada
edit: and PDK does this practically instantaneously in both directions!
Last edited by Cokerrat; Jul 7, 2024 at 11:35 AM.
Advanced
Joined: May 2024
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From: CA
PDK is ok because it’s a wet clutch so slippage is more acceptable as there is less heat buildup. In fact it is so acceptable that the software operates virtual gears sometimes where it can slip gear 1 and 2 simultaneously to create a gear between the two ratios. And when it downshifts it is always rev matching. In the downshift scenario it never wears the clutch.
In addition it does an incredible job of modulating the clutch perfectly to smooth out shifts with little interruption of torque. the computer modulates the engine torque and clutch force so precisely that it makes the forward lurch of an upshift feel like the same amount of torque as your existing acceleration and that’s what makes it feel smooth
Last edited by wujax; Jul 7, 2024 at 11:59 AM.
Advanced
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From: CA
Last edited by wujax; Jul 7, 2024 at 12:07 PM.
Advanced
Joined: May 2024
Posts: 96
Likes: 73
From: CA
I was taught the same thing, I find myself doing it for multiple reasons: It sounds cool, auto blip makes you feel like a hero, ready to go in gear if traffic eases or a situation arises where you need to accelerate (e.g. avoid a rear ending), and yes it saves brake wear (and DUST!). I feel like with auto blip the clutch engagement is so smooth, that clutch wear is minimal. I actually can’t recall reading about anyone needing a replacement clutch on a 992 (but maybe someone will chime in).
Though the manual allows one to operate it in a number of ways I believe in a number of particular best practices
- The transmission should always be kept in gear until a few mph before a stop. You should basicaly always keep the clutch out until right before you come to a stop and shift into neutral.
- Never do anything to hold the clutch in for more than the amount of time it takes to complete your shift. So don’t depress it and let the RPMs drop to idle. The clutch goes in to either upshift, downshift with rev match, or go into neutral. It should always be an in and out, never held. I believe I read somewhere that in some European countries with driving tests for manual this is actually a requirement.
- Gear shifts should generally be sequential, unless you have the skill to rev match beyond a single ratio. Skip up shifting is fine if you let the rpms drop a bit more before putting in the gear, a slow shift. Rev matches beyond one gear I personally recommend double clutching but I wouldn’t force that idea. Though the synchros can probably handle it, you may find some resistance in putting the stick into gear if you go beyond one or two ratios.
Rennlist Member
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From: St. Louis, MO
Let’s keep in mind that if the revs are matched, the clutch isn’t slipping and isn’t providing any braking force or additional heat. The engine is. The clutch is operating the same as when you accelerate, the applied torque is just in the opposite direction.
Advanced
Joined: May 2024
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From: CA
- engine braking: fully engaged clutch but using engine friction to slow down the car. This is fine
- “clutch braking”: using the difference between engine rpm from a shift to slow down the car which results in lots of clutch slip until rpm matches desired - this is unequivocally the wrong way to drive a manual
Drifting
Joined: May 2021
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I mean….yes you can think of it that way but the clutch is just not designed to be a brake for the car. You can do this on occasion and maybe you’d be ok but a clutch doesn’t have the same heat dissipation mechanisms as brake rotors. I learned a crazy comparison recently: the heat generated by braking from 50 to 0 in 3 seconds is enough to boil 2 liters of water. Your brakes have air ventilation that allows that heat to dissipate. Your clutch doesn’t. Over heating your clutch will cause it to glaze but also you risk heating the splines that provide clutch force. Passing this limit a few times will cause you to lose clutch force and in that instant your clutch will go. It’s not purely just a matter of a linear amount of wear but you risk sudden damage if you go too far a small number of times. And losing your clutch in the middle of the highway is just unsafe. You have no indication of when it will die, whereas your brakes let you know many miles ahead of time.