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      07-29-2014, 04:26 PM   #1
lichenlt
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I remember a while ago someone asked a question about the rev going higher when braking. Some said it was like a rev matching thing.

I never had a car with rev matching so no idea how that actually works, but the other day I was coming to a hard stop coming off the freeway (~65 to 0 in not so short of a distance).

I felt like the rev matching made it more difficult to stop and I nearly hit the car in front me but eventually it stopped in time. I think I used full braking power and the car just wasn't slowing down efficiently as it was reving up with the downshift. Gave myself quite a scare. My interpretation could be totally wrong, but would like to hear what you guys think about this.
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      07-29-2014, 04:50 PM   #2
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I witness the same and unlike a manual tranny where you can control with the clutch...the sports mode downshift/rev match is dangerous, I hope they will do a software update to make it better
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      07-29-2014, 06:59 PM   #3
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All it's doing is momentarily adding throttle to match your engine speed to the drivetrain speed (in a manual, while the clutch is depressed or while an automatic transmission is decoupled). The goal is to reduce driveline shock, prevent the driven wheels from locking up, and maintain balance. It shouldn't affect your braking.
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      07-29-2014, 07:03 PM   #4
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Plus your brakes will have plenty of force to override any kind of partial throttle that the engine would be creating, although I don't see any reasoning as to why it would do something counter-intuitive like that.
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      07-29-2014, 07:12 PM   #5
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Quote:
Originally Posted by lichenlt View Post
I remember a while ago someone asked a question about the rev going higher when braking. Some said it was like a rev matching thing.

I never had a car with rev matching so no idea how that actually works, but the other day I was coming to a hard stop coming off the freeway (~65 to 0 in not so short of a distance).

I felt like the rev matching made it more difficult to stop and I nearly hit the car in front me but eventually it stopped in time. I think I used full braking power and the car just wasn't slowing down efficiently as it was reving up with the downshift. Gave myself quite a scare. My interpretation could be totally wrong, but would like to hear what you guys think about this.
i mean.. it does this with any to most auto cars. revs will go up when u brake. but this shouldn't be a big issue. i wouldn't know though since im not auto
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      07-29-2014, 07:25 PM   #6
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Quote:
Originally Posted by Year's_End View Post
Plus your brakes will have plenty of force to override any kind of partial throttle that the engine would be creating, although I don't see any reasoning as to why it would do something counter-intuitive like that.
Ya even if you go full throttle... your brakes should have no problem in blocking the wheels... although I don't recommend you to try as you put a lot of stress on the whole drivetrain for no reason....

If it's such a big issue just drive in COMFORT it will not rev match
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      07-29-2014, 07:25 PM   #7
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I feel the 6MT blips the throttle when you shift under hard acceleration as well...or is it just in my head?
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      07-29-2014, 07:34 PM   #8
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Quote:
Originally Posted by Year's_End
All it's doing is momentarily adding throttle to match your engine speed to the drivetrain speed (in a manual, while the clutch is depressed or while an automatic transmission is decoupled). The goal is to reduce driveline shock, prevent the driven wheels from locking up, and maintain balance. It shouldn't affect your braking.
Technically thats how it should work but with the m235, turbo kicks in when the downshift rev match happens and you can feel the car accelerate while you're hard braking and thats not good
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      07-30-2014, 12:11 AM   #9
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Quote:
Originally Posted by HX_Guy View Post
I feel the 6MT blips the throttle when you shift under hard acceleration as well...or is it just in my head?
In your head unfortunately. I had been hoping for this feature in the M235i - hell, BMW puts it in the Mini for heaven's sake. It will no doubt be in the M2 as it's in the new M3/4.
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      07-30-2014, 08:10 AM   #10
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Quote:
Originally Posted by Devon K View Post
In your head unfortunately. I had been hoping for this feature in the M235i - hell, BMW puts it in the Mini for heaven's sake. It will no doubt be in the M2 as it's in the new M3/4.
Not really in "your head", watch the tach while upshifting - disengage the clutch, the revs will drop a bit, and then raise a bit, and stick for a fraction before dropping again.
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      07-30-2014, 11:16 AM   #11
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Quote:
Originally Posted by ska///235i View Post
Technically thats how it should work but with the m235, turbo kicks in when the downshift rev match happens and you can feel the car accelerate while you're hard braking and thats not good
I think that's exactly what happened. Couldn't quite put my finger on it until you mentioned it.

In addition, when it slows down to certain speed I can feel some sort of engine braking kicking in because the stopping power suddenly increases without me pushing the brake pedal further.

Last edited by lichenlt; 07-30-2014 at 11:22 AM..
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      07-30-2014, 12:08 PM   #12
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Quote:
Originally Posted by ska///235i View Post
Technically thats how it should work but with the m235, turbo kicks in when the downshift rev match happens and you can feel the car accelerate while you're hard braking and thats not good
Quote:
Originally Posted by lichenlt View Post
I think that's exactly what happened. Couldn't quite put my finger on it until you mentioned it.

In addition, when it slows down to certain speed I can feel some sort of engine braking kicking in because the stopping power suddenly increases without me pushing the brake pedal further.
That doesn't make any sense though. I don't understand why the engine control would be calibrated to increase throttle during deceleration while it's in-gear. Do you mean that you see the rev counter increase while slowing down and the transmission hasn't downshifted? It could be the torque converter unlocking.

If you feel the engine braking kicking in at a certain point during deceleration, it's probably the transmission shifting down to a lower gear which would add more drag. Rev-matching is supposed to minimize that sensation.
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      07-30-2014, 12:16 PM   #13
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Quote:
Originally Posted by Year's_End
Quote:
Originally Posted by ska///235i View Post
Technically thats how it should work but with the m235, turbo kicks in when the downshift rev match happens and you can feel the car accelerate while you're hard braking and thats not good
Quote:
Originally Posted by lichenlt View Post
I think that's exactly what happened. Couldn't quite put my finger on it until you mentioned it.

In addition, when it slows down to certain speed I can feel some sort of engine braking kicking in because the stopping power suddenly increases without me pushing the brake pedal further.
That doesn't make any sense though. I don't understand why the engine control would be calibrated to increase throttle during deceleration while it's in-gear. Do you mean that you see the rev counter increase while slowing down and the transmission hasn't downshifted? It could be the torque converter unlocking.

If you feel the engine braking kicking in at a certain point during deceleration, it's probably the transmission shifting down to a lower gear which would add more drag. Rev-matching is supposed to minimize that sensation.
I know what rev match is and i drive manual for years

The sudden downshift rev match has a slight acceleration that will launch the car while you're hard breaking...just enough to give u a scare if a car is in front of you

But it doesnt happen in all cases/braking...this is on the 8z auto
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      07-30-2014, 12:17 PM   #14
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Rev match on 6MT?? Confirmed?
That will need to get DISABLED for my 2er, stat! That's half the fun of getting the downshift matched.
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      07-30-2014, 02:53 PM   #15
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Quote:
Originally Posted by e90post_user View Post
Not really in "your head", watch the tach while upshifting - disengage the clutch, the revs will drop a bit, and then raise a bit, and stick for a fraction before dropping again.
That's called "rev hang". It's an ECU / emissions thing. It's not matching anything, it just doesn't fall like you would expect.
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      07-30-2014, 03:30 PM   #16
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Quote:
Originally Posted by chris719 View Post
That's called "rev hang". It's an ECU / emissions thing. It's not matching anything, it just doesn't fall like you would expect.
The rev hang is understood, however, watch it yourself - the RPM will raise a bit upon initial clutch disengagement.
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      07-30-2014, 04:01 PM   #17
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My Mazda 3 does that also, it's some software / throttle thing and the revs jump a bit when the clutch is disengaged on hard acceleration.

It's not rev matching like is present in the M3, 370Z, or C7 unless it happens on downshifts, where it's extremely noticeable by moving the stick and seeing the revs jump and hold until you complete the shift.
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