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E90/E91/E92/E93 (2006 - 2013)
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Old 05-17-2013, 09:20 AM
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Rev Matching

I have been driving extra spirited lately which leads me to the following question. My sport package tiptronic with paddles is a lot of fun when used correctly. I hear about similar transmissions, like the new Toyobaru twins BRZ and FR-S, that have available paddle shifters with Rev matching. Does my vehicle have rev matching? What is rev matching exactly?


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Old 05-17-2013, 09:35 AM
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rev matching is when you throttle RPMs in between gears to match the RPM that were used when the last gear was engaged so you dont experience loss of acceleration due to lower RPMs when in the new gear. steptronic does it but not in manual mode of course.
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Old 05-17-2013, 09:53 AM
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Originally Posted by chris328 View Post
rev matching is when you throttle RPMs in between gears to match the RPM that were used when the last gear was engaged so you dont experience loss of acceleration due to lower RPMs when in the new gear. steptronic does it but not in manual mode of course.
Steptronic rev matches in manual mode.



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Old 05-17-2013, 11:03 AM
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if you press the pedal, yes
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Old 05-17-2013, 11:14 AM
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if you press the pedal, yes
In manual mode the Steptronic will rev match a downshift whether you press the pedal of not.

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Old 05-17-2013, 06:32 PM
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it's semantics
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Old 05-17-2013, 06:51 PM
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Rev Matching

It is not semantics it is a fact.

Any time that the Steptronic is in manual mode and a manual downshift is executed the engine will rev match before the lower gear is engaged. You can feel it, you can hear it and you can see it on the tachometer.

This will happen whether you are braking, have both feet off the pedals or are on maintenance throttle.


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Old 05-17-2013, 06:53 PM
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Rev Matching

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Originally Posted by captainaudio View Post
It is not semantics it is a fact.

Any time that the Steptronic is in manual mode and a manual downshift is executed the engine will rev match before the lower gear is engaged. You can feel it, you can hear it and you can see it on the tachometer.

This will happen whether you are braking, have both feet off the pedals or are on maintenance throttle.

In this respect it acts exactly like a DCT.




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Old 05-17-2013, 06:54 PM
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Rev Matching

Rev matching is primarily used during the downshift when the RPM's need to be higher when going from a higher to lower gear. It allows for a smooth transition when shifting gears. Automatic transmissions rely on software to put you in the correct RPM range, while manual transmission cars require a driver to blip the throttle - there were made advances in manual transmission cars that implemented rev match without driver's intervention, e.g. the Nissan 350/370z and the new F10 BMW M5.


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Old 05-17-2013, 06:54 PM
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with a true manual tranny, would you ever revmatch just for the hell of it without accelerating? is it even possible?
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Old 05-17-2013, 06:59 PM
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Rev Matching

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Originally Posted by chris328 View Post
with a true manual tranny, would you ever revmatch just for the hell of it without accelerating? is it even possible?
Going uphill when you are in a higher gear and avoid lagging the engine, slowing down with engine braking assistance.


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Old 05-17-2013, 07:01 PM
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both which require you to step on the pedal...
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Old 05-17-2013, 07:05 PM
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Rev Matching

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Originally Posted by chris328 View Post
both which require you to step on the pedal...
Well that depends which one haha. Going uphill to maintain speed you should keep your right foot on the accelerator, while slowing down you might need to use hill and toe to brake while downshifting to avoid jerking motion by just downshifting.


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Old 05-17-2013, 07:08 PM
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Originally Posted by chris328 View Post
with a true manual tranny, would you ever revmatch just for the hell of it without accelerating? is it even possible?
Absolutely, I do it every time I down shift an MT and it is the correct way to shift a manual transmission. It is not done for the hell of it, it is done to keep from unsettling the car. That is the whole point of the heel and toe technique. This is absolutely essential for track driving with an MT if you want to stay on the track.

The idea of the rev match on a down shift is to "blip" the accelerator to get the engine turning at the same speed as the drive train. If this is not done the car can very violently decelerate when the shift is executed which will suddenly shift the weight to the front of the car. This will increase the size of the front contact patches and decrease the size of the rear contact patches. This can, and if your are anywhere near the limits will, cause the rear end to spin out. This is called trailing clutch oversteer or "TCO". The ZF Steptronic that BMW uses and DCT transmissions will automatically rev match a down shift. There are even some manuals available that will automatically "blip" the accelerator to rev match a down shift. The Nissan Z and the new BMW M5 both have this feature on the MT equipped versions,

This is a good video showing heel and toe downshifts with a manual transmission.



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Old 05-17-2013, 07:12 PM
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Originally Posted by chris328 View Post
both which require you to step on the pedal...
As I stated pressing on the pedals has nothing to do with the Steptronic or DCT rev matching. Both transmissions will rev match a downshift when you are off both the brake and the throttle.

Also it is not necessary to rev match an up shift.

Obviously you need to press on the clutch pedal to rev match an MT (actually technically you don't since you can shift an MT without using the clutch if you know what you are doing) but you will need to manually "blip" the accelerator to rev match an MT.

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Old 05-17-2013, 07:12 PM
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Quote:
Originally Posted by chris328 View Post
both which require you to step on the pedal...
Be clear about what you are asking. Applying more throttle does not necessarily mean accelerating. Another reason to rev-match without changing speed, up or down, is to choose a different gear based on observations of traffic. See a situation developing from which you might need to escape? Blip down a gear or two while holding constant speed. The moment passes without event? Upshift to cruising gear, again without changing speed.

That's not a semantic difference, it's understanding the throttle (and gearing) can be used to control engine speed separately from vehicle speed.
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Old 05-20-2013, 10:34 AM
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i was under the impression that you rev match to avoid putting undue stress by matching before you engage the clutch, or to get a consistent acceleration, both which require you to blip the throttle (what i meant by pressing the pedal). since the steptronic's manual mode can revmatch both with and without pressing the pedal, i was saying that calling it revmatching is semantics because while it technically is revmatching in manual mode, you aren't required to blip the throttle, so one could argue it isn't a "true" revmatch with respect to a true manual transmission.

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Old 05-20-2013, 11:41 AM
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Originally Posted by chris328 View Post
i was under the impression that you rev match to avoid putting undue stress by matching before you engage the clutch, or to get a consistent acceleration, both which require you to blip the throttle (what i meant by pressing the pedal). since the steptronic's manual mode can revmatch both with and without pressing the pedal, i was saying that calling it revmatching is semantics because while it technically is revmatching in manual mode, you aren't required to blip the throttle, so one could argue it isn't a "true" revmatch with respect to a true manual transmission.
The purpose and the principal of rev matching are identical regardless of what the technology being used to shift the gears. DCTs, Steptronics and now some MTs will "blip" the throttle to rev match automatically. The fact that the rev matching is done automatically does not mean it is not "true" rev matching any more than the fact that a DCT or steptronic can shift gears automatically means that they are not "really shifting gears".

With a manual transmission the throttle blip for a rev match is at best a really good guess regardless of the skill of the driver. An expert driver will be so close that it can appear to be perfect but it is virtually impossible to manually get an exact speed match between the engine and the drive train, A DCT or a Steptronic (and some other planetary gear ATs) will rev match under computer control and will get it perfect every time.



It is not necessary to rev match an upshift.
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Old 05-20-2013, 12:51 PM
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At the end of the front straight at NHMS is a sharp downhill left hander. I normally am in 3rd at 114mph on the straight and stay in 3rd through the chicane. Once, to see if I could take advantage of 4th for even a short while I quickly upshifted, got another 2 seconds of throttle, and then proceeded to downshift to 3rd but unfortunately muscle memory said nothing about rev matching, having been around the corner using brakes only (not downshifting) for so long.
Needless to say, Captain's use of the word "unsettled" is understatement at its best. Fortunately I was able to straighten out the car, get back on the brakes, and make a very late entry into turn 1. As others said, rev matching is critical for downshifting and maintaining grip when running at 95%. For upshifting, not so much. Up shift rev matching is to optimize speed, downshift rev matching is to maintain grip. Captain?
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Old 05-20-2013, 01:13 PM
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Quote:
Originally Posted by captainaudio View Post
The purpose and the principal of rev matching are identical regardless of what the technology being used to shift the gears. DCTs, Steptronics and now some MTs will "blip" the throttle to rev match automatically. The fact that the rev matching is done automatically does not mean it is not "true" rev matching any more than the fact that a DCT or steptronic can shift gears automatically means that they are not "really shifting gears".
exactly, it is semantics. try to tell everyone who drives a 6MT here that ppl who drive autos are shifting gears just as much as they are with their 6MT, and tell me how far you get.

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Old 05-20-2013, 02:05 PM
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exactly, it is semantics. try to tell everyone who drives a 6MT here that ppl who drive autos are shifting gears just as much as they are with their 6MT, and tell me how far you get.
OK you win, It's semantics.

Steptronics and DCTs dont rev match.

I made the whole thing up to compensate for my complete lack of ability to master the unbelievably difficult task of learning how to drive a manual transmission.
And all of that stuff in my sig is a lie.

And by the way thanks for the excellent suggestion.

The next time I have want to learn about how transmissions work instead of asking some of my friends who race in ALMS, Trans AM, Grand Am and have competed in Formula One, won the Daytona 24 Hour, the 12 Hours of Sebring, placed 5th in the Indianapolis 500, been national champions, etc. I will simply ask the 6MT drivers here on Bimmerfest and tell you how far I get.





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Old 05-20-2013, 02:09 PM
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Quote:
Originally Posted by DSXMachina View Post
At the end of the front straight at NHMS is a sharp downhill left hander. I normally am in 3rd at 114mph on the straight and stay in 3rd through the chicane. Once, to see if I could take advantage of 4th for even a short while I quickly upshifted, got another 2 seconds of throttle, and then proceeded to downshift to 3rd but unfortunately muscle memory said nothing about rev matching, having been around the corner using brakes only (not downshifting) for so long.
Needless to say, Captain's use of the word "unsettled" is understatement at its best. Fortunately I was able to straighten out the car, get back on the brakes, and make a very late entry into turn 1. As others said, rev matching is critical for downshifting and maintaining grip when running at 95%. For upshifting, not so much. Up shift rev matching is to optimize speed, downshift rev matching is to maintain grip. Captain?
What you experienced was classic trailing clutch oversteer (TCO). By not rev matching when you downshifted the engine was spinning much slower than the drive train, When the clutch was engaged the wheels were trying to drive the engine. The compression braking of the slower turning engine caused the car to decelerate very suddenly which caused a weight transfer to the front wheels. You are lucky that you were able to recover and keep the car on the track. I am sure that your previous track experienced helped.

Did you have all of the nannies shut off?

I would suggest that in the future you keep your smart phone with you in the car and as soon as you lose control and feel a spin coming on post here in Bimmerfest and ask the 6MT drivers what to do.
Quote:

Help Needed.
"To all you MT drivers. I am at the track and forgot to rev match a down shift. The rear end broke loose and I am spinning out. What should I do?
By the way your loss of control on the non rev matched downshift was semantics.

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Old 05-20-2013, 02:15 PM
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How can you tell that a steptronic performed a rev match if the downshift was smooth.
DCT's jump down multiple gears quickly during hard driving, but steptronics don't, yes?

I rev match as much as possible during normal driving, by way of a throttle blip between shifts, no heel toe.

Last edited by boramkiv; 05-20-2013 at 02:19 PM. Reason: Multiple gears
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Old 05-20-2013, 02:49 PM
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Originally Posted by boramkiv View Post
How can you tell that a steptronic performed a rev match if the downshift was smooth.
DCT's jump down multiple gears quickly during hard driving, but steptronics don't, yes?

I rev match as much as possible during normal driving, by way of a throttle blip between shifts, no heel toe.
You can tell that the Step rev matched because:

1. You can hear the engine rev
2. You can watch the tachometer
3. The car will not suddenly slow down when you downshift



The 8 speed Steptronic can go from 8th to 2nd and will rev match perfectly to keep the shift smooth.



Many race cars (including the racing version of the M3) will not allow you to skip gears as they have sequential manual transmissions.

The only time you need to heel toe is when you are downshifting while braking. I got in the habit of heel and toeing and double clutching (totally unnecessary on a BMW with synchros) because my track car had straight cut gears and no synchros. I did that to stay in practice but now both of my street cars have ATs.

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Old 05-20-2013, 07:08 PM
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Quote:
Originally Posted by captainaudio View Post
What you experienced was classic trailing clutch oversteer (TCO). By not rev matching when you downshifted the engine was spinning much slower than the drive train, When the clutch was engaged the wheels were trying to drive the engine. The compression braking of the slower turning engine caused the car to decelerate very suddenly which caused a weight transfer to the front wheels. You are lucky that you were able to recover and keep the car on the track. I am sure that your previous track experienced helped.

Did you have all of the nannies shut off?
Yes. What really helped me was knowing I didn't have to dive down into the left hander, there's a runout at the end of the straight in case one finds oneself in my situation. There's an 8' concrete wall on the immediate right which can lead to a bad paint day, but my momentum was carrying me left and I was careful not to overcorrect.
As I was doing the little twitchy dance there was only one thought on my mind, Sh*t, did I over rev? Bumpers and fenders are cheaper than engines.

My personal thoughts on DSC: It's a fantastic feature which will save your butt on many occasions . That said, when learning to really drive it's a drawback. With it on you never get to learn where the edge is until you're actually over it and then nothing is going to set things right. You're in way too deep. Without DSC you learn early on where the edge is and what you feel as things begin to go. Also, traction control cutting power on bumpy sections is a real downer. There's one notoriously bumpy spot at NHMS, that's where the esses end and you're entering the front straight. Just as you're pouring on speed with tons of traction due to the uphill easy left you hit the bumps and the computer decides you'd be better off without all the torque.
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