Nothing really, but you are putting a bit more pressure on your clutch.

Worse is downshifting from 3rd @ 6000rpm into 2ndoohhh:

 

As bayerischemotor said, nothing really bad ... but, you will feel a little jolt on engagement of the next gear ...

You should work to get it right every time ... much easier on the clutch ... and, your back ... and, your neck ... and, your passenger ... and ...

And, how do you get it right? Practice, practice, practice ... I find it is much easier to get good downshifts when Sport Mode is ON. I find, for me, that it is hard to get downshifts right when Sport Mode is OFF, and I am shifting from 5th to 4th and from 3rd to 2nd.

 

That is usualy the number one reason most M5s burn their weak clutch. I still have the original at 100K miles.

 

The easiest way to get a good downshift is to

1. drive at steady speed (no acceleration, accelerator pedal in a steady position)

2. Keep accelerator pedal steady, and declutch.

3. Change gear. Still keeping accelerator steady.

4. Wait a second for the revs to come up "by themselves". Keeping accelerator steady.

5. Ease off the clutch. Kepping accelerator steady.

6. When foot is completely off the clutch pedal, if desired hit the accelerator.

Aim your timing at getting a slight forward jolt when the clutch is relesed. This is indicative of a slightly too high RPM, but that is far mor comfortable for the passengers than if the RPM would be slightly low.

David

 

Rev matching

Correct me if I'm wrong, I'm no expert, but . . .

In track conditions, you could lose control of the car by not rev matching on the downshift.

When I attended the M school at VIR, we had one driver that consistantly downshifted without rev matching. His back tires would bark and the back end of the car would loosen up before he entered the turn. The instructor reinforced to the whole class the importance of rev matching on the downshift.

 

Correct me if I'm wrong, I'm no expert, but . . .

In track conditions, you could lose control of the car by not rev matching on the downshift.

When I attended the M school at VIR, we had one driver that consistantly downshifted without rev matching. His back tires would bark and the back end of the car would loosen up before he entered the turn. The instructor reinforced to the whole class the importance of rev matching on the downshift.

True, but as you said this is track use.

 

I swear by matching revs when downshifting and not doing "power launches" and other nasty things to my clutch.

Having seen the training videos by Greg it confirmed my driving style is "optimal" for the notoriously weak clutch of the E39 M5.

Still have the original OEM clutch at 109 000 km.

My two cents.

Rudi

 

Im surprised noone has mentioned this. The main reason for matching revs is that the stress is taken off of the syncronizers in the transmission. Ours are quite strong however they are not invincible. Not matching revs when downshifting will kill your syncros and tranny eventually. Also, its a fun way to lose control when the rear wheels lock up (DSC has a fun time catching this).

 

Im surprised noone has mentioned this. The main reason for matching revs is that the stress is taken off of the syncronizers in the transmission. Ours are quite strong however they are not invincible. Not matching revs when downshifting will kill your syncros and tranny eventually. Also, its a fun way to lose control when the rear wheels lock up (DSC has a fun time catching this).

It's also a quicker shift (if that matters) not having to wait for the synchro's to spool things up.

 

Hmm all good points

but then what is truly the purpose of engine braking???? if the revs match then there is no such thing as engine braking is there???? the point of downshifting and matching revs would be to get the car ready to pass not slow down ( i go up in revs before I shift up... hence speeding up)

or am I missing something there

 

Im surprised noone has mentioned this. The main reason for matching revs is that the stress is taken off of the syncronizers in the transmission. Ours are quite strong however they are not invincible. Not matching revs when downshifting will kill your syncros and tranny eventually. Also, its a fun way to lose control when the rear wheels lock up (DSC has a fun time catching this).

This is not true. Rev matching or not, with single-clutch downshifts, the synchros synchronize the transmission. You have to double clutch/rev match to eliminate wear on the synchros. The other reasons for rev matching even with single-clutch downshifting stated above are also valid - the PRIMARY goal is smoothness - otherwise you're gona have a sloppy tail - and on the track that is a big problem - you're already braking hard and the tail is already light.

The statement that this is the primary cause of premature clutch wear is also incorrect. In a non-rev-matched downshift, the weight of the car accelerates the engine to the proper RPM. It certainly wears the clutch more than a rev-matched shift, but the engine doesn't "fight" this - and the revs will get matched in fairly short order (while the passenger's heads are lurched forward) - with little heat generated in the clutch. The PRIMARY cause of premature clutch wear is UPSHIFTING, flooring the throttle and letting the revs get ahead of the wheel RPM before the clutch is hooked up. In this case you're asking the clutch to absorb 400 ft-lb of torque while it is slipping - and this will generate a huge amount of heat in a hurry. This condition can also last MUCH longer than in a botched downshift, and if the driver doesn't do the right thing (ABORT = LIFT) - toasted clutch in short order.

 

You have to double clutch/rev match to eliminate wear on the synchros.

Yes, I double clutch. Snicks it right in much faster. But maybe my synchro's are slow. I have the feeling of puuuushing the shifter into gear and it takes a bit. Never driven another M5.

 

Hmm all good points

but then what is truly the purpose of engine braking???? if the revs match then there is no such thing as engine braking is there???? the point of downshifting and matching revs would be to get the car ready to pass not slow down ( i go up in revs before I shift up... hence speeding up)

or am I missing something there

You do have less engine braking, but you still have some. A higher reving engine has more frictional horsepower loss and that translates to braking. You do lose out on using the engine's rotational inertia, though.

But remember, not all downshifts are for braking! Wooohooo...

 

But remember, not all downshifts are for braking! Wooohooo...

Strictly speaking, the only time I would use engine braking to slow down a car is in an emergency (street or track).
Engine= $20,000.
Transmission=$6,000
Clutch =$1200
Brake pads=$100
Now, which components do you want to use to slow the car?:cheers:
Regards,
Jerry

 

Engine braking is NOT the deceleration that comes from slipping the clutch while the engine revs up. Engine braking is what happens when you lift, in gear, clutch hooked up. Downshift to get more of it. You should ALWAYS rev match! The above is poor technique, pure and simple.

On the track you use your brakes ONLY to slow down. Engine braking is a brake-saving technique for long downgrades. On the track you downshift WHILE braking to be ready to accelerate out of the corner in the proper gear.

 

Yes, I double clutch. Snicks it right in much faster. But maybe my synchro's are slow. I have the feeling of puuuushing the shifter into gear and it takes a bit. Never driven another M5.

A properly rev-matched double clutch downshift places virtually no load on the synchros. You still have to move the lever "through" them to full engagement. But when you DO have synchros, if you botch a double clutch downshift the synchros still do their job, so this might be what you're feeling. (when you shift a car without synchros and fail to properly double-clutch/rev match, the results are far more, shall we say, ... audible.)

 

A properly rev-matched double clutch downshift places virtually no load on the synchros. You still have to move the lever "through" them to full engagement. But when you DO have synchros, if you botch a double clutch downshift the synchros still do their job, so this might be what you're feeling. (when you shift a car without synchros and fail to properly double-clutch/rev match, the results are far more, shall we say, ... audible.)

Right. I meant I have the feeling of pushing if I DON'T double clutch. Double clutching just "snicks" it right in.

 

These 6spd transmissions just don't shift as well as a Honda or Miata tranny. My car is so difficult to shift when it's still cold, but once warm it's acceptable.

 

BTW. Hi I am a newbie and just purchased my 02 540i-6, and it's my biggest complaint about my car.

 

On the track you use your brakes ONLY to slow down.

I disagree. You ALSO use the brakes to put more weight on the front wheels so they will grip better during the turn ... In this senario, you may even touch the brakes to shift the weight forward, even though you don't need to slow down.

Just my opinion, but I have tried it ... and, they teach it for that purpose in the M schools.

 

I swear by matching revs when downshifting and not doing "power launches" and other nasty things to my clutch.

Having seen the training videos by Greg it confirmed my driving style is "optimal" for the notoriously weak clutch of the E39 M5.

Still have the original OEM clutch at 109 000 km.

My two cents.

Rudi

I treat my M5 clutch nicely also and have 125,000 km on it with no problem. I am having it changed today however as I got a ripper of a deal on a flywheel and clutch kit and I'd rather it not leave me stranded someplace.

Got the clutch kit for USD$414 and Flywheel for $628.

I forgot to ask them to give me back the old ones to take a photo of, but never mind ... they might given that I supplied the parts..

 

Correct me if I'm wrong, I'm no expert, but . . .

In track conditions, you could lose control of the car by not rev matching on the downshift.

When I attended the M school at VIR, we had one driver that consistantly downshifted without rev matching. His back tires would bark and the back end of the car would loosen up before he entered the turn. The instructor reinforced to the whole class the importance of rev matching on the downshift.

Ya pushing the limits in a corner and downshifting without rev matching might make the wheels break loose from the engine compression.

 

These 6spd transmissions just don't shift as well as a Honda or Miata tranny. My car is so difficult to shift when it's still cold, but once warm it's acceptable.

Put Royal Purple fluid in your transmission for your next fluid change. The difference is amazing. Its not going to shift like a Honda, but you will be very pleased with the improvement. It shifts almost as well as a 400 horsepower Honda.

 

Always rev match!! I pull the clutch out without rev matching when I want to shock the rear tires to get a car sideways. Not something you want to accidentally do with your family in the car when it is raining. DSC can't defy the laws of physics.

I disagree. You ALSO use the brakes to put more weight on the front wheels so they will grip better during the turn ... In this senario, you may even touch the brakes to shift the weight forward, even though you don't need to slow down.

Just my opinion, but I have tried it ... and, they teach it for that purpose in the M schools.

Greg is pretty keyed into advanced driving techniques like trail braking. I think he was keeping it simple and on topic. But you are right, you need to transfer weight (and more importantly use the rear end to do some steering) to keep from killing the front tires. Also keeps your mid corner speed a lot higher.
:cheers:

 

I disagree. You ALSO use the brakes to put more weight on the front wheels so they will grip better during the turn ... In this senario, you may even touch the brakes to shift the weight forward, even though you don't need to slow down.

Just my opinion, but I have tried it ... and, they teach it for that purpose in the M schools.

JCLYMAN - you're right, but I think you misinterpreted my response, which was relative to the topic of engine braking. So I didn't mean the only function of the brakes was to slow down - weight transfer is very important in track driving as you point out. I only meant that to slow down, you use your brakes, NOT engine braking. (Even that isn't completely true - you balance a car in a corner with throttle specifically because of the weight transfer.) But you get my point , I hope...