Do you engine compression brake?

[Angrybird 12]

Wow the Gravity of the situation sure is causing a lot of friction in this thread...

[Bodih]

The way I see it, God put two sides on a gear tooth for a reason. Use them.

[thahemp]

Originally Posted by 13lstuner

Gosh the semantics debated on this forum blows my mind. My major will be physics in two years when I graduate, but truthfully all of this seems like everyone trying to prove the last man wrong. The original purpose of this thread was making sure that downshifting would not exponentially increase the mechanical wear on his tranny, or whatever you would like to say. Now it is just useless bantering and everyone trying to prove the last man wrong. The OP doesn't need to understand the forces acting upon his car. Especially completely irrelevant information like if the ground wasn't there, and neither does anyone else. So just answer the question to the best of your ability, or if you have no clue just move on. I will learn the "string theory" and quantum mechanics another time.(I know that is not what you all were explaining please do not start flaming me for joking)

I hope your quantum mechanics class never discusses anything slightly off-topic. Maybe the OP is curious about the forces acting on his car. I don't think you get to decide what everyone else is or is not interested in understanding.

[thahemp]

Also, you spent a whole post ranting about what pisses you off and never addressed the question.

"So just answer the question to the best of your ability, our if you have no clue just move on."

[upflying]

Brakes are cheaper than revs, gas and synchros.
I downshift just before rolling to a stop.
I do downshift as needed when not coming to a full stop.

[ChrisBlair]

The OP is talking about rev matching, not throwing the gear lever into 2nd from 5th and hanging on for the ride while the tires bark. Jeez, guys.

No, this does not hurt, provided you're not over-revving to begin with. How can it? And what "stress" is this providing? You've matched revs.

[13lstuner]

Originally Posted by thahemp

Also, you spent a whole post ranting about what pisses you off and never addressed the question.

"So just answer the question to the best of your ability, our if you have no clue just move on."

Would like to clarify. I never stated anything made me mad or "pissed me off". And my apologies for not
Including my thoughts on OP's post, as it was my intentions to do so. And yes I can not speak for OP, but I can point out that it was not stated anywhere in his original that he cared for any of this. It is beyond being able to understand, as I'm sure OP is a completely competent guy that is capable of understanding, but why would you want to? If he wanted to understand the forces acting on his vehicle and you proved me wrong fine, but I do have to state that your comment of "Technically, the ground keeps you there. Move the ground out of the way and you'd be off and accelerating again." Had nothing to do with the car at that point. Simply trying to prove the previous man wrong. On top of being completely speculative. The same type of speculation you display in stating "I hope your quantum mechanics class never discusses anything slightly off-topic." As in the same argument that you state myself not knowing what the OP wants neither do you know what anything within my college experience will be like.


As for you OP I am sorry all of this is occurring it is all ridiculous from everyone including myself. I apologize for moving your thread further off topic. As for your question I agree with ChrisBlair as long as you are not "over-revving" I don't see how much more mechanical erosion you could be causing but this is my interpretation. As I do not do this so I have not delt with the repercussions if any.

[thahemp]

Originally Posted by ChrisBlair

The OP is talking about rev matching, not throwing the gear lever into 2nd from 5th and hanging on for the ride while the tires bark. Jeez, guys.

No, this does not hurt, provided you're not over-revving to begin with. How can it? And what "stress" is this providing? You've matched revs.

Agreed. Synchros are happy. Clutch is happy. Gears could care less.

[ChrisBlair]

Originally Posted by jd10013

I'm guessing that would depend on what rev you were matching and for how long. if your revving it to 5k to slow the car and traveling half a mile like that to slow the car, then that undoubtedly puts strain on the transmission. I don't see how it's possible to use your transmission to stop slow your car without putting stress on it. it's just a question of how much.

I'm not sure you're understanding. You match to the rev the engine would see if the trans was just downshifted. But the clutch is in while you bring up the rpms. You don't de-clutch until the revs are matched. You raise the rpms when rev-matching, so there is no "stress". And more importantly, the car is not unsettled.

This is not 'using the trans to slow the car' at all. In addition what many people feel is 'using the manual trans to slow down' is actually using engine comrpession to slow down. But that is not what I've described either.

Your example of the half-mile stretch is no more 'damaging' to the trans than simply being in the high range to begin with. That's the same as traveling 30 mph at 5K rpms. Plus, the point of rev-matching is not to simply practice blipping the throttle correctly so you can be in a gear too low to travel in. What would be the point of your scenario, regardless of whether it harms anything or not? It's as useless as being at 5K rpms at 30 mph when driving down the street: you've picked the wrong gear. That's not the point of rev-matching.

I think you don;t quite grasp the thing. If you know somebody that does this well- even better if he or she can heel and toe well- go for a ride with them and have them demonstrate. The car, to you, will feel a lot like an auto trans

[thahemp]

Originally Posted by 13lstuner

Would like to clarify. I never stated anything made me mad or "pissed me off". And my apologies for not
Including my thoughts on OP's post, as it was my intentions to do so. And yes I can not speak for OP, but I can point out that it was not stated anywhere in his original that he cared for any of this. It is beyond being able to understand, as I'm sure OP is a completely competent guy that is capable of understanding, but why would you want to? If he wanted to understand the forces acting on his vehicle and you proved me wrong fine, but I do have to state that your comment of "Technically, the ground keeps you there. Move the ground out of the way and you'd be off and accelerating again." Had nothing to do with the car at that point. Simply trying to prove the previous man wrong. On top of being completely speculative. The same type of speculation you display in stating "I hope your quantum mechanics class never discusses anything slightly off-topic." As in the same argument that you state myself not knowing what the OP wants neither do you know what anything within my college experience will be like.


As for you OP I am sorry all of this is occurring it is all ridiculous from everyone including myself. I apologize for moving your thread further off topic. As for your question I agree with ChrisBlair as long as you are not "over-revving" I don't see how much more mechanical erosion you could be causing but this is my interpretation. As I do not do this so I have not delt with the repercussions if any.

There is no need for apologies here. Lighten up. Were all just talking. Shooting the sh!t. Have some fun!

[MADBADGER]

thanks for all your posts. I read them all and found it quite amusing. I just acquired my degree in mechanical engineering. So I do not need a lesson on physics or the mechanical properties of a clutch or transmission.

Some of you are right, and some of you are wrong. What's slowing me down from engine compression braking is the force required to compress the air in the cylinder of the engine, not friction.... "engine COMPRESSION braking!"

Anyway this post answered my question

Originally Posted by 2SS 2011

The automatics do it automatically.. the RPM levels are controlled by computer.. With an M6 it's controlled by our foot..Unless your letting it rev down from 6,000 RPM's .. You should be fine lol

I mean think about it .. The only true friction involved is actually engaging the clutch ..(clutch plates etc)

Once you are in gear.. you are in gear.. Revving down is the same as revving up to the next gear when you normally drive.. it's basically the same.. It works both ways

an acceleration is an acceleration. slowing down is an acceleration, just in the negative direction or deceleration. if no wear occurs on the transmission when you accelerate. then no wear would occur when you decelerate.

[thahemp]

Word.

[JohnnyBfromPeoria]

I'm not as good as I could possibly be at rev matching, nor do I really fell like it's necessary in daily driving. As such, I usually do not downshift to allow compression braking. If there's a sense that I could put myself into a situation where acceleration could be necessary just after decelerating, yes, I'll be in the right gear to do so, but if I'm just slowing on an off ramp or coming up to a light I know is going to stay red until after I stop, I'll use the brakes. I can change those in about ten minutes per wheel when necessary and at a far lower cost than I can the clutch components, made necessary by mis-managing my clutch, attempting to rev match and downshift because it sounds or feels cool.

But that's just me.

And who forgot to include the effect of toe-in/toe out on slowing a vehicle? Not this guy.

John B.

[thahemp]

Rev matching is very handy for making turns too. It just makes your overall driving more crisp when you make it a priority to master. You could argue that good rev matching can lengthen the life of your clutch because you tend to hit it right on the money more often.