Assuming any engine and transmission has a finite lifespan (as do all mechanical components) the more you use them (more revolutions on the engine and transmission), the sooner they wear out. The more revolutions of the engine you use on deceleration, instead of just idling the car to a stop using just the brakes, the fewer you have to use in the future. Of course, if you're using them for a reason, downshifting to prepare for the next corner, then it's a worthwhile cause. If you like the sound, I suppose that's worth it too. Yes, the wear is very minor, but again, all mechanical components have a finite lifespan, so you have to decide in which situations it's worth using up your 'cycles'.

The other point I want to make is that you're only making the shifting smoother by rev-matching, your NOT saving your tranny. You're actually wearing your synchros. Why? Because unless you're double clutching, you're only speeding up the engine to match where the engine speed should be. Perhaps by explaining how the process works, you'll understand better.

1. Push clutch in, shift into neutral, let clutch out.
2. Blip the throttle.
3. Push the clutch in and shift into the lower gear.
This all happens in less than a second.

What happens is by letting the clutch out and then blipping the throttle, you're actually increasing the speed of the whole tranny. This is because with the clutch out and therefore the tranny engaged with the engine, you're accelerating all the internal components of the tranny. Conversely, with the clutch in and a throttle blip, the tranny doesn't speed up because the clutch is in, thus disconnecting the tranny from the engine, therefore the engine isn't accelerating the tranny components. Now the synchros have to work harder because the tranny speed is much lower than the driveline speed.

Here's another way to think about it:
You're driving at 45mph. In 4th gear your engine is turning at 3,000 RPM (arbitrarily). If you were to go to 3rd, your engine would need to be turning at 4,500 RPM. The engine blip takes care of getting the engine to 4,500 RPM, but of course the input shafts of the tranny also would need to increase in speed. With the clutch out, the engine blip turns the internals of the tranny so that you can slip easily into gear.

One way to try this out is to do a downshift both ways. You'll notice the gear shifter goes into gear much more easily when you double clutch.

I know this is complicated, but for those of you have have experience in this, please chime in. On older cars that had poor synchros, this was essential, almost paramount to even execute a shift. Because most modern cars have double or even triple synchros, the issue has been masked, but again, you'll still notice a much easier and smoother shift with a double clutch than without, and you're tranny will thank you for it.

 

I'm late to this thread but yeah - I was hoping for an "as conditions require" option for this question.

The friction surfaces on the respective parts are designed to provide friction under entirely different sets of circumstances and on this car the factory parts do a great job as designed.

One misguided/poorly executed launch will do more clutch damage than 150K miles of well executed rev matched downshifts imo.

 

Mike, I'm glad you've gotten involved in this thread.

Here is a perfect example of WHY I'm glad you've gotten involved. It never even dawned on me that someone might actually use the clutch to slow the car down. That is so stupid it never even crossed my mind. IF that is what some of the people here mean when they talk about slowing the car by downshifting, then I have to agree that it's a crazy thing to do.

In general, this is as true as it gets. However, there are times when any driver with any smarts at all is going to downshift to help slow the car; The most frequent, and possibly only situation under which most of us ever encounter this is when decending a long mountain road with a steep incline. Using a lower gear can prevent overheating the brakes, and will produce less brake wear than depending totally on the brakes to hold the car at a constant speed. There are times when engine/compression braking SHOULD be used, and failure to do so when needed does result in more wear and tear.

But in general, you always use the brakes to stop or slow the car. We downshift for other reasons. Engine braking going down an incline, or so that we'll be in the right gear when we want to start accelerating. When the downshift is done smoothly, the car does not slow or speed up as the clutch is reengaged, so the clutch isn't being used to slow the car. Has nothing to do with saving the brakes, and downshifting, done "properly," doesn't wear the clutch enough to even be a consideration.

I don't think this is "an ill-posted poll," becaue I believe that some people will learn and benefit from the discussion (and apparently some will learn nothing ). Indeed, you can leave the car in gear, and/or downshift, while also using the brakes at the same time, and that is what a skilled driver does, almost all the time, in infinite variations, depending on both the prevailing conditions and the drivers mood.

Even semi-skilled drivers like myself do this, and anyone who doesn't do this is mistaken to think that they actually know the best way to operate a vehicle with a manual transmission. HOWEVER, there is a big difference between "best way" and "right way." Odds are that you and I have somewhat different "styles," and in some cases, it's just a matter of style, and has nothing to do with right or wrong.

Wrong would be using the clutch to slow the car, coasting out of gear for long distances, holding the car on an incline using the clutch, or other things that are obviously and/or needlessly hard on the car or driveline, or for that matter, anything that might result in a lessening of car control options at an inopportunine time.

As always Mike, your thoughts and posts are most appreciated.

 

While what you say is true, it can be misleading if not understood in the proper context. The context here is engine wear, and all engine wear has to be considered, lest we come to some false conclusions. Let's look at the bigger picture and see if we can't figure out what all this BS really means.

First off (and I'll be damned if having to repeat this isn't irritating ), THE VAST MAJORITY OF ALL ENGINE WEAR TAKES PLACE DURING COLD STARTS. 90% or more of all engine wear takes place during cold starts. So, everything else you do to the car can, AT MOST, only reduce the engine life by the remaining 10%. So lets say that the F20x engine in your car, used the way you use it, will last 200,000 miles as long as you never rev it above 6k, that it will wear out ten times as quickly at 9k (which is insane, but let's pretend that it's a hell of a lot worse than it actually is), and that you spend 50% of your driving time in that high wear range. At most, you would only be able to reduce the engine wear by 10%, beause 90% of your wear is coming from cold starts, no matter how you drive (assuming that you're not over reving the engine and are maintaining it properly). Even if you lose the whole 10%, your 200,000 mile engine is still going to last you 180,000 miles. Well $hit!! If you're worried about using a vehicles performance causing such a tiny difference in engine life, then you should be driving a low reving, economy car or high end deisel.

There is NO metal to metal contact in an engine; Even the piston rings are lubricated, and slide against an oil film. When (and if) the oil breaks down, or when it is not present (as in a cold start) there is high wear. High revs break the oil down faster, because of the increased loads, etc. THEY BREAK DOWN THE OIL, but as long as it is changed frequently enough, there is NEVER any metal to metal contact except during a cold start, so the oil takes the wear rather than the engine. Once the engine is running and has full oil pressure, you can drive if for DAYS, any way you like, and you will NEVER cause as much wear as you did when you started the car.

People who don't have a clue what actually causes wear in an engine or other parts of the car should not expose their ignornace in threads like this one, especially after the facts have been laid out repeatedly. At this point, this crap is just getting STUPID. Bullshit "theories" from people who know virtually NOTHING about cars and internal combustion engines just doesn't cut it.

OTOH, I think I'm in substantial agreement with the rest of your post, but you are still confusing rev matching and double clutching. Read the rest of the thread to learn about the difference before adding any more to people's confusion. That's the last thing we need at this point.

 

That's not true. Not every rev the engine turns is equal, in terms of wear and expected life.

 

[QUOTE=RED MX5,Apr 8 2008, 03:24 PM] Here is a perfect example of WHY I'm glad you've gotten involved.

 

Mike, I honestly do not believe I've ever seen anyone do that (use the clutch slip to slow the car), and frankly, I'd have been shocked if I had. It just never even occured to me that this might be what people were talking about.

One of your comments merits special mention, as the most succinct and to the point comment in this entire thread.
"Not every rev the engine turns is equal, in terms of wear and expected life."

Mike, I'd pay to be able to say things that briefly and effectively.

 

After reading this thread...and pondering how so many people can be so confused as to how to properly decelerate...


If I'm decelerating to turn, I begin by heel-toeing (only, sort of a lazy heel-toe, waiting until I've completed the turn to let the clutch out...) or sometimes I just double-clutch/brake/rev-match...

If I'm decelerating in a straight line, I rev-match from 5th/6th to 3rd/4th (depending on speed) and compression brake till I deem it necessary to begin braking. I shift to neutral as I come to a complete stop.


Not that I'm the smoothest with my rev-matching, but I try. I don't see what's so hard to understand about how to properly bring the car to a stop... When properly executed, a rev-match and double-clutch or heel-toe (technically, heel-toe is a form of rev-matching...just combining a few steps...) decrease clutch/engine/tranny wear to negligible amounts.

Downshifting w/out rev-matching shouldn't even be an option in this poll, IMO.

 

How long have you been driving a stick?

Nobody gets every rev match dead on, and being dead on doesn't matter; All you really need to do is be close enough to get a smooth clutch release without much clutch slipping. It really doesn't do much to the clutch if you let it slip just a tad, because it's just accelerating or decelerating the engine a little to make up for the small error in your rev match.

I try to "pick up the power smoothly" as I engage the clutch on an upshift, and I try to do the same thing more or less when slowing and downshifting. You don't want to downshift and rev too high; It's better for the rev match to be a little on the low side.

Anyway, if you haven't been doing this for long, just give it a little time. At some point, you'll stop thinking about it, and start doing it automatically, without even having to think about it. It's really not all that hard to have up and downshifts (in street driving) that are way smoother than any automatic transmission, and it doesn't require a dead on rev match every time.

 

Ive seen lots of people downshift like that, they downshift and let out the clutch really really slowly as the revs climb up and the car jerks forward slowly, I think to myself that cant be good but theyre reasoning for that is that it sounds cool. So I dont even bother