at which RPM should i shift my MT to increase synchro life?

The same RPM as you would need to save tires.. 0 RPM..

-- History is only the past if we choose to do nothing about it..

When starting out, I try to stay just above idle (around 1,000 RPM) with my Chevy pickup until the clutch is fully engaged. Then throttle up normally. This is obviously assuming I'm not pulling out into heavy traffic where I need more hustle. This will minimize wear on the clutch. When changing gears, you want to try to match the RPM required for the next gear before engaging the clutch. Hard to do exactly all the time, but with experience with the vehicle and practice you can come pretty close.

Matt

Clutch wear through use is down to 'clutch slipping'.. a little bit of practice and you will soon be engaging the clutch like a professional.. applying too little revs will either end in a stall or extensive clutch slipping to maintain takeoff.. applyng too many will result in tire squeal takeoffs and synchro breakage.. there is no hard and fast rule here as it depends whether the takeoff is up or downhill or just on the level.. practice is the key..

-- History is only the past if we choose to do nothing about it..

Student mechanic strikes again. All of the synchros wear in a transmission as few people can perfectly RPM match for each shift at each possible RPM. If we all could do that, then we'd not need synchros at all!

Almost every gear will enable acceleration at any RPM high enough to keep the engine from bucking. The proper gear for a given speed will enable much better acceleration than the others.

If you change your gear oil regularly, most cars will be shot long before the synchros in the tranny are worn out. And you can easily shift into 1st at 15 MPH if you double clutch. Most people don't know how to do this, but I drove OTR trucks for many years and do this without even thinking about it, even though it is largely unnecessary with synchromesh trannies.

True, but at the price of increased wear to the clutch. I believe this is a good trade-off though and always downshift and use engine braking.

The main reason motorcyclists know to do this is because motorcycle transmissions are shifted quite differently than are car transmissions. Cars can go directly to any gear from any other gear. Motorcycles must change gears sequentially in both directions, so there is no saving of effort by coasting to a stop in 5th and then downshifting. You still have to go to 4th, then 3rd, then 2nd and then neutral. And many bikes don't shift well through the gears when stopped.

This paragraph is so full of errors that I don't have time to correct them all. Check the EPA ratings of modern cars with automatics vs. manual transmissions. For all but the smallest of vehicles, the automatics are within 5% of the manual transmissions. The advantage is greater for smaller and lighter vehicles, but still seldom exceeds 10%. And this assumes nearly perfect technique on the part of the driver shifting the manual ... which is seldom seen these days. I'll bet that the average driver will get just as much performance and fuel economy from an automatic (especially the new 5 speed autos) as they will from a standard gear box. I agree that a really good driver can do better with a manual tranny, but even then the difference is fairly slight.

Matt

Brakes are a lot cheaper and easier to replace than clutches. In my opinion downshifting and engaging the clutch during the downshift is stupid. You should downshift as you come to the stop but keep the clutch disengaged and allow wind resistance and friction to stop the vehicle, using the brakes as little as possible.

If your pressing the brakes hard for every stop your not driving properly. Only during panic stops or commuting in heavy traffic should you be using the brakes hard. Otherwise you should be looking far ahead and when you see a stop coming up in the distance you should take your foot off the gas and let the engine braking slow the car down until the engine is near stalling, then disengage the clutch and allow the car's momentum to slow gradually. In a perfect stop you only have to use the car's actual brakes from 10Mph to 0Mph.

Far too many people drive around with the accellerator pegged to the floor and when they see a stop coming up they keep it pegged until the last possible moment and then slam on the brakes.

Keep in mind that every time you have brakes applied your converting the forward motion that you spent gasoline creating, into heat. By contrast engine braking will create extremely high vacuum in the intake manifold and while the engine is braking, your car is using even less gasoline than at idle.

Ted

I disagree. Clutch wear is minimal if you know how to downshift properly, that is, blip the throttle to RPM match. I've done this for nearly 30 years and have yet to wear out a single clutch. I've driven standard shift vehicles to well over 100,000 miles and have never worn out a clutch yet.

That's for sure. Our driver education is so pathetic in the US.

Yep, I prefer to let wind resistance, engine braking, etc. help slow me in other than emergency stops. However, proper downshifting greatly enhances the engine braking.

Matt

blipping the throttle wastes gas. Not so much on modern fuel injections but on carbureted cars you blip the throttle and the accellerator pump squirts a nice fat shot of fuel down the carb throat. If you have been doing this for

30 years you certainly should have known this. Frankly, once you know that you have to slow down (ie: you see the stop sign in the distance, etc.) any application of the accellerator is just gasoline down the rathole.

Ted

I disagree, but I don't have any data to back it up and don't know where to obtain it. I believe that the extra engine braking obtained by downshifting more than pays back the gas used to blip the engine a couple of times. The alternative is that you use the brakes more heavily and this turns gasoline into heat. So the heat either goes out the exhaust pipe or out through the brakes, take your pick.

Matt

This is a factor but I was not arguing that wheel brake braking saves gas over engine braking. In fact I explained that it doesen't. What I was saying is that engine braking whether you blip the throttle in order to engine brake through 4th, 3rd, 2nd & 1st, or whether you do as I advocate and just allow the engine to brake in 4th gear until the engine is near stalling then disengage, is always WORSE from a fuel standpoint than if you allow the car to coast to a stop.

Now, as for the debate on whether it's better from a fuel economy standpoint to allow the car to gradually slow while engaged in high gear then when near stalling, disengage the clutch and keep it disengaged, instead of blipping the throttle to enable you to get 0 slippage on the clutch as you reengage the engine through the other 3 gears, I think that I think the best you can do is break even on this, on a fuel injected car, if the moon is in tune and the planets aligned and your a perfect driver.

To start with the fuel savings on fuel injected cars of engine braking at gears lower than 3rd gear compared to just letting the engine idle and keeping it disengaged is very small anyway. The bulk of the decelleration and engine braking is obtained when you let go of the accellerator and the engine is still in 4th gear, and slowing down to stall RPM. Once the engine gets to stall RPM and you initiate downshifting into 3rd, 2nd, and 1st gear, your down around 30Mph and engine braking stops being effective around

5-10Mph, so there's very minimal time that the engine is actually braking in 3rd, 2nd & 1st. And this is a habit in which you would have to make a perfect blip every time - meaning the absolute shortest time and the smallest accellerator depression needed to match RPM - and that is not going to be possible for most drivers to do. If you make 1 mistake during the braking maneuver such as racing the engine because you miss a shift, you instantly burn up any savings. Honestly, if absolute best fuel economy is required under braking, your better off burning up your clutch allowing it to slip on the downshift and not to touch the accellerator at all.

And also like I said, for carbureted cars, ANY kind of rapid depression of the accellerator (blipping) is horrible, your just dumping raw fuel down the carb throat. There is no way your going to save gas on blipping a carbed car.

No not true. This is only if your going too fast to begin with, or you don't allow enough distance for optimal braking.

Consider the following. You have a 1 mile track and 3 cars. The first car accellerates to 60Mph and maintains this until the last 200 feet then disengages the engine and slams on the brakes and comes to a screeching halt. The second car accellerates to

60Mph and maintains this until the last 400 feet and the driver makes perfect downshifts (without blipping) and uses engine braking til the last 10Mph then gentle application of regular brakes. The third car accellerates to 50Mph and 600 feet before the end of the track simply lets up on the accellerator, and disengages the engine and does NO engine braking or regular braking and rolls to a complete stop at the end of the track. Who has used the least amount of fuel to cover the 1 mile track?

Car 3 has, because of several reasons, first since he didn't get up to 60, the wind resistance consumed less fuel, but most importantly, ALL of the fuel that went into his engine was converted into forward motion. With car 1 and car 2, a small amount of that fuel that went into creating forward motion was wasted on braking. Granted, car

2 was better than car 1 because he dumped the forward energy back into the engine, thus his fuel consumption during decelleration was lower than the idling car was during decelleration, but engine braking does not produce gasoline, and it does not save as much gas as was burned to obtain the initial forward motion.

Ted

All of these arguments seem to assume that the traveling time of the driver and any vehicle occupants is of no value at all. Never driving over 50 mph and coasting to stops is a big waste of time unless you have nothing else to do all day (not to mention obstructing other vehicles whose drivers and occupants may have jobs or otherwise may actually be trying to get somewhere and getting something done in the 24 hours a day allotted to them).

IOW, unless people's time has absolutely no value, what is the practical application of any of this? WHere does the value of time get factored into any of these arguments?

Bill Putney (to reply by e-mail, replace the last letter of the alphabet in my address with "x")

Yes, no question about that. But coasting to a stop takes a LONG time and isn't practical for most driving. I believe that downshifting through the gears and using engine braking followed by, or combined with, the wheel brakes is the best overall compromise of reasonable time to stop, brake wear, clutch wear and fuel consumption. Virtually all OTR truckers drive this way as do most race car drivers (for different reasons in the latter case though). It is also what is taught in most driving schools I'm aware of. It is simply the right way to do it and works for motorcycles (which I also ride) as well as cars ... even automatics!

I won't argue that coasting to near stall in 4th will use less fuel. I think you are right about that. However, to compare apples to apples we have to come to a stop in the same distance. If we pick a more practical distance for a stop, say 500', then you can't do that with your method without significant braking. I can slow substantially in this distance using engine braking alone. Now, if we're willing to take a quarter mile to coast down, then I won't argue that your method will likely use less fuel. However, keep in mind that engine braking in high gear is nearly nil at less than 40 MPH in most cars with an OD high gear. And above 40 MPH wind resistance is a larger factor than engine braking. I suspect if you do a test, you will find that leaving the car in high gear doesn't buy you all that much compared to simply coasting to a stop.

Yes, but that is because above 40 MPH most of your "braking" is from air drag, not engine braking. I start downshifting well above 30 MPH. I typically drop out of OD into 3rd (I have a granny gear tranny so it is labelled L-1-2-3-OD, rather than 1-5) at 50 - 55MPH. I then downshift at roughly the same speeds I upshift at going the other direction. I try to have the RPM come up above 2,000 on each downshift, but not more than about 2,500 (redline is 4,500 so I've plenty of margin here).

I haven't driven a carbureted car since my 1979 Chevette. Well, maybe my 84 Accord was carbureted, I honestly can't remember. The proportion of carbureted cars still on the road is pretty small at this point.

I'm taking comparing apples to apples, that is with the same stopping distance. Sure, if you can coast for 1/4 mile, you probably won't need either engine or wheel braking. However, this isn't practical for anywhere other than parts of Iowa and Nebraska! :-) I'm talking about practical every day driving. If traffic is light, then I'll coast 800' before turning off the main highway, but usually I have a semi on my tail so I need to slow from 55 to turning speed in more like 200 - 300'. A couple of downshifts combined with simultaneous braking works great in this scenario.

I agree with your assessment entirely, however, you also have to consider the time factor. If time isn't a factor, then we should all drive about 35-40 MPH which gives the optimal fuel economy in most IC powered cars and not even equip them with brakes to force a coast to every stop. I think the OP here was taking about driving in real life, not on a test track where the goal is to optimize mileage at the expense of all else. In that case, your method is best. In the real world, mine is better.

Matt

When everyone believed the world was flat, they all were taught that it was flat. It didn't make the world any flatter than it was.

Truckers and race car drivers have valid control reasons for ensuring that the engine is ALWAYS (or as much as possible) coupled to the rear wheels. So I wouldn't argue that downshifting and re-engaging the clutch for them during each gear is the best way to do it. But just because this works for truckers and race car drivers doesen't make it right for passenger cars.

You named off several things in the compromise:

stopping time brake wear clutch wear fuel consumption

I'll take each of these one at a time.

Stopping time - the optimal stopping time is going to be using full braking and ignoring engine braking completely. When you are re-engaging the clutch and blipping the throttle you have your foot off the brake - and for a brief period of time there's no braking force whatsover applied. Add in the fact that a great many new vehicles have ABS, and that makes it even easier - just slam on the brakes and let the braking computer apply maximum braking force. Now, how does this affect the other

3 factors? Well it is optimal for clutch wear, (since the clutch remains disengaged) it is the worst for brake wear, and as for fuel economy, since vehicle decelleration is such a short period of time, the balance between idling during decelleration and applying engine braking during decelleration really is negligible since decelleration is over so quickly.

Brake wear - the optimal brake wear is if you don't use the brakes at all, or extremely little, which means engine braking through all gears through almost the entire decelleration. This is bad for stop time since the engine does not brake nearly as well as the brakes, and if your not blipping it's optimal for fuel consumption since your forcing manifold vacuum to the highest point and using the less fuel during decelleration than at idle. If you are blipping then fuel consumption is equivalent to idling during decelleration. For clutch wear it's not ideal unless your blipping.

clutch wear - the optimal clutch (and transmission) wear is to disengage at start of decelleration and not reenegage at all until after stop. This makes no difference to stopping time since you can slam or not slam on the brakes while doing this, it is bad for brake wear since all braking force is provided by brakes, and it is slightly worse for fuel consumption since you can't force manifold vacuum above what idling produces.

fuel consumption - the optimal fuel consumption is to coast to a stop using no brakes and no throttle blipping, without engine braking. (as was already settled in prior posts)

Thus putting all these together into a compromise, your saying that the best compromise is to reengage the clutch during braking? Well only 1 factor - brake wear - is helped by reengaging the clutch. SO, what we come up with is full circle - in short, it's brakes vs clutch. All the other "overall compromise" factors you cited have no bearing.

And, I can slow in the exact same distance by not using engine braking at all and just using brakes. You cannot slow faster than me by using a combination of engine braking and brake braking, or the ABS computers all would be programmed to use engine braking at the same time as pulsing the hydraulic fluid.

I agree with this as well.

The exact same decelleration scenario can be done with brake braking alone.

No, actually the OP was looking for a factor that you didn't even bring up - the least amount of synchro wear. In which case using engine braking is not really a factor because whether your engine braking or not, you still have to shift the transmission down in order to get rolling again from a stop. In fact you yourself already pointed out that the rpm that the shifting takes place at is irrelevant on the amount of synchro wear.

_that_ has NOT been established by this discussion at all. You have made several assumptions in order to say something like this. First, you assume that clutches in every car, optimally driven, last the life of the car. Unfortunately, some cars have rather inadequate clutches, and no matter how well they are driven, they are going to wear out quicker than others. In addition, clutches in city cars are going to wear out a lot faster than clutches in suburban or country cars. Second, I think you assume that the cost differential between a brake job and a new clutch is not that significant. Well there's lots more people that can do brakes on their own car but not the clutch, so for those people they can probably do 5 or

6 brake jobs for the cost of a clutch replacement. You also have not really clearly explained what benefits there are for engine braking. You also haven't really clearly explained why someone would want to sacrifice fuel on "blipping" in order to get engine braking in the first place. And finally your saying "my way" is optimizing mileage at the expense of all else, when I said in a previous post: "Only during panic stops or commuting in heavy traffic should you be using the brakes hard." Well, commuting in heavy traffic is like 70% of all driving out there, so how in the world would this be optimizing mileage at the expense of all else?

Geeze Matthew, your being rediculously inconsistent here. Your making this long post that delves a fair bit into analysis, showing that some actual thought has taken place, then ending it with this short, "all problems are nails and I have a hammer" sentence that's about along the lines of what Noman Nesco would spout.

Ted

Haven't withdrawn any assertion I made. I agree that it doesn't apply in the track scenario that you contrived, but it applies in the real world as I stated. My assertion was meant for the street and normal driving.

It is the best way to drive on the street in normal traffic. I said that and stand by that. Now stop trying to put words in my mouth. I only agreed with you in your ridiculous contrived scenario. That was pretty clear in my post I think.

Matt

Ouch!! (No problem) 8^)

Bill Putney (to reply by e-mail, replace the last letter of the alphabet >

Truckers downshift in cities because they need to keep control and because using the 'engine brake' is frowned upon.. race drivers downshift to maximize braking and to ensure that they have the right gear for exiting the next corner.. hardly regular car driving!!!!!!!!.. acknowledging that trainee drivers are encouraged to downshift all of the way (presumably so that they keep control and to eliminate the slight increase in speed as the clutch is depressed and not released in a lower gear), there really is no need to use all gears in order to stop for a red light.. 2nd gear should be the lowest selected and that should be just prior to stopping.. clutches and synchros wear out due to the operator having no idea about the relationship of engine rpm and how it affects a transmission that may or may not be turning at the right speed to effect smooth and trouble free operation.. double de-clutching and 'blipping' the throttle went out when synchros came in.. if people can't handle a manual transmission, there is an answer.. it is called 'auto' transmission..

Drivers that persist in trying to slow for lights and other obstacles using gears only, making slow changes while trying to balance engine rpm, cause frustration to many and generally slow the flow of traffic across lights..

-- History is > >

Mike, Is that genreally true, or only with a jake brake because of noise? Otherwise, why is engine braking frowned upon (I ask because if it's due to extra stress on the engine, then I have to wonder why jake brakes would ever be installed).

Bill Putney (to reply by e-mail, replace the last letter of the alphabet in my address with "x")

Actually, it does. You never know what someone coming up quickly behind you might require rapid acceleration. You simply can't do that in high gear at near idle engine speed.

Only if you are optimizing braking distance only. To me, optimal braking is using the right balance for the situation at hand. In a panic stop, then full force braking with the clutch on the floor is optimal. In a short, but not panic, stop, then using engine braking combined with wheel brakes is optimal. If you have loads of room, nobody behind you and aren't in any sort of hurry, then very casual engine braking with minimal use of wheel brakes at the end is optimal.

If you learned how to drive a stick shift properly and have a car with well designed pedals, you can shift and brake at the same time. It is called the heel and toe method.

Yes, I'm saying that is generally the best compromise when you factor time into the equation. You are assuming equal weight to all the variables being optimized, which isn't true in this case and seldom true in the real world. The reality is that using the wheel brakes creates LOTS of wear on them, but using the clutch properly and blipping the throttle properly causes almost no wear to the clutch and not even a measurable increase in gas consumption. If you really think that a 1/2 second blip of the throttle uses much fuel, then you don't know much about fuel systems. Even an old accelerator pump carb uses very little of the accelerator pump volume for a blip. You don't press the throttle to the floor when downshifting. Probably don't even use 1/4 of the throttle travel. Most accelerator pumps dump very little fuel in the first 1/4 of the throttle travel.

I never said this. I said I can stop faster using the same amount of wheel braking combined with engine braking from downshifting than you can staying in high gear all the way to a stop. You will need to use your wheel brakes much more than me to stop in the same distance using your technique. I think it is better to trade off very little clutch wear and extra fuel consumption for a significant savings in wheel brake wear.

But it is your car so obviously you get to choose how you want to do it. I'll bet that if you ask any competent driving instructor or driving school, they well tell you that your way is not safe and not recommended whereas my way is.

So that means there is no reason to do so and you are sacrificing safety at speeds less than 30 MPH as you have virtually no acceleration there in high gear ... unless maybe you are driving a Viper. :-)

Sure can, but at the cost of more brake wear and not being in the right gear to accelerate should I need to abort the turn and get out of the way of something unexpected.

That's right, that was the question. It is basically true if the shifting is done properly. If the shifting isn't done properly, then you can add significant wear to the tranny.

Blipping the throttle was in response to the OPs question about minimizing wear to the transmission. RPM matching means that the synchros see very little wear during a downshift. I've never bought a vehicle with a weak clutch so I haven't experienced premature wear out. Which vehicles have wimpy clutches?

I've been entirely consistent. The only inconsistency was when you tried to twist my words to say things I didn't say.

As I said earlier, call any reputable driving school and ask them what is the best way to stop when driving a standard shift car. Please post back here the answers you get.

Matt

Name one driving school that recommends the technique you recommend above. Every article I've ever read suggests that you downshift as you stop so as to always be in a gear that allows you to accelerate if necessary. The exception is obviously a pedal to the floor emergency stop.

I don't think anyone here ever suggested gears alone if you were in traffic. That was my objection to Ted's coast down in high gear method.

Matt

Noise the the reason. There is no other reason not to use the Jake brake. Many areas now have signs that say something to the affect of "Engine brake use prohibited." I always liked the sound of the Jake Brake, but then I was in the cab at the time! :-)

However, we weren't talking about engine brakes, we were talking about using engine braking. Not the same thing at all. But a Jacobs engine brake does make engine braking MUCH more effective!

Matt