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Does the act of downshifting to slow your vehicle down have any negative side affects?

I don't downshift more than one or two gears at a time and I let out on the clutch slow enough that I don't rev very high. My red line is at 5.5 and mine are around 3 - 3.5 when I do it. This process makes my brakes last much longer but I'd like to ensure it's not at the cost of something else.


Edit:
Thanks everyone for your answers, but I'm seeing very conflicting information. I found this on wikipedia but then again it's wikipedia. Does anyone have anything to support their thought one way or another?

Engine braking passively reduces wear on brakes and helps a driver maintain control of the vehicle. Active use of engine braking (shifting into a lower gear) is advantageous when it is necessary to control speed while driving down very steep and long slopes. It should be applied before regular disk or drum brakes have been used, leaving the brakes available to make emergency stops. The desired speed is maintained by using engine braking to counteract the gravitational acceleration.

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When you do this - just blip the throttle (while clutch-pedal is pressed) little bit (it depends how much). Be careful - it's not that easy/intuitive at first. But soon you'll get used to it. If you do this RIGHT, there will be NO extra clutch/crankshaft wear && downshifting will be much smoother (on the car and the passengers) :). –  sabiland Jun 8 '12 at 10:07
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13 Answers

up vote 25 down vote accepted

Most of the time when you drive, you're putting a load (and causing wear) on what I'm going to call the "forward" face of each tooth on each gear in your drivetrain. The front of a tooth on the crankshaft pushes against the back of a tooth on the next gear in line, which pushes the next gear, etc. When you use "engine braking", all you are doing is engaging the teeth in the opposite direction, and putting force and wear on the faces that normally are just along for the ride.

Now, does that mean you're wearing your engine out faster? Marginally... but the parts you're wearing out would normally have to be replaced (if at all) because they'd worn out from the other side; you're wearing surfaces that would usually be thrown out with hardly any wear at all. To borrow a phrase from the medical field, your engine/transmission will die with that wear, not of it.

To the people who say that you're transferring the wear from your brakes to your clutch, all I can say is... you're doing it wrong! If you downshift as quickly and smoothly as you upshift, then the added wear and tear on your clutch will be a statistical blip - seriously, how many times do you downshift for this reason, as opposed to normal shifting? (If your answer is "at every light", then the poster who advised you to calm down your driving habits had a point.)

Having said that, there's a seriously wrong way to do this; I used to do it when I was first learning to drive stick, and it was incredibly stupid: pushing the clutch all the way in and letting the RPMs fall to idle, then letting the clutch out and allowing the engine to slow the car down in the same gear. If that's how you're doing it, STOP IT! That way wears out the clutch very fast (which might be what the other posters had in mind), drops your speed dramatically without lighting up your brakelights (I confess, that's why I started doing it - trying to sneak-slow past a cop), and runs a high risk of stalling the engine and seriously ^&*@ing something up. Don't be that guy.

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My Mk.3 VW Jetta actually have a device that keeps throttle open a little longer to ease gear shifting, and prevent the problem you had described in the last paragraph. –  theUg May 31 '12 at 22:56
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The conclusion might be valid, but the explanation is wrong. Damage doesn't only occur on surfaces in contact with one another. Firstly, given the asymmetric usage of the "forward" and "rear" faces, you'd see failed gears with vastly higher wear on the forward faces. Not true. This isn't how stresses and strains work. You can load one face, and have stress transmitted all the way to the other side. See here for visualization. Stress reversal also kills fatigue life. –  Nate Aug 1 '13 at 6:03
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I agree with MT_Head's and Donovan's answers, but I'd like to add that the downshift itself can be quite heavy on your synchromeshes if you don't do it right.

When you up-shift, the input shaft drops in speed by ordinary friction, and the synchromeshes don't need to work much in order to match it to the speed of the output gear. However, when you down-shift, not only does all the work of getting the input shaft revolutions up to that of the output shaft fall on the synchromeshes, but they also have to counteract that same friction which normally helps. This is why cars often develop a bad second gear over age (since the second gear is the one most commonly down-shifted into).

If you want to downshift frequently without wearing out your synchromeshes, you should learn to double-clutch correctly and as such RPM-match the transmission against the engine manually instead of letting the synchromeshes do that work for you. When you downshift, do as such:

  1. Disengage the clutch once and let the transmission into neutral,
  2. Engage the clutch again.
  3. Rev up the engine to the approximate revolutions you'll need on the new, lower gear; or perhaps a little higher to give yourself headroom for the next step. (This is preferably overlapped with steps 1 and 2.)
  4. Disengage the clutch once again (hence double clutching) and shift into the lower gear. If you've RPM-matched correctly, you'll feel the gear just falling effortlessly into place, rather than needing time to rev up the input shaft.
  5. Engage again and continue driving.

If you're not used to driving like this, it may sound a bit burdensome, but it doesn't take a vast lot of training to get used to it, and once you do, you'll find that you can actually downshift faster than without anyway, since this method of downshift synchronization is usually faster than what most synchromeshes are capable of. And it really does make your transmission age a lot better, especially if you downshift a lot.

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Ok, personally to me the best thing you can do is find out what your car idles at, downshift at the lowest rpm possible to maintain traction and engine quality. Brake when needed but try and predict when you need to have already let off the accelerator.

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Just some anecdotal evidence. I downshift at least a few times a day. Only one gear at a time and never send my tach anywhere near the red, BUT I NEVER RIDE THE CLUTCH. Unless it is an emergency I'll downshift and come off the clutch almost as quickly as I do when I upshift, If I'm going to fast for this I don't downshift yet, UNLESS IT'S AN EMERGENCY.

Ok all that being said here's my anecdotal evidence. I have 180000 miles on my pontiac vibe and from what I hear the clutch goes on average around 90k. Mines still going strong. I'll regret posting this if it goes tomorrow.

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If you double-clutch the downshifts and ensure that the engine is running at exactly the right speed before you engage the clutch, any additional wear will be insignificant. Double-clutching will, if done properly, eliminate any additional wear of the synchronizers and if the engine is running at just the right speed before you engage the clutch after the downshift, the clutch will not have to drag the engine up to speed.

Here's how to double clutch:

Declutch and shift to neutral.

Engage the clutch and, at the same time, use the accelerator to bring the engine up to the proper speed for the gear to which you will be downshifting.

Declutch and shift to the lower gear

Quickly engage the clutch.

If you do it just right (which may take practice), the shift lever will easily move to the selected gear and engaging the clutch will be totally smooth. Eventually, the operation will become totally automatic.

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I'm a driver trainer/examiner and most of the time you rarely need heavy braking in traffic. If you drive calmly, allow plenty of distance between you and the vehicle in front (even at low speed)) and just take your foot of the accelerator early you avoid stopping and starting. If you let the car slow down and use the gear until it is no longer appropriate (too slow that the engine starts to struggle) then change down you will always be in the right gear and transfer very little shock through the clutch or transmission. You can still use the brake but you don't need as much. Brake pads wear out much quicker than any gear box will and the number of brake pad and rotor changes will probably add up to one gear box over the life of that gear box. I drive the same way to work everyday and I rarely have to stop and I always beat the lane changers and racers. Drive calmly, accelerate and brake smoothly and you will get there sooner with much less stress on your vehicle and you. Leaving earlier helps.

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First, everyone who said that the braking effect comes from the compression stroke is wrong...the air in the cylinder is compressed which takes energy, yet after top dead center acts as a spring and helps force the piston back down, returning the exact same force as was put into it in the first place. Probably more, actually, since the compression heats the air charge up and causes it to expand, like a very minor version of a power stroke. No, the braking effect comes from the INTAKE stroke, from the engine drawing air through the closed off throttle-body. It's like trying to suck air through a tiny straw. Braking is from vacuum, not compression. That and a bit of engine friction, which is less significant with modern engines than it used to be. As for using engine braking, using it mildly for keeping speed on downhills isn't really bad for your car. I'd avoid driving like a rally racer and aggresively downshifting to slow down for every turn or stoplight, but when done right, it doesn't effect anything any differently than driving normally. Yes, it causes more engine revs, but they are no worse than the revs you get accelerating onto an on ramp. If you're planning to keep the car for 250,000 miles, yeah, you might want to keep the revs to a minimum, but otherwise, assuming nothing is wrong with the motor itself, the car will be done-for long before you wear the engine out by adding revs. Tha same applies for the clutch...yes, every time you use it, it wears a little, but no differently than using it during normal driving. If you're worried enough about the clutch that you try to keep your car in one gear as much as possible, sure, avoid engine braking. But if you're like most people, you use the clutch 5 times every time you get up to speed, two or three times every time you leave a stoplight. A few more engagments isn't a big deal. And you don't always have to use the clutch; often you just have to let off the gas and leave it engaged and it will work to slow you down. It will add some wear and tear to the drivetrain, but like the above, you could consider it the same as driving an extra half-mile every day, only without the fuel cost. If that wouldn't scare you, neither should engine braking. The only thing that wears out differently is, as the other poster said, the rear faces of the gear teeth, and that really doesn't matter. You use them every time you back up, the rest of the time they do nothing. IF they should wear significantly, the only effect will be that the transmission will be louder when your reverse. And you'd have to put a lot of wear and tear on them to get them that worn out.

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I believe you're correct re: engine braking coming from throttled intake rather than from compression. –  mac Nov 27 '12 at 23:03
    
Why is this downvoted? +1. When the throttle plate is closed, the engine draws a vacuum on the intake stroke, so strong of a vacuum, rod failure may result if rpms are high enough. The compression stroke is compressing a vacuum, which does nothing to slow the car. –  Randy Aug 7 '13 at 19:12
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Donovan's is the only answer that has any truth in it.

  • Downshifting and engine braking will have NO effect on the clutch, as you don't slip the clutch
  • it doesn't wear out the engine, as you use the compression stroke
  • and it is far better on tyres and handling as any advanced driving instructor would tell you.

It is just more difficult, as you need to coordinate a number of factors, so not suitable for beginners.

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Well I can drive a manual very well but I know very little about the mechanics of a vehicle. Your answer seems the most plausible to me but that may be wishful thinking. –  Gary Jun 25 '11 at 22:54
    
every time you disengage the clutch, it slips and you also reduce the life of the throw-out bearing. And yes, it is normal wear and these are serviceable items. But if the clutch is typically designed for 150k, if you downshift as much as you shift up (every single stop light as OP has indicated), you are reducing the life in half. And this assumes you match RPMs as you down shift, which is not the case either. Notice the OP said "I let out on the clutch slow enough that I don't rev very high". Guess what has to slip while the car is slowing down so the engine doesn't rev that high? –  DXM Jun 27 '11 at 8:21
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@DXM - Not correct - you should not let the clutch slip at all, except on initial move off from rest. The OP is using the clutch incorrectly. It should be binary. There is absolutely no need to slip the clutch - matching revs is relatively easy. You can drive quite happily with no clutch or synchromesh with a little practice. –  Rory Alsop Jun 27 '11 at 9:01
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I would agree with the previous posters but I'd like to add that in my audi's handbook they actually advise downshifting early to save fuel.

They also make plenty of money on parts though don't they! Also from my experience their gearboxes don't last long these days at all.

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..are you sure that your owners manual doesn't advise UPshifting early to save fuel? i.e. make the shift from 2 to 3 early? –  mac Nov 27 '12 at 23:01
    
Indeed I am, but yes also UPshifting early when accelerating it's a TDI and I believe the logic is that when the engine is being turned kinetically the fuel consumption is brought to zero by the electronics. Therefore the longer this is the case the less fuel will be consumed. –  barrymac Nov 28 '12 at 10:16
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If you downshift into a gear at a RPM that is within the norm of driving then no, no harm done. When you downshift what is slowing you down is actually the compression stroke and is recommended over hard braking. Like another said, it is a bit of a mix of the two but engine braking is ok as long as the engine stays under redline, so do not go from 5th to 3rd.

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I never come close to redlining so that's not the issue, but to keep me from slowing down to quickly and spiking the RPMs I have to ride my clutch a little bit. From what I gathered here, it boils down to clutch v brakes. –  Gary Jun 24 '11 at 13:00
    
@Gary, it is better to give it a little gas and shift fast and smooth than riding the clutch. Riding the clutch works with wet clutch transmissions (many motorcycles have common sump wet clutch), but should be avoided for dry clutch. –  theUg May 31 '12 at 22:59
    
Its not the compression stroke which slows you down. See Jake Brake function en.wikipedia.org/wiki/Compression_release_engine_brake#Function " The throttle itself provides engine braking through friction in the air flowing through it." –  Randy Aug 7 '13 at 19:04
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Which would you rather change - your brake pads or your clutch?

By downshifting to decelerate you are trading wear on your brake pads for wear on your clutch (among other things).

Brake pads are much cheaper and easier to replace than a clutch. Personally, having done both, I'd rather do 50 brake jobs before I'd do one clutch job.

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To reiterate, I wasn't proposing a trade-off of brakes v clutch. I do this because it drastically reduced the wear on my brakes and my fear was that I was actually doing more harm than good. Thanks for the response though. –  Gary Jun 22 '11 at 18:27
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"..it drastically reduced the wear on my brakes.." -- that sounds exactly like the trade-off being mentioned here. You increase brake pad life at the expense of something else, which you just found out is the clutch. Second wearable item are synchros (clutches inside the transmission). I used to downshift my integra until it got worn to a point where 2nd and 3rd gear could not be shifted into unless you precisely match RPM. Learned to always match RPM which I now do at all times but I also don't downshift nearly as often as I used to because of that lesson. –  DXM Jun 23 '11 at 4:21
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@DXM's experience is typical, and probably where you are headed. Downshifting purely for the purpose of slowing the car is generally regarded as a bad thing (except for emergencies). If you want to save brake wear, the best way is to try to drive more strategically. Don't run up to red lights and then slam on the brakes at the last moment, etc. Select speeds that allow you to keep moving rather than start/stop. The more mindful and less reactive your driving style, the longer the brakes will last (and the better gas mileage you will get). –  Brian Knoblauch Jun 23 '11 at 12:11
    
You don't slip your clutch to slow using downshifting. It isn't a brakes vs clutch tradeoff. You use your clutch as a binary, matching revs by blipping the accelerator, not by slipping the clutch or using your synchromesh. –  Rory Alsop Jun 26 '11 at 22:19
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@Rory: Maybe in a perfect simulation that could be true. It seems naive to think you can operate a clutch in "binary," without any wear, in the real world. –  qes Jun 27 '11 at 16:52
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You are 100% putting wear and tear on your engine plus transmission. Not only that but you're also increasing the wear on your clutch. Having said that, I rev match every time I downshift. This still puts wear and tear on the components but not as much as physically slowing the car down when bringing it down a gear.

Brake pads are cheaper and easier to replace than a clutch!

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Is this true no matter how gradual it is? My RPMs don't go over 3.5 when I'm doing it. Or is it a difference of bad or worse? –  Gary Jun 22 '11 at 16:03
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Letting out the clutch slowly might be a tiny bit easier on the transmission and engine, but is horribly hard on the clutch. –  Brian Knoblauch Jun 22 '11 at 16:15
    
I personally use a mixture of brakes and engine-braking (downshifting). Yes, as the other commentators have said, it increases clutch wear, but it also means you are always in the right gear for the moment - it also helps if you're in an older vehicle with poor brakes! –  Nick C Jun 23 '11 at 14:38
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Short answer is yes. You are running the engine through more revolutions that you would have done if you had used your brakes. This is adding wear and tear to your engine. Not sure about the transmission.

Now from a cost savings perspective the wear that you save on your brakes might actually be more than the small amount of wear that you add else where. There might even be a fuel savings by having the vehicle momentum power the engine.

One negative of doing this is that drivers following you have no visible warning that you are slowing down. (Using your brakes will engage your brake lights).

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Thanks for the input jzd. I didn't know what may be adversely affected, my guess was just if anything it would be the transmission or clutch. I'm definitely saving money on brakes; my last set lasted about three years. I have considered other drivers not being able to see my brake lights but I do it so gradually (as to not be too hard on my Jeep) that it's not too drastic of a speed change. –  Gary Jun 22 '11 at 15:09
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@Gary, besides, if someone is tailing you too closely, you can always warn them by tapping the brake pedal. Or slam it if you feel like insurance would pay for a new car. :) –  theUg May 31 '12 at 23:04
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