Manual Cars and Popping the Clutch (to re-start engine)
 

Over the summer I recently got a new car, the current one I driver, and it was manual rather than automatic. I found that you can turn the car off and coast saving mass amounts of gas, not an entirely novel concept I know. But I am not totally aware as to what the possible negative effects of constantly turning off a car can be. I know the the starter can go bad eventually, not a cost I want to incur, so I found out about the idea of popping the clutch, which I have found can be done in any gear. Generally I turn the car off at around 50, coast to a desired speed, then pop the clutch in the conditionally required gear. I know little to nothing about the interworkings of a car, so might someone shed some light onto what problems this could cause if any?

It'll increase clutch wear a little (depending on how smooth you are). Thats really about it. If you do it wrong you can damage your engine of course (bump start in 1st = boom).

See: http://ecomodder.com/forum/showthrea...gine-1141.html

I don't remember who here said it first (not me, can't claim credit), but a good rule of thumb when bump-starting is use the gear that's two higher than what you'd normally use for that speed. E.g., in my bucket, if I need to bump-start at 25mph, that's normally 3rd gear, so bump the car in 5th, depress the clutch, and select 3rd to continue driving.

Another consideration: The faster you're going, the less aggressive you can be with engaging the clutch to spin the engine. If I'm trying to bump the engine at 20 mph, I'll put it in 4th and let the clutch out pretty briskly and pretty far, to make sure it engages firmly to spin the motor. But at 50 mph in 5th, I can just "feather" the clutch out a few inches into its travel, very quickly, and the engine catches.

I agree with Joe. Using the method he describes is the way I perform "The Bump". As far as increased wear, it is negligible, as you are only *just* touching the plate to the flywheel to give it a turn. In fact, one could argue that you are saving wear on the plate and flywheel, depending on whether you would have shifted during the coast or not, as with "normal" driving.

Just like that... http://www.youtube.com/watch?v=6Gxl152rs_I

I always bump start in 5th around 20 mph, that makes it really easy and completely transparent to passengers.

If your the guy that is going to be doing the clutch replacement, then I don't think you could ever argue that there is not going to be clutch wear from popping the clutch. You save $0.01 but incur the cost of replacing the clutch sooner? Any time sooner is to soon.

The thing we forget here is that the mean time between failure on manual transmissions vs automatics is so far in favor of the manual that it is not even funny. I replaced my clutch in my current ride at 96,000 miles, and did the replacement myself with the help of a friend and $400. It wore out that soon because I learned how to drive stick on that car, and so did my then girlfriend, now fiance. The clutch, no matter how many bump starts I perform on it, will never incur the abuse that it did when two people learned how to drive on it. Enough said.

I think it's important to say that "popping" the clutch isn't what people are doing. It's much more subtle than that.

Maybe you're only using the common expression and not the technique itself, but "Popping" the clutch will impart more shock to the engine/drivetrain components and is probably uncomfortable for the passengers.

Even "bump" starting is a misnomer. As Tasdrouille pointed out, done well, restarting the engine with the clutch should ideally be imperceptible to anyone riding with you.

See http://ecomodder.com/forum/showthrea...gine-1141.html

PS - Tas - amazing video. The grip of those front tires must be phenomenal!

Your clutch gets worn by driving it, far more so in accelerating the whole car than in bringing an engine up to idle speed. much more mass and slippage there.

And your $0.01 is more like thousands of gallons. You are comparing the lifespan of a clutch to the gas saved on a single short coast maybe?

The clutch cost me ~$50 and a day, like once every 10 years. Compared to thousands of gallons saved over the same timeframe, it's a no brainer for me.

static friction, Fs = Fn * us (weight of car * coefficient of static friction) Dry, warm tires on asphalt basically all have a coefficient of static friction of .95 to 1.0. When the car rocks forward due to the slowing of the car, the weight all sits on the front tires, so the frictional force becomes essentially equal to the weight of the car, which is a lot!
One of my friends did this in an old beretta; he'd shift to R from like 3 mph forward and hit the gas to do a reverse wheelie. luckily it didn't break the ol' car.
Pretty sweet video - would be scary as the driver! I've seen similar videos where a RWD car breaks its driveshaft and it catches the ground, sending the rear end flying.

Do not "pop" the clutch, but rather side step as if you were taking off from a stop...no more wear ad tear than shifting into another gear. The higher the gear selected the smoother the transition. If I am as low as 5 mph I use third. The vehicle you use will determine the best method, but try 4th or 5th first. When I do it my back seat passengers do not even know what I have done.

Certain gearboxes I believe will not distribute oil when the gears are not being driven. May be worth pointing out.

I always use 5th as well. The starter turns the motor over at less than idle speeds. Maybe 200 RPM?

Top gear at idle speed
 

I've been engaging the clutch at about 25mph in top gear. A little testing around town - I live in a really small town with 20mph speed limits - shows that my truck will putter along at idle in top gear on the flat at about 20mph, so letting the clutch out on 5th at 20-25 turns the engine at or just above idle speed, pretty low-stress. Passengers never notice. If I'm heading down a longish hill, I'll ride it with the engine turning but the ignition off to top up the brake vacuum booster, or to keep coolant circulating. No blown heads yet and I've been doing this engine-off thing for a long, long time. I reckon it'll be okay.

My truck's at ~185,000 on the original clutch, so if it fries at this point I'm still ahead of the clutch curve.

I know that's an issue with a lot of automatics, but I'm not so sure about manuals. If you've got the owner's manual for your car, a quick check in the section on towing ought to tell you whether your car can be safely towed any distance on all fours, or whether it should be flatbedded all the time. If the manual says it's safe with the drive wheels down, your car should be okay.

The manual for my wife's car says it's okay at low speeds for short distances, but considering the hills I like to coast, that's not an option - and they don't really tell you how slow is "low speed" or how long is a "short distance." I don't trust weasel words like that.

you shouldn't have any problems restarting with the clutch. i drove my old truck (yes, standard) without a battery for about a month or 2. i just always parked on hills. its only on the second clutch in around 300,000 miles.

Bump starting can be done amazingly smoothly.

The first time I road with Doax, it took me a few mintues to even realize why he was messing with his key.

It's because he was pulse-and-gliding on the freeway, and I couldn't even tell when he had his engine on or not!

That's smooth bump-starting! :thumbup:

I tried this in my civic, but later turned to slip-shifting into and out of gear, rather than using the clutch at all... frankly, I don't feel that the time taken to turn the engine off and restart is really that gainful for me, as it only takes 10-15 seconds for me to go from 60-40, even down slight hills.

I leave the engine idle (it idles lower than normal already, due to my preference), and pull the selector out of gear as I'm letting off the gas. Then, when I want to put it back in gear, I just match my speed with the accelerator, so I don't have to touch the clutch.

It's pretty obvious why I personally don't work out well doing it the other way though, I've hard-taught myself not to use the clutch unless I have to. (Bad knees, less stress if I don't use it.)


By the way, I pop start my car from a stop in my driveway frequently... usually use 3rd gear, sometimes I just lift in 1st though. It only takes a quick slip to start the engine.

ya I have been driving a lot more city lately and not turning off the car at all because it just causes too many problems, especially when it's so cold outside, but what is this slip-shifting idea?

slip shifting = when you are letting off the gas, apply pressure to the stick as though you're shifting gears. You'll feel it slip out of gear smoothly, and it won't damage anything.

As you're coasting, you kinda get a feel for when you have to put it back in gear and start accelerating again.. so you start to slowly rev the engine to the speed you'd need to smoothly put it back in gear, no grinds, no clutch use.

The second part is called speed-matching.

And slip-shifting in it's real terminology is exactly what everyone else calls "half-clutching" it's still using the clutch, but not fully disengaging it, forcing it to slip while shifting to another gear, but not losing as much inertia. It's a ricer thing, although, I'm sure it had real-world application somewhere.

Actually, you're likely causing wear on the synchronizers.

Yep, except in the case of the person that actually knows what they're doing, the shifter will "fall" into gear when you're at the correct RPM. You don't need to put pressure on it.

well I usually just try the matching revs thing with the clutch, but unfortunately I have yet to figure out a way for my scanguage to continue reading stats with the engine shut off, so the one I want to measure most, whether you really have to be sitting idle for 3 minutes or more to make it worth shutting your engine off. But either way the clutching differences should certainly help to increase my efficiency, at this point I will be asking around to see what different people think about the wear I would saving the interworkings of my car by driving normal or certain other styles such as slip shifting. At the start of this thread though I was strictly referring to popping the clutch in the getting the car started aspect, because I have not found a way to make that transition smooth at all, what particular tricks are there to make that smooth, or is it pretty much the way it is?

To get it started, just use like 3rd gear, and slowly leave out on the clutch pedal until you feel it grab a lil, then let it out more. It takes some getting used to.

Like I said before, I have no problem with starting mine in 1st, but I don't care about the little bit of "shock" when the car jerks a lil. I use 3rd when there is a "drink-in-hand" situation... no cupholders in my car.

probably removed for aerodynamic purposes? :)


that may be another one of those things, given that I really don't have the experience and hypermiling is rather new to me, that I see it having a physical effect on the car later down the road that, despite saving the gas at the time, might negate or overstep the money saved just by how much the things take to fix...maybe daox has a better idea on the subject, but if your on the highway your having to start the car at say 50 mph so the starting it two gears above what you would drive at doesn't really work there, cause that would be 5th already, at least for my little 1.7L

LOL, no, it's a 88 civic. They never had them.

Use 5th anyway, and slip the clutch like you're starting it off a red-light. You'll get used to it.

My owner's manual doesn't distinguish between automatic and manual transmissions in the section about flat towing when it says you have to stay under 35mph and not tow more than 50 miles. I found a pdf of the page.

https://techinfo.honda.com/rjanisis/...606O00285A.pdf

What do you guys think about EOC with the manual transmission?

eoc on manual shouldn't be an issue at all.

When i am coasting and i want to start back up i pretty much always use 5th. I quickly lift my foot about 1/3 of the way off the clutch and then i push it back in again. Always works when the engine is warm. Even if i should be in 5th i will push it back in again, then i will match revs to where i should be before letting the clutch back out. This totally minimizes and RPM differences and wear. If you can feel the car jolting, you are lifting the clutch too far up to start it.

1. Are you switching the key back to "run" after you kill the engine?

2. You should have the SG set to "hybrid" as fuel type so it stays on longer when it detects the engine has stopped.

i always use what ever gear i think will put me up to 1500rpm, cause my truck hates below that.

Thanks metro I will do that

I love starting my Civic out of my driveway in 3rd or 4th, as it just needs a slight roll to get started, then I can pretty much let it idle it's way up to 15mph without touching the gas... it's probably not good on the engine, but o'well.

Once I get to 15mph, I can be in 3rd gear idling anyway (1000RPM) so I just give it some light gas and go.