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I was curious about what problems may arise if clutch is not used when shifting gears. Are the problems similar for both cars and bikes?

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3 Answers

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If you match revs correctly you should be able to change gear with no ill effects at all. The challenge is of course to match revs. This is pretty easy when accelerating, but when decelerating you'll need to use the accelerator to bump the engine revs up to match. Google for heel-and-toe (this also helps make for faster downshifts when using the clutch)

Getting started into first is tricky though. If your clutch does fail, parking on a down hill can help with this:-)

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you should probably point out that on a synchro gearbox, you might think you're matching speeds really well when, in fact, you're making the synchros do the speed matching. – Bob Cross♦ Mar 25 '11 at 18:55
@bobcross - very true. Most people don't get to practice on a box without a synchro but should be able to learn the difference in feel and noise. – Rory Alsop Mar 27 '11 at 8:26
In my first car I tried to learn to shift without using the clutch and instead just rev-matching... I eventually gave up, it was just too often likely to fail and, well, I have a clutch that prevents the need. It was nice to learn to do it, in case I ever had a clutch failure, but saving the clutch at the expense of the gearbox and in particular the synchros seems like a bad trade-off. One of my current cars has 200K on the original clutch, so what exactly am I hoping to save? – Sean Reifschneider Mar 28 '11 at 9:59
@Sean - not really a save of a clutch at the expense of something else. If you do it right nothing will wear. I learned it for racing, as some gearboxes in use don't have synchromesh so you need to get the revs right anyway. Don't really use it much on the road, but heel-and-toe-ing techniques learned from those days mean I get very smooth clutch/gearbox action. – Rory Alsop Mar 28 '11 at 10:29
In my experience, it's so hard to get right that it is at the expense of the gears. If you can do it perfectly every time, my hat's off to you, but I never felt like I was making progress beyond a certain point. I'd get it right around 10% of the time. If you practice 20 hours a week or something at the track because you don't have synchros on the track car, yeah, you'll probably get good at it. And knowing how to rev match before engaging the clutch when downshifting is a good skill to have. – Sean Reifschneider Mar 28 '11 at 23:48
up vote 1 down vote

There are synchro rings that match the speed of the gears when you push the stick. Synchro rings are not designed to accelerate/decelare the engine / whole car and will wear out quickly if you don't use the clucth.

...unless you are a real ninja with the gas pedal and match the gear speeds manually.

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up vote 2 down vote

Excessive wear on the gears and a complete breakdown of the gearbox will be very likely to occur soon. Also the crankshaft and it's bearings will suffer a beating everytime you shift gears which will cause (fatal) damage to the engine.

The results will be similar (but definitely not the same) on a bike. If you keep pedaling while shifting gears you'll keep tension on the chain. This will momentarily put excessive sideways forces on the sprockets which will cause bent teeth and broken chain links.

If you must drive a bit when your clutch breaks down, for example on a railroad crossing, you can use emergency propulsion. You leave the car in gear and use the starter to drive the car for a few meters. Park the car at a safe location and call a tow truck.

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2  
I'm pretty sure the OP meant "motorcycle" when he was referring to "bikes". Also, the last time I rode my bike (admittedly, it's been awhile) I'm pretty sure I wasn't able to change gears without pedaling the bike. You need to keep pedaling so that the chain can move and be guided onto the new gear. At least, that's how it is on your typical mountain bike. – Iszi Mar 25 '11 at 13:21
+1 - Definitely use the clutch. Don't risk the rest of your car by forcing it to do things it wasn't designed to do. – jmort253 Mar 27 '11 at 1:16
@Iszi @Alex right, there's no clutch in mountain bike :-) – Pēteris Caune Mar 29 '11 at 20:59
Note that on most cars you can't use the starter to drive the car because there's a switch on the clutch pedal that prevents the starter from engaging unless the pedal is depressed. It's easily bypassed (unplug the terminal from the switch and jamming a paperclip in it usually works) and this is a good modification to make in advance in case you're ever in a situation where you need to drive the car with the starter. – R.. Aug 30 '11 at 23:46

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