ninjette.org - View Single Post - My friend dropped my bike! and doesn't know why..

Numbersix · November 14th, 2011, 03:05 PM

One more thought about clutching:

The clutch (obviously) disconnects the engine from the drivetrain. Somewhere in here there was a comparison to a bicycle; you can analogize (roughly) to not pedaling while the bike coasts about.

The really important difference is that on a bike, if you start moving your feet nothing happens until your pedaling provides forward power, and a bike's mechanism doesn't provide any deceleration when you stop pedaling (no 'engine brake) except for some very old one-speeds.

You can, on a bike, break (not brake) the rear wheel free from a coast if you really stomp on the pedal. By 'break free' I mean cause the tire to spin rather than roll. Maybe this is obvious, but that's the same kind of traction you get in a skid; less, aka 'bad.'

In a car (or motorcycle) you can get the same effect by dropping the clutch with the revs up significantly higher than your travelling speed.

The converse can happen if you declutch and your revs are significantly *lower* than your travelling speed. Any time the engine+transmission suddenly says X mph, and you're doing Y mph, and the difference between X and Y is more than your tire's --->spare<--- grip -- what's not already being used to handle whatever maneuver you're doing -- your tire is now a slidy thing and not a rolly thing.

Also bad for grip is suddenly shifting the weight about. Sudden engine braking will cause weight to shift to the front, putting weight on it and increasing its tire patch (the bit in contact with the road). Lots of grip on the front wheel. Then, and unlike manual braking not so much under your direct control, the forks uncompress, the weight goes off, the tire patch shrinks, and all the front wheel grip goes away.

If your wheels weren't perfectly straight during all this the effect is that the bike straightens up or even highsides and the rider may go over and off in the same direction (hmm, this sounds like the first post...). This tendency is exacerbated if the initial engine braking takes so much weight off the rear that it slides first.

In a car this 'just' causes oversteer because the center of gravity of a car is well inside of its outside wheels (aka it's in the middle of the car). It still isn't a good thing unless you're trying to initiate a drifting contest.

With the clutch out, even dropping the throttle won't (usually; I haven't tried closing the throttle in 1st from 12k RPM and I'm not going to) cause this disaster. Maximum maneuvering grip is obtained by keeping throttle neutral, not clutching.

November 14th, 2011, 03:05 PM	#107
Numbersix ninjette.org member Name: Michael Location: MI Join Date: Aug 2011 Motorcycle(s): Honda Elite 110 (deceased), Green 2012 Ninja 250 (sold on Pi day); Grey/Green 2019 Ninja 400 ABS Posts: 238	One more thought about clutching: The clutch (obviously) disconnects the engine from the drivetrain. Somewhere in here there was a comparison to a bicycle; you can analogize (roughly) to not pedaling while the bike coasts about. The really important difference is that on a bike, if you start moving your feet nothing happens until your pedaling provides forward power, and a bike's mechanism doesn't provide any deceleration when you stop pedaling (no 'engine brake) except for some very old one-speeds. You can, on a bike, break (not brake) the rear wheel free from a coast if you really stomp on the pedal. By 'break free' I mean cause the tire to spin rather than roll. Maybe this is obvious, but that's the same kind of traction you get in a skid; less, aka 'bad.' In a car (or motorcycle) you can get the same effect by dropping the clutch with the revs up significantly higher than your travelling speed. The converse can happen if you declutch and your revs are significantly lower than your travelling speed. Any time the engine+transmission suddenly says X mph, and you're doing Y mph, and the difference between X and Y is more than your tire's --->spare<--- grip -- what's not already being used to handle whatever maneuver you're doing -- your tire is now a slidy thing and not a rolly thing. Also bad for grip is suddenly shifting the weight about. Sudden engine braking will cause weight to shift to the front, putting weight on it and increasing its tire patch (the bit in contact with the road). Lots of grip on the front wheel. Then, and unlike manual braking not so much under your direct control, the forks uncompress, the weight goes off, the tire patch shrinks, and all the front wheel grip goes away. If your wheels weren't perfectly straight during all this the effect is that the bike straightens up or even highsides and the rider may go over and off in the same direction (hmm, this sounds like the first post...). This tendency is exacerbated if the initial engine braking takes so much weight off the rear that it slides first. In a car this 'just' causes oversteer because the center of gravity of a car is well inside of its outside wheels (aka it's in the middle of the car). It still isn't a good thing unless you're trying to initiate a drifting contest. With the clutch out, even dropping the throttle won't (usually; I haven't tried closing the throttle in 1st from 12k RPM and I'm not going to) cause this disaster. Maximum maneuvering grip is obtained by keeping throttle neutral, not clutching.