A friend of mine is a mechanic, and long ago he told me if my motorcycle’s battery fails and I can’t get another vehicle to help me with jumper cables, what I have to do is have the ignition ready, get it into 4th gear, and after giving it some momentum to suddenly release the clutch.
How does this work, and why 4th gear specifically?
In: Engineering
To start, the engine just needs to be spun fast enough that it can ‘catch’. Releasing the clutch connects the wheels to the engine, causing the bike’s momentum to spin the engine if the bike is moving.
Each gear will spin the engine a different speed. Lower gears will spin it faster but with less efficient use of the bike’s momentum. It sounds like your mechanic friend has decided that fourth gear is the right balance of speed and momentum-efficiency.
Interestingly, this can also be done with manual transmission cars.
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