pedal threads, confused.

[lewis1641]

so dricve side pedal is normal thread, left hand pedal is left hand thread.

i understand the theory of making one opposite to the other (so that the turning motion of the cranks tightens the thread rather than loosening) but surely pedal threads are the wrong way round.

am i confused?

 

[We_are_Stevo]

It would seem that way; but try fitting a pedal loosely then turning the cranks and you'll see it's correct...

 

[Andy R]

It's all down to the phenomenon known as mechanical precession. No doubt there's a Wikipedia page (or two) about it but as a quick demonstration, hold a pencil upright in your fist and rotate the top of the pencil in a clockwise circle - see what happens to the pencil itself?

 

[jax13]

yes.

tighten them by turning to the front of the bike, loosen them by turning to the rear.

seems logical to me

 

[rosstheboss]

And tighten them up from the same side of the bike and they both go in the same direction (if you see what I mean!)

 

[lewis1641]

It's all down to the phenomenon known as mechanical precession. No doubt there's a Wikipedia page (or two) about it but as a quick demonstration, hold a pencil upright in your fist and rotate the top of the pencil in a clockwise circle - see what happens to the pencil itself?

buy when the crank it turning clockwist, the pedal is rotating anti clockwise on its axle, thus loosening the threads, not tightening. surely?

 

[AR-CoolC]

It's all down to the phenomenon known as mechanical precession. No doubt there's a Wikipedia page (or two) about it but as a quick demonstration, hold a pencil upright in your fist and rotate the top of the pencil in a clockwise circle - see what happens to the pencil itself?

buy when the crank it turning clockwist, the pedal is rotating anti clockwise on its axle, thus loosening the threads, not tightening. surely?

The pedal is rotating anti-clockwise on it's axle, turning the thread clockwise (on drive side)

It sounds wrong, but it does work :?

 

[MikeD]

There are bearings between the pedal body and the axle, which reverses the motion again. It's a very slight effect, but it'd be enough to undo the pedal over time if the threads were the other way around. I've got a tandem with kiddiecranks on the back that -- for reasons too complex to explain here -- have the pedal axles reversed. There are set screws in the ends of the cranks, if I forget to do those up the pedals fall off within a couple of miles

 

[lewis1641]

Never thought about the rotation of the bearings. Makes perfect sense now.

 

[Anthony]

What is the explanation for the pedal threads having to be the opposite way round from the bottom bracket threrads?