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Pedal and BB threads - why do they seem backwards?(6 posts)

Pedal and BB threads - why do they seem backwards?NewDayNewWay
Nov 8, 2003 6:54 AM
This has confused me to no end! This just seems backwards to me. I'll use the left side pedal for example...

The left-side pedal is reverse threaded. So, looking at it from the left side of the bike, the pedal spindle turns counter-clockwise to tighten the pedal on the crank. Now, when you pedal (in the counter-clockwise direction looking from the left), the pedal stays semi-level and turns clockwise relative to the fixed spindle. So, it would seem that the pedal would tend to loosen because any (minimal) force on the spindle is in the clockwise direction! So it would seem that the RIGHT side pedal should be reverse threaded, not the left!

Please help me out of this mental conundrum!
Ask the Wizard for a new brain ;) -nmfiltersweep
Nov 8, 2003 7:08 AM
Think about the bearing.Spoke Wrench
Nov 8, 2003 10:38 AM
There is a bearing between the spindle and the crankarm. When you pedal the bearing rotates so the part that faces the crankarm is turning backward relative to the direction of pedal rotation. That small but constant force can cause the pedal to unscrew itself. If you doubt this is true, ask somebody who has an Italian bottom bracket.
Think about the bearing.NewDayNewWay
Nov 8, 2003 2:16 PM
Bingo! I see the light!!! You just saved me a night of tossing and turning in my sleep over this. Thanks!
You guys are wierd53T
Nov 8, 2003 8:49 PM
NDNW, you are correct that the first order force applied to a pedal body while pedaling will tend to unscrew the pedal. i.e. on the RH side of the bike any friction in the pedal bearing will act to unscrew the pedal. For example, try to install the RH or LH pedal by holding it in your hand, which way do you spin the crank? Backwards! That's right, backwards to tighten, forward to loosen.

Why then the wrong threads? Orbital progression! This a wild concept, but if you apply cyclical forces to a cylinder inside another cylinder it will tend to walk out opposite of the direction you are forcing it. Wierd but true, do a google search. Remember Spirograph? Or are you too young for that?
If you think about it this way it might make more sense.LC
Nov 8, 2003 12:22 PM
You tighten the the pedal in the same direction that you pedal the bike.