Unintentional upshifting is a common complaint among cyclists, particularly with strong riders who use fairly flexible frames. The typical moaning is that the *%#* bike shifts up to the next smaller rear sprocket when standing or pedalling hard.
To remedy the situation, the first thing most guys check is the shift lever. In ages past, the friction shift lever required periodic re-adjustment. The thing is, most friction shift levers have a screw or wing nut to keep unwanted upshifting under control. However, at times the screw becomes too loose. Note that in some cases the problem is not insufficient friction, so tightening the lever won't cure it.
Today, with the indexed shifting, the problem is much less prevalent, but sadly, it does still exist. When unintentional upshifting occurs, the problem is not the friction regulation screw, but the cable guide that the derailer cable uses to get around the bottom bracket. As you pedal the bike, the bike frame flexes from side to side. This will cause the gear cable to get tighter then looser with every other pedal stroke.
If the bottom-bracket cable guide has too much friction, it can act as a one-way clutch, pulling the cable down from the lever, but not allowing it to retract on the opposite pedal stroke. Thankfully, greasing the cable guide is all that is usually required.
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2 comments:
Um, if you're going to plagiarize Sheldon Brown, you should at the very least cite your source. Yours is clearly a very clumsy "re-write" here of his original article, found here: http://www.sheldonbrown.com/autoshift.html
If you are going to blog be original! That is the point of having your very own blog. It's fine to copy and paste and backlink, but don't deliberately "borrow" material found on another site.
Dude, not cool. Sheldon Brown was the man, and you get no respect for not citing him as your source. You suck.
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