New answers tagged shifting
As the Nuvinci system has been mentioned in other answers, I'll mention one more. SRAM makes the Automatix hub now. It's a 2 speed system (ratios 1:1, 1:1.37) with a centrifugal clutch. There's no manual shifting possible and no cables involved.
I know Im a little late for this posting but this is the first time I came across such question. I do own a Trek Lime, purchased back in 2007. This is a fully automatic bicycle. It has 3 speeds a front hub dynamo (speed sensor), a shifter module-solenoid (computer) under the center frame, and the 3 speed auto-shifter hub in the rear wheel. As far as I know ...
I HIGHLY doubt this, but it could be possible that you are running a compact chainring set-up on cranks originally set up for triple chain-rings. I derped around with this before, and noticed that the chain would slip from the big-ring into a void between the two chain-rings and make you spin endlessly, creating a horrifically loud and embarrassing grinding ...
This is not that uncommon on mountain bikes. Many times a small pebble or trail or road debris is picked up by the tire and deposited in the pivots of the derailleur. It will sometimes dislodge if you shift onto the biggest ring. Other times you have to remove the object it by hand.
The derailleur was sticking. A bit of lubrication and all was good again.
I would concur that the solution here is to increase the length of the cable housing that is inferring with the rack. If the rack is putting any pressure on the cable housing, then it will interfere with the ability of the derailleur to shift properly. Depending on how much free cable is left over coming out of the derailleur, You will most likely need to ...
34/50 is a standard combination, so 34/48 should work without problems. Friction shifters just make it easier to overshift and trim on the fly.
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