Bicycle Mechanics - Observation on sheldon's article

http://sheldonbrown.com/autoshift.html

I experienced this myself today. I did some serious climbing (mount soledad) and finally gave my largest sprocket some use. However, I noticed that the sprocket would tend to shift me into the 2nd gear after just a few pedal strokes. Better yet, it would actually tug my shifter hard enough to knock the indexing into 2nd gear! The problem was not what sheldon describes. The tension in my cable was high enough so that it would shift into the sprocket but, in 1st gear, the tension was so taut that any distrurbance to the cable would pop me into second gear. So, just a little addendum to His article...

This only reinforces my belief that 99% of shifting problems stem from improper cable tension.

I'm thinking that, once you get everything else right, 100% of shifting problems can be attributed to cable tension.

In your case I'm pretty sure that a 1/4 turn adjustment on your low limit screw will keep your bike from auto-shifting. Your derailleur hanger may be tweaked a bit too.

Thanks for the link. I get this problem every once in a while. It's very frustrating... but I may adjust my low limit screw just in case. I don't think it's my derailleur, though, in my case. The bike is too new.

Koffee

I'm thinking that, once you get everything else right, 100% of shifting problems can be attributed to cable tension.

In your case I'm pretty sure that a 1/4 turn adjustment on your low limit screw will keep your bike from auto-shifting. Your derailleur hanger may be tweaked a bit too.
Uh-uh. I lowered the cable tension, and presto! It is perfect now. The problem was that the cable tension was simply too high in the first gear, and this caused the shifter to snap itself into second gear. Giving it a tad bit of slack kept the shifting crisp, but avoided tensioning the cable so much in first gear.

It's like there was so much tension, I was BARELY able to get into first, but the shifter would not hold it there.

The low limit screw may be an issue, but I was having trouble with the der. rubbing the spokes, so I think it's set up properly now. And the deralleur hanger tweaked? I doubt it. I did ahve a crash, but that was on the other side of the bike. Plus, on my frame, it is integrated into the frame, and the hanger is 7mm thick titanium. The der. bolt would snap before bending the hanger.

Uh-uh. I lowered the cable tension, and presto! It is perfect now. The problem was that the cable tension was simply too high in the first gear, and this caused the shifter to snap itself into second gear. Giving it a tad bit of slack kept the shifting crisp, but avoided tensioning the cable so much in first gear.

It's like there was so much tension, I was BARELY able to get into first, but the shifter would not hold it there.

.

Sometimes this kind of problem means you need to lubricate or replace the shift cables and housings.

Al

Sometimes this kind of problem means you need to lubricate or replace the shift cables and housings.

Al
Maybe, but in my case, this bike is less than 2 months old and has barely 400 miles on it. I built it myself, so obviously, there will be some adjustmet issues popping up...

It's like there was so much tension, I was BARELY able to get into first, but the shifter would not hold it there.

The low limit screw may be an issue, but I was having trouble with the der. rubbing the spokes,
Dude, you're going to get the RD in the spokes one fine day if that's the case. Not being able to get it in 1st gear with too high tension is a limit screw issue. The trouble is the limit screw's fighting the index point.