shop testing a chain skip problem
 

Wife's bike has a chain that will skip or jump only on steep climbs. This only happens on one of our normal routes, and it's one that is a 20 minute drive away and then the hills start 4 miles into the ride. What I'm saying is that it won't be easy to do a quick road test. Is there any way to simulate this in my garage so that I can tell if I am doing any good?

chain, cassette, chainring condition? also check the freehub

Do you have an indoor trainer? If so, can you crank it down and use the same gearing?

Skipping is usually a result of a worn chain or cassette. There's a tool to measure chain stretch/wear. But cassette might be shot too.

Try this, which requires 2 people. Shift the bike into the problem gear combination and put it in a corner of the room with the front wheel against the other wall. Have someone sit on it and load the pedals (try to ride through the wall) while you carefully observe the chain on both sprockets Front and rear. If there's enough wear to cause skipping under load you'll see the chain slide forward or back on the sprocket and climb outward on the teeth.

If it does so significantly, either the chain is stretched, or the sprocket is worn. Start by measuring the chain, if it's OK (less than 1/2% stretch) it's the sprocket, but if the chain is stretched the sprocket may or may not be worn also. You won't know until you replace the chain.

The first thing I'd do is measure the chain stretch. You only need an accurate ruler to do this. If the chain is significantly worn you should replace it.

Can you remove the rear wheel and take a picture of the cassette and post it here? We could probably judge the condition of the sprockets with a good clean picture.

Thanks everyone. Bike is new to us, but a 2005. PO claimed it was only ridden a few times, and the condition seems to agree. My wife has ridden about 100 miles. I have not gone through the bike well enough yet. First I need to really clean the chain and relube it, and measure the stretch at the same time.

I can borrow a trainer, and I like the wall idea.

I'm on the road, but will take a picture this weekend

Probably not the problem, but confirm that the chain is the proper length and the B-adjustment is correct. Most probably worn components.

Could be a simple cable adjustment. Does the chain act like it wants to change gears when it skips?

I know that there are some gear combos (but don't remember which ones) where the chain jams when back pedaling. This issue improved by itself with about 20-30 miles of riding.

on a mild hill the chain skipped but I don't think that it wanted to change gears. On a steep hill, the chain ended up off of the front gear