I have a road bike with a Shimano Tiagra rederailer. When the bike is stationary and I pedal backwards, I hear some clicking and then the chain jumps to the next smallest cog. Does anyone have an idea of what might cause this?

if your bike is relatively new (as in you got it from your shop brand new within the last few months), try tightening the derailer cable by backing out the adjustment screw on the shifter, go about half a turn then shift through all the gears (to make sure it still shifts properly), then try pedaling backwards. Do this until either it stops jumping gears while back pedaling, or until the adjustment screw comes out, if it comes out screw it back in, cause that ain't the problem. But from my experience the rear derailer will start to do funny things do to initial cable stretch

That's just total BS. If the RD is shifting properly don't start mindlessly fiddling with the adjustments.

It can be caused by stiff gunky chain, and or resistance caused by chain angle depending on the gear you are in.

Dude, you come on a little strong. I know what BS stands for. Do you need to use profanity to make a point?

The deraileur might need a little tuning but if it shifts OK, I would suggest not pedaling backwards.

Your derailuer is out of adjustment because of cable stretch. It is probably making noise when you shift and when you ride but you don't notice it. One of the other posters was close but his advice was a little off (the other one is just off). Put the bike up on a repair stand (or hang it from a roof rafter). Shift it all the way to high gear (i.e. the cable should be in its most relaxed condition). Gently pull on the cable where it runs next to the downtube. It should be just slightly tight with a small amount of play in the cable. It shouldn't pull out from the frame too far nor should it be as tight as a guitar string. If it is loose, you should be able to take the play out with the derailuer adjusters and/or lever adjusters.

Shift to the next lowest gear and pedal if forward, not backwards and run it through the gears. If adjusted properly, the gear train should be relatively silent. If it clatters or makes popping noises or if the chain appears to skip on some cogs, you need to adjust the deraileur. Turn the cable adjuster on the derailuer to the left (towards the wheel) to tighten it and to the right it loosen it. Work in small increments, a quarter turn at a time, and the pedal it again. Shift gears often (up and down) while adjusting until the bike starts shifting as you like. Sheldon Brown, as usual, has a good indepth explanation of how everything works and how to make it work like it is supposed to.

Hope this helps,
Stuart Black
"Dancing chains, good. Skipping chains, bad."

"Here's a dime. Call your mother and tell her you will never be a mechanic." -liberally taken for the "Paper Chase"

DO NOT PEDAL YOUR BIKE BACKWARDS. Bikes are not designed to do this. It can be done, yes. But that is a side effect from other design considerations. There is no guide to keep the chain on the sprockets when pedaling backwards. And there never will be.
DO NOT ADJUST YOUR BIKE BASED ANY ANYTHING IT DOES WHEN PEDALING BACKWARDS.
Without a derailleur to guide the chain backwards onto the sprockets the chain may jump off when in certain gears. That has nothing to do with the derailleur. It's normal
in some cases. Like when there is an extreme chain angle.
Without a guide, of course it will jump off. DON'T pedal backwards. Don't mess with the derailleur either.

finally... someone says it.

Some bikes pedal backwards poorly in some gears... it's a function of chainline, chain stiffness, cog design, etc.

Adjust the derailleur to work properly in the forward pedalling direction only.

People. People. People. Bicycle and their derailluers are not some magic thing that should never be touched. Bicycles are relatively simple devices that are easily adjusted and repaired. Sure a bike is not designed to be pedaled backwards but it can be, it's just not productive (unless it's a fixed gear). There are plenty of reason to pedal backwards for up to a full stroke. When mountain biking, if you couldn't pedal backwards, there is a whole lot of stuff you couldn't ride! Try track standing without being able to pedal backwards! If the chain is skipping or ghost shifting to another gear when you pedal backwards there is something wrong with the bike that will show up while pedaling forwards. It needs to be fixed!

Stuart Black

Well, that's a more likely cause than derailer adjustment being off. If it shifts ok the adjustment also ok and in no need of fiddling.

Do you really?? How about BS= Bull Snot?

I think you were right, especially if the chain is in a crossed gear, it can jump cogs when back pedaling. Probablty the deraileur could use a little adjustment. Every one is right. Don't back pedal, keep dr adjusted etc. Good job on keeping it civil after getting dissed like that!

If it runs decently forward and skips in backpedal, then its simply a misalignment. The chainline is what is involved in backpedaling. The difference in side to side alignment with the crank vs the cassette. The only thing in the equation worth even mentioning is the chain condition, but seriously there is little to be concerned with. Backpedaling is one thing they trained us out of as mountain bikers because it opens oneself up to problems such as that.

Well, the easier way to do it rather than trying to get ones head around all the subjective cable tightness(guitar string) BS is to shift to the second cog, and while pedaling forward,adjust cable tension to where the chain stops just short of making noise against the 3rd gear.This being the final adjustment,and asumes one has started at the beginning and all other adjustments are correct.

No that's not what if means to the reader. Don't use that abbreviation, it is short for a common vulgar expression. When you say BS people will think you mean BS.

Thanks for all the advice. I tried a few things and here is what I found. I lubed the chain, but that really didn't help any. The problem only happens when the chain is in the larger cogs on the rear cassette. I have a triple, and the gear jump problem only happens on the 52 and 42 front cogs. So I am assuming it has something to do with the angle of the chain. Right before the jump happens, the front cog doesn't catch the chain correctly and snags. This causes the rear hanger to move forward. On a side note, the bottom of my hanger seems to be tilted slightly towards the wheel, so it is not perfectly vertical. Would that be apart of the problem?

Most Certainly.

Yes it is. And you should get it fixed. Take it to a shop and ask them to do it or ask them for advice on how you can do it (there are ways but I'm tired of getting my chops busted today). If it is a steel hanger, it can be bent back without problem. If it's aluminum you might need a new hanger, if your bike has replacable ones. Get it fixed, your bike will thank you.

Stuart Black

This is just Syd's way of tell us he loves us. Rather than offer advice, he just want to tell people how full of BS they are.

Been riding a mountain bike since 1983 and do the back pedal thing every time I go out. It's the only way to get the pedals to clear things sometimes. Have to do it if the chain sucks also. I also keep my gear train running smoothly at all time for that reason.

Stuart Black

The chains on many (most?) bikes will grind or shift toward the center of the cogset when you backpedal in a cross- or near-cross-chained combination, such as large-large or small-small. You should be able to backpedal pretty freely in most of the other gear combinations.

That derailleur hanger needs to be straightened (slowly and gently) so that the entire assembly hangs vertically.

The only derailleurs which are SUPPOSED to shift while backpedaling are Tullio Campagnolo's Cambio Corsa and Paris-Roubaix.

Mine does't skip either, but that's in most cases. If you backpedal in say, a trail race, it can suck the chain off the chainrings. Bad habbit unless expressly needed or in favorable conditions.

if the bike is new.. just take it to your LBS and have them look at it. i dont know why none of you guys have suggested it..

$.