I currently have a 2011 Trek 1.2 (Tiagra/Sora) and I'm seriously thinking about upgrading my derailleurs. I've seen a lot of pretty good deals on ebay on Ultegra components, but I noticed that the rear derailleur is for bikes with 10 speeds. Will this work if i only have 9? If not, does this mean i have to upgrade my cassette as well? I really only want to upgrade my derailleurs for now... with that said, what are my options? Thanks in advance for the help guys!

Any modern shimano road derailleur will work on 9 speed just fine. That said, unless you've broken the present derailleur, there are any number of ways to spend your money that would be better.

dscheidt - thanks for the feedback. If you had $100 to spend on bike parts, what would you use it on? I figured the ultegra derailleurs would shift a lot smoother than my sora/tiagra ones... or would it not be noticeable?

Modern derailleurs are all so wonderful, it makes little difference, beyond looks and weight. There's a lot more difference in shifters. If there's nothing broken on the bike (and there shouldn't be), beer. Or, if you insist on spending the money on the bike, some accessory. lights, a computer, pedals/shoes, some clothes, beer, something like that.

Really. It's a nice bike. Go ride it.

Can't you see you guys are ruining the impulse buy!?

I support ya buddy! If you want to feed the bike, I'm all for it. Bikes need love

My experience jibes with dscheidt's. I have a low-end Trek with Sora. I have three other bikes with 105, Ultegra and Dura-Ace. The Sora RD shifts no better or worse than the D-A RD.

Where I do notice differences is in cables and levers. Once I tried them, I switched all my bikes to the D-A cables intended for use with 7900/6700/5700 levers. Silky smooth. The one upgrade I put on the Sora bike was R-500 levers, to get rid of the thumb buttons so that it was like the rest of my bikes.

It's sort of like a door, where the RD is the hinge, the cables are the fit in the frame, and the knob/lock the levers. Replacing the hinges won't fix a door that binds in the frame (cables) or where the knob is wonky (levers).

TD, For the price of a chain whip, cassette tool and another cassette you can fine tune your gearing to your riding style and needs.

Brad

When set up properly, I managed to get a cheap SIS derailleur to shift perfectly well, even on an old freewheel without the shaping common on modern sprockets to aid shifting, though this was a 5-speed with wider spacing. 'Better' derailleurs just seem to be lighter, and more expensive.

With $100, you could probably pick up an almost-roadworthy bike at a yard sale and get it on the road again as a 'beater' for use in winter or in dodgy areas if you don't already have one. Depending on what parts you have already, I'd spend money on: brakes if the current ones aren't up to much, decent fenders if you don't have them already, a different handlebars if you don't like the current ones, lights, cycle computer etc. If you have all of these and everything works, save the cash or spend it on something else you need.

+1, changing the ratios will get your bike better suited to you,
more than which mech shoves the chain back and forth.
look at cassette and chainring sizes [tooth counts]

Thanks for the analogy/advice. That definitely helped. So, i guess if i wanted my shifting to be silky smooth, i would need to change the cables and levers huh? i just did some research on the R-500 levers you mentioned and it looks like you can upshift while in the drops, is this correct? If so, that'd be great, since i can only upshift while my hands are on the brake hoods...

I definitely do love my bike... i don't have lights, so that might be a possibility. However, I really want it to shift like my buddy's Specialized S-works... riding it was amazing!

As mentioned above, shifting quality is mostly related to cables and tuning. If you want to spend your $100 on something that will improve the feel of your bike, buy some nice tires.

Brooks handlebar tape. Real leather tape is not only cool looking when it's new but it actually improves with age. Also, nobody else has it on their bike so your's will stand out.