Bicycle Mechanics - Rear derailleur question

So i have a 8 speed cassette, and a Tiagra rear derailleur, so i was wondering, if i were to upgrade RD, would it have to be an 8 speed RD? I'm not sure if a 9 speed works with it and i can just adjust it or not. A LBS is closing, and having an Out of business sale, and if i come across a nice derailleur, i would like to have the confidence in knowing whether it will work with my bike.

So i have a 8 speed cassette, and a Tiagra rear derailleur, so i was wondering, if i were to upgrade RD, would it have to be an 8 speed RD? I'm not sure if a 9 speed works with it and i can just adjust it or not. A LBS is closing, and having an Out of business sale, and if i come across a nice derailleur, i would like to have the confidence in knowing whether it will work with my bike.

Yes, any Shimano 9-speed rear derailleur will work with your 8-speed Shimano cassette. The indexing is in the shifters. 9-speed and 10-speed Shimano rear derailleurs have the same actuation ratio as your Tiagra RD. However, if your derailleur is in good condition there is not much to gain by replacing it.

hm.. okay thanks! and also, what makes the 105 ultegra or any high model of FD any better than the sora? is it just lighter?

hm.. okay thanks! and also, what makes the 105 ultegra or any high model of FD any better than the sora? is it just lighter?

Lighter weight, higher quality materials.

If you have components that need replacing a close out sale may have some good buys in 9-speed. With 9-speed shifters you could run a 9-speed cassette and 9-speed chain. On the other hand, it is really easy to spend too much on upgrade components.

Al

Good question. I have a Sora equiped 8-speed that I was planning on upgrading when the parts wore out. It is my daily ride and I've had it for 5 years. I got it as a "rain" bike, and it ended up being my favorite bike. I've changed the RD to a Mtn bike RD because I'm running a 12-34 cassette, so I don't know how good they are. Nothing else has worn out yet. It shifts better than my touring bike with Tiagra, and my "good" bike with 105's! It seems like a lot of the touring bikes in almost all price ranges come with Tiagra FD's. I suspect there is a reason for that.

If your bike is shifting well, I'd just wait for the parts to wear out and then repalce them. However, if you have the smame experience that I have that could be awhile.

hm.. okay thanks! and also, what makes the 105 ultegra or any high model of FD any better than the sora? is it just lighter?

If I move up or down just one group level, I can't notice any difference at all. If I move up or down multiple grades, there is an obvious "crispness" difference. I think that it's due to the precision of the assembly.

I also think that they work best if the derailleur is matched with the shifters. A bottom of the barrel Tourney derailleur, for example, works better with a lower end shifter. I suspect the low end shifters have a little give built into them that allows them to overshift and make up for the slop in the derailleur.

I have a cheap tourney RD on a surly LHT believe it or not. It works fine with friction shifting barends...just like you mentioned above, probably due to the forgiveness factor of friction. I don't know if I would trust it for index, and the b-adjustment screw doesn't do anything as far as I can tell.

On my old road bike I had a 105 RD and loved it with tiagra shifters (brifters). I eventually wore it out and put a sora RD on there....I couldn't notice any difference. I think a lot of cheap parts actually work great.

Yea, my tiagra shifts just fine to me, the only issue i have is with my index shifters, to downshift/upshift, i need to use my thumb, and it's quite hard to do with the soras when in the drop down position. I suppose i won't ugrade anything, although i did go to a lbs that was going out of business, all their road bike equipment and accessories were gone, so no upgrade for me. I ended up buying some dry lube =/

hm.. okay thanks! and also, what makes the 105 ultegra or any high model of FD any better than the sora? is it just lighter?

Higher level front derailers may have more aluminum in them but the weight savings are likely to be rather low. Depending on your usage, going to a higher level front derailer may not even be that much of an upgrade. For example, the Sora and Tiagra level triple front derailers are much better derailers than their more expensive cousins. They are easier to set up and require less trim to keep the chain from rubbing for a wider range of gears on the rear cluster.

I have a Tiagra level and a Ultegra level front derailer on two bikes the same gearing range and I can't honestly tell a difference in performance between the two other than the afore mentioned issues.