Rear Derailleur Question

[octobert]

Will a 9-speed rear derailleur work with a 7-speed cassette?

I have a 7 speed road bike that I bought on ebay last year. I bought it to try road riding before I went and spent the big bucks on a new bike. Now, I want to start replacing the lower end parts with better quality parts, but I want to do it piece by piece. I'm not ready to replace the hub, cassette, chain and STI Shifter, but I can get a good price on a 9-speed Ultegra. Any thoughts? Also, can a shifter on a 7-speed bike work for a full 9-speed set-up? It seems that I have an extra index or two on the shifter.

Thanks.

 

[J-MAT]

As long as it's a Shimano 7 speed, you shouldn't have any problems. I say again, "shouldn't." It might not work, but I think it will. I have used many combinations of 7-8-9 speed drivetrain components over the years.

The most important thing do is to properly adjust the "high" and "low" screws on the back of your derailleur. With 9 speed STI levers on a 7 speed rear, you will throw the derailleur into your spokes resulting in a severly bent derailleur hanger on your frame if not properly adjusted. Proper adjustment of the high/low screws will prevent excess range-of-motion of the derailleur.

If this happens you better have a chain breaker with you. You will have to remove the derailleur on the roadside and break the chain to take up excess slack since you will now be riding a single speed bike!!! Something like a 39x15 is a good gear in this case.

Also, don't force 9 speed STI levers past your largest diameter 7 speed gear!!!

Good luck!!!

 

[octobert]

Thanks for the reply, but just to get clarification on one point...Can I use an 8 or 9 speed derailleur on a 7-speed casette?

Also, does it make sense to replace Shimano RSX components with Shimano 105? I am probably going to sell the bike sometime in the next year...I your (or anyone elses) opinion, will 105 compnents bring a higher price than RSX?

 

[Shabby]

I think you'll find that a 7 speed hub is narrower than an 8 or 9 speed hub, so the frame might need to be bent a bit wider. Also, there might be enough of a difference in the spacing between gears such that a 9 speed shifter never really works perfectly.

You won't get back what you spend on components. I'd just save the cash and put it into the next bike, and sell the one you have for whatever you can get.

 

[J-MAT]

You shouldn't have any problem using a 8-9 speed derailleur on a 7 speed hub. Derailleurs move back and forth, what determines how they move is the shifter.

Be sure to properly adjust the high/low screws on the back of the derailleur though. This is very important. If for some reason the derailleur goes into the spokes, you will bend the derailleur hanger on your frame.

On most bikes, they can be bent back into shape once or twice. Some bikes might be trashed if the hanger gets bent, requiring a new frame. Makes you really appreciate bike manufacturers that have replaceable derailleur hangers like Cannondale, Gios, and Look. You could carry a spare hanger/dropout in your saddlebag, pull the derailleur into the wheel, and fix everything on the roadside!!!

Shimano RSX and 105 components are on the low end. Upgrading to 105 is not worth it. For most components, Ultegra components are fine like hubs, shifters, etc. If you are really strong or heavy, or strong and heavy, use Dura Ace components in high-stress areas like cranks and bottom brackets.

Good luck!!!

 

[Shabby]

Have to disagree on a couple of points in the last post. What determines how far the deraileur shifts is the indexing on the shifter itself - the derailleur moves by the action of the cable only, and the distance the indexing shifts is less for a 9 speed than a 7 speed due to the chain being narrower. It's probably not a huge issue, but might explain why you never get it set up to change smoothly.

Cranks and bottom brackets rarely wear out, so it's not worth spending $600 on a Durace cranket when you can get a Tiagra for $150, especially if you're going to sell it in the short term. It's best to save the cash and buy a new bike, as an entire groupset on it;s own costs almost as much as new bike.

 

[J-MAT]

Shabby:

What do you think I meant when I said the shifter is responsible for moving the derailleur?

7 speeds have 126 mm spacing, and 8-9 speeds have 130 mm spacing. Even though 8-9's are the same, In my experience, a bigger shifter will sometimes adversely effect the normal range of motion. I'm being cautious about throwing the derailleur into the spokes, because if he does this, his hanger/dropout will be severly weakened when (if) straightened. Proper high/low screw adjustment is most important.

As for the cranks breaking, I guess you don't ride very much. I have broken every part you can break on a bicycle except for brake calipers, brake cables, and seatposts.

Dura Ace are the strongest parts you can get. Even so, in the last 3 years I have broken 1 Dura Ace bottom bracket (snapped it clean), and one set of Dura Ace cranks. I have broken other cranks and BB's as well, in addition to forks, frames, wheels, pedals, etc. If you ride hard/long enough, you will break something. It's only a matter of time!!!

If you are selling the bike, just sell it now. I put out the Ultegra/Dura Ace parts just as general info.

 

[Shabby]

Not wanting to get into a slanging much, but:

"7 speeds have 126 mm spacing, and 8-9 speeds have 130 mm spacing." Thanks for supporting me on that one. Hence, the indexing on the 7 speed pulls the cable approximately 126/7 mm ~ 18mm. A 9 speed shifter pulls the cable 130/9 mm ~ 14mm. Hence, they're unlikely to work as well together in an optimal way.

"Proper high/low screw adjustment is most important." Yes, to set the limits of where the cable can pull the derailleur. But this has no effect on hte spacing between cogs.

"As for the cranks breaking, I guess you don't ride very much. I have broken every part you can break on a bicycle except for brake calipers, brake cables, and seatposts." You lose credibility when you sink to the "I can ride further/faster/better than you level". I've got bits from every groupset Shimano has made in the last ten years on my training bike due to replacement requirements and availability at the time, but breaking cranks is pretty rare unless there's some sort of manufacturing defect.

"Dura Ace are the strongest parts you can get." I don't think even Shimano would claim that. They're the lightest, but I doubt if they're any stronger than the Ultegra cranks. I'd rather have three sets of 105 cranks for my training bike than one Duraace crank.

 

[J-MAT]

Shabby:

I always said that mixing drivetrain components was an experiment and may or may not work. There are so many possible combinations of things out there now, that it is hard to tell what will work. The situation I wanted to avoid was sucking the derailleur into the wheel by improper derailleur adjustment.

The high low screws are the most important adjustment. I never said it had anything to do with cog spacing.

I didn't sink to any level when I said I break cranks. I know many, many, riders over the years who have broken cranks and bottom brackets, etc. I'm sure lots of people here have had similar experiences. I have seen it so much that I'm surprised to hear you say they don't break. Defect-free cranks and bottom brackets will eventually fail if you put enough load on them.

Dura Ace parts are the strongest. Shimano headquarters is about 15 minutes away from my house, and when I break something, I get replacements in person. Dura Ace parts have a longer warranty than the other groups.
I know people at Shimano, and they will tell you that Dura Ace is the strongest!!!