AMoney

For a bike that I'll be working on, I'm trying to decide between a Ultegra RX 800 Derailleur and a 105 7000 long cage derailleur. Would the chain length be the same for each derailleur? The reason I ask is because I'm leaning towards the 105 derailleur. However, if I change my mind later, I would prefer not to have to lengthen or replace the chain.

MikeWMass

My limited understanding is that as long as you don't change the gearing you should not have to change the chain length.

SoSmellyAir

First, the 105 RD-R7000 is only available with a short cage (-SS) or a medium cage (-GS); I assume you meant the latter.

SHIMANO 105 Medium Cage Rear Derailleur 11-speed | SHIMANO BIKE-EU
SHIMANO ULTEGRA RX Rear Derailleur 11-speed | SHIMANO BIKE-EU

Given that both derailleurs have the same capacity (see links above), and that each has a pair of 11T jockey wheels, it is likely that the chain length would be the same using one vs. the other. But just in case ...

Be a little conservative when you are sizing your chain; you do not have to shorten the chain to the absolute minimum length which would allow you to shift onto the big chain ring and big sprocket combo. Leave an extra link pair or two, which should give you enough wriggle room in case the path taken by the chain through the other derailleur is a little longer.

AMoney

My bad, yes

shelbyfv

I assume you are thinking you might want the clutch feature at some point? If so, just get the RX to start with. You can turn off the clutch and not know it's there.

AMoney

For me, that would be a pro of starting with the RX derailleur. I do have a few questions about the RX derailleur:

Do they require more maintenance than a regular derailleur?
If the clutch stops working over time due to wear and tear, can it be replaced without having to replace the entire derailleur?

shelbyfv

Good questions, hopefully someone can answer. I've only ridden with the clutch off and it's like any other derailleur.

Hondo6

This article indicates that regular maintenance/service for a RD clutch is a "good thing". It also gives the general procedure.

https://www.singletracks.com/mtb-gea...illeur-clutch/

Assuming you can get the parts, per the diagram included in the article (for a Shimano XTR) it likely should be possible to rebuild a worn-out RD clutch when it's so worn that servicing it no longer helps. But at that point, if you've been regularly servicing the clutch I'd guess the rest of the RD might be pretty well worn also.

Disclaimer: I've never used a clutched RD, so I can't say from personal experience how much additional maintenance is required. I'd suspect that varies greatly with riding conditions, with dry road riding requiring the least service and wet trail riding needing the most.