Rear Derailleur Compatability
 

Hello All,

Don't laugh, but I'm riding a 1988 Rockhopper and am looking to replace my rear derailleur which is now too thrashed to continue. The problem is that I have a 7 speed cassette and most new derailleurs seem to be 8 or 9 speed. Anyone know which current models would be compatible with my 7 speed?

Thanks,

Joner

If it's Shimano drivetrain, just use a shimano 8 or 9 speed.

sydney is right, most derailleurs can be tuned to 7 speed. Just make sure if its not shimano, that which ever you get is compatible with your shifter. Sram ESP only works with ESP

When you see a rear derailer listed as "[n]-speed" that's just marketing talk. Derailers don't care how many speeds you have. That's an issue for the shifters and the cassette, also the chain.

With front derailers it gets more complicated, but it's a 2- vs 3 issue, the number of sprockets in back doesn't matter.

Assuming your bike uses Shimano stuff, any Shimano rear derailer will work as long as it has a cage designed to clear your largest rear sprocket. ("Road" models with short cages may have problems with rear sprockets larger than 28-30)

Sheldon "Speed" Brown

though not really topic related, am just wondering, will ultegra triple front derailleur work with cranks of 24-36-48?

It isn't a problem to use a 8/9 speed derailleur on a 7 speed system because you can just dial in your limit screws.

The problem is using a 7 spd derailluer on an 8/9 system. The 7-speed wasn't designed to be wide enough. You can however, use it if you sacrifice one of your cogs (smallest or biggest) on a 8/9 speed cassette.

As far as the front derailleur 24-48 spread, you will probably have the chain rub the bottom of the front derailleur cage when in the granny gear and the smaller 1/2 of your range in the back. Otherwise it'll work.

The best I've been able to adjust is a 46 front chainring with only a little rubbing in the 24/11 gear ratio, but you never want to cross chain anyways.

thanks for the quick answer!

That is just not true.

Actually, Grant at www.rivbike.com recommends the 105 triple FD for similar applications. Cheaper and nothing is really gained with an ultegra,unless you already have one.

7-speed derailleur works perfectly with 8 or 9-speeds.

Really, I've had numerous problems with 7 speed RD's not shifting onto the big cog in the back of a 9 speed system. Usually with lower spec'd stuff like Deore it'll reach, but XT's/XTR's have always ended up with problematic shifting.

I'm not so proud to say I'm absolutely right. Might also be due to the jockey pulleys.

I will add that I have NOT tried a 7-sd on an 8 speed system conversion in probably about 4 years. Just when I worked in shops off and on over the years we shyed away from this due to problems when 9 speed stuff first came out and conversions were more common.

It will work, but not as well as with chainrings it was designed for. That is optimized for a[*]-42-52. The outer cage plate curvature matches a 52, and the inner cage plate depth is optimized for a 10 tooth jump. (doesn't much care about the size of the small ring, we routinely substitute 26s or even 24s for the silly 30 that comes stock.)

If you're using it with indexed shifters, it will probably shift OK, but you may find that the more extreme cross-chain angled gears will rub on the cage, despite the limited "trim" capacity of the STI shifters.

If you're using a "friction" type front shifter (bar-end, downtube or Campagnolo ERGO) this won't be an issue. However, if you're using a "friction" shifter, you'd probably get better results with a "mountain" style front derailer for these chainring sizes, because it will be closer to matching.

If you're handy, you can re-shape the bottom edge of the outer cage plate on a bench grinder to match the curvature of the smaller chainring. I do this on a semi-routine basis for non-standard chainring options.

See also my article on Derailer Adjustment http://sheldonbrown.com/derailer-adjustment

Sheldon "Sparks" Brown

well, it arrived the other day so i guess i´ll just go with it.

yes, thankfully i use downtube shifters. the re-shaping suggestion sounds good, but i´m afraid i don´t have experiences in doing so, i´ll try that on my old derailleur though to see how it works.

Sheldon-

Not to disagree but to ask for clarification, I haven't found this to be true. I tried to set up an old 8 speed front derailleur with a 9 speed chain and index shifting. It seemed as if the cage was too wide to move the chain efficiently. If I set it up to upshift quickly it wouldn't downshift consistently and vice versa. I had to set it up to downshift consistently and overshift a bit to force it to upshift. There may have been other incompatibilies, however, as I can't remember exactly which derailleur it was.

-s

I have some older shimano 8 speed FD that work fine with shimano STI, and I have some that don't.It seems to have to do with arm length and arm angle.Either works ok with downtube of barend.

I have a 105 with 44-34-22 and an Ultegra with 48-38-24 and they both work without problems. The only slow move is going up from 22 to 34 (and it's not that slow, just a bit slower than other moves). So if you already have the derailleur, it's probably a good choice. One thing I need to highlight, is that I use bar-end shifters, which means I shift the front end in friction mode. As Sheldon said, with STI it might be different (though I'm aware some people were quite successful).

But there is another issue not covered so far. Is it for new rings you are installing on a crankset? If so, if it is a Shimano crankset, it uses 130/74 mm bolt diametre and accepts 38 mm and 24 mm as the smallest middle and small chainrings.

yes, it´s new, it is sugino xd with 110/74mm. i chose this crank because of this (and its shape too).