Cyclocross derailleur cage length- long or short

blorg

I managed to destroy my rear derailleur and so have to replace it. I was wondering between long or short cage. The bike originally came with a long cage RD but it was bent so I replaced it with a short one. Gearing is 50/34, 12-27 so short should be fine (have the same on my winter road bike with a short cage.)

This short cage enjoyed one race before jumping into the spokes at the end.

Are there any disadvantages to a short cage on a cross bike? I'm primarily thinking that a long cage might tension the chain better when in the small-small combo, reducing the chance of chain drop. When I changed the derailleur I had to shorten the chain and even after doing this it was a little "slack" in that combo. If I had shortened it any more I don't think big-big would have worked. (I know these are not ideal ratios to be in.)

Any thoughts for which I should go for are appreciated. Will probably be replacing with Ultegra SL again as it seems about as cheap as 105.

John.T

Could you manage with a smaller ring than a 50. If so then a short cage will be fine. Your present setup is at the limit for a short cage (2 teeth beyond by Shimano but we all know it works fine) and may be pushing it for the rigours of CX. With a 46 or 48 you will have no chain tension trouble and may have a more usable spread of gears and not need to use the small / smaller combinations. If you need the 50 a long cage may be a safer bet.

blorg

I could certainly manage without the 50 for cross racing but I'm not sure I want to go to the expense of changing the chainring. Also the 50 is useful if I am using the bike on the road etc.

I do get that a tighter front pair would be more optimal for CX racing, maybe if I get more serious next year! I have just started and currently am useless!

I have to buy a new derailleur anyway so may go for the long cage so, thanks for the advice.

John.T

Just had a close look at your picture. Where is the mech actually damaged. If it is just the cage you can work small miracles with a hammer and vice/anvil. It may be recoverable.

godihatehills

sorry to interrupt
Ive got a long cage 7800 rear mech for sale, mint ( 100% probably been used for about 25/30 miles) before I swapped to sram......40 squid if youre keen

blorg

I only had a quick look at it this morning but there are other issues, the B-screw has sheared off for example. When I took it off the bike it didn't really look "right" - I'll have a better look this evening.

I actually have a 105 long cage with just a bent cage- you reckon take the cage off and then try to straighten it?

John.T

Worth a try. I costs nothing.

Monty Dog

I'm running a 36/46 at present and the 46 sees very little use expect on long, open downhill stretches - most of the time I need the downhill for recoveries after the first lap or two, so it never ocurs to shift it onto the big ring - Next year I'm contemplating a single ring up front - less to go wrong. In terms of the mech, if you want to stick to double, I'd look at reducing your big chainring size - the shifts are noticeably faster both front and rear with a short-arm mech too - mis-shifts and derailed chains are often a recipe for problems - a long-arm mech is more likely to get bent in an 'off' too.

Monowai

I'm running a single ring for cross racing for the first time this year and I'm very happy with it. 39T up front with a 12-27 cassette on the back gives all the gears I've needed in any race this year. Also attracts much less mud around the bottom bracket area and saves a bit of weight. Might be under-geared for early season races where it is like a crit on grass, but then could change the cassette to a 11-23 for example.

Mike67

Monowai

Could i ask what set up you have at the front on your bike.
Is it a single ring crank or are you using a double?

I was thinking of losing my outer ring for cross and was wondering if I need to replace it with say a bash ring, or just adapt the chainring bolts to allow for one ring only.
Also, did you leave the front derailleur in place to act as a chain guide/retainer type thingamybob.