I'm buildling up a new bike (first build) and am going with basically a full 10sp Ultegra group. I was going to go compact with the fancy schmancy new Shimano R700 compact since I ride a compact now on my cross bike, but probikekit sent me the Ultegra "standard" 53/39 crankset by mistake. No biggie, I'm going to run a 12-27 cassette and will just have to work a tad harder on some big hills near me, but I'll get over it.

My question is, I ordered a short cage RD... do I need a long cage with the 53/39? I don't think I do, but I thought I'd run it by the experts.

Thanks

You don't need the long cage with the 53-27. Neither should you run that combination.

You can use the short cage with the 12/27. Anything bigger than 27 and you'll likely need a longer cage.

Cool... thanks.

Today was like xmas in August for me... boxes of "stuff"... frame arrives next week (cervelo soloist team). Dying to get started.

Ahhhh yessss - the first build. The anticipation and the excitement. Plus a touch of frustration. It is truly an experience to enjoy and learn.

One word......

Patience.

Good luck - take pictures.

55/Rad

Both the short cage and long cage are rated to handle up to a 27t cog. The difference is in chain wrap. The long cage takes up the slack from running a small (30t) chainring on a triple.

Good luck on the build grahny, and post some pics!

Will definitely be taking pics... I've upgraded/changed/worked on everything but cable routing/shifters on my Trek X01 which has served me well in the past year as an offroad workhorse and an onroad speed demon (yeah.. ok.. maybe more like a cruising demon with bursts of speed here and there), so I think I'm good to go.

Only mistake I've made so far was not paying attention and putting on a non-drive side crank in some out of whack position (ie, not in line with the drive side)... I got it on and thought.. hmmmm... this is going to be awfully difficult to pedal .. haha..

As barba already said the long and short both are limited to a 27t big cog. The short cage can handle 29t of slack and long cage can handle 38t. To figure out how much slack the RD needs to handle add the number of teeth on your large ring to the number of teeth on your large cog, then subtract the number of teeth on your small ring and small cog. Example: 53/39 with a 12-27 cassette (53 + 27) - (39 + 12) = 27t. Note a 50/34 with a 12-27 actually creates 31t of slack, which technically requires a long cage but most people successfully use that combo with a short cage RD.

If you want to use a larger cog than a 27t you have to get a mountain bike derailluer which are designed to handle up to 34t cogs.

Interesting... good info... thanks.

Actually, I just got home from work and was going through my goodies when I realized, I have a 12-25 cassette... because I had ordered the compact crank that was what I was going to go with since it would pair up nice with the 50/34 set up... I was going to get the 12-27 if I went with the ultegra 53/39... so now since the order was messed up, I've got a combo of the two... which means I guess my legs are just going to have to get stronger.

edit: I just did some calculations with Sheldon Brown's fancy gear ratio calculator and with what I'm riding with now (50/36, 12-26), riding in the 36 & 23 combination, the ratio is exactly the same as riding in a 39 & 25 combination on a standard... so tomorrow when I go out riding, I'll make sure not to use my 26T cog at all and see how I fair... the hills around me are no more than 3/4 mile to a mile at the most, but they're steep, equaling 8% grades and up which isn't easy for me. I'm sure the soloist team geometry will put power to the rear wheel on the road better than my X01 does too, so that will be interesting to test out as well and see how it helps in climbing.