Road Cycling - 12-27 Cassette Question

Can you put a 12-27 cassette on with a double chain ring or do you need to have a triple front for this type of gearing in the back? I was thinking of gettnig a Dura Ace 12-27 cassette for a trip we are going to be doing in the rockies but want to make sure I do not have to change the front rings.

Thanks

Mike

As long as the der.s you are using will accomadate the ratio I do not see why not.

I am currently using a DA 12-23 rear cog set and a 53/39 front. Will this accomodate the larger ratio of the 12-27?

According to the Shimano website, the rear derailleur for a double cranked bike will handle a large rear cog up to 27 max. I don't know how to figure the front specs, but someone should know the formula.

Originally posted by Captain Crunch
I am currently using a DA 12-23 rear cog set and a 53/39 front. Will this accomodate the larger ratio of the 12-27?

I went from a 12-25 to a 12-27 on my double w/out having to do anything. If you're putting on a new cassette, check your chain for wear, you might need to replace it anyway.

The chainrings won't be a problem, and the short pulley cage is fine. There's a small chance your chain won't be long enough. My guesstimate is that the big-big combination will require about 1/2" more chain than you're using now. The next length you can make the chain is 1" longer. See how tight it is now in the big-big combination. Is there still some extra (i.e. it isn't pulled tight/straight through the pulleys) if you shorten it about 1/2" by pinching it? If it were 1" longer, would it be too loose in the small-small combination?

Also, when you put on the larger cassette, you may need to readjust the B-screw, so that the guide pulley doesn't contact the cassette when you're on the 27.

Originally posted by Captain Crunch
I am currently using a DA 12-23 rear cog set and a 53/39 front. Will this accomodate the larger ratio of the 12-27?
I have the same chainrings and 11-23 in the rear (all Ultegra).
Sometimes in the early spring when I'm feeling like a weenie :eek: I swap my 11-23 for a 12-27 for a few weeks till I get some leg muscles.
Never have any problems.

I'm an old man, and I wanted a bailout gear for hills, so I run a 42-53 on the front, and 11x28 on the back! Works like a charm with my old Ultegra groupo, no mods made at all.

Thanks for all the info. I am going to order one up today. Anyone know of a good place to order from in Canada. It looks like Performance Bike has the best price I have seen yet but it is in the U.S. It will likley still be cheaper to get it there than in Canada anyway but would like to check out Canadian order sites if I can.

It's still in the US, but Jensonusa usually has good prices. And, like everyone else has said, you'll be fine. Well, the bike will be fine. You'll be climbing in the Rockies, so hopefully you'll be fine, too.

Are you headed to the Canadian Rockies or coming down here?

Canadian Rockies.

The only bad thing about riding in the Canadian Rockies is....... you have to come back. Stay if you want, it's beautiful.

NOTE:

You can use the 12x27... However your current chain may be too short.

Once you adjust the chain, if needed, for the 12x27 then you have the right leght of chain for any setup 12x21 thru 12x27...