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simple question(11 posts)

simple questionsmolenice
Jan 29, 2004 8:57 AM
I usually go mountain biking but got a cannondale R700 road bike second hand. Got 53/39 double at the front and 12-25 9-speed at the back (105 RD). What is the largest sprocket I could reasonably get away with on the cassette which would work with the 105 RD. I am guessing 27 or 28. Feel like I might need something extra for climbing hills.

Thanks,

Steve
You're right.Spoke Wrench
Jan 29, 2004 10:19 AM
Shimano says 27 and that's where the road cassettes end. Don't expect to feel very much of a difference between a 25 and a 27 big cog.

There are a couple of work-arounds for using a mountain cassette, but that usually involves bigger steps between gears than most guys are used to and trading a useable cog for an 11. If you can turn a 53-11 you don't need a 32.
Shimano says 27 ...KeeponTrekkin
Jan 29, 2004 10:23 AM
for road derailleurs; Many others say 28, some even say 30. With a road crank, I'm pretty sure you'll need "something extra for climbing hills." To go realiably to larger cogs, get a mtn bike derailleur and cassette - up to 34t. Lots of cassette options, including modifying yours - see Sheldon Brown's website.
simple answerChen2
Jan 29, 2004 11:29 AM
You can easily modify your 12-25 to a 13-28. You'll need a single 28t and a 13 with built-in spacer. You can usually buy these parts from www.sheldonbrown.com Harris Cyclery, or try www.brandfordbikes.com. Or you could buy a 12-27, and you can modify a 12-27 to a 13-27 adding a 16 in the middle and replacing the 12 and 13 with a 13 with built-in spacer.
Shimano says 27, butcyclopathic
Jan 29, 2004 12:27 PM
it will clear 28 and possibly 30. When Shim went from 8sp to 9sp they changed write up on RD since they stop making road cass with 28t. Der itself will clear 30t, but on some frames you'd need longer B-screw (the one which adjusts tension). The friend of mine runs Ultegra RD on his hyperlight Ti hardtail wih 8sp 11-30 XT cass, no problem.

However, noone makes 9sp 28/30t cass, you either have to make one or get 12-27t. Ridden both 25t and 27t must say the diff is minimal.

How old is your R700? Older Cdale would have Shimano HG-50 cassette, newer SRAM. Either can be taken apart and modified, just get 28/30t cog.
re: simple questionRULY
Jan 29, 2004 2:27 PM
Buy a Full Speed Ahead Carbon Pro Compact Crankset 50\34 and 12/27 cassette.
re: simple questionsmolenice
Jan 30, 2004 2:26 AM
thanks guys, your responses were really useful. New crank and cassette and chain a little pricy I imagine. Just ordered myself a 28 tooth sprocket from Sheldon's site, wow that is a good site! One last question, can i just take out the 13 sprocket and stick the 28 on the top? any problems with that? Hope the cassette isn't too worn, would that screw things up?

Cheers, steve
should workcyclopathic
Jan 30, 2004 6:44 AM
Sheldon has instructions on "how to" good luck
Yes, butChen2
Jan 30, 2004 7:04 AM
shifting from a 14 to a 12 is a big ratio jump and will kill your cadence unless you are going down a big hill.
It makes my knees hurt just thinking about it. As an example, 14 to 12 is a 12% change, 23 to 21 is a 9% change, even though both cases there is only a 2 tooth difference.
~Al
Ive done this with a 28....Caadrider
Jan 30, 2004 6:26 PM
I bought a 28 and droped the 15. I used the spacer from the 15 on the 28 and it worked mint. Ive got DA but I cant see why it wont work on 105. I used this to help with knee rehab so losing the 15 was no big deal. It helps alot climbing.......
Yes but (again)Al1943
Jan 30, 2004 7:16 PM
Why not replace the 12 with a 13 and keep the 15, better still for the knees. I run 9-speed Shimano cassettes, all start with 13 and include 14, 15, and 16. I like smooth shifting and consistent high cadence. My wife runs a 9-speed 14-28.
I guess if you're a big sprinter you may need the 12.