Lewis Yelin

I recently bought a 2003 Fuji Roubaiux Pro which has a 11-23 cassette on a Shimano RD-6600 SS short cage derailleur. I'd like to replace the cassette with one that has more teeth on the granny gear. It looks like the RD-6600 is rated for 29 maximum total capacity ((chainring high - chainring low) + (cassette high - cassette low)), but I understand I can probably exceed that with a longer chain. It's also rated for a 27t low cog maximum. I'm trying to figure out how low I can actually go without impairing shifting. I'd appreciate any advice!

EDIT: For those who want to do the math, I should have mentioned that the front chainrings are 53 and 39.

Chuckles1

Maybe consider a medium or long cage derailleur replacement for your short cage. I replaced a 105 short cage with a Shimano Sora RD-R3000-GS 9-Speed Medium Cage Rear Derailleur and it allowed me to go from a 12/25 to an 11/36 cassette on my road bike. Am getting older, and really appreciate the hill climbing help. Similar GS RDs are no doubt available for your 10 speed.

Lewis Yelin

Thanks! That's something I'm considering, but I'd like to see how low I can get with the current derailleur.

70sSanO

I would figure what low gear you need first. If you “need” a 30t, maybe even a 32t, then that is the cassette you need to buy. But there is a point where it won’t work, such as a 34t and 36t.

Every derailleur has a bit of fudge factor, but some of it is based on the derailleur hanger on the bike. You won’t know until you install the cassette and see if it works. Also some people use a longer B screw to get a bit more clearance for a larger cog.

Chain wrap is another issue, but it generally is only an issue if the derailleur cage has folded onto itself to where the correct length chain is literally hanging loose in the small/small.

John

Edit added: Not that it matters on the max cog/capacity, but I thought the RD-6600 came out after 2003 and is 10 speed.

Iride01 

Your max cog size for that SS DR is 27. You might can go a few teeth bigger with the same DR. Or you might can make that DR work by adding a hangar extender.

But those extenders sometimes cost almost as much as just getting a DR that can support that big a cog.

squirtdad

Shimano has rep for being conservative in it's ratings, but when exceeding spec there is no black and white it works or does not, there are variables and you just have to try

I would think you would have no problem going to a 12-28 cassette which is just bit out of spec.....but if you want to do something like 11-32 you will need a different derailler. Remember Shimano does trickle down technology, so today 9 speed sora will probably compare well with the 9 speed ultegra in terms of function