mcr2c384

What is the "True" high teeth count for the cassette with a 6500 Ultegra SS (short cage) and is it ok to run a compact crank with a 16 tooth difference? Sorry for the novice question and have tried to search the website but haven't found anything. So thanks, for your help on the matter.

Psimet2001 

Anything more than a 27 with a compact and you'll most likely run into issues. I have gotten many short cage Shimano derails to work with compacts running 27 cogs, but you run from barely scraping to over-extended.

I am currently running that setup on one rig right now. Hold over from Horrible Hilly Hundreds last year.

mcr2c384

Thanks for the response, another question, if I decreased the chain-wrap by getting a smaller chainring, (not concerned about going fast, for Touring purposes) then could I in practice go with a larger cassette, or would it rub?

Psimet2001 

It will intensify the effect. With a smaller chainring you will have to wrap more chain with the derail. when in smaller cogs.

With larger cogs you run the possibility ot "detonating" a shorter cage derail. when you accidentally cross chain your large-large combo....chain is too short and the cage gets pulled too far forward - snap.

In other words you are not necessarily worried about the wrap in a small ring large cog combo. That will actually wind up in the middle of the rd movement. It's the extremes that require chain length and cage length adjustments.

mcr2c384

ok, Thanks that makes sense. I'm Just trying to weigh my options. I already have the Short cage, and I can't find an Ultegra 9 speed gs anywhere. Ten speed is way to expensive right now. but i certainly don't want to "detonate" a dr/

shayel

Just get a 10 speed RD. The pull is identical, so it'll work with your shifters.
And with the current eBay prices, it'd be cheaper than a 9 speed RD...

rogerstg

As a practical matter you should be OK as long as the chain is long enough for the big/big combo (not that you'd normally use that). The chain might be a little loose in the small/small combo, but it likely that you won't use that anyway since a) you don't need it because it's in the ratio overlap range, and b) your chain would likely be rubbing on the big ring in that combo anyway.