Gear conversion

Wily-Quixote

I'm looking at trimming my bikes down to one: a cannondale cx bike. I would like gears a low as my current MTB ( giant anthem 29 er) which is a shimano xt double chainring setup. Could I ( well, a shop actually) fit a xt double setup on this bike? I'd also like to keep ultegra sti shifters, will xt work with these? If not, what are the implications? MTB brake levers and barend shifters? Any advice appreciated.

The Rookie

If you want gears as low as your MTB you'll need to change the cassette to an MTB one as well as dropping the chainring size (assuming it's bigger than a double's lower ring size as it is).

So what size is the smallest ring on your MTB and largest rear sprocket?

t4tomo

if you change the front chainring sies you may well need a different front derailleur if teh jump between them is higher, if not you will just need to move the FD down the seatpost a bit.

if you gop to MTB cassette you'll need a long cage (MTB) rear derailluer (such as an XT one). Pretty sure you dont need to change shifters for either.

Chain length will need alteringtoo but if you are changing chianrings and cassette then you should always put on a new chain anyway.

Wily-Quixote

Ta for the advice, and, yes, I realise that I'll need a whole new groupset. I guess my question should have been framed as: can I fit a MTB groupset onto a CX frame and keep the STI shifters.

The Rookie

9 or 10 speed?
9 speed is easy, all compatable, 10 speed more complex.

Wily-Quixote

10speed. let me clarify:

Imagine a cannondale cyclocross bike with ultegra gears (10 speed). Now imagine all gear related stuff has been removed except for the STI shifters. Now imagine all the gear related stuff has been replaced with a double chainring shimano XT gear setup (10 speed).

The purpose of this setup is to mimic my exisitng setup on my Giant anthem: ie I'd like a cx bike that can climb insanely steep fire roads and still has decent 'top-end' gearing for road riding.

Will this work?

The Rookie

You'll need a 9 speed rear mech, that is compatable with your shifters, for 10 speed MTB (and MTB only) they changed the cable pull.

To summarise
10 speed cassette
10 speed chain (use existing if it's not stretched too much)
MTB Crankset (9 speed works fine, or 10 speed if you have the choice at the same price), maybe consider a trecking gearset with 48T large ring
9 speed MTB rear mech.

Wily-Quixote

Thanks, Rookie:
I'm assuming that if I go down this route I'll have a 10 speed shifter, a 9 speed mech and 18 gears...

I might be better going a ultegra triple option and keep a wider range of gearing.

thank you (and all others) for your advice.

wily

The Rookie

No with a 10 speed shifter and a double up front you'll have 20 gears, why on earth would you have 18?

Wily-Quixote

I see... I was assuming that the 9 speed mech on the rear would only move the chain over 9 cogs.

So the 10 speed ultegra shifter on the front will move a 9 speed rear mech over 10 cogs in the 10 speed cassette? Why is the 9 speed rear mech called a 9 speed then, I wonder...

The Rookie

It's a 9 speed as on an MTB it can only be used for upto* 9 gears in the designed for application, 10 is a specific pull ratio on MTB's, road bikes kept the 9 speed pull ratio for 10 speed. All the mech sees is the amount of cable pulled and moves accordingly.

If you fit a 10 speed MTB rear mech it won't work at all.

*Pull ratio is the same for 5,6,7,8 and 9 speed mechs are mech the number is fairly meaningless except that a mech designed for a lower gear count may not move far ebnough sideways to accomodate all the gears, as 8 and 9 speed cassettes ate the same width, 8 and 9 are interchangeable (a 9 speed shifter pulls less cable per shift but the ratio is the same) and will work on any of those listed. For 10 speed they through compatability out of the window.

Wily-Quixote

got it. cheers.