[jimmyihatetoregister]

I wrecked my LeMond Zurich, looking to put most of the parts onto a cross frame & buy a new road bike! I have Ultegra 9sd crank 39/53, ultegra rear der and shift/brake combo plus 12-25 cassette. I've got lying around nice Avid shortys, plus my bar, stem, seat post, 1 1/8 head set, saddle. I've also got lying around a 105 rear der, and probably some 105 triple cranks, square taper. I'd need some wheels, not a problem figuring that out. Regarding the crank, can I put lower gearing/smaller chainrings on it, since it came with 39/52? Or would the triple work better? Typically what size front & rear rings/casettes are used and will the ultegra short cage der. work? I'll do a mix of road, commute and flat-ish trails & dirt. CO front range mixed riding.

 

[Mike T.]

Cyclo-cross chainrings are usually in the range of 34 - 36t inner rings and 46 - 50t outer rings. The biggest issue you will have with those cranksets is the BCD - Bolt Circle Diameter - of the crank arms. Most "road" cranksets are 130 BCD (76.4mm between adjacent bolts)and the smallest inner ring they will take is a 38.

Mountain bike cranksets use 110BCD (64.7mm between adjacent bolts) and they will take down to a 34. Triples will take (I think) a small 22 or 24.

So with those cranksets you're limited with that 38 inner ring. Of course the easy way out is to get a cassette with a big enough range to make up the difference or use the triple. The short cage derailer should be ok with the two-ring cranks but not with the triple.

Of course with your terrain of "mix of road, commute and flat-ish trails & dirt" you might find the road gearing is just fine. Only you will know.

 

[pretender]

I'll do a mix of road, commute and flat-ish trails & dirt.

Standard road gearing will be fine but a triple might be nice for versatility in the future (touring or technical trails and climbs).

If it were for racing I'd suggest a single ring or downsizing the 53 big ring to a 48 or 46.