jaltone

I am not knowledgeable on these matters, so please bear my ignorance. Could I simply replace the R565 crankset on a Trek Domane 2.3 with an FC-CX70 crankset? Of course, I would need to have the LBS actually do it for me. I just want to know from you whether it is possible. And if it is, would I need to get the FD-CX70 derailleur as well or would the existing FD-5700 derailleur work with it? And I suppose I do not need to change the bottom bracket since it's already the Hollowtech II kind? If I'm mistaken in any of these statements, please correct me. Much thanks in advance.

gadabout007

The crank will slide in no problem, they'll have to remove a few links from your chain.

you will have to replace the FD with the FD-CX70 which is designed to work with the 46 tooth chainring. You could also go with the FC-CX50 crank which is essentially a 105 crank with 46 tooth chainrings for a couple bucks less.

I just checked Trek's website and it says that bike comes equipped with a compact and a 12/30 cassette which is a climbing friendly setup. If you're not planning on doing cross on it, can I ask what you're hoping to achieve?

droppedandlost 

I put a CX70 on my Spec Roubaix, primarily for the gearing. I had no issues with installation and it works great. I kept the same FD-5600 and lowered it slightly. I would have liked to lower it a bit more but the cage would bump against the frame if I did. I believe the FD-CX70 is a bit shorter so it would fit better. I haven't had any problems shifting though, and in fact I like it better. The more aggressive ramps make shifts quick and smooth. The issue I had with the 50/34 was that I was always cross-chaining, my normal cadence was in between the rings. The 46/36 gives me more overlap and cut down on shifting quite a bit.

Fiery

There's no need to buy the whole crankset, just swap the big ring for a 46 tooth one.

jaltone

Thanks for all your helpful answers, gadabout007, droppedandlost, Fiery.

gadabout007, it's a very personal need. I'm new to bicycling and am not strong enough. I'm middle aged and am doing this for health, though I find myself enjoying it a lot. I replaced the factory cassette with a junior 16-27 cassette because I like the narrow jumps, and the smaller cogs are wasted on me.

If I can have a 46t ring to pair with the 23t cog for the flats, then I can use the 25t and 27t cogs for momentary inclines without having to double shift to the front small ring. Btw, is what I'm intending to do a sensible thing? I welcome any further constructive criticism from anyone.

droppedandlost, thank you very much for your affirmation. I am exactly in the same situation as you.

Fiery, thank you for your suggestion. That didn't occur to me, which just shows my lack of knowledge. I Googled, and would the "FSA Super Road 46t 110mm" ring be a good replacement for the factory R565 50t ring? Again, much thanks in advance.

cpach

Be aware that you'll be slightly raising your lowest gear, as the cross crank has a 36t small ring. Otherwise it should work fine as a swap into your frame. Your existing front derailleur will be fine, tons of cross racers use normal road FDs racing, though the CX derailleur might shift slightly faster. It would be cheaper to simply install a 46t ring on your existing crankset, and you'd maintain the same lowest gear you have now. The FSA ring would work fine.

A 46/34 crank sounds practical for what you want. If you ever end up wanting to descend some hills quickly an 11-28 cassette will let you spin up to about 40mph or so.