Hello I’m new to the board , I’ve often viewed as a guest over the past for tips but recently I purchased a CX bike and I would like to upgrade the cassette and big chainring and make it more like a road bike , it’s currently running a 11-25 cassette and a 46-36 chainring the bike is a BH RX TEAM
I would like to fit a 52 chainring if possible but I’m at a loss at what size cassette should go on the rear , I should say I’ve updated the rear mech as it was an Ultegra Short so in doing so I’ve got the GS whilst doing this I’ve also got a new front mech ,I’m not very knowledgeable on bikes to be honest as I only got into them to get fit but now seem to be hooked and help in my little problem will be grateful appreciated
Sion
52/36 x 11-28 is a common combo, but really depends where you ride and how your fitness is. Technically speaking you could pair almost any chainring and cassette combo with the right length chain and derailleur cage
1 Like
My fitness is slowly coming along and where I ride is quite a mixture of flat and hills as I live on the outskirts of the Brecon Beacons in South Wales ,
As I’ve said previously I’ve changed the front & rear mech in readiness for the update but it’s just the cassette that was the stumbling block , I actually purchased an 11-32 cassette online but a mate who has also started cycling said that he read that it wouldn’t work so rather than lurk I’d thought I’d better ask the experts .
You need a medium cage rear derailleur for the 11-32, I think that current Shimano short cage derailleur accept an 11-30 at most.
You should verify the specs on your frame. The front derailleur hanger needs to be at a certain height or offer a certain level of adjustment if you wanted a 52. CX bikes are typically designed for smaller chainrings so it might be a tough fit or you may be limited to a 48 or 50 so you need to check it out before buying parts.
Honestly, 46x11 isn’t bad if you don’t bomb down hills at high speed.
The cassette is really determining what hills you can go up. If you live in a flat area then the current cassette could be just fine. If you struggle with a 36x25 then you’d want larger cogs on the back. A 34 chainring on the front is another option.
2 Likes
Having ridden around there (Gospel’s Pass 
) I can’t imagine anything bigger than a compact (50-34) and 11-32 is a good idea. I would happily pay the price of spinning out on very rare occasions, if at all, for having a little extra gear on those steep pitches. And as others have mentioned, check compatibility with the front mech as you may be forced smaller anyway. On the cassette, I’m quite sure others have made an 11-32 work even though it’s not approved, Shimano are usually conservative on these ratings.
2 Likes
I’m based in Bath, so lots of steep hills in and around the city surrounded by more rolling country. I run a 52/36 chainset with an 11-32 cassette (Shimano Ultegra di2) on one of my bikes and that feels like a really good combination. You have real top end speed if you can manage to spin the 52-11 (so great for longer descents) while still getting a good climbing gear with the 36-32.
My other bike has a 48/31 gravel / sub compact chainset with an 11-32 cassette. The 31-32 gear doesn’t get used often, but its really nice to have on really long hilly rides. You obviously can’t power on quite so much on descents, and I do find myself spinning out the top 48-11 gear on occasions, but I’ll still be doing over 55kmh at 100rpm in that gear and although I’m pretty quick, I’m not quick enough to find myself hitting those sorts of speeds all that often on a general road ride. Having slightly smaller top gears doesn’t really have that much of a negative effect for most road riding (obviously racing would be different) whereas having the smaller bottom gear can be really helpful.