Rumpled

My CX bike is my only road bike and in an effort to actually be able to climb some hills; I want to change my gearing. I really don't have the best climbing abilities without gearing. Before you get into the HTFU comments; I've previoulsly ridden my MTB with road tires and find myself often in my 22 front chainring and 32t cog going up 6% and higher grades; grinding very slowly. At about 13% I have to hike a bike.

My bike is a Fuji Cross Comp with a 36/46 FSA crank and a 12-25 105 cassette. This gives me about 39 gear inches as my lowest; whereas my MTB goes down to about 18. I found that one of the hills I ride often had me at my max on the CX bike - it wasted me. It's only about a half mile long and about a 9% max climb. On my MTB, it was hard but very doable for me. Racing my first races in CX; I've found myself mostly in my 23t cog and my inner chainring. I joke that if I had a single speed I'd use a 36-23!

I've gotten ahold of a 34t FSA chainring and an Ultegra 12-27 cassette. Changing both of these items will bring my gear inches down to about 34. For the rest of the difference to my MTB, that's where my HTFU comes in.

Does anyone see any problems or complications with my idea?
I know my derailleurs will need to be adusted for the changes. I think I should be able to use the same chain as a calculator I found shows only 1 link difference in going from a 25t cog to a 27t with a 46t chainring.

thenomad

Should work fine. May want a long cage RD?
I built my wife's bike with a regular 105 front crank 39/53 (had it) and made a custom 9 speed cassette that goes up to about 30t with a med cage 105 RD.

I built my bro's Fantom CX up with a 32t mountain 8 speed rear with Sora components.
Was going to just put a MTN front crank on it but the shifters wouldn't work for triple.

You shoulf be able to take the cassette apart easily and get a mountain cassette to se if you can do a little custom work to find the max rear gear you can fit. Kind of like the old "megarange" offerings.

Each shift is more of a jump in gearing but you get used to it. You might see if you can fit a longer RD hanger on it if the jockey wheels contact the large gears.

Fat Boy

While the 34 front will help, the limiter you have right now is your rear derailler. It's only good for a 28t cog. If you're running Shimano stuff, then you can change out the rear derailler to a medium cage MTB and then stick on a cassette that gives you some real grunt with a 32 or 34 big cog. Of course the jumps between gears will be bigger, but that's part of it. If you're on SRAM, then go with the Apex setup.

Either way, you can also go for a mountain double crankset. The SRAM XX is super expensive, but FSA makes one too, (https://www.universalcycles.com/shopp...01&category=62). This one is a 27-40, but they make a 29-42 as well.

If you get the gearing down to a 27-32 you should be able to climb a tree.

Rumpled

I'd rather not mess (=$$$) with changing derilleurs or cranks. My RD is an Ultegra if that matters.
I know my proposal won't allow me to climb like my MTB; but I do want it to get a bit closer.
Without major changes; I think the 27 in back and 34 in front is as low as I can go.
The rest will be up to me and HTFU.

Andy_K 

I've been there, and let me assure you that your climbing will improve if you keep at it. Changing gears is a good way to help yourself keep at it.

I agree with Fat Boy's comments about chaning out the rear derailleur. You can get a Shimano SLX cassette with a 36T cog. That'll do nice things for your gearing.

thenomad

I think your new setup will give you essentially two lower gears than you had before, you may actually feel this difference is substantial once you try it. We always have times when "one more gear" would have been good. This may be adequate for what you want your cross bike to do.

I've got a 39-27 maximum right now and am thinking of just getting the 38t front and adding a 50t or 46t big ring for the commute.

Fat Boy

The biggest big cog you can get with your present RD is with an 11-28 SRAM cassette (I think Shimano only makes a 27 big gear). The SRAM cassette is a direct swap. If you want to do the rear derailler, it's not expensive. This one would work https://www.performancebike.com/bikes/Product_10052_10551_1085941_-1_1534003_20000_400178 That would allow you to run the SRAM 11-32 Apex cassette.

As far as your original question, your present chain will almost definitely work with the 27 unless it's already tight as a guitar string with the 25. You're better off not spending much time in the 46/27 combo anyhow. A 34/27 combo should make climbing a 9% hill not too bad and I promise that won't be a problem. Beyond that, sometimes you just have to get mean and not quit!

crocodilefundy

be sure to check your chain length on the small end. when ever i ride a 34 small ring there is a lot of slack in the bottom half of the cassette. you might not have that issue if you are running a 46 front ring.

M_S

Counter-intuitively, if you do get a shimano mountain rear derailleur, you'll need to avoid the 10 speed options (Dyna-Sys) as Shimano in their infinite wisdom actually decreased road-mountain compatablity when they moved mountain stuff to 10 speed this year by using different cable pull ratios for road and mountain. An older 9 speed derailleur will work fine

fietsbob

NB :
IRD offers a 110 tripleizer , If you have a square taper crank, compact sort,
the 3rd ring will then bolt to the middle .

but the BB axle has to be wider on the right end.

SOL with new external BB stuff..


have a good setup using Campag Race triples , 50-40 on 135 bcd , took off the 30
on a 74mm bcd, and swapped a 24t.. another bike is a 52-42-26 .

note <c> Dropped Square Taper Cranks & BB's