Transitioning from a Triple with 170mm cranks to 5800 - Advice?
 

Hi,

I had a bike with a triple (52, 42, 30) and a 12-25 cassette which I found great. I spent just about all of my time on the middle ring. On the flats I'd be on lower end of the cassette and I would occasionally drop to the small ring and easiest gear when climbing which I rarely do given I live in a flat area.

My cranks are 170 and I don't have the leg strength to pedal at a slow cadence at a very high gear, my cadence on the flats is about 80-90.

With the 5800 Shimano dropped the triple so I was thinking of going with a 39/53 chain rings and 11/32 cassette. My reasoning is the the 39 is closest to my 42 chain ring which I spend most of my time on and I can drop to the 32 gear on it and still have a gear ratio of 1.2 which is what I get on 30/25. In addition if I ever get stronger I can move to the 53 ring.

Any general comments about this?
My only concern is that the 11/32 cassette has some pretty big jumps. Does anyone have any experience with the 11/32 cassette and the 105 groupset?

I'm assuming the 5800 FD has good trimming so no chain rub.

Finally I was thinking of going with the 165 cranks since I like to spin and this will help me spin faster as I understand it.

Thanks.

Are you replacing the drivetrain on an existing bike, or buying new? It's not clear from your post.
If the former -- why not go 1x11. SRAM Rival or Force (choose your budget); choose your chainring size (e.g. 42); choose your cassette range. Done.

I'm building up from a frameset. I've just heard such great things about the 5800 105s I thought it was a no brainer. Also you can get the entire 5800 groupset (brakes, FD, RD, cassette, cranks, chain) from the UK for $350.

Makes sense re. the cost, and 5800 105 is terrific. There's also the cost of wheels if you want to use SRAM's 10-something cassette. That said, though, from the way you describe your typical riding style/terrain it sounds as though 1x11 would do exactly what you want. Just something to consider.

I would do a 50/34 imo. I've been riding my cx bike w/ 46/36 and 11-30. I don't like the big jumps on the cassette. I would love to change to compact with a 12-28ish. You also shouldn't have too much to worry about w/ the new 5800 you can fit any size chainring to the crank arms so if you change your mind it won't be crazy expensive to change, especially the smaller ring (ie. 36->34 would be around $20 and thats at merlin for ultegra).

EDIT: My experience is on 10speed 105. Adding 1 cog might actually change things, but I'm not sure.

Simply going to a shorter crank arm will not help you spin faster. You also need shorter gear ratios to go along with it. Given your goals and description of use, I'd recommend you go with a 34-50 chainring size and the 11-28 cassette. That way you'll have much closer gearing and still a lower gear available in the 34ring-28cog than you get with a 39ring-32cog.

Here are the gearing charts using Mike Sherman's Bicycle Gear Calculator:

First the 11-32 cassette with a 'standard' double 53-39:
http://i.imgur.com/TCQc3hGl.png

And then the 11-28 cassette with a 'compact' double 50
http://i.imgur.com/XPTW7Jkl.png

The second setup will give you significantly closer gearing than the first while also giving you a tiny bit shorter lowest gear option and will not require the "GS" medium cage rear derailleur like the setup with the 32cog would. The steps on the 11-32 cassette aren't just bigger on average, but they make some big jumps in key parts of the range, such as the 14 to 16 jump. You'll definitely notice the missing 15t cog since it's right in the sweet spot for a lot of riding. The shorter overall gear ratios will also support your goal of spinning higher cadence too.

I have a 50/34 11/32 (Ultegra) combination on my bike. I live where it is pretty flat with occasional rolling hills. I never find the need to take it out of the 50, even though I am old and slow. The jumps between gears on the 11/32 have not bothered me. If one is racing, they might find a need for a tighter grouping.

One of the best things about 11 speed is that you can have an 11-25 10 speed cassette that also has a bonus 27 tooth cog. This gives you a pretty tight range without being a full on race cassette, but still enough to cover lots of terrain.

From there, I would look at your top end and bottom end gear ratios. For instance, how often do you currently use the 52/12? If the answer is almost never, then do you really need a 53/11? (Hint: the 50/11 is already a bigger gear than the 52/12) And And on the bottom end, did you ever drop into the granny gear? If not, then I can't see why a 39/27 (1.44 ratio) or a 34/27 (1.26) wouldn't be sufficient while you're already pushing a 42/25 (1.68).

In short: look at what gears you are currently using, then compare the top and bottom end to what you would get with 105, and from there you can decide how important the tightness of the range is.

I agree. Or alternately, go with 2 x 11, but go with 42 - 30, 44 - 30, or maybe 46 - 30 rather than 50 - 34. Particularly if you mostly ride a 42 tooth chainring and like it, why would you switch to having to choose between a too large 50 or a too small 34?