Hi,

I recently bought a 2011 Specialized Allez off of craigslist. The bike is in great condition but the owner put on a really weird drive train on it. It comes with Shimano 105 ST-5601 shifters, which are meant for a 2x10 system, but he had a truvativ triple crankset combined with a 9 speed cassette on the back. I've decided to keep the shifters and put on a double crankset and a 10 speed cassette at the back. My question was regarding the combination I should go for and the ratios. I'm currently thinking of a 50-34 compact crankset up front, mostly because I'll be in California for a couple of months and the compact will be helpful with the hills. But I'm also moving to Dallas soon so I'm wondering if a standard double is the way to go.

Here are the parts I'm currently thinking of.

Shimano 105 5750 Crankset - wiggle.com | Shimano 105 5750 Hollowtech II Compact Chainset | Road Chainsets
Shimano 105 5700 Cassette - wiggle.com | Shimano 105 5700 10 Speed Cassette | Cassettes And Freewheels
Shimano Ultegra 6701 Chain - wiggle.com | Shimano Ultegra 6701 10 Speed Chain (116 Links) | Chains
Shimano BB-R60 Ultegra 6800/ 105 - 5800 Hollowtech ii BB - wiggle.com | Shimano BB-R60 Ultegra 6800/105 5800 Hollowtech ii | Bottom Brackets

Also I'm assuming that I need an English threaded BB but haven't confirmed this yet (gotta find the manual for the frame). On another, does the crank arm length make a significant difference?

Thanks.

If the BB does not have external bearings, it is most likely English 68mm. Not sure what axle length you'll need.

The difference in crank arm length from 165mm to 175mm is only 1cm. The longer crank offers you a greater mechanical advantage but could also be long enough to cause foot-strike issues when pedaling while turning depending on the geometry of your frame. Also, depending on your physical geometry you may or may not like a shorter or longer crank. If you like the length of crank arm you have, stick with that, but still take some measurements.

because of the hills you should try to get smaller chainrings and bigger cassettes, and when using the bigger cassette you could find, it will match with your crankset if the bigger chainring is not so big, maybe a 46T or 44T, instead of the 50. You should try to find the shimano components tech docs and then you will find the range they recommend and you would choose the best for you. There is also the road link at the wolf tooth components website, this part might allow you to use a deore cassette. Hope it makes sense.

I've ridden standard and compact on hills, flats, mountains. With 10+ cogs and so many different cassettes, you can find the right range with any crank. It's a matter of personal preference, imo. There are multiple compromises - so all you can do is prioritize. I grew up with standard cranks and still like that best for the shift pattern. For standard, one shift left is about 2-3 shifts right. I like this. With compact, one shift left about 3-4 shifts right. I don't like this since I almost always need to trim rear after shifting front - it's annoying. I like 53/39 with 12-30. You can do it with short cage 105/Ultegra. It works anywhere. OTOH, 50/34 with 12-27 has tighter spacing and some people find that more important. But, I'd rather keep 53/39 and swap to 12-27 or 12-25 to get tighter spacing instead if there isn't a lot of climbing.