I rode 650s for a couple of years and frankly, I don’t think the difference is that great. If you are averaging less than 20 mph then I would recommend finding an inexpensive compact (110mm bolt circle) crankset and going with a 46x34 front gearing paired to at least a 25, preferably a 27 tooth rear. That is what I use for training and it helps to have the 34x25 low on recovery days when it is very windy, I’m climbing hills or both. I just used a 12-27 10-speed cassette at World’s Toughest Half and really like it. Of course, that race was the toughest course I’ve encountered in a tri, so the 27 is not always going to be useful for everyone, but it never hurts to have it just in case.
http://www.nashbar.com/profile.cfm?category=81&subcategory=1034&brand=&sku=11459&storetype=&estoreid=&pagename=Shop%20by%20Subcat%3A%20Road%20Cranks
Here is a Nashbar compact for $75. Buying new chainrings will cost you at least half that much. eBay always has a host of chainrings as well.
Chad
Compact is 110 BCD…
Hey Rod…how’s that new ride treating you? Doing Eagleman this weekend?
Yeah, I don’t understand the rationale for wanting those big 55, 56 tooth chainrings on 650c bikes. It may have made some sense back when everything was 7spd, with 13 tooth small cogs, but today a 53/39, using an 11-23 cluster (personally I like the SRAM 11-26 for Colorado) gives one all the gearing necessary for most mortals. My wife is running compact 50/36 with a 12-27 on her 650c Felt. She’s not a real strong rider at all, but with this gearing she can climb anything around here. Our street has about a 12% grade for maybe a quarter mile and she can stay in the saddle for that. I was running 53/39 on my 650c Cervelo, with an 11-25 rear cluster and had no trouble climbing, yet didn’t spin out the downhills until about 44mph. Now that I’m running 700c wheels, I’ve gone to compact front and still using the 11-25 rear. Haven’t found anywhere yet that I don’t have enough gear inches.
I dunno, on normal-to-flatter courses around here or other places she’s raced, my wife really like running a 55-42 combo on her 650c bike. If we lived in Colorado like you though, I’m sure it’d be a different story.