Originally Posted by
camper8
Thank you John, so simply put if I want to use my race wheels and the bike I've bought is currently a 10 speed bike I need to buy a 10 speed cassette for my race wheels to fit - if I've understood correctly. That makes sense thank you. I then just have to choose which one, 11/23, 11/25, 11/28, 12/23, 12/25 or 12/30... that's where I get a bit confused. The terrain is pretty flat here, only one short sharp hill (12% climb over 1/2 a mile) and another more gradual one, other than that it's just the wind I'm fighting! So I just need to figure out what cassette I need to pick....
...honestly, nobody really needs an 11 tooth rear cog. It's a gimmick.
Take your bike out as it sits now on a windy day, somewhere approximating where you might race in terms of up and down hill, and then pedal off into the wind. shift your gears until you get what feels like a comfortable cadence into a strong headwind on a slight uphill. Now stop, get off your bike, and look at the gear you are in in terms of how many teeth are on the rear cog, and how many teeth are on the front chain wheel.
That is now your preferred low gear measurement point. You probably want to go one or two teeth more for the low gear you choose for your racing cluster, as a bailout for when you get tired. Possibly three teeth as your low reserve. Use 12 for your high. Nobody really needs an 11.