Just started cycling as cross training for running, bought Giant OCR3 and got a little Schwinn trip computer for it. But to program it, need wheel size, and I can't find anything on the wheel or tire that matches the list of sizes in the computer manual, eg, one of the possible sizes listed in the manual is 2024. How do I figure out what the size is from the info on the wheels or tire. I know when I get answer I'm gonna feel pretty stupid cause it's probably obvious, but gotta ask. Thanks.