I know this has been covered before in the forum, but here is an excerpt from an article that I was just reading.
Using a smaller diameter wheel affects the output of your bicycle’s gearing ratio. For the most part, this actually puts the gear ratio within the reach of most of us. For the strong, however, changing the big front chain-ring to a 55 tooth puts things back to normal.
Is this true? I have ordered the Cannondale Ironman 800 with 650c wheels. Will it take a 55-42 tooth chain ring to be equal to my TCR's 53?
Yes, final gear ratio depends on rear wheel size. If you change to a smaller wheeled-bike, you will need to increase the big chainring size or decrease the smallest cog size to offset the change in wheel size if you require the same top gear.