I found that 17's vs. 21/18 did not handle rough paved roads as well. The larger 21" front rolls over humps and drops better. It's smoother and more controlled.
If you are just riding on smooth roads with the 17s, you probably won't notice it much.
Nitro Circus Movie best quote: "This is just a factory for bad ideas"
2012 Yamaha FX HO Watercycle