For years I'd cycle along with slightly underinflated tyres. It was only when I started inflating the tyres to the top of their recommended range that I realised what I'd been missing. You just ZOOM along. You get less punctures too for some reason. Try it - your tyre will have the recommended pressure somewhere written on it - get a footpump with a pressure guage attached so you can see how hard they are and go towards the top of the allowed range. If you are like me you won't believe how fast you'll be able to go!