[piers.singer]

I once inflated my Pirelli City Demons from 28psi (recommended) to 36psi. They were striped within 500 miles. They were cross-ply though, so, as a general point, if you're going to mess about with tyre pressures, it's safer to use radials.

Specifically, redpoint, your tyres are radial and so shouldn't distort if inflated higher than recommended. As for under-inflation, this will cause uneven wear and increased drag on the drive-train components (thus a loss of drive-train efficiency and therefore a drop in MPG). It may also increase the bike's propensity to slide in the corners. I once rode my old Honda 125 with a rear puncture and it handled like it was on ice. The only reason that I didn't realise that I had a puncture was because it was so wintry that I thought that it WAS ice!

Clearly, that's an extreme example of under-inflation, but I shouldn't risk spirited riding with under-inflated tyres. If in doubt, stick to the manufacturer's recommended pressures.

I believe that the chap who rides the 100mpg Ninja 250 inflates to 60psi, so clearly, like cars, motorcycles also benefit from greater inflation.