Rolling resistance

I've ridden a bike of one form or another ever since I was at school. More recently I bought a bike when I came to Peterborough. Flat handlebars, lots of gears and knobbly tyres, which I occasionally found a use for along the river Nene. On occasion I went out for a ride with a 70 year old, on a more conventional road bike. 1¼" tyres for a start and far smoother. I found him leaving me when on any real length of ride, especially on tarmac. He quoted the reduced rolling resistance as the reason which made sense to me.

Recently I changed the tyres for 1½" tyres, far less tread - in fact darned near bald in the centre section. They are marked as requiring 50psi which I didn't measure, just pumped them up until they felt right. Yesterday I changed tack, screwed on an adaptor and pumped them up using a car foot pump until the guage said 50psi. What a difference! I'd swear I was 2 or 3 mph faster no matter what. Not that I've ever been in a hurry on a bike, I do it for fun, but being left by a 70 year old, even if he was a county level cyclist in his youth, left me miffed! Can't wait to go out with him again to see what the difference is.