Why are four-person bobsleighs faster than two-person bobsleighs? Is it because they have two extra people pushing at the start and therefore are faster throughout their run or is it to do with weight and momentum? Surely there comes a point when the extra weight slows the bob too much? A few friends and I spent an hour or so arguing over this the other week, divided into those who thought it was the extra weight and others who thought it was the extra runners.

Alan Kane, Glasgow, UK