Not to be bragging (honestly) but I am wondering how accurate Strava's speedometer is, and what kind of things could make it go wrong, because looking at my speed stats for today's evening ride one can deduce that there is either something far wrong with Strava, or I really am capable of propelling 15 kilos of 52 year old British steel to 29.3 mph, on a fairly flat road. Can that be true?