During the Edinburgh race, Dot and her new mate keep up with the main pack right up until their bike breaks down. But their bike's an Ariel Arrow - 250 cc, ridden 2-up - so it's unthinkable that it could keep up with much-more-powerful bikes with single riders.
It's not clear exactly what time of year the film takes place, but it's certainly cold - yet the characters undertake long high-speed motorbike journeys with no fairings and indifferent clothing. They would be frozen to the marrow like non-bikers can't imagine - but show no sign of it.