Pothole impacts on rental e-scooters and the case for a larger front wheel: measurements in Oxford and a dynamics model

A small front wheel drops further into a pothole and strikes its far edge harder, which may make
e-scooters more likely to fall. We asked whether a larger front wheel would help, using the Voi
Voiager 5 rental scooter, whose tyre markings show an 11.1 in front wheel and a 10.1 in rear wheel.
First, we recorded three legal rides in Oxford (6.08 km in total) with a smartphone fixed to the
handlebar. It picked up 100 sharp jolts, each at least as strong as the pull of gravity (1 g), or about
one every 61 m. Ten places jolted the scooter on more than one ride, and 6 of these 10 had no public
road-surface report within 25 m in the year before. Second, we ran a physics simulation (MuJoCo)
of a scooter and rider crossing potholes, comparing the Voiager 5’s wheels with a smaller 10 in
reference, with bigger front wheels only and with bigger wheels front and back. With the Voiager
5’s front suspension, the simulated rider fell in 9 of 81 runs with its 11/10 in wheels, as often as with
10 in wheels, but in 6 with a 12 in front wheel and in 1 with a 14 in front wheel. A bigger front
wheel on its own matched bigger wheels at both ends in every case of the main set of runs, and
stayed within one fall of it when the pothole edges were sloped, which supports our hypothesis that
the front wheel matters most. These results come from one rider and a simplified model that has
not been checked against physical tests; they do not show that today’s scooters are unsafe, and the
1 g level is our own threshold, not a danger limit. They suggest that front wheels larger than the
Voiager 5’s, around 12–14 in, deserve physical testing, and that current wheel-size rules for rental
trials (11 in in London, none in the national rules) may be set too low to make a difference.