Small Wheels Punish a Bad Road Surface

These are listed in the order worth acting on, which with wheel diameter is not the order they are usually presented in.

The geometry of hitting a kerb edge

When a wheel meets a step, the contact point sits at an angle determined by the wheel's radius and the height of the step. A large wheel meets that step at a shallow angle, so more of the impact force pushes the wheel upwards and over it.

A small wheel meets the same step at a much steeper angle, so more of the force pushes backwards against the direction of travel. Past a certain ratio of step height to wheel radius, the wheel simply cannot climb the obstacle and stops instead. The rider, having considerable momentum and a high centre of mass, continues forwards, which is the classic small-wheel accident.

Potholes and the depth problem

A wheel bridging a hole only drops as far as its own geometry allows, and a larger wheel bridges a wider gap without falling in. That is why a drain grate or expansion joint that a bicycle rolls over unnoticed can catch a scooter wheel completely. Longitudinal gaps such as tram rails are the worst case, since a narrow wheel can drop in and be steered by the slot.

In the saddle, crossing such features as close to perpendicular as the traffic situation safely allows is the standard technique for any wheel size. On very small wheels it is not a refinement, it is the difference between crossing and falling.

What the tyre can do about it

Air volume is the primary suspension on any small-wheeled vehicle, so a pneumatic tyre is far more forgiving than a solid one. Solid tyres eliminate punctures and transmit almost everything else to the rider, which is a trade many scooter buyers make without realising.

Mid-traffic, a larger air volume also spreads the impact over more time, reducing the peak force reaching the rim and the rider. Small wheels run higher pressures for a given load because the contact patch is small, which further limits how much they can absorb. If your scooter takes pneumatic tyres and you ride on poor surfaces, that is the single most valuable specification available.

Suspension and its limits

Suspension on small-wheeled machines is genuinely useful because the tyre alone cannot absorb enough, and it improves both comfort and traction. It does not, however, change the geometry of climbing a step, since the wheel still meets the obstacle at the same steep angle. Suspension also adds weight, cost and maintenance, and a poorly damped system can make handling worse rather than better.

In the saddle, front suspension helps most, because the front wheel meets every obstacle first and unsettles the steering when it does. Treat suspension as a comfort and control improvement rather than as permission to ride faster over broken ground.

Riding technique on small wheels

Look further ahead than you would on a bicycle, because the reaction distance you need for the same hazard is effectively longer. Unweight the machine before an unavoidable edge by bending the knees and shifting weight back, which lets the wheel rise more freely.

Slow before the hazard rather than during it, since braking while a wheel is dropping into a hole loads the front wheel exactly when you do not want it loaded. Keep both hands on the bars and both knees soft, using your legs as the suspension the machine does not have. Avoid riding close to the kerb, where drainage grates, sunken covers and accumulated debris are concentrated.

Range and charging figures are quoted under conditions nobody commutes in.

Choosing a machine for real streets

Wheel diameter is the specification most worth prioritising if your route includes poor surfaces, and it is the one most often ignored. Pneumatic tyres of the largest diameter the machine offers will change your experience more than motor power will. Folding bicycles with small wheels manage this better than scooters because the rider sits with weight distributed between three contact points.

On a standing scooter almost all the mass is high and above one wheel or the other, which is why a stopped front wheel is so unforgiving. If you cannot change the machine, change the route, and choose the smoother road even if it is slightly longer.

Everything above, in order of what to do first

1. The geometry of hitting a kerb edge. When a wheel meets a step, the contact point sits at an angle determined by the wheel's radius and the height of the step.
2. Potholes and the depth problem. A wheel bridging a hole only drops as far as its own geometry allows, and a larger wheel bridges a wider gap without falling in.
3. What the tyre can do about it. Air volume is the primary suspension on any small-wheeled vehicle, so a pneumatic tyre is far more forgiving than a solid one.
4. Suspension and its limits. Suspension on small-wheeled machines is genuinely useful because the tyre alone cannot absorb enough, and it improves both comfort and traction.
5. Riding technique on small wheels. Look further ahead than you would on a bicycle, because the reaction distance you need for the same hazard is effectively longer.
6. Choosing a machine for real streets. Wheel diameter is the specification most worth prioritising if your route includes poor surfaces, and it is the one most often ignored.

The takeaway

Bigger wheels and real air in the tyres beat every other specification on a street that has not been resurfaced in years.

Most of riding well is being boring and predictable to everyone else on the road.