An Electric Bike With a Flat Battery Is Still a Bicycle

This is written to be used rather than admired. Each section below is a decision about riding an e-bike unassisted, and each one has a default.

What actually changes when the power goes

An electric bicycle is heavier than an unassisted one, and that mass has to be accelerated away from every junction by your legs alone. Weight matters far more when climbing than when rolling along flat ground, so the difference appears on gradients rather than on the level. The riding position on many electric machines is upright and relaxed, which is comfortable but presents a large frontal area to the wind.

Tyres tend to be wide and heavy with thick puncture protection, which adds rolling resistance you never noticed while the motor was compensating. None of it makes the machine unrideable, and riders are frequently surprised by how normal it feels once they accept a slower pace.

Gearing is the part that catches people out

Gearing on an assisted machine is often chosen assuming the motor will contribute, which means the lowest gear is higher than it would otherwise be. That is fine on assistance and becomes a real problem when you meet a climb with a heavy bike and no help. Mid-drive systems put the motor before the gears, so at least the gearing you do have works with your legs the same way.

Hub motors do not touch the gearing at all, so the bicycle behaves exactly like a heavy unassisted machine when the power stops. Knowing your lowest gear before you need it is the difference between climbing slowly and pushing the bike up on foot.

Drag, freewheeling and system differences

Some motor systems freewheel almost perfectly when unpowered, and the machine coasts much like an ordinary bicycle would. Others introduce noticeable resistance from internal gearing or from the magnetic drag of a direct-drive hub turning without power.

The bit that actually matters: direct-drive hubs in particular produce a constant slight braking effect, which is the same effect that allows regenerative braking to work. The practical consequence is that two electric bicycles with flat batteries can feel very different to ride home. It is worth finding out which kind you have by riding a few kilometres with the system switched off, deliberately, before it happens by accident.

Planning around the possibility

Range estimates vary with wind, gradient, temperature, load, tyre pressure and assistance level, so any figure is a starting point rather than a promise. Treating the final section of a long ride as unassisted, and choosing a route accordingly, removes the worst version of running out. Reducing assistance early leaves capacity in reserve, whereas riding on full assistance and hoping produces a sudden cliff at the end.

Cold weather reduces the energy a pack can deliver, so winter planning should assume less range than the same ride gave in summer.

A second charger left at work is a small expense that changes an evening's range calculation completely.

Riding it home without wrecking anything

Use lower gears than instinct suggests, keep the cadence up and let the speed drop, because grinding a heavy bike up a hill loads the knees hard. Ride the flat sections rather than trying to make up time, since the wind resistance penalty of pushing hard is worse on an upright machine.

The bit that actually matters: brake earlier than usual, because the extra mass has to be dissipated by the same brakes over a longer distance. If the route is genuinely too hilly, a bus, a train or a slow walk alongside the bike is a legitimate outcome rather than a failure. Do not be tempted to push the machine along by holding the bars while walking on a busy pavement, since a heavy bike is awkward to control that way.

Choosing a machine that fails gracefully

A bike with a genuinely low bottom gear is far more pleasant to ride unassisted than one geared entirely around the motor's contribution. A freewheeling system, moderate weight and tyres that are not armoured to the maximum all help when the assistance stops. Two smaller batteries carried separately fail differently from one large one, since the second becomes a reserve rather than a repeat of the first.

By the second week of riding, none of this should dominate the decision, because most riders run out of battery rarely if ever. It is worth knowing what your specific machine does in that situation, though, because finding out at the far end of a ride is a poor time to learn.

The takeaway

Ride your electric bike home with the power off once, on purpose, and the day it happens unplanned stops being a crisis.

The bike you ride daily beats the better bike you keep indoors.