How Fast Do Electric Bikes Go?

20mph, 28mph, or faster than either — what the assist limit means, and what actually caps your speed.

The short version

A legal e-bike in the US assists to either 20mph or 28mph depending on its class. That is the speed at which the motor stops helping — not a speed limiter. You can pedal or descend faster than that under your own steam.

What the limit actually is

Class 1 and Class 2 bikes cut assist at 20mph. Class 3 cuts at 28mph. Above the cut-off the motor simply stops contributing and you are riding a heavy bicycle, which is why most riders settle a little below the limit rather than at it.

Outside the US the numbers are lower. EU and UK rules cap assist at 25km/h, about 15.5mph, with a 250W motor limit. A bike bought in Europe will feel notably slower than a US Class 3.

Where	Assist cut-off	Motor limit
US, Class 1 and 2	20mph	750W
US, Class 3	28mph	750W
UK and EU	15.5mph	250W

Why yours may feel slower

The advertised figure assumes near-ideal conditions. In practice your sustained speed is set by:

Rider weight and cargo

More mass takes more power to accelerate and to hold on a gradient. On the flat it matters less than people expect; on a hill it dominates.

Wind

Air resistance is the single biggest force at speed, and it rises with the square of velocity. A 10mph headwind can cost several miles per hour and a large share of your range.

Motor placement and torque

A geared hub motor with 100Nm will hold a hill far better than a 45Nm one, even where both are rated 750W. Torque, not wattage, is what you feel when the road tips up.

Tyres and pressure

Fat tyres at low pressure cost real speed. Running them at the top of the recommended range is the cheapest upgrade available.

State of charge

Many controllers reduce output as the pack drops, so the last few miles are slower than the first few.

Speed costs range, steeply. Holding 28mph can use 50% to 100% more energy per mile than 20mph. If you ride fast, size the battery for it — see electric bike batteries explained.

Can you make one faster?

Technically usually yes, through a settings change or a controller modification. Legally it takes the bike outside the definition of a bicycle, and once it exceeds 28mph on motor power it is an unregistered motor vehicle in most states. That voids the warranty, generally voids your insurance, and in the event of a collision it is the first thing anyone will look at.

It is also harder on the bike than people assume. Brakes, tyres and frames on a 28mph bicycle are specified for those speeds, not for 35.

So how fast is fast enough?

For most commuting, 20mph is plenty and gets you the widest path access. Choose Class 3 if you ride on roads with traffic moving at 30mph or more, or if your commute is long enough that the time saved is worth the extra battery drain. The Class 3 guide covers the rules that come with it.