How to make an e-bike faster without breaking the law

Your e-bike feels slower than it did, or slower than your friend’s, and you want more speed. There are two very different problems hiding in that wish. This guide fixes the first one, drag you can remove for free in half an hour, and explains the legal limit on the second.

How can you make an e-bike faster?

You can make an e-bike faster by removing drag from the bike and rider; once the bike reaches its legal cut-off, more motor speed means a different class of bike.

The whole check takes about 30 minutes with a floor pump, a rag and chain lube. If a brake keeps rubbing after alignment, or the bike can’t reach its cut-off on the flat in its top mode, take it to a shop. That can be a sensor or motor fault.

Why does riding position make such a difference?

Riding position makes a big difference because air drag is most of the work at e-bike speeds, and your body is most of the drag.

In our physics model for an upright 120 kg rider and bike, air drag is about 78% of the power needed at 20 mph and about 87% at 28 mph. Drag power rises with the cube of speed, as Wikipedia’s bicycle performance page explains. Bending your elbows and lowering your chest shrinks the area pushing through the air. A flapping jacket or a big backpack adds to it.

This matters most above the cut-off, where your legs do all the work. It’s also why a headwind feels like a hill: drag depends on your speed through the air, not over the ground. Our speed versus range guide puts numbers on each mile per hour.

What else slows an e-bike down?

Load, low tire pressure and a low assist mode slow an e-bike down the most after air drag.

Extra weight costs most on climbs, where gravity and rolling resistance dominate. Wikipedia’s worked example on a 7% grade has air drag at only 2.1% to 6.1% of the effort. So on a hilly commute, emptying a heavy pannier helps more than tucking. Tire pressure inside the sidewall range keeps rolling resistance down; Wikipedia gives rolling coefficients of 0.003 to 0.006 for tires at their maximum recommended pressure.

Why are e-bike tuning kits a bad idea?

E-bike tuning kits are a bad idea because they raise the assist limit that makes the bike legally a bicycle, and the paperwork, insurance and warranty that came with it don’t follow.

In Great Britain the line is 15.5 mph and 250 W continuous, set by the GOV.UK EAPC rules. In the EU, Regulation 168/2013 exempts pedelecs only when assistance is “finally cut off before the vehicle speed reaches 25 km/h”. In California, Vehicle Code 312.5 defines each class by the speed where assistance ceases. A kit that moves that speed moves the bike out of the class.

Kits also put loads on brakes, tires and the frame that the maker didn’t design for at that speed. If a modified bike is in a crash, you’re the one who changed it.

Many systems now look for tuning. Bosch eBike Systems says its software can detect tuning with a sensor while you ride and then switches to an emergency mode, with an error code on the display and reduced support. Riding for about 90 minutes restores normal mode, but the check repeats; after the third detection, only a dealer with the Bosch DiagnosticTool can clear limp-home mode. Bosch also warns that tuning risks your guarantee and warranty claims, and notes that the EN 15194 e-bike standard calls for measures against manipulation.

Which bike should you buy if you need more speed?

Buy a bike approved for the higher class: a US Class 3 e-bike for 28 mph, or an EU speed pedelec with its type approval, AM licence and moped paperwork.

Our high-speed e-bike guide compares the two, and the fastest e-bikes guide lists the models we could verify at each step. In the UK, any bike assisting above 15.5 mph is a moped or motorcycle, so most riders get more speed from fitness and drag, not a new bike.

Mistakes to avoid

1. Fitting a bigger or higher-voltage battery to go faster. A bigger pack adds range, not legal speed, and a pack the system wasn’t designed for can damage the controller.
2. Changing the wheel size setting in the display to fool the speed sensor. The bike then reads the wrong speed and assists above its legal limit.
3. Skipping the shop when the bike can’t reach its cut-off. Weak assist on flat ground in top mode can be a sensor, motor or battery problem.

Where this advice comes from

Legal limits come from GOV.UK, EU Regulation 168/2013 and California Vehicle Code 312.5, and tuning detection from Bosch eBike Systems, all checked November 3, 2026. The drag shares come from our physics model with the assumptions in the speed versus range guide, and from Wikipedia’s bicycle performance page. We haven’t tested specific bikes for this guide.