Home › Problems without a code › E-bike speed limited / stuck at 15 mph or 25 km/h
E-bike stops assisting at 25 km/h or 15 mph? What's normal and what's a fault
In the EU, UK, and Australia pedal assist legally stops at 25 km/h (15.5 mph); in the US, Class 1 and 2 bikes stop at 20 mph and Class 3 at 28 mph. If your bike cuts assist well below its legal limit, something is wrong with the speed reading, the wheel size setting, or the mode.
Quick checks, in order
- Confirm the limit that applies to your bike and region: 25 km/h in the EU/UK/AU, 20 mph for US Class 1/2, 28 mph for US Class 3. A bike that stops at that speed is working correctly.
- Compare the display's speed with a phone GPS. If the display reads higher than GPS, assist will cut early; the wheel-size setting is wrong.
- Check the wheel circumference setting in the display menu (Bafang, generic) or ask the dealer to verify it (Bosch, Shimano, Yamaha set it in the tool). A 26-inch setting on a 29-inch bike cuts assist around 22 km/h.
- Check the assist level. Some systems reduce the effective top speed in Eco; try Turbo or Boost.
- Check the tyre size. Fitting narrower or smaller tyres than the bike was set up for changes the circumference by a few percent.
- On Bafang and generic displays, look for a speed limit parameter in the settings and check it is at the legal maximum.
- If assist fades out gradually from about 22 km/h, that is normal; systems taper power before the limit so it is not a hard cut.
Likely causes
Legal limit reached
How to tell: Assist stops at 25 km/h or 20 mph consistently and the display speed matches GPS.
Fix: Nothing to fix. Beyond the limit you pedal unassisted. Modifying the limit changes the legal status of the bike and voids the warranty.
How to tell: Assist stops at 25 km/h or 20 mph consistently and the display speed matches GPS.
Fix: Nothing to fix. Beyond the limit you pedal unassisted. Modifying the limit changes the legal status of the bike and voids the warranty.
Wheel circumference set too large
How to tell: Display reads faster than GPS, odometer over-reads, assist cuts before the real limit.
Fix: Set the correct circumference (measure it: roll the wheel one turn and measure in mm) in the display or have the dealer set it.
How to tell: Display reads faster than GPS, odometer over-reads, assist cuts before the real limit.
Fix: Set the correct circumference (measure it: roll the wheel one turn and measure in mm) in the display or have the dealer set it.
Speed limit parameter set low
How to tell: Bafang or generic bike cuts at 15-20 km/h; the display's limit setting shows a low value. Common on rental or second-hand bikes.
Fix: Set the parameter to the legal limit for your region. Do not set it higher.
How to tell: Bafang or generic bike cuts at 15-20 km/h; the display's limit setting shows a low value. Common on rental or second-hand bikes.
Fix: Set the parameter to the legal limit for your region. Do not set it higher.
Assist profile weak in the chosen mode
How to tell: Assist fades early in Eco but holds to the limit in Turbo.
Fix: Normal on many systems; use a higher mode, or adjust the profile in the app.
How to tell: Assist fades early in Eco but holds to the limit in Turbo.
Fix: Normal on many systems; use a higher mode, or adjust the profile in the app.
Speed sensor giving a doubled reading
How to tell: Display speed roughly twice GPS. Two magnets on the wheel, or a magnet close enough to be counted twice.
Fix: Remove the extra magnet or adjust the gap so the sensor counts once per revolution.
How to tell: Display speed roughly twice GPS. Two magnets on the wheel, or a magnet close enough to be counted twice.
Fix: Remove the extra magnet or adjust the gap so the sensor counts once per revolution.
Tuning device fitted and misbehaving
How to tell: Second-hand bike with an inline box on the speed sensor cable or a dongle; the display speed reads half of real speed or assist behaves oddly.
Fix: Remove the device and restore the original cable. Bosch detects manipulation (code 504) and locks the bike for a period.
How to tell: Second-hand bike with an inline box on the speed sensor cable or a dongle; the display speed reads half of real speed or assist behaves oddly.
Fix: Remove the device and restore the original cable. Bosch detects manipulation (code 504) and locks the bike for a period.
By drive system
- Bosch: The wheel circumference is set by the dealer in DiagnosticTool and is in a locked range. Assist tapers from about 23 km/h and stops at 25 in the EU. If the display speed matches GPS and assist stops at 25, the bike is correct. Code 504 means the system detected a tuning device and has reduced assist until you ride a distance at legal speed with it removed.
- Shimano STEPS: Wheel circumference is set in E-Tube by the dealer. Assist on STEPS tapers noticeably before the limit; that is by design. If assist ends around 20 km/h on an EU bike the circumference is likely set for a smaller wheel.
- Bafang: The speed limit and wheel size are set in the display's advanced settings; on the DP-C18 hold + and − for a few seconds, on the 750C via the settings menu. Keep the limit at the legal value. If the bike was bought with a low limit it is often a dealer's compliance setting for your region.
- Yamaha PW: Yamaha sets the limit and wheel size in the dealer tool. Assist stops cleanly at 25 km/h in the EU. If it stops earlier, check tyre size versus the original and have the dealer correct the circumference.
- Generic: KT displays: the P or C parameters include wheel diameter and max speed; set the diameter to match the tyre and the max to your legal limit. Some controllers also have a speed limit wire or jumper; if the bike cuts at 20 km/h and the display says 25, that wire is the culprit.
When to stop: Go to the dealer when the wheel-size setting needs changing on a Bosch, Shimano, or Yamaha system, and be clear that raising the limit above the legal maximum is not something a reputable shop will do.
Related error codes
Still stuck? Take a photo of the display and show it to a local e-bike workshop. Bring the bike's system name (e.g. Bosch Performance Line CX) and the exact code; that saves diagnostic time and money.
Frequently asked
My bike says 32 km/h but assist stopped at 25. Faulty?
No. Above the legal limit the motor stops helping and you are pedalling on your own. The display keeps reading speed as long as you are moving.
Can I raise the limit to 32 km/h or 28 mph legally?
In the EU and UK, no; the bike would become a moped requiring registration and insurance. In the US, Class 3 allows 28 mph pedal assist but the bike must be built and labelled as Class 3; you cannot reclassify a Class 1 by changing a setting.
Why does assist fade out before the limit instead of stopping sharply?
Manufacturers ramp the power down over the last few km/h so the cut is not a jolt. It feels like the bike is weaker at 23 than at 20; that is intended.