The speed on your screen doesn't match a friend's bike, or your trip distance looks short. The numbers aren't plucked from the air, but they do rest on settings, and a wrong setting skews every figure that follows.
Where speed and distance come from
A bike computer counts wheel turns. A magnet on a spoke, or a sensor at the hub, notes each turn1.
From there it's sums. "Distance is determined by counting the number of rotations, which translates into the number of wheel circumferences passed"1. Circumference is the distance round the tyre. Speed follows from the distance and the time taken.
Where the sensor sits on your bike varies, so your manual is the place to check.
Why the numbers can be wrong
The display counts wheel turns and works out distance from the wheel size set. The source is plain about this: "different wheel sizes will translate to different measures of speed and distance for a given number of rotations"1. If the wheel size set in the display doesn't match the real wheel and tyre, every reading is out by the same proportion.
Check these in order:
- The unit. Setup includes "selecting distance units (kilometers vs. miles)"1. A number that looks low or high may simply be in the other unit.
- The wheel size setting. Compare it with the size marked on your tyre, and follow your manual to change it.
- The sensor and its mount. If it has shifted, turns may be missed. Don't force parts. Ask a dealer.
- A second opinion. For a bike computer, the source says "The computer's reading is then compared with the known distance and any necessary corrections made"1. Your manual says whether your display allows that.
Trip distance and odometer
A trip figure is a running count you can clear. The source says buttons can "reset values such as time and trip distance"1. A basic bike computer lists "trip distance, trip time, total distance traveled"1, and the total is the odometer. Some makers use it for service prompts. One maker's list gives a cause for a maintenance code: "The e-bike's ODO has reached the preset maintenance mileage"2.
Whether your odometer can be reset, and what happens when the power is cut, depends on your bike. Read your manual. Don't try to alter an odometer reading. Dealers and buyers rely on it.
Why range is only an estimate
Range is the distance the screen says you've got left. It leans on the battery figure. The charge figure it leans on is itself worked out from other readings3. Load on the battery can affect a voltage-based reading3.
Then the display has to turn energy into distance, and the ride ahead isn't known. Your maker's manual may explain which factors the range figure takes into account and which it doesn't. Where a manual is silent, treat the figure as a rough guide and leave a margin. Reading Assist Level and Battery Charge on the Screen covers the battery side.
Where the numbers stop being useful
If speed, distance and range all look wrong together, the cause may be a code, not a setting. See the error code page.
Cited material
- Cyclocomputer, Wikipedia
- DST - Hyena Error Codes, Trek Bicycle Help Center
- State of charge, Wikipedia
More on the display
What an E-Bike Display Does and What It Does NotWhat the screen on your e-bike handlebar is for, what it reads from the bike, and why it isn't the same part as the controller.
Display, Controller and Remote: How the Parts Fit TogetherWhich part of an e-bike is the screen, which is the controller and which is the button pad, and why a code can name any of them.
Common E-Bike Display Icons and What They ShowWhich kinds of symbols appear on an e-bike screen, what each kind usually reports, and why your manual has the last word on yours.