How we picked
Measurement method came first, because it decides how much setup a unit needs and how much can go wrong: GPS units need no sensor and no wheel-size entry, magnet units need both but never lose a signal. Readability at speedcame second — at 20 mph you get a glance, not a read, so screen size beats feature count. Then power: a coin cell that lasts years versus a USB battery that needs charging is a genuine lifestyle difference, not a spec-sheet one. We have not ridden every one of these; this is exactly what we do instead.
GPS or wheel magnet?
GPScomputers take speed and distance from satellites. There is no sensor to align, no magnet to knock out of place on a fat-tire spoke, and no wheel-circumference number to get wrong — which matters more than it sounds, because entering that number incorrectly is the single most common reason a bike computer disagrees with reality. The trade-offs are a few seconds to acquire a signal at the start of a ride, weaker performance in dense city canyons, and a rechargeable battery.
Wheel-magnetcomputers count wheel revolutions. Fitted correctly they are accurate immediately, work under bridges and inside garages, and run for years on a coin cell. The costs are setup fiddliness — fat tires and disc-brake calipers leave little room for a fork-mounted sensor — and the fact that a knocked sensor silently reads zero.
For most e-bike owners we would take GPS, because the setup is the part people get wrong. For a bike that lives in a garage and never gets fettled, a wired CatEye will outlast several e-bikes.
Why the numbers disagree with your e-bike’s display
If your new computer reads slower than the bike’s own screen, the computer is usually right. Three things cause the gap:
- Wheel size assumptions.The controller is set at the factory for a nominal tire size. Fit a different tire, or run 15 psi in a fat tire instead of 25, and the rolling circumference changes — but the controller’s figure does not.
- Optimism. A display that reads high makes a bike feel faster. Nobody publishes this, but the pattern is common enough in the value bracket to be worth verifying yourself.
- Different sources. The controller counts motor revolutions; GPS measures ground distance. On a slipping surface or a slow climb these genuinely differ.
This matters legally as well as practically. Class 2 assist stops at 20 mph and Class 3 at 28, and those limits govern where you may ride — see our classes and laws guide. An independent speed reading is how you find out which one you actually own.
What a computer will not do
It will not read your battery state. Watt-hours consumed, assist level and state of charge live on the controller side, and a $25 computer has no access to them. Pair the computer with the arithmetic instead: our range guide shows how to divide battery watt-hours by measured miles to get your own watt-hours per mile, which is the number that actually predicts range.
It also will not navigate. If you want turn-by-turn directions, a phone in a proper mountis the better device — and the computer becomes the thing that keeps recording when the phone dies.
Mounting on an e-bike
E-bike handlebars are crowded: display, throttle, brake levers with cutoff switches, bell, mirror, phone mount. Before you buy, look at where the unit will actually go. Most of these use an O-ring mount that fits either the bar or the stem; the stem position is usually free on an e-bike where the bar is not.
One more e-bike-specific point: vibration. Fat tires at low pressure transmit less road buzz than skinny tires, but a 70 lb bike hitting a pothole delivers a real shock to anything clamped to the bars. Check the mount after the first few rides, the same way you would check any of the bolts in our maintenance checklist.
