Speed sensor needed?

Hello. I have a Bolt 2. When I first installed it I did not have the speed sensor installed. It seemed to calculate speed anyway, with what I assume is GPS.

I installed the speed sensor and linked it. Now my distances are a couple of percent different.

Which way have you found to be more accurate?

Is there really a reason for the speed sensor?


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If everything is set up correctly (wheel circumference matches the tire at current rider weight, pressure and wear level) and there are no signal drops, a speed sensor will be more accurate than GPS because GPS-based speed/distance is calculated based on location every second, and every turn will result in calculated distance shorter than actually traveled because the sample describes a set of straight line segments rather than the curve actually traveled.

But things are never set up correctly. I use a speed sensor and if the mileage on a segment I regularly ride is slightly too high, I check the tire pressure.

Also, GPS location accuracy can be compromised by tall buildings or heavy tree cover, and that will affect calculated speed/distance.


GPS also exhibits position wander, so sitting still, your position will move around. This is interpreted as some low speed which can add/subtract from you instantaneous speed, throwing off features like auto-pause. I have speed sensors on all my bikes. Most recently, about a year ago, I got a Magene S3 sensor for $17 on Amazon and it has worked well. These can also be attached to a crank and configured as a cadence sensor instead.