Question regarding your speedometers

[CodyDog]

How does your speedometer react to change in speed? Here's why I'm asking the questiion.

Recently my speedometer (Rad Rover) changed in the way it reacts. Up to the other day, the speedo would change immediately with the change of speed, both up and down. Now it takes seconds to adjust downward. If I'm riding at 20 mph and come to complete stop, it will take 4-5 seconds to register back at 0. also, it seems to record higher speeds before that speed is aquired. This is new for my ebike.

I communicated with Rad Power Bikes, which by the way responded immediately, and they asked me to send some video clips which I did. They said this was normal speedometer behavior. They indicated that their test ebikes responded the same way. I have questioned why the change but that can not be explained as of yet. I also told them that with this issue, my bike has become more zippier (which I like). I was thinking somehow there was a some change in the controller.

 

[ebikemom]

I have a Pedego, but my speedometer is very consistent and in sync with my riding behavior. That said, it is interesting that my ODOMETER is always slightly different from that of whomever I ride with. I Iearned here that lateral movement also impacts odometers, as does level of tire inflation (which changes the circumfrances of the wheel!)

Maybe other Rad riders can chime in about their speedometer behavior.

 

[harryS]

Ebikemom, controllers on ebikes use wheel circumference to calculate the speed, and that input can be quite coarse. For example, mine allow several common wheel sizes like 19", 20", 22", 26" and 29" and that can be way off. Meanwhile, a $10 bike computer wants the actual circumference in cm, and that can even change a little depending on whether someone is sitting on the bike. I've checked the bike computer against Google pedometer and both match up.

Codydog, I've found my ebike speedometers to mostly reflect the instantaneous speed, although they may vary from what a bike computer will say, as described above. All of them get the speedometer info as a digital packet from the controller, which reads it from a speed sensor either inside the motor or on the wheel. By the way, is this the same display as is used on your RAD? It's an SW900 display, but the controller never worked right for me..

 

[AlanDB]

On my Bosch Intuvia display, I have noticed a slight lag in speed change, but it is not 4 or 5 seconds. If I come to a quick stop, it may take a second (at most 2) before the Intuvia displayed speed drops to 0.

I don't really know how these speedometers work, but I assume there is a sensor that receives strobes from wheel revolutions. If you know the circumference of your tire (distance traveled per revolution) and the number of strobes (revolutions) in a given time, the average speed over that time is a relatively simple calculation. If my math is correct a typical e-bike with 700c rims would get approximately 1 wheel revolution per second at 5 MPH. I am guessing these speedometers average the speed recorded by the strobes received over the past few seconds, and this technique would cause a slight delay in the displayed speed.

Like I said, I am just guessing how it works so I may be way off base. I hope someone who has more knowledge will comment.

 

[Volt_Ampere]

Most bike speedometers only update once per wheel revolution since they sense the magnet mounted on a spoke. The update rate is a function of how fast you are riding.

 

[Bruce Arnold]

The speedo on my Juiced Bikes CCS is based in the hub rather than the magnet-on-the-spoke model (I've had that type on other bikes.) That being said, there is a little lag, but nowhere near what you're describing. Hmmm.