Gadget displaying speed

[Ch.Eng.62]

On 6/29/2019 at 1:17 AM, esaj said:

Back in the day I used a very simple approach: bike speedometer (wired). Glue the magnet on the tire rim, glue or tape the "receiver" (a magnetic reed-switch) on the shell, tape the wire to the shell and attach the speedometer to the handle. GPS is "good enough" for general speed gauging and odometer, but nowhere near as accurate as correctly adjusted (the tire circumference) "old-world" meter. The GPS can (at times) locate you within something like 1 meter (3 feet), but it only updates a certain amount of times per second, and the errors add up. Not a problem with a car driving in straight line at steady speed, but if you're swerving or accelerating/braking a lot, it's not going to be very precise. With a properly "calibrated" (again, the tire circumference, accounting for how much the tire "pushes in" with your weight) you can notice a slight drop in tire pressure, as the wheel circumference has dropped. The most accurate method would be to have multiple magnets over the tire at equivalent distances, so you get multiple "ticks" per revolution over the time, but the meter should support this then (I don't know if such speedometers exist).

 

You are right. I test measuring the speed via my cellphone GPS and the reading was very unacceptable. For example I was almost stopped, the GPS reading was 15 km/h, after acceleration my speed was more than 15km/h, the reading was 2km/h

[ir_fuel]

Cellphone GPS is useless. They only update at 1Hz.

[Planemo]

1 hour ago, ir_fuel said:

Cellphone GPS is useless. They only update at 1Hz.

Another reason to read directly off the wheel using Wheel Log (or any other app that pulls data from the wheel pulses).