A recent product review on the SpeedoHealer, a recent forum post and my own observations got me hunting for more information on the accuracy of GPS speed measurements.

Here was the forum comment that I found intriguing:

I have been reading hundreds of posts on different sites about the Burgmans speedo being out about 10%. A group of us got together to sort this out. We had Yamahas, Suzuki, Honda and Duccati. We compared our speed with each other and found them to be almost the same. We had them checked by our local cop shop with hand held and static radar, again almost identical. Then we did the test with GPS and every bike was out by about 10%. Our local sergeant and I have GPS on our bikes and they read the same. We have since been told that a GPS on a bike will not be the same as in a car. I ride by my speedo and with the amount of miles I do, if my speedo was out by 10% I would be getting abused for going too slow or fined for going too fast.

Here is what I think most Burgman riders have discovered, the speedometers are not accurate, they read fast. I’ve noticed it myself. One person observed, “The speedometer error on the Burgman (AN400/AN650) is about 8% in stock condition.”

Many have postulated that this is an intentional trick put in place by motorcycle and scooter manufacturers to get us to think we are going faster than we actually are. One person posted, “The laws are written so that speedometer errors are asymmetric. It is OK to have them read too fast, but not to have them read too slow. As a result, manufacturers tend to make them read just a little bit too fast.” Plausible.

So What Can We Do About It?

One option if you ride with a GPS is to rely upon the GPS indicated speed, but is that accurate? Obviously some feel that a GPS device is not accurate on a motorcycle. I firmly believe that many think that is the case but it struck me as odd. After all a GPS device is measuring your speed over land using telemetry from multiple orbital satellites and is measuring the speed of movement of the device, independent of what type of mode of transportation it is attached to.

GPS Sats in Motion

GPS Sats in Motion

After looking around a bit I found the following relevant study that might help to dispel some of the rumors:

Accuracy of non-differential GPS for the determination of speed over ground.

Accurate determination of speed is important in many studies of human and animal locomotion. Some global positioning system (GPS) receivers can data log instantaneous speed. The speed accuracy of these systems is, however, unclear with manufacturers reporting velocity accuracies of 0.1-0.2 ms(-1). This study set out to trial non-differential GPS as a means of determining speed under real-life conditions. A bicycle was ridden around a running track and a custom-made bicycle speedometer was calibrated. Additional experiments were performed around circular tracks of known circumference and along a straight road. Instantaneous speed was determined simultaneously by the custom speedometer and a data logging helmet-mounted GPS receiver. GPS speed was compared to speedometer speed. The effect on speed accuracy of satellite number; changing satellite geometry, achieved through shielding the GPS antenna; speed; horizontal dilution of precision and cyclist position on a straight or a bend, was evaluated. The relative contribution of each variable to overall speed accuracy was determined by ANOVA. The speed determined by the GPS receiver was within 0.2 ms(-1) of the true speed measured for 45% of the values with a further 19% lying within 0.4 ms(-1) (n = 5060). The accuracy of speed determination was preserved even when the positional data were degraded due to poor satellite number or geometry. GPS data loggers are therefore accurate for the determination of speed over-ground in biomechanical and energetic studies performed on relatively straight courses.

It certainly appears that the GPS receiver can be relied upon to measure MPH +/- 1 MPH and is certainly more reliable than the speedo on the Burgman and many other scooters and motorcycles.

The other alternative is to rely upon a device like a SpeedoHealer, reviewed on this site, to re-calibrate your stock speedometer using a GPS.

I’m positive others will have more to add about this subject. Please feel free to add your comments below.

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3 Responses to “Burgman Speedometer Accuracy Versus GPS Speed Accuracy”

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