Don’t worry, you are not alone. We have also noticed the difference between the speed readings on our speedometer and our SatNav. European countries are enforcing fines to other EU countries drivers. So, we thought it would be good to find out which reading is more trustworthy. You don’t want to come back from a trip and have a fine waiting for you at home!
The speedometer in a vehicle is based on calculations using tyre rotation. GPS devices calculate speed based on your GPS position. The accuracy of the speed displayed on the vehicle and GPS device can vary depending upon whether the vehicle’s speedometer needs to be calibrated and/or how accurate your GPS reception is. – Garmin
Garmin says, that if the vehicle’s speedometer is calibrated we should rely on it instead of the SatNav. This could do different readings depending on the reception.
The techy bit
Your bike’s speedometer measures the speed based on the turns of the wheel of your motorbike. The speedometer has been calibrated based on the bikes standard configuration. This is why if you change the size of your sprockets or wheels, the speed displayed will not be accurate.
But the SatNav calculates the speed by measuring the time taken to move from one position to another.
Due to how this speed is calculated, your speedometer can never be 100% accurate. The circumference of your tyres can change, such as when you lean your bike, which will affect the readings. Likewise, if your SatNav has weak signal, it can lead to inaccurate positioning which will lead to wrong speed calculation. Inclines can also affect the accuracy of these readings.
Which one do we trust?
We tend to trust our SatNav as it is more likely to be more accurate. But, it is better to rely on your motorbike’s speedometer as it will never understate your speed.
GPS devices should be used as a navigational aid and should not be relied upon for precise measurement of speed. – Garmin