Joined
·
58 Posts
I was having a think about how I can check the accuracy of my speedometer and I have come up with a suggestion, shoot me down in flames if you think it is a daft idea.
You guys who have GPS can easily check if the analogue speedo is accurate but I am still in the map and compass era.
So...
The way the system works is by a sensor on the rear wheel sending pulses to the computer, these pulses will be as accurately related to the speed as the designers calculations and the variations in rolling radius due to tyre wear and pressure will allow. So lets for the sake of argument say this is spot on.
Now the speedometer itself is an analogue device so somewhere there will be an D/A (Digital to analogue converter) this will output a voltage which then goes to the speedo. As we know from elsewhere, this can be changed by varying resistor values. So the accuracy of this unit is in question.
Now we also have an on board computer that displays average speed, this is a digital device being fed from the same wheel sensor.
So the process is, find a good long straight flat bit of road, get up to say 60MPH and engage the cruise control. leave it a few seconds to settle and then press the reset on the On Board Computer whilst Average Speed is selected. Again leave it settle for a few seconds and you should now have a fairly precise actual speed reading that you can compare to the speedo reading.
With my speedo sat at 50MPH my OBC stated 44.9MPH so roughly 10% fast.
At some time when I have the bike apart I will do the resistor mod to hopefully make the analogue speedo more accurate but until that time I will have a good idea of my actual speed.
May be of use to someone ...
Regards
Tony
You guys who have GPS can easily check if the analogue speedo is accurate but I am still in the map and compass era.
So...
The way the system works is by a sensor on the rear wheel sending pulses to the computer, these pulses will be as accurately related to the speed as the designers calculations and the variations in rolling radius due to tyre wear and pressure will allow. So lets for the sake of argument say this is spot on.
Now the speedometer itself is an analogue device so somewhere there will be an D/A (Digital to analogue converter) this will output a voltage which then goes to the speedo. As we know from elsewhere, this can be changed by varying resistor values. So the accuracy of this unit is in question.
Now we also have an on board computer that displays average speed, this is a digital device being fed from the same wheel sensor.
So the process is, find a good long straight flat bit of road, get up to say 60MPH and engage the cruise control. leave it a few seconds to settle and then press the reset on the On Board Computer whilst Average Speed is selected. Again leave it settle for a few seconds and you should now have a fairly precise actual speed reading that you can compare to the speedo reading.
With my speedo sat at 50MPH my OBC stated 44.9MPH so roughly 10% fast.
At some time when I have the bike apart I will do the resistor mod to hopefully make the analogue speedo more accurate but until that time I will have a good idea of my actual speed.
May be of use to someone ...
Regards
Tony