Speedo accuracy

[Miks15]

Has anyone checked there speedo against a reliable source like a sat nav for example?

Just wondering how acurate they are. I have a KPH speedo

Thanks

Mikkel

[arkell]

yeah got a tomtom rider, its accurate to about 70mph, but then overestimates after that by about 10 percent

[cargo]

A speedo is only required to be accurate to 10%

And what makes you think a satnav is a reliable source ?

[arkell]

satnav reliable- pinpoints your position to within a couple metres doesnt it, so speed distance time blah blah and there we go!


sat nav should be reliable over flat ground, but would change if you were going up or down steep hills.

[RedexRobB]

i think public GPS is acurate to about 10-20 metrers. Its military GPS thats acurate to a few metres.

[Caz]

speedos cannot (by law) tell you that you are going slower than you actually are. Typically they read 10% high though

[Mr.Mash]

I know there ment to read right when you tyre's are on the wear limit its something to do with the difference in circumferences

[Xphyral]

I know there ment to read right when you tyre's are on the wear limit its something to do with the difference in circumferences

it'll never read correctly regardless of tyre wear because of tyre pressure which changes with heat and the weight on the bike. sat-navs also have a margin for error, they do not read your road position accuratly enough to be dead on and suffer from latency on the signals although time stamping packet transfer and better processing power in newer models has helped sat-navs to be a lot more accurate than they were on earlier models. a new sat-nav will be more accurate than an older one, theres no difference between these "military" satellites and public ones, it was originally the same satellite network in europe as the US military for gps and was leased by companies for use with public domain gps transmitters and receivers. it was only a matter of processing power on older sat-navs that caused a lag when translating data into the visual representation on the screen.

and so we get the 10%-ish higher speed to keep you in the safe zone when approaching any kind of speed trap so that it allows for the numerous final drive variables to be taken into account.