Speedo misreading

[Das Viviers]

Hi all.
Does anyone know why my speedo show 100 km/h and the GPS shows 50 km/h.? That is the same for 140km/h and GPS shows 70km/h. Aways half the speed. Used different GPS modules.
ABS rings straight, no dents.

 

[Bill the Bong]

 

[Puls0nic]

 

[TheBear]

 

[Das Viviers]

 

[Bill the Bong]

 

[Das Viviers]

 

[Bill the Bong]

 

[Das Viviers]

 

[Bill the Bong]

 

[Das Viviers]

 

[Das Viviers]