Speedo Under Reading

[RayHutch]

Hi, I noticed that my speedo is under reading, so when I'm doing 50 on my satnav the speedo is reading 40 or so. The needle does not wave around so I don't think it's a rounded speedo cable.

Not ideal with the endless speed cameras around !

Any ideas ?

 

[Alex VW Heritage]

Tyre size can throw it out, what tyre size are you running?

 

[RayHutch]

Tyres are 185 R14