Speedo calibration

[chopperman]

Last weekend checked out my speedo after fitting 195x65x15 tyres.
Against my GPS, at 30, 40, 50, 60 there was no difference, at 70 my speedo read 2 mph faster. Of course I didn't check at any faster speeds as this is illegal, but I'm pretty sure that at 80, 90 and 100 mph, my speedo would have been showing up to 5 mph faster.
I,m sure that my speedo is now more accurate than when I had 14inch wheels fitted with standard tyres.
Keith

[Jeff]

Check again after the tyres wear down.

[Paul Roberts]

I thought that; (there being both distance and time in mph) as one travels faster - time slows down.... ?

So, does this mean that the speedo' reads faster????