265/40/20 Speedometer

[Digester-Man]

I recently fitted Goodyear 265/40/20 tyres which makes the van a little bit taller. I was recently in France and noticed that Waze was recording 130kph when the van was showing 125kph. Does this mean the speedo is under-reading? I assume Waze takes its speed reading from gps. I actually got flashed by a speed camera with cruise control set at the speed limit, I can't be sure it was definitely flashing at me but Waze was showing that I was over the limit by a few kph.

 

[The Flying Scotsman]

I’ve got 275/40/20 tyres on my van and according to gps I’m 73mph when my Speedo reads 70mph.
So yes your Speedo is under reading because of the 20” wheels

 

[Shaggy1969]

I’m exactly the same as @The Flying Scotsman .

 

[Frigo110]

I drive 255/45/19 and the speedo is compared to the phone GPS spot on.
Your tyres are 10mm taller in diameter so yes - you're speeding when you follow the speedo.

 

[JimmyAK]

I recently fitted Goodyear 265/40/20 tyres which makes the van a little bit taller. I was recently in France and noticed that Waze was recording 130kph when the van was showing 125kph. Does this mean the speedo is under-reading? I assume Waze takes its speed reading from gps. I actually got flashed by a speed camera with cruise control set at the speed limit, I can't be sure it was definitely flashing at me but Waze was showing that I was over the limit by a few kph.

Take a look at this thread.