They're all out - they usually read about 10% faster than real speed. It's common not only to these bikes but just about all bikes with analogue speedos, since there's only a few places that make bike speedo units and most manufacturers use them rather than making their own to save money.
There's a digital bicycle speedo that I've seen used on our bikes to give you a more accurate reading with a small magnet mounted on the front disk and a sensor on the forks but I just treat it as a "safety margin". I know I can "speed" without risking a ticket.
