Go to this website
http://www.caigauge.com you can reprogram your own. When you get to the website go Q&A Smiths electronic speedo. It is quite easy to get to programming mode but then some careful measuring is involved.
The 3.7 Raodster has VDO gauges not Smiths, I'm not sure that they can be calibrated accept through the ECU.
I have the same issue, when Speed reads 70 mph, car is actually doing just under 60mph. Be careful with GPS readings, speed reading on my iPhone was 5 mph lower than that on Neilm's using the same software. Going to try re-install and recheck.
