How to recalibrate speedo to match new gearing

Kevin Ash in his Insight column a few weeks ago described raising the gearing to improve fuel economy. I would love to do this on my Tiger 800, which like most bikes is unnecessarily undergeared at 14mph per 1000rpm and would easily pull 20mph per thou, but what to do about the speedo? The speedo drive is taken from the gearbox, so the speedo would be out by the percentage change in the gearing. A front sprocket one tooth bigger and rear sprocket two teeth smaller would give 15.75mph per 1000 rpm, an increase of nearly 13%. So the speedo would show 70mph when the bike was actually doing nearly 79, great for economy but quite illegal.
David Lawton, email
 
Fret not, there are several electronic speedo recalibrators that will answer your problems. Thethree I came up with through the web are: Yellowbox, Speedohealer and Speedotuner. They do need some programming once they are plugged in, but they are all pretty straightforward.