Easiest check is to get a GPS based speedo on your phone ...lots of free apps available.
I changed everything in the driveline and totally confused the speedo on my '82 plus 8 - 225/45/15 tyres instead of 205/60; R380 box instead of LT77 (mine might have expected a different final drive); 3.08 diff from a Holden V8.
It felt a little quick for the speedo readings so I got an app and found I was doing 57mph at an indicated 50, with the same proportional error at other speeds.
I think it will be too hard to recalibrate so I'll just remember the adjustments to be made on the run. (I am open to advice about how to recalibrate though)
I know people who have used bicycle speedos too on devices from cars to race karts, although they can take a bit of setting up and might not have enough range of values of wheel diameter
Terry
(Canberra)
