Modern Vespa

My GTS has indicated 10-12 mph high since I got it. Today I decided to see if I could remedy that. I dismantled the headset as described in other posts. I took the cover off the speedo and GENTLY pried the needle off. I turned it about 10 mph counter-clockwise and pushed it on the shaft. Just enough to get it started as the needle was now on the wrong side of the zero peg. I rotated it past the peg, then pushed it on the rest of the way.

Checked against the car speedo it now reads about 2 mph low. YMMV.

Alternatively, you might be able to use the speedohealer.

Call me cheap but 1/2 hour of my time and the satisfaction of fixing it myself, plus no aftermarket parts on the bike, OR spend $100 and the time to install it, calibrate it etc.

I'll settle for calling you crafty...

Interesting remedy Mr. Old Hog Rider. Looks like we can learn something from scary guys like you after all.
My ET4 speedo has remained surprisingly accurate for the entire time I've owned it, even after replacing the cable.

BMW airhead twins ('70 & 80's models) speedos are easily calibrated this way also. Good idea, I really never thought about doing the GTS speedo this way, will give it a try.