This is an old complaint wrt the actual speed vs speedometer displayed speed, on the V-Strom.
At one point there was a replacement gauge face plate that was available for 1st gen analogue gauges, but if it still is I don't know. See Reply #119 in
https://www.v-strom.co.uk/smf/index.php?topic=36557.msg369602#msg369602, for a pix example of the face plate transfer. Previously the face plates where available from
https://www.raceratb.com/austin/car/buyGauges.htm, but I not sure if they are still selling the face plates. I recall reading that there may be something similar available on ebay. Sorry I don't have a link to share.
A speedo healer / speedoDRD was also available as an option to correct the speedometer speed, but if I recall, it didn't help correct the trip meter mileage. The face plate was the better solution for the 1st gen models, where as the models with the newer digital speedometer, the speedo healer was recommended.