Hey guys. just got a reading of 55+ MPG over a course of 145 miles! besides that, how much do the speedos vary from bike to bike? My dad's '86 at 4k rpm, is ~60 mph. my 2001 at 4k rpm is 55mph. how much will new tires vs. worn tires effect it? My bike has a NEW front and rear. my dads has a NEW rear, worn front. what are some of your speeds at various rpms. I really wanna check mine with a gps.
According to my calculations both the 150/90-15 and the 170/80-15 rear tires have nearly identical diameters and circumferences.
At 4k rpm both should give a true speed of ~58mph.
The vn750 speedo has been reported by many riders here to read about 10% high with the stock 100/90-19 front tire.
The odometer is fairly accurate however.
Changing out to the 110/90-19 nearly corrects the speedometer, but the odometer will now read a bit low.
The ~10% difference in speedo readings between your father`s bike and your own could be explained by these different sized front tires. The worn front tire on dad`s bike will cause a few more revolutions per mile and may add an extra mph or so to the reading as well.
There is also the possible difficulty of making very accurate readings on two gauges at speed while riding. Other than these two scenarios, I`m not sure how else to account for the different readings, as all previous reports that I recall have verified the approximate 58-60 mph at 4k rpm.
Both readings seem to fall within a reasonable margin of error, given the conditions under which they were made. <shrug>
True calculated speed using gear ratios for the vn750 is 14.52 mph per 1k rpm in 5th gear, but will vary a little with tread wear.
Simple multiplcation calculations will give the speed at any rpm.