Join Date: Aug 2011
Location: Oklahoma Panhandle
I haven't checked the odometer, but, with a stock front tire, my speedometer is ~10% faster than actual. I've accurately (measuring wheel) marked out a 1 mi stretch of road and used a stopwatch to check my time at various speeds to reach this conclusion. Because of the dials on the odometer, it's just not accurate enough to check that. You'd need a longer run of verified distance where a tenth or so comes out in your error.
FWIW: Instant speed, or whatever your GPS calls it, can fluctuate quite a bit. Some units include an automatic 'averaging' in this speed (i.e. average distance traveled between 'fixes' for last 5 readings). If your unit doesn't do this, you should look at what the unit calls 'average speed', but be aware stops are often factored into this unless you reset while traveling at speed.