Hi all,this has probably been covered before but I was wondering if anyone knew which would be the more accurate?
I have a tomtom 520 and have noticed that my vehicle speedo indicates a slightly higher road speed than my satnav indicates, EG…Satnav says 60mph whilst speedo shows 63mph!! I have heard that the satnav is in fact a more accurate indication of true road speed than a vehicles speedometer, just wondered if anyone here knew if this was true or not?
I havent changed the vehicles wheel size etc so it should be caliberated as per when it left the factory.
I always go with the sat nav and mostly find the speedo is showing a bit slower. You need to be on a straight piece of road which is level and thats the best place to get the right speed from a sat nav.
are your tyres still brand new? if not the speedo will be showing a faster speed than what you are actually doing, the best time to get a speedo calibrated is just before new tyres are fitted…As for the sat nav, it measures speed at sea level, so is not 100% accurate, the higher your altitude the slower it will read. You should notice it will show a slower speed when you go up or down a hill for example if you go down a 1 in 10 hill it will show 10% slower than your road speed.
jimti:
are your tyres still brand new? if not the speedo will be showing a faster speed than what you are actually doing, the best time to get a speedo calibrated is just before new tyres are fitted…As for the sat nav, it measures speed at sea level, so is not 100% accurate, the higher your altitude the slower it will read. You should notice it will show a slower speed when you go up or down a hill for example if you go down a 1 in 10 hill it will show 10% slower than your road speed.
I have a Tom Tom 520 and the speed is linear, i.e it shows the same difference to the tacho at whatever altitude. Tacho reads fast by 2 or 3 mph. Tend to believe the satnav.