Join Date: Nov 2007
Location: Bergen County, NJ
Re: speedo vs. gps speed
As far as I know, the "optimistic" speedometer is a constant on European cars and bikes, all speedos somehow show and higher speed than the real one.
The point is the following: it's not allowed by law, that your speedo fails on the "pessimistic side" (i.e.: telling that you're going slower than your real speed) because that would let you travel faster than the speed limit, without you knowing that.
The law includes the mechanical/electronic tolerances, and must also count eventual variations inducted by a different tyre shape (and different tyre size, if allowed in the vehicle options). So, the "centre point" of the speedo setup is made higher than it should, so that it never happens that it goes lower.
The fix in the hall of wisdom is probably removing this higher setup and reverting to the zero centre point... at your own risk though.
Both my BMW car and the LT show 136 Kmh on the tachometer and on the cruise control (digital, for the car) when I'm actually travelling at 130Kmh (legal speed), so it's an error of about +5%
Trust your GPS, it's usually very accurate for the speed. We have roadside signs every 1km exactly and I used them once to check the GPS... it turned out to be 100% accurate.
'12 R 1200 RT
'06 K 1200 LT (sold)
'05 Cagiva Navigator 1000 (sold)
'90 Kawasaki ZX10 (sold)
'82 Moto Guzzi V35 II (sold)
'82 Benelli Export 3V