Speedo vs GPS
Speedo vs GPS
The wife and I went on a 200 mile ride today so I thought this would be a perfect time to try out the new GPS mount. While riding I looked down and compared my speedo verses the GPS and at 80mph on the speedo, my GPS was reading 75mph! I thought WOW that is pretty far off. Is this normal?
Seasoned HDF Member
Joined: Sep 2007
Posts: 9,208
Likes: 374
From: Central Illinois, Between I-80 and I-74
Other than police certified, Speedometers are all designed to read faster than actual speed using the largest diameter for new tires of the proper size.
It is normal.
It is normal.
Tourer
Joined: Jul 2010
Posts: 479
Likes: 2
From: IL
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Road Warrior
Joined: Mar 2011
Posts: 1,456
Likes: 132
From: Deep South, Louisiana
On all vehicles (except police vehicles) the speedometer will show 2 mph faster. This is done to keep you under the max speed limit incase you not paying attention. As your tires wear down the the difference will get greater. New tires will go back to 2 mph off. A GPS will show true speed and they can both be checked easily by setting cruise at 60 mph, then as you pass a mile marker on the interstate it should take you 60 second to travel to the next mile marker. 60 second = 1 mile = 60 mph. In the old days the police cars had a small settable gear box outside where the speedometer cable connected into the transmission. I use my GPS for setting my speed I want and set the cruise.
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Club Member
Joined: Jun 2007
Posts: 45,429
Likes: 2,898
From: Bedford UK
What is normal is that a speedo only has to be accurate to a modest degree, so the gps is the more accurate. Speedos are generally optimistic, in other words tell you that you are going faster than you really are. It's a fact of life!
