When I had my metric, I compared it to both a Magellan and a Garmin. The two GPSs read exactly the same. I do know the speedos on metrics are deliberately set high. I'm sure the LEOs make sure their bikes are properly calibrated. I'd to get cited by a LEO that clocked me with a bike speedo that was running up to 10% high!!!

 

My speedo shows 2-3 MPH fast compared to the GPS. Other than using this information to moderate my speed I haven't done anything about it.

 

There are two factors at play here: liability and laws.

In the U.S. I am not aware of any specific legal requirement regarding speedometer accuracy. However, because a speedometer which reads low by design could open the manufacturer up to liability claims, there is a tendency to engineer them to read slightly high.

In the EU there are specific requirements. As I've posted to other forums:
European Union Directive 2000/7/EC set the requirements for speedometer accuracy.

There are two main requirements when tested:
1. That indicated speed is never below actual speed.
2. That indicated speed is never above 110%+4 km/h of actual speed.

For actual production motorcycles and motor tricycles, the upper limit increases to 110%+8 km/h (but remains 110%+4 km/h for mopeds).

So for a production motorcycle rolling at an actual 80 MPH, the indicated speed can't be below 80 MPH, and can't be above 92.97 MPH.

As this upper limit is 16.2% higher than actual, a built-in 8% error puts a motorcycle with 8% error built in firmly in the middle of the legal range at highway speeds (as is the case with my Ducati, where the manual specifically states that the speedometer is designed to read high by 8%).

Link: http://eur-lex.europa.eu/LexUriServ/...00L0007:EN:NOT

Interestingly, it's been found by one of the automotive magazines (I don't remember which) that American speedometers tend to be the most accurate, reading slightly below actual to within 2% above. Japanese speedometers tend to read bit higher. European makes' speedometers, especially BMW, tend to read very high.

That said, while my Ducati reads high by the advertised 8%, my Harley reads high by maybe 2%, and my Pontiac's speed reads dead on.

 

My bike speedo is off 5%...When it reads 100, the GPS reads 95.

 

My speedo seems to be about 5 % less than the actual speed. When it reads 100, actual speed is more like 105. I think this may be the result of gearing changes and that the speedo is no longer calibrated.

 

Changing the diameter of your rear tire will also change the accuracy of the reading. The larger the tire, the more your reading slows down. Some of the metric people put a larger tire on the rear in the effort to make it more accurate. The other side of the coin is that as your speedometer slows down, so does your odometer. The added benefit to going this route to correct it is that if you put a larger tire on the rear, your motor will need a little less RPM to to get up to the same actual speed as before which can mean a little less wear and tear on your motor...

 

Well on my old bike the speedo lies like a cheating wife , always has when they worked at all . I figure the one I have now is 15 -20 under actual speed , I've always ridden by feel for highway speeds anyway and when checked I'm always within 5 MPH .

 

winter do you only ride during the winter what about summer? anyway if i am doing 80 my speedometer is off 5 miles from GPS if i am doing 60 it is only off about 2 miles from GPS for me its not enough to mess with

 

My speedometer was reading about 2-3% high compared to my GPS. I calibrated it with the TTS Mastertune and now it matches the GPS exactly.

 

I have a 2008 FLHX, the speedo always read 3 MPH higher than the GPS. After I installed a Thunder Max the speedo and GPS matched.