Just did a 2500mile trip. Me on my 2012 SG and my buddy on his 2014 SGS. I always set my cruise based on my Garmin as my bike reads a few mph faster. Well, my buddy's 14 reads even a couple mph higher because when we stopped he asked me why I was flying.

 

After the wreck and subsequent rebuild I installed a Dakota Digital speedo that you calibrate upon installation. Not only was my old speedo off, but the odometer was even worse. So I checked my wife's car (Nissan,) and even my Porsche (60 mph takes 60 seconds to cover exactly one mile for those that don't have a GPS,) and they are all optimistic apparently. (So much for those outstanding gas mileages that I thought I was getting.)

 

Mine's a little fast too. When GPS shows 70, the speedo shows 73.

 

I've owned a Honda cruiser, a Honda Accord, and Acura TL, a Toyota Solara, A BMW 335i and 2 Harley Baggers and ALL of their speedometers have been higher than what several different stand alone GPS units as well as smart phones with GPS have read.

This is done intentionally by automobile manufacturers on American vehicles. I guess the idea is to not have you drive as fast?

On my BMW, I was actually able to get into the coding in the ECU and there's an option for setting the digital speedometer in the dash to the read actual speeds or +3% for the US market.

 

Which is why most of us think we're getting away with '10 over' the speed limit, when actually we're not.

 

Timing between mile posts my 04 is going 73 when indicating 75.

Have your father time between mile posts and do the math, 3600 (seconds per hour) divided by seconds per mile, so he can see for himself how far it is off. It is best to do this over 3 to 5 miles and average the time.

 

Yes and no. The reason you've given 10 miles over is to account for inaccuracies in your speedo and in the speed reading equipment of law enforcement. That's not everywhere though. VA state troopers for example are notorious for writing summonses in that 10 mph range, and this is coming from another cop...

 

Both of HD's that I've owned were optimistic, I ride with a handlebar mounted GPS 99% of the time and it's what I use when I want an accurate reading. Thought of calibrating it with my Power Vision unit but I'd rather it read to high than to low. My car on the other hand seems to be about dead on with my GPS. BTW odometer does not seem that accurate too.

 

GPS -



Speedometer was 101-102. Not making a speed run, that just was passing a semi on a 2 lane, very brief.

I passed one of those radar speed signs at 55 on the speedometer, had 46 on the sign. I just go 5 over on the speedometer to 40, then add 10.