Here is the data I collected:

Speedo / Bike GPS / Uleysee GPS
20 / 20 / 19
30 / 30 / 30
44 / 44 / 44
61 / 60 / 60
72 / 70 / 70
82,83 / 80 / 80

The pictures show it too. I think I was incorrect when I said 4 mph as at 80, it is more like 2-3 mph. Except for when I first got the bike, I don't have speed displayed normally. I can say that in my neighborhood, I have two active speed signs. I can't go past them fast but they say 40 when my speedo and gps say 40 as well. Not much help for this speed.

The bike GPS and my Ulysses app always read the exact same no matter what the speedo said.

 

I checked mine today, Bike GPS and speedo up to 80 mph were pretty much the same

 

Thanks guys, having been only riding a year now, so I had no clue the speedo was off. Checked today and sure enough. Pulled out my laptop and got the Thundermax adjusted. Now to check tomorrow and see if I got it right.

 

Personally, I don't give a ****. As long as it's fairly accurate, who cares?

The only speedo I've owned - car, truck, motorcycle, whatever - that's dead-on is the one on my '94 Dyna, and it's mechanical. Every other speedo that I've ever bothered to check always reads slightly faster than I'm actually going.

I read something about the manufacturers intentionally designing them like that to prevent them from being sued over speeding tickets due to their speedometers indicating lower than the actual speed of the vehicle.

Don't know if that's true or not, but it makes sense in our lawyer/lawsuit-based culture.

 

I wouldn't have noticed it except that my wife was following me in the car one day and called me to ask if everything was ok because I was riding at 75mph in an 80mph zone. While still on the call I bumped it up to 85mph on my speedo and she said her Garmin was now showing 80mph. Like one other person posted, I would like to at least do the speed limit, so knowing how fast I am really going matters.

 

This whole thread begs the question,
"just how accurate is the speed reading on a stand alone GPS??"

 

I think pretty damn accurate. An even bigger question is "how accurate is the radar gun in the cop's hand?" I think they're required to be calibrated fairly regularly but I don't really know.

I also find it annoying that the speed and mileage are so far off. Really looking forward to the FP3 update with the new speedo calibration.

 

Wow, this is impressive. I didn't know that this was going to happen. Looking forward to it as it seems my speedo is up to 5 MPHs off as I approach the higher speeds as I have compared vs. GPS.

 

It was mentioned, with screen shots, on another thread somewhere. Looks really cool - I think it uses your phone GPS to automatically calibrate the speedometer. No manual tweaking and experimenting necessary. There's no release date yet.

 

Bike speedo 70, external Garmin 67...never checked the built in, I'll do that next time I'm out. Good that you're actually going slower then you think but bad that the bike mileage is more then the actual (Garmin) reading.