My GPS on my CVO gives me the same speed as the speedometer. When I use a gps on my RKC, my speedo shows about 3 mph more than the gps.

 

As a rule, speedos aren't terribly accurate. I've had a Honda ST1300 where the speedo read 5-7% faster than the GPS or radar, and I ended up getting a SpeedooHealer to correct it.

On the other hand, all 3 of my Harleys are within 0.5 MPH of GPS at highway speeds, anyway. Go figure.

 

If your CVO is a Rushmore and is the built in one, it will always give the same speed as the speedo because it isn't reporting speed from satellites, but rather from the ecm. If it is a stand-alone GPS, then you are a lucky guy.

 

Maybe those things are true but, the math behind GPS speed calculation is exceeding accurate. Running down the road and watching the speed display will be close enough for the human brain. If accelerating or decelerating there may be a delay. But on average I trust GPS. In fact i got into my ecm when tuning my Roadie and corrected the factory speedo to match Garmin.

 

Gps may "lag" speed and/or direction changes but are very accurate at straight steady speeds. Speedos are purposely calibrated 3-5% fast and are effected by tire changes and/or wear.

 

On my Mazda B3000, the GPS shows me doing 60 when the speedo shows about 63-4.
Same GPS on the Electra Glide shows the bike speedo is slow by about 2.
Remember, the manufacturers also use the odometer with much the same error to short out the warranty claims too.
By the way: Who EVER said the non-polce bikes had calibrated speedometers?

 

I agree. I use my zumo in my truck as well as the bike. Truck is only a mile or two off bikes are around 4%

 

not so much an issue with hd. the warranty is not mileage based, but time based. no matter how off your speedo is, a day is still a day.

as far as calibrated speedos go, hd used to use them. the speedo on my 2002 sportster was calibrated. it'll say on the face 'certified'

 

GPS is right speedo and odometer are wrong.

 

Actually the odometer very close to right. It is not calibrated fast as the speedo is.