Lately I have been noticing about a 5 MPH difference between my GPS and my Speedometer. The speedo shows I am going faster than my GPS shows. I know the speedo is supposed to be calibrated but the GPS is a time/speed/distance signal.. Given that distance divided by time equals speed I would tend to believe this more than my speedo. Whats the thoughts on this?

 

A gps is not a great speed measurement device. in fact the courts have ruled it to be unreliable for speed.

GPS doesn't get constant updates but random ones. GPS will usually lag.

 

but by the same token, speedometers have been known to be as much as 10% off. 5-7% is usually what most folks are reporting.

I know my speedo indicates faster than my gps. so I just go by what the speedo says (without compensating) and figure that it'll help keep me under 'ticketable' speeds. to hd I say thanks for looking out for my wallet

 

GPS is communicating 33K miles to at least 3 satellites to get your coordinates, that takes about 2 seconds. that lag time makes a difference.

 

I've had 3 dofferent gps units on my bike all 3 were at5-7% fast. depending on tire wear. I'm going with the gps being more accurate than the speedo.

 

those same units in my truck were dead on.

 

You can test it pretty easy with a stopwatch. Set the cruise at 60 mph. Start the time when pass a mile marker post. Stop the timer when you pass the next mile marker post. Anything other than 60 seconds on the timer means your speedo, or gps is inaccurate.

Speedos are usually off by a percentage. If the gap between what the speedo and the gps reads gets bigger as you go faster, it's probably the speedo that is off.

I have two different gps units that are very accurate. The speedo on both HD's I have owned have read 5-7% faster than real speed.

Dennis

 

My GPS is by far more accurate than either of my HD speedos.

 

Yup, GPS seems to be more reliable than any of my speedos. They all seem to be "slower" than the GPS by a few mph. I trust the GPS.

 

GPS all day long. HD gives us at least 3 MPH to make us feel better. Do a Google Maps or similar program route with mileage, if the route is at least 100 miles, guarantee your tripometer will give you at least 4 or 5 more miles when the trip is done. On a big trip I use the GPS to set my cruise, the speedometer is always 5 mph higher.