As i was following the sat nav most of the time i noticed a big difference in the speed between the sat and the speedo. At 70 speedo the sat only indicated 65. At 60 speedo only 56. Which is right? Anybody messured it accurately?

Rob

On a flat road the GPS is at its most accurate as it measures your speed across the surface of the earth. The speedo on my Tenere overreads by 5mph at 70 when checked against both my old Mio 269 and my new TomTom XL sat navs.

The speedo is around 10% out on the side of caution (as are most vehicles, except my Landrover, which for some reason is bang on, maybe the previous owner has a healer fitted!)

Another thing to consider is your GPS. It is not 100% accurate, at any one time it will be around 5% out. The more 'focused' GPS units (such as the Zumo) will give an indication of the accuracy.

Also, most GPS units will only cover 2 dimensional speed, so up and down hill will change how accurate the unit is. To add, the same units only measure samples it is not in real time, usually very short distances, maybe a few meters. This is demonstrable by slowing down and seeing how fast the GPS corrects your speed.



Speed limits are just that, a limit not a target and riding to them is risky. It is for this reason the Police have the power to 'give' a little, but it's not an obligation.

Have a look around the XTZ Forums, as this has been covered in a number of threads.

__________________
>-------<

Never underestimate the power of stupid people in large groups.

Mine reads similar to that.

My other bike and my car are far closer to the GPS.

I vote for the GPS being accurate and the Tenere speedo being wildly optimistic !!!

__________________

http://www.freewebs.com/my2wheels/

I checked today using a garmin 60 csx which has a highly accurate sensor and it would seem the speedo underreads by 4 mph

__________________
check out www.redbikejohn.com for all the latest race reports from the CHEC and enduroland.

Indicated 33mph comes up as true 30mph and 76mph seems to come up at true 70mph, so I'm with the 10% error also. Shame really as it means that when I was doing an indicated 102 I was nowhere near