I got a cheapo Garmin Geko 101 to track miles when road riding and to half-*** check speed when tuning or gearing. I got several readings around 78.5 mph (top of 80.5 on downgrade) with 13-42 gears, 22" razors, piped, jetted, and no airbox. To satisfy my disbelief I checked it against my truck and it read 1 mph slower than my trucks speedo at every speed and seemed to react quickly.

So I guess I'm asking if I can belive my GPS or does the max speed that stores hit irregular spikes giving me false readings?

 

ive heard they are within 2-3 mph.

 

I have an eTrex and It seems to be very accurate, I have had it in my truck and it is always very very close.

 

I'm a pilot and we use Gps as a primary source of navigation and it works with speed also. I can fly 6000 miles and never look out the window and it will line us up on a runway in Hong Kong.......so to answer your question, it is more accurate than your truck speedo......no mater what model you are using.

 

There is an accuracy gauge on all GPS's. Accurate to within 3' or 12' 40' etc. The lower that number on your GPS the more accurate your max speed will be.