According to the radar trailers they put at the roadside around here my speedo is dead on.

 

I'm off about 5-6% (high on the bike speedo) compared to my Garmin. My dad is off a little more on his bagger. When I indicate 100 mph my gps reads about 94.

I trust the GPS.

My busa is worse. It's off right at 10%. At an indicated 175 at Texas World Speedway's front straight my datalogger tops at 157.

 

Mine topped out at about 95, but I'm 6'4", and somewheres around 270 lb. so IDK. I would say right near 100.

 

Could be that far off as the little radar trailers are on the side of main roads, usually doin 45 to 50 mph. At higher speeds with the percentages that would be a larger gap. I would trust a data logger before I would trust a Garmin though. When I put larger tires on my truck I used a stop watch and mile markers to figure the percent off on the speedo. It's a little difficult to do that on 2 wheels!
(it's 13% low btw I got it used and the fool that ordered it new got a 4x4 with little bitty passsenger car tires on it)

 

You got that backwards. The data logger can't figure out what your tires are doing, so it has the same problem as your speedo. They get their speed info by counting the revolutions at the transmission. Tires get smaller with wear, but still stretch some when spinning, so you never really know precisely how far you go for each revolution of the wheel.

The GPS might be a few yards or meters off in your position, but the rate at which your position changes is going to be VERY accurate in a straight line and steady speed.

If anything, the GPS will actually read a little low. A GPS calculates speed assuming you went in a straight line since your last position fix. If you didn't go straight, you actually had to travel farther in the same amount of time.

 

I've hit 115 on my 1200 And It could have given me more If I wasn't such a chicken

 

119 on my old 2004 883C with pipes, jets, SE air breather

 

GSX-R1000 92 MPH

























in 1st gear

 

I've had my CBR 600 rr at 170.

amateurs

 

Who cares how fast you can go ? I would rather ride safe and stay alive ! just my 02