It doesn't have to be linear.&nbsp\\; The sensor feeds the computer which in turn drives the speedometer display.&nbsp\\; The computer can interpret the pulses from the sensor any way it pleases.

 

My speedo says I am going 3 mph faster than the zumo 550 displays. I guess I haven't paid much attention to it at lower than highway speeds. At 70 on the speedo, zumo says 67. Stays about 3 mph off until I get up to about 100 mph.
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After 100 mph, the speedo starts climbing faster than the zumo. When the speedo is buried, the zumo says 114 mph.
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Dennis

 

Same here... GPS shows 3 mph slower and odometer is off (reads high) as well.

 

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My speedo sucks ... 2008 Ultra Classic
When my speedo shows 75, I am actually doing 69-70 (6.7% deviation). Dealership says that is acceptable (to them, NOT to me) ... idiots.
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I'm looking at the SpeedoHealer and the SIM-1 product from Dakota Digital. If I can ever figure out how to install one of these, I'll probably do it.

 

The speedo difference also runs your odometer up artificially.&nbsp\\; The bike will show more miles than it actually has. It also makes your gas mileage look pretty good.&nbsp\\; :-(
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I've got just the opposite.&nbsp\\; My odometer records less mileage than actual.&nbsp\\; Checked it with Gps today.&nbsp\\; Across 21 miles, it was off 3/10.&nbsp\\; Going to try it on a longer ride to see if the ratio holds up.&nbsp\\; So, I guess I have been underestimating my mileage, and I was actually rather happy with what I was getting.&nbsp\\;

 

We have those self contained towable radar machines everywhere here in CT.&nbsp\\; I can't help but blow threw them at twice the speed limit and set off the lights anyways they usually read about 3mph slower at 60.

 

On my '07 SG my GPS shows 2mph lower than the speedometer at highway speeds, and the GPS is correct.