If the speedometer is off by 5% then how much is the odometer off?

My understanding is that the odo is pretty much spot on. I've never checked it with my GPS though. I will next time I have it on the bike.

If the speedometer is off by 5% then how much is the odometer off?

My guess would be 5%

If the speedometer is off by 5% then how much is the odometer off?

My '09 C14 reports accurate speed with the aid of a Speedo Healer that was calibrated with the aid of a GPS.  This apparently does not effect the odometer as it is 3% pessimistic by reporting 97 miles traversed when the correct distance is 100 miles.  I have verified the accuracy of ground position sensors as I own three of them and a fourth is incorporated in my Escort Passport radar detector.  I have compared their speed and distance readings with one another and they all show identical information.

Where does the 5% number come from?  My speedo is off more the faster I go, assigning a value of "X percent" isn't realistic.

Where does the 5% number come from?  My speedo is off more the faster I go, assigning a value of "X percent" isn't realistic.

It can be realistic if the error is linear.  For example:

At 40 mph, 5% equals 2 mph or a reading of 42 mph.

At 60 mph, 5% equals 3 mph or a reading of 63 mph.

At 80 mph, 5% equals 4 mph or a reading of 84 mph.

At 160 mph, 5% equals 8 mph or a reading of 168 mph.

More than likely though, the reading is not linear and deviates somewhat.  However, applying a description of the error expressed as a percentage is convenient and satisfies the demands imposed by the lack of precision required to express the experiences of the people reporting their own speedometers' varying inaccuracies.

The 5% used in your question and in my example is the number applied to the experience of the person who wrote it.  A larger or smaller percentage may apply to the speedometer readings of others. 

Where does the 5% number come from?  My speedo is off more the faster I go, assigning a value of "X percent" isn't realistic.

What you described when you wrote "My speedo is off more the faster I go..." is precisely what a percentage is. If your speedo reads 5% high, then when you're really going 20 mph your speedo will show 21 mph (off by 1), but when you're really going 100 mph your speedo will read 105 mph (off by 5).

+1, the % deviation is an estimate and is far more accurate than an absolute number. I tested by bike at 30, 40, 50, 70, 80 and 85 mph to get the estimate. Did not test it above 85. Other riders confirmed the 5% as a reasonable estimate.

That's ok Steve, you take nice pics at least. Leave the math to Lita.     

That's ok Steve, you take nice pics at least. Leave the math to Lita.     

My experience with my 2008 was about 5%. On my 2012, I would say it is closer 10 3, 3.5%. When my GPS says 100 Km/h, the odometer shows around 103, 104. So I would say the difference might only be due to tire wear. Both error overestimate the actual speed based on my GPS. I trust the GPS value to be true, not the odometer.

My experience with motorcycles odometers have always shown to overestimate the actual speed while my cars have always been in accordance with my GPS. Before the GPS, I would drive side by side with a friend in a car and the motorcycle was always showing a higher speed. I don't know if it's the fact motorcycle is a sport and we all know sport is very closely related to performance so... If your motorcycle shows you are going faster than yoa actually are going, a sportsman gets some sort of satisfaction from it...Faster )-60 mph (you get to 60 faster)... I drove it up to 155mph... etc. etc. (155 sounds faster than a real 147)

That's my theory on why motorcycle odometer are off on the high side...always! (to my experience)

My last three cars were right on the button. My last four bikes were off on the high side of exactness.

Mine is not a linear 5% from 20 MPH to XXX MPH.  Not even close. Maybe by Kawasaki's "accuracy acceptance scale" it is   

Mine is exactly 5% off at 80 actual (84 indicated), but it's pretty much 4 mph from 30 to well over 100, then it creeps up to about 5 mph off when you get WELL into triple digits.

My experience with my 2008 was about 5%. On my 2012, I would say it is closer 10 3, 3.5%.

That's interesting. My '08 shows a fairly consistent 3.5% error on the optimistic side across the speed range compared to my Garmin. But I tested only until 165 mph and it wasn't really appealing to take my eyes off the road to read the instruments...

To the OP's question, the odometer seems more accurate than the speedometer, but still counts about 1.5% more mileage than my Garmin when I'm back from a long tour.

The oddest situation happens with the K1600 from BMW, which comes from factory with the navigation system, so you would think that the speedo and the GPS on the bike would show the same speed. They don't. The speedo still shows about 3% faster