No comprendo, senoir.

 

Wait, maybe I do comprendo, and if I do, I don't think your method would work, since the speedo should read about the same for both bikesat 5k in 6th- it's the actual speed, not indicated speed, that would be different.

 

Since the amount will be fairly linear, I like to think in percentages. For instance, I know that according to my gps the indicated speed is 10% high. At an indicated 110 I'm actually doing 100. So that stays pretty constant all the way through the entire range. Except of course at 0 mph it's totally accurate.
So if your sprocket change gives you a 5% difference then it's 5% through out the range. Or close to it. So an indicated 50, you would really be doing 50-5% = 47.5 Or if your speedo is already 10% off and you change then it would be 50-15%=42.5
So given that malbojah was nabbed going 86 but an indicated 105 means his speedo was a wopping 20% off. That's huge! I would suspect that typically the CBR speedo's indicate about 10% too fast, then add a 10% ratio change that would account for the 20% difference.

Is it too much to ask that manufacturers send accurate gauges? Geez... even the temp gauge is weird! The first quarter of needle travel is 180 degrees, the next half of travel is like 20 degrees... sheesh....

 

The speedo error is normally a fixed percentage, like e.g. 8 %. It will then show 54 km/h at 50, 108 at 100, 216 at 200and so on. If the front sprocket is changed from 17 to 16 tooth (17/16=1.0625) , that will add 6.25 % to the error, i.e. give 14.25% misreading in thisthe example.

 

It's kinda hard for them to do that. Think about the rear tire design: yes, our bikes call for a 170 size tire, but most of us out on a 180 because it's more readily available. That throws off the reading a little bit. Then the shape of the tire: is there a high point in the middle or is it a smooth curve across the carcass. And just how worn is the tire. And then you get into the sprockets and how far the chain is stretched

With the newer electronic speedometers, a couple of companys make a tool that going inline with the speedo hookup that allows you to change the reading to help correct some variables.

And I would be happy with an accurtate fuel guage.

When I dynoed my bike a couple of years ago, I took it all the way to the top (185) and the dyno report 165mph.

 

That was the point...

The measured mile works however.

Set the odo to 0. Ride a highway with marked distances. Ride 10 miles (100 is better). Comparo odo to the mile marker.

12 miles on the odo, 10 miles on the sign - that's your error.

READ - REAL divided by REAL
(12 - 10)/10
2/10
+20% error.

 

You are correct - The speedo error is ALWAYS a fixed percentage unless the clutch is slipping or you are counting very small changes in tire preasure and tire flex at very high speed.

This is becausethe transmission is a fixed set of ratios and the sprocket ratios are fixed.