A lot of confusion, here!
The transmission gear ratios (1st through 6th), rear tire size, or the size of the final drive sprockets have nothing to do with what the Tachometer readout is.
That is abolutely right.
The Tach readout is set by the ignition system.
Changing rear tire size (ie. diameter), final drive sprocket sizes changes the true road speed of the bike as it relates to the RPM displayed by the Tachometer, as well as the indicated speed displayed by the Speedometer. That the true road speed has changed, it causes the Speedometer to display a + or - error.
Mike I'm sorry, but you wrote "as well as the indicated speed displayed by the Speedometer", which is wrong:
Yes, it does change the true speed
But never the indicated speed.
it causes the Speedometer to display a + or - error.
But it still indicates the same speed at the same rpm of the engine!
b/c the sensor is only reading the driveshafts rpm
Which have not changed.
Which can not change.
Unless the clutch slips!
Transmission gear ratio
Nothing, that comes behind/outside the driveshaft, has anything to do with the indicated
speed on any Speedometer.
"Only" with the real speed!
Not only on our bikes.
Not only on driveshaft sensors.
This (CBR250R) speedo is set to show always the same km/h at the same rpm of the driveshaft.
And the driveshaft is hard connected, thru the chosen gear, with the rpm of the crankshaft.
In our case, ~6000prm at the tach are ~6230 rpm at the driveshaft.
And always, without a Speedometer Corrector, the Speedo "read" this amount of rpm at the driveshaft as about 100km/h.
Like he did from the first day.
As long noone "tells" the Speedo this with a correction factor, it indicates a wrong speed.
Which would be right, with the right chainset ratio, the right tire pressure, the ....!
it's called indicated, because it is set by honda with several given factors:
xy,z rpm of driveshaft + chainset 14/38 + tiresize 140/17-70
Change one thing behind the driveshaft, the setup is wrong.
But it still indicates the same numbers. It only reads the driveshaft rpm
If rpm on Tach is 500 higher at the very same indicated speed and gear, there is only one mechanical thing, that will let the rpm rise but keeps the Speedometer readout unaffected: Clutch
I can't think of any electrical problem, that could affect the tachometer to read 500 rpm more, as the engine is turning, so....!
By the way: Has anyone "seen" Webster?