... I had a complete flat on the freeway at 65MPH. When my speedo indicated 65, I was doing slightly less than that (and my RPM's were lower as well). GPS said actual speed was 6 MPH less than indicated.
Ah, here you point it out yourself:
You're fighting a lost fight, mate!
I even believe you this "and my RPM's were lower as well"
Because it is a analog tach, there is "a bit" difference to expect.
Every time, every day, every now and than.
But not 500 rpm on ~65mls/100km/h!
That is a 12% difference!
That would be a very flat tire, dont you think?
Even flater as your "complete flat" tire, you "did" 65 mls/h with
And your "speed was 6mph slower", on a flat tire, because of a flat tire?
Here goes the myth of "mls speedos are spot on", huu?
Or are you saying, with your flat tire it was 10% less real speed?
And, of course, you where driving on the rim, 65 mls/h, right?
And had nothing else to do, as to check GPS, Tach, Speedo. And all together.
I get it now!
It's not about real speed, this topic, it never was!
So forget about gps and such.
This topic is about shown speed on the speedo, compared with the rpm on the tach.
"I've noticed over this last winter that my tachometer indicates about a 500 RPM increase than when I was riding last summer."
The real speed, and the speed, that honda lets show the speedo, has nothing to do with each other. They (Honda) "tell" the speedo, to show this "exact" speed/numbers
at that amount of rpm of the driveshaft!
And as long you don't change the gearing between the crankshaft (thanks to CBRLOCAL to tell me about that mistake) and the driveshaft, even in case you change the CBR 250 rearwheel to one from a groom, the bloody speedo will show 100km/h at about 6000 rpm on the tach.
Because the connection/ratio from the crankshaft to the driveshaft is fix, set by the chosen gear, not negotiable, as long the clutch is working and closing 100%.
Or maybe simple:
Put the bike on a pitstand
Run the engine in 6.
Go to 6000 rpm
read the speedo
Now dismantle the rear wheel and the chain
With this setting of reading the speed at the driveshaft, RPM on the tach and km/h (mls) are "hard" connected. With the ratio of every gear in the gearbox.
Nothing behind the driveshaft has influence on the shown speed to tach rpm's.
NEVER, with this setting!
But even reading the speed at the wheel will not change that!
Because the speedo is not knowing, if the tire is flat or overpressurized
Or a 17", it's made for, or a15", a12" rim
It reads rpm's of the wheel. And is showing, what is the default setting (in meter) for (one rpm) x rpms.