Quote Originally Posted by 2wheelsforme View Post
Relationship between RPM and speed does not change with load, weight or headwind. They are mechanically linked.
Agree 99.9999%. BUT - there is one other factor at work here that can cause a very small change in the engine RPM based on the load (but most likely not noticeable on an analog tachometer). And that is tire slippage. There is always an incredibly small amount of slippage between the tire and the road - that's why it wears. If you stand on the brakes, the tire slides and the wear increases. If there were no slippage, there would be no wear. More load (weight, increased throttle, headwinds) all equate to more work and thus more energy used in the form of tire slippage assuming a constant of tire to road friction.

Bring on the flames!