SNIP
Physics is physics, and I have no doubt the bigger wheel shows a detrimental affect under the microscope. But in "the real world", which is what my test tries to replicate, there just was no statistical advantage of one over the other, given the power we were pushing and the weight of the cars.
Which data set is more "accurate"? That's up to the reader to decide
What happens to the HP if you take an engine with 500HP at 6000 rpm and double the weight of the flywheel? Nothing. It still has 500 HP @ 6000 rpm. It will have the same torque at 6000 rpm. The only difference is that under the same load it will take considerably longer to rev up (or down).
The problem is many dynos don't measure force at all. Instead they measure acceleration and *calculate* the force. If you did the above test on an "acceleration" dyno, the HP and torque readings would drop when you doubled the flywheel weight... but in reality, the engine would have the same HP and torque.
IIRC... the "****" testing was done on a high-end dyno that can actually measure *force*? That might be the answer.
Flywheels are like batteries. They store energy. At the same rpm a big, heavy flywheel will store more energy than than a small, light flywheel. That big flywheel is harder to get spinning and harder to stop... just like a big battery takes longer to charge and holds that charge longer.
Wheels and tires are like flywheels. It's not the diameter of the wheel that matters, but the weight of the whole tire/wheel assembly and how far from the center of the wheel the weight is concentrated. Adding heavier wheels and tires... or wheels and tires with the weight concentrated further from the center of rotation... will make the wheels harder to get spinning and harder to slow down. This
will affect acceleration and braking in the real world.
Were the 20" wheels and tires appreciably heavier than the 17" wheel/tires? Or was the combo lighter? How far was the center of mass away from the axis of rotation for each? Those are questions that need answering before you can say what effect a wheel/tire combo might have on acceleration/braking. (ie "straight line" performance)
P.S. The fuel economy change will be proportional to the number of starts/stops in the testing. At a steady cruise for the whole test, heavier wheels/tires will not make a difference in economy. Start speeding up and slowing down and now you have to expend a lot more energy to get those wheels turning...
