Quote:
Originally Posted by RedDevil
Jason Fenske (Electrical Engineering channel) had an interesting take on tire and wheel size versus economy:
[Video omitted ]
He focused on the effects on economy at 75 mph from a theoretical point of view, but also using EPA data. And he doesn't waste time; it is 11:47 packed with data and calculation.
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The problem with the video is that he exaggerates the affect of aero (He used 100mm more: Normal would be 10mm to 20mm increase), the rolling resistance effect (He uses coefficients of 3 times when the extreme range is about 60%, and like to like is a percent or 2.), then doesn't address the weight (moment of inertia). He then takes data submitted for the Mulroney label (the one on a new car's window that says the MPG's) which is the combination of all 3, and declares that to be the definitive difference.
What he leaves out is that the coast down values come in increments - which is one of the reasons why there is a difference in the models (15%, 8%, and 9%) for more or less the same 2" wheel diameter difference.
Do not get me wrong, I think his overall conclusion is correct, but he is doing a smoke and mirrors presentation and exaggerating the difference.
Here's my take on the tire portion of this:
Barry's Tire Tech