On Wednesday, July 19, 2017 at 2:22:17 PM UTC-4, Roy Tremblay wrote:
Bob F actually wrote:

+ The engine delivers ~25% less driving force to the wheel contact patch

That's crazy! Where on earth did that come from. 1" diameter increase
would only cause that change if you started with 4" O.D. tires.

Maybe I read the article wrong that was referenced by Ed Pawlowski?
https://www.carthrottle.com/post/how...t-performance/


Low profile tires compensate for the wheel diameter increase, so no
increase in tire diameter occurs, and no torque loss should occur.

+ Which results in a decrease in acceleration
+ And which decrease in fuel economy (presumably at all times)
It should increase economy. Just like driving in a high gear does.

I understand your intuition, which is the same intuition we all have but if
it's true what that article from Ed says, then 25% less torque at the
contact patch means 25% less torque to combat increased wind resistance at
highway speeds.

That means, in the words of the article, the engine has to 'work harder' to
combat that wind resistance.

You tell me how making the engine work (presumably a lot) harder increases
fuel efficiency.

Look at the energy required to lift a 100 lb rock two feet. I can do
it two ways, with a 2ft lever that provides low torque, or a 10 ft
lever that applies higher torque. Which takes more *energy* to lift
the rock? Answer: they both take the same amount. Now apply that
to the fuel economy issue.

Or take the example of a bicycle with different gear ratios. While
the ratios vary, and with some ratios you couldn't get up a hill,
while with other ratios it's possible or even easy, it doesn't
change the energy input required.