On Wednesday, July 19, 2017 at 12:53:09 PM UTC-4, Mad Roger wrote:
On Wed, 19 Jul 2017 12:17:36 -0400,
Frank wrote:

I found it interesting and first sentence says it, "They look cool."

I agree that people do things for looks alone, but what is strange is that
there doesn't seem to be a single beneficial performance impact of an
overall larger diameter "tire-and-wheel assembly".

I wasn't expecting huge performance gains, but I would have expected at
least one or two benefits - and not all negatives based on the two articles
noted.

If the diameter of the wheel and tire assembly increases by one inch
overall due to the one-inch increase in rim size - and assuming everything
else is kept equal in materials and aspect ratio and tread width - then the
two articles stated...
+ The engine delivers ~25% less driving force to the wheel contact patch
+ Which results in a decrease in acceleration
+ And which decrease in fuel economy (presumably at all times)

I don't see the decrease in fuel economy. Just because a car
accelerates slower doesn't mean that it will use more fuel.
I think there is a difference in rolling resistance between tires
of different diameters, but as said previously, when going to
larger diameter wheels, the tires other characteristics, eg profile
change too. That would have an effect on rolling resistance.



+ And unsprung weight goes up by a few pounds

The main astounding number is the fact the torque felt at the wheels is
astoundingly less for a single inch in overall diameter change.

Presumably that torque loss happens at all speeds (why would it not?) so
that denies us the one intuitive performance advantage of highway MPG.

Again, torque does not translate directly into fuel economy. I
could apply less torque over a longer time period, get to the same
speed and not necessarily use more fuel.