On 7/19/2017 12:27 PM, Mad Roger wrote:
On Wed, 19 Jul 2017 12:13:37 -0700 (PDT),
trader_4 wrote:

The problem is that you don't understand the physics.

I am not going to disagree with you.

That's why I want a reliable reference that backs up any claim of better
gas mileage with a larger diameter tire.

This article from Cooper Tire says that our intuition is wrong for example.
Do larger tires improve gas mileage?
http://www.dunntire.com/blog/Do-larg...ve-gas-mileage

"The common belief is that a tire with a larger diameter will cover more
ground per revolution, thus reducing overall gearing and enabling the
engine to run at lower revolutions per minute (RPM). People generally
associate lower RMP with less fuel used to travel the same distance. While
this may be true in a few instances, it is not the case for most vehicles.
There are too many variables to make a universal statement that larger
tires are more fuel efficient."

They then explain that the torque curve is critical, which makes the
equation too complex for a Usenet discussion instantly (because of the huge
number of variables involved).

Now you're just deliberately throwing obfuscation into the problem.
Sure there is more wind resistance at higher speeds. But you were
talking about a car moving at the *same speed* down the highway
and saying that it involves more or less energy because of differing
torques.

Huh? You misinterpreted what I said versus what was quoted but that doesn't
really matter since all we need is a reliable reference that backs up both
our intuition that the larger diameter setup will result in better fuel
economy.

So far every reference I can find (e.g., Car & Driver & Cooper/Dunn Tire
and the Physics Forum) say that is not the case.

So let's just look for a reliable reference that actually claims that
better gas mileage results from just changing overall diameter.

Here's the best I can find, from that Dunn/Cooper reference above:
"In a nutshell, the vehicles which stand to benefit from a larger diameter
tire are those that produce more torque than they need to in order to
maintain speed."

However, it concludes, probably correctly, that...
"There are just too many factors to consider to make general statements
that larger or smaller tires are more fuel efficient."


If you have a car geared for drag races, putting larger tires on it will
give you better highway mileage. Backing off on the leadfoot will give
you better mileage in the city.

If you own a car designed for mileage, not performance, the larger tire
will probably not improve the mileage, because that's not what the
manufacturer designed it for.