On Wednesday, July 19, 2017 at 2:31:49 PM UTC-4, Mad Roger wrote:
On Wed, 19 Jul 2017 11:14:46 -0700 (PDT),
trader_4 wrote:

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 will agree with you that most people say that you get better gas mileage,
but we haven't seen a reliable article that says that yet.

I never said that most people say that you get better gas mileage.
I have no idea what most people would think.




All we've seen is the two articles that say nothing good performance-wise
will come out of increasing the overall diameter.

I understand your intuitive argument that one spin of the wheel is a few
inches more but if that one spin comes at a cost in the engine working
harder, then we may not get the economy we intuit.

I didn't say that either, in fact I said the opposite. You're looking
at torque, not energy expended. If I lift a 100 lb rock with a 2ft
lever or with a 10 ft lever, one involves 5 times the torque, but
the energy used is exactly the same.





The wind resistance has to be overcome.
Torque isn't only for starting at a dead stop.
Torque is also needed to overcome wind resistance (which gets appreciable
at speed).

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.

I did not consider when I originally asked that there are two situations:
+ Larger wheels with lower profile tires resulting in the same diameter
+ Larger wheels resulting in a larger diameter

Then you must not pay much attention to all those wheels out there.



Again, torque does not translate directly into fuel economy.

Maybe. Maybe not.

No, it definitely does not, per the rock example.


It's fair to ask whether fuel economy is increased when
the overall diameter of the tire-and-wheel assembly is increased.

So far, neither of the two articles has said that.

I agree with your intuition - but our intuition isn't good enough for a
correct answer. We need to find a reference that reliably backs up our
intuition.


Clearly you don't agree with my intuition, which is backed with physics.