Higher tire PSI lower MPG

Tyres often fail when they are punctured on a truck before they run completely flat and the culprit is heat.
A tyre that is inflated to a lower pressure will run at a higher temperature than one at higher pressure. This is where economy losses accrue with soft tyres and also why tread compounds make a difference. The greater the difference between the tyre temperature and the ambient temperature the greater the heat loss to the atmosphere. This works just like a friction brake in that tyre movement due to under inflation converts kinetic energy into heat which is lost to the atmosphere. This heat is generated both at the tyre contact with the road where lower pressures lead to more movement of the tread as it contacts and leaves the road (push a car with a under inflated tyre and you can hear it), and within the tyre as it flexes the friction within the tyre like how bending a piece of wire many times makes it hot.

Now to check the theory about your tyres growing I suggest this test.
Next time you have a barbecue on a propane fuelled barbecue and run your gas bottle empty measure around its girth before and after refilling it. The difference would be what you would expect a steel radial tyre to grow by when inflated beyond the car manufacturers recommended pressure to the tyre manufacturers maximum pressure. I suspect there will be no measurable difference.

 

Now I have not measured this, but I think the laws of Physics would dictate that the area of a tire's footprint (in square inches) times the air pressure in the tire (in psi) would equal the load on the tire. Do this for each of the four tires and add them to get the total weight of the car.

Or, to work backwards, you could use the weight of the car, make a few assumptions about relative weight of each tire, and divide by the pressure to estimate the amount of each tire area that touches the ground.

Have any of you measured this to verify?

 

I havent measured but I can generally see if a truck is overloaded by looking at the tyres, If they have a big contact patch they are generally loader to or beyond the limits or flat. This is part of my job.

 

1) Find the modulus of elasticity for steel.
2) Calculate the hoop stress for tires inflated to 32 and 44psi, respectively.
3) Calculate strain in the steel belts of your steel-belted radials.
4) Calculate change in diameter. Hint: You will need a lot of decimal places unless you use small units. (Metric is your friend.)
5) Rejoice in your new-found understanding of why something else is responsible for your lost mileage.