Incomprehensible fuel mpg

[Bellow]

Back to the OP's predicament... any possibility there was a binding brake which then freed? Maybe a handbrake cable nipped/displaced during tyre fitting that righted itself later?

On the subject of winter mpg. Everyone is red hot on the need to check tyre pressure cold and accepting that the pressure increases with the generated heat during driving. But no one equates the lower tyre pressure in cold conditions to loss of mpg.

 

[Bobby Dazzler]

....which is surely offset by having to use less throttle for the same amount of power?????

What’s the energy value per unit volume of air?

 

[DSM10000]

What’s the energy value per unit volume of air?

Depends on it's temperature!

 

[Bobby Dazzler]

On the subject of winter mpg. Everyone is red hot on the need to check tyre pressure cold and accepting that the pressure increases with the generated heat during driving. But no one equates the lower tyre pressure in cold conditions to loss of mpg.

If the pressures are checked and adjusted regularly, then the “cold” pressure will be the same at the beginning of each journey regardless of season and ambient temperature.

The tyre pressure will increase during the journey, and theoretically this would happen at a very slight slower rate due to the greater temperature differential with the ambient air and road surface, however tyre carcasses aren’t a bad insulator reducing dissipation.

I have no data to support it, however it theoretically might make a difference in short journeys but I personally believe that it’s similar to denser air increasing aerodynamic drag, ie outweighed by other influences.

 

[190]

On the subject of winter mpg. Everyone is red hot on the need to check tyre pressure cold and accepting that the pressure increases with the generated heat during driving. But no one equates the lower tyre pressure in cold conditions to loss of mpg.

Tyre pressure has only a minor effect on MPG. It depends on the type of driving but the average figure I arrived at after some research was a 10% drop in pressure reduced mpg by only 0.8% which for me makes a nonsense of the higher pressures that manufacturers would have us use at a substantial sacrifice in ride quality.

For the effect of a truly gross reduction in pressure, Auto express did a a test with pressure reduced by approx. 45% and still only found a reduction from 30.5 mpg to 29.7 mpg or 2.6%. It's hard to get your head around it being such a small reduction but while it will have increased rolling resistance substantially, rolling resistance is only a small part of the equation at higher speeds.

Worth reading this for what else has an impact on MPG

The mpg mythbusters | Auto Express