Thread: Tyre treads and sizes, gearing and fuel economy.

Agree, wind resistance is huge contributed at highway speeds. Getting your gearing right will help you maintain speed in 5th and take off in first

The right ratios on 255/85/16 skinny talls may give you very similar economy as standard set up. 285/75/16 being wider probably not so good.

I went from 285 to skinnier 255 recently noticed little improvement in economy, pretty much the same. But that was AT to MT.

I am also considering diff ratio changes as 1st is too tall and I sometimes have to hold 110kph in 4th!

So the consensus seems to be aerodynamic drag is the cause of the extra fuelrather than gearing or rolling resistance.

It doesn't surprise me at all. From previous experience and the fact that Imonitor fuel consumption very closely, I know the difference aerodynamic dragcan make.

I wonder if there is much thought into the underside of new 4x4 vehicles? Iknow higher end sports cars have near a completely closed in flat bottom andheat is considered through venting elsewhere.

Under body aerodynamics is not something to be played with lightly. I haveheard that just those mud flaps that people put across full width of the rearof their vehicles to protect their caravan or whatever they are towing increasespressure under the vehicle and reduces air flow. The reduction in airflow canthen reduce the cooling of the rear diff and greatly shorten the life of thediff. This is just one example.