Improving Your Mileage

Understand your Engine Understand your Vehicle Understand your Mileage Measuring your Efforts Cost Effectiveness
The Four Cycle Engine Gears & Wheels Mileage vs Gear Vavg vs mpg miles / $  (mp$)
A Four Cylinder Engine Force at the Wheel per gear Acceleration vs Mileage Upper & Lower Bounds THEN
(20 years ago)
The Power Curve   Hyper-Mileage   NOW
        Then vs Now

Understand your Vehicle

Gears & Wheels
The engine by itself cannot produce sufficient force to move the vehicle from a dead stop.  We use gears to multiply the engine's force.

In the animated GIF to the right is depicted how a manual 5-speed  transmission might use gears to multiply engine power to the vehicle's wheels.  When we so multiply power, we simultaneously divide speed by the same factor. 

 An automatic transmission will have a different design, but the same purpose.

All motor vehicles use gearing to achieve a mechanical advantage (more power to the wheels) at the expense of speed.

Force at the Wheel per Gear
In the chart to the right are graphed the engine power transformed through the vehicle's gears to a force at the wheels.

For each gear, we have a different mechanical advantage (and corresponding penalty in vehicle speed.)

1st gear is the lowest gear.  It serves to break the at-rest inertia.  The resistance force of inertia is depicted by the dashed red line.  1st gear gets a moving from a dead stop, but not very fast.

2nd and 3rd gears allow us to progressively move a little faster, but at significantly less force at the wheels. 

4th and 5th gears allow us to move up to even higher speeds (while losing even more force at the wheels) until the opposing forces (losses -- solid red line) catch up with us and we can no faster. 

Losses and Inertia are counter-forces that act against the vehicle. 

Inertia is the mass of the vehicle at rest that must initially overcome. 

include rolling resistance from the load on the tires, and parasitic wind drag from moving through the air.  

Vehicle Maintenance

Just like the engine, the rest of the vehicle, especially the drive train -- from the transmission down to the tires, have regular maintenance requirements in order to perform at peak efficiency.  And the owner's manual will have a recommended schedule for inspection and replacements.

Fluid levels for the radiator, transmission, power steering, and brakes need periodic checking and re-topping.  

Tires, which directly transmit the engines power to the road, especially need attention.  Keep them properly inflated, and replace worn tires in pairs.      

Typical Shop Vehicle  Maintenance Schedule
(Click on thumbnail, above, to see expanded view)

2014, Simon R. Mouer III, PhD, PE 
All rights reserved.