Improving Your Mileage
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
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
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
Losses and Inertia are counter-forces that act against the
Inertia is the mass of the vehicle at rest that
must initially overcome.
Losses include rolling resistance from the load on the tires,
and parasitic wind drag from moving through the air.
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
Typical Shop Vehicle Maintenance Schedule
(Click on thumbnail, above, to see expanded view)
© 2014, Simon R. Mouer III, PhD, PE
All rights reserved.