Effect of Weight Reduction on Fuel Economy
 

We know that weight reduction in cars helps fuel economy to improve, but understanding that deeper will help with cost benefit decisions. Ricardo produced an excellent report which deep dives into the topic, and I have pulled out what I think is the key ideas that can help a back of the napkin calculation.

Let's start with the simplified data: 

Looking at the table above, weight reduction has a larger fuel savings effect in city acceleration than at highway speeds. Takes a bit more energy to get a car moving than to keep it moving. From my experience, 5% is a realistic weight loss target for most cars.


Things like spare tires, lightweight wheels, seats and batteries are some examples of items that can be changed to achieve this goal. There is an added advantage of better dynamics and acceleration for the vehicle too! 

The ratio of a car's power to it's weight determines what it consumes, and how it feels.

 

Source: 
Ricardo - Impact of Vehicle Weight Reduction on Fuel Economy for Vehicle Architectures