How much does weight actually effect fuel consumption?
 

I have heard that you could see a 1-2 percent drop in gas mileage per 100 extra lbs, but would the effect of 100 lbs extra really be that small? If the effect is that small, I think it would be safe to say that DIY weight reduction is not likely to make a measurable difference in gas mileage. If a car weighs 2,500 lbs, 100 extra lbs is 4 percent more weight. Obviously weight is most significant when accelerating or going up a hill, but it would still increase rolling resistance and friction in wheel bearings and such. What do you think?

Per EPA every 100# of weight reduction is about 1-2% improvement in MPG.

So, conversely, every 100# of added weight is gonna be 1-2% MPG reduction (or more).

This has been discussed more thoroughly before, but in general weight is not a very significant factor, but your mileage will vary.

Obviously, frequent stop and go driving will be more impacted more greatly by weight, but at sustained cruising, it's an insignificant factor.

Rolling resistance is not affected too greatly with added weight.

For most cars, the biggest drag is aerodynamic.

I should make this my sig:

For a hypermiler, it's zero:

http://ecomodder.com/forum/showthrea...tml#post538484

The reason to save weight is performance, not economy.

Driving from Florida to Vermont with 500lbs+ of cargo in my Insight and pulling my trailer trailer with ~1000lbs in it, I averaged 57mpg driving through mountains, aiming for 60mph. I'm certain the trailer was not a net gain in aerodynamics, even though I cleaned it up pretty well. An empty car without the trailer probably could have achieved between 80 and 90mpg at those speeds.

http://i1072.photobucket.com/albums/...pslhk0twwv.jpg


Last fall when I picked up my tires, I averaged ~90mpg driving to get them (~50 miles) and got 54mpg on the way back, with speeds between 40 and 50mph.

http://i.imgur.com/fCFVBox.jpg


So, really, doubling the weight of the car and pulling a relatively aero-clean trailer (which almost certainly still adds some drag) is worth a good bit less in terms of fuel economy loss than leaving the hatch open in the back.