Car Weight impact on Mileage

How much does weight in the trunk of the car influence the mileage I get? If the trunk carries 20 pounds worth of stuff, or 100 pounds worth of stuff … how much does it matter in terms of mileage?

The more mass or weight of a vehicle the more energy it requires to get that mass or weight to move. So it requires more fuel to get the vehicle to start to move.

Take a wagon with nothing in it and pull on it. It takes little energy to get it to start to move. Now pile a bunch of cinder blocks in the wagon and then try to pull on it. It takes more energy to get the wagon to move. So the more extra weight in the vehicle, the more gasoline it uses.


Experiment. Drive A Couple Tanks With A Hundred Pounds And A Couple With 20 Pounds.

I’ll bet it doesn’t make much difference. Our Dodge Caravan gets weighs nearly two tons and gets about 28 MPG HWY with one occupant or three.

Besides, trunks were made for storing golf clubs, several sets at a time.



If you ran mileage tests with a control unloaded trunk, and another run with a fully loaded 500 lbs in the trunk you might be able to measure a difference. With other variables, such as wind it is likely you couldn’t control the variables enough to have a reliable test.

Over the life of the car a less loaded trunk means a few less gallons used. So carrying only what you really need in the trunk is good general practice, but hard to see any benefits in the short term.

If you reduce weight in the trunk of your car by 100 lbs., you might never notice, but you would save fuel. Reduce weight by 20 lbs., and you would definitely not notice the fuel you save, but you would still save fuel.

The methods we use for measuring fuel economy, measuring the amount of fuel needed to fill the tank and recording the odometer readings, are so crude that they really only amount to estimates. However, reducing weight in your car, even small amounts, will save fuel in the long term. Just don’t expect to notice the fuel savings. So don’t go crazy. Don’t remove something that can’t stay out long term, like the spare tire or the emergency jack. If you only play golf once a week, take the clubs out when you are done. If you bowl in a league, do the same with your bowling bag.

With 1 million plus miles of driving a commercial truck and keeping close records of the costs it is with some certainty that I can say the fuel economy is not noticeably affected by increased loads up to a point. A half truck will be as economical carrying 1,000 pounds as it is empty. But once the load reaches the point that it requires pushing the shift points up to considerably higher rpms there is a significant increase in fuel consumption. That seems somewhat in line with both previous posters, I guess. But, loads attached to the roof or above the rails of a pickup, regardless of the weight, will drastically increase fuel consumption. In fact, a trunk mounted bicycle rack can decrease fuel efficiency by 10% as noted in a recent trip.

Let’s see, if the car weighs 2500 pounds and averages 25 mpg, 100 added pounds should take 1% more fuel, bringing the consumption down to 24.75 mpg.

This is a rough estimate, of course. The weight will affect the amouont used to accelerate, go up inclines, and rolling resistance, but not wind resistance. So, if the trip consista of hilly terrain and low speeds the effect will probably be more than if it consists of all highway mileage.

A little weight makes a little difference. What’s hurt cars these days is that they weigh 500-1000 pounds more than cars 30 years ago. Course, they’re safer, faster, better in most every way, except mpgs.

FWIW, my comment on MPG and bike racks is from a recent trip to the west coast. On the return, sans bikes, the 2007 Toyota Camry 4 cylinder got 33+ mpg with the cruise set at 79 mph from S California to Mississippi. I recall working on Beetles in the 60s and being quite proud to get them up to 27 mpg and they had no AC or power options of any kind. My ambivalence toward technological innovations is well grounded I think.

In regards too a cars weight and safety how are the statistics relating too weight reduction and increased accident fatalites computed? I have read claims that lighter cars will result in more deaths and even a number of how many more.I will say that it does seem reasonable that a lighter car will not protect its occupants as well but to actually be able to predict how many extra deaths is stretching things.

I do think that reducing a cars overall weight is the quickest and easiest way too increase its mileage but only to a point, you can only shave off so much weight easily,then things start getting tougher.

I think it would depend more on how good your rear springs were. If they’re crappy, and it makes your vehicle squat down at the rear wheels (like those 90’s Buicks we’ve all seen that we suspect have dead bodies in the trunk), your front end would raise up, lowering your coefficient of drag and therefore impacting your mileage.

Assuming your springs are OK, the extra weight would be a factor, but only during acceleration would the weight carry any appreciable significance from a mileage standpoint.