Weight, where is the loss?

[TheEnemy]

Originally Posted by ATaylorRacing

I use my 96 Geo 3 banger as a delivery truck. I usually carry from a min of 100 lbs to a max of 400 lbs. Over nearly 3 years I have found that every 100 lbs of extra wt in my car at the normal 60-65 mph costs me an extra one mpg.

My experience is a bit different, but I dont have much in the way of instrumentation so don't swear by it. When moving a few years ago we moved about 150 miles with about a 1000 foot climb in altitude. I would load up 1000lbs+ of stuff, and didn't notice a difference in FE, I'm pretty sure I would have noticed anything greater than a 1mpg loss, which would have been about 4%.

I was adding about 30% extra weight, which is about the same you added at 400lbs (guess). What % loss in FE is yours?

[Thymeclock]

Originally Posted by TheEnemy

My experience is a bit different, but I dont have much in the way of instrumentation so don't swear by it. When moving a few years ago we moved about 150 miles with about a 1000 foot climb in altitude. I would load up 1000lbs+ of stuff, and didn't notice a difference in FE, I'm pretty sure I would have noticed anything greater than a 1mpg loss, which would have been about 4%.

I was adding about 30% extra weight, which is about the same you added at 400lbs (guess). What % loss in FE is yours?

From your description, it appears you are driving a big, heavy vehicle to begin with, seeing that you had 1000 lbs. in it. With larger, more fuel thirsty vehicles that have bigger engines, they tend to burn approximately the same amount of fuel whether empty or fully loaded. If there is any difference, it will be slight, or at least harder to discern.

[Thymeclock]

Thymeclock: Of course, increased mass means that the pull of gravity will be stronger. The added weight comes at a disadvantage for uphills. However, my initial post assumed level roads.

Then of course, you are correct. Sometimes gravity is your friend, and sometimes it's your enemy.

[TheEnemy]

Just looked at the weight of my truck, 2380lbs, GVWR a little over 4000 and it runs a 2.4L 4 banger. And I was getting about 26mpg regularly at the time.

[brucey]

Car weighs 4000 lbs with a full tank of gas and me in it. I added roughly 150 lbs of weights, my toolbox (75 lbs), and a hydraulic jack (100 lbs) and went about my trip. This is an extra 8% of dead weight.

This weight could be felt on the downhill glides, but not the uphill pulses. I averaged 37 mpg for an entire tank of 600 miles. Which is roughly what I normally get.

I don't doubt it is making a difference. But in this car, in this terrain, with this driving style, it really seems to average itself out and make no noticeable difference.

[Dr. Jerryrigger]

Originally Posted by brucey

Car weighs 4000 lbs with a full tank of gas and me in it. I added roughly 150 lbs of weights, my toolbox (75 lbs), and a hydraulic jack (100 lbs) and went about my trip. This is an extra 8% of dead weight.

This weight could be felt on the downhill glides, but not the uphill pulses. I averaged 37 mpg for an entire tank of 600 miles. Which is roughly what I normally get.

I don't doubt it is making a difference. But in this car, in this terrain, with this driving style, it really seems to average itself out and make no noticeable difference.

This is quite interesting. I seem to remember you having a 2.5L, and frankly, I find the 2.2's to be over powered for a Legacy. So your engine should have no problem with the load difference when climbing.

One thing no ones brought up is the aerodynamics of a loaded car. If we're talking high way speeds and flat ground, and not considering acceleration at all, then the variables are: the amount of tire touching the road, and how high the car is sitting.
The aerodynamic change would be quite minimal, but it would likely favor the loaded car. But how it's loaded could make a difference.
The tire resistance is quite obviously greater when loaded, normal people could compensate by uping the pressure, but eco modders like to kill the middle tread first


I used to commute 27miles with more than a 1000 foot elevation change (which was really only in the first 10 miles). I was planing on getting some water tanks. Fill them at home, and then dump them at work, or better yet, wile driving once i got into the valley. But that was not a winter project, and I've moved into the valley since.

[brucey]

I think I'm going to do a more scientific test when I have some time off on Pulse and Glide runs with/without extra mass.

Yeah, I think the motor don't seem to mind the extra weight at all either, climbing.



(Wheel figures, and mine is the SOHC)

[RobertSmalls]

Originally Posted by brucey

(Wheel figures, and mine is the SOHC)

Lucky you; that looks like the better torque curve.

It's always frustrating to see how high most dyno plots start. I used to upshift my Subaru at 2000RPM, so this plot captures none of what I care about.

[Dr. Jerryrigger]

Originally Posted by RobertSmalls

Lucky you; that looks like the better torque curve.

It's always frustrating to see how high most dyno plots start. I used to upshift my Subaru at 2000RPM, so this plot captures none of what I care about.

so true, I also up shift at about 2k (with an automatic, so with minimal throttle)
But once your on the highway in top gear this chart becomes useful (well not so much if you have a 2.2 like me)

[brucey]

With the automatic in the subie: I've found that accelerating quickly(1/2~3/4 throttle) (at least to 30 mph or so) is no more harmful than accelerating slowly. It gets you into the wonderful top gear much quicker that, at least according to the scan gauge, it makes no real difference.