Weight Reduction for better FE
 

I was thinking about some of the things you can do to your car to get better fuel economy and thought weight reduction is a great way to up the MPG. The rule of thumb is for every 100 lbs you shave off you get 1-2 % better MPG.

I have a Civic VX and I am going to weigh my spare tire and other parts when I get a chance. I will update this post accordingly so please checkback.

Weight Reduction:

Spare Tire - Take out (18.6 lbs)
Jack and Tools - Take out (4.9 lbs)
Hood - upgrade to Carbon Fiber or Alloy Hood (appx 15 lbs savings?)
Fenders - upgrade to Carbon Fiber or Alloy Hood (appx 5 lbs savings?)
Passenger Side Seat - Take out (appx 15 lbs savings?)
Battery - Upgrade to Lighter Weight Battery (approx 25 lbs weight savings)
Wheels - What could be lighter than the Civic VX rims?
AC Compressor - Removal ( I will weigh the weight savings, appx 15 lbs)

What other mods can you think of?

well, skipping the blah-blah about stripping a car for FE and the ramifications, here's some examples:

1.strip out the sound deadener under the carpet. It's tar based, and very heavy. My car has (had) 45-50lbs in this.
2.The carpet. Mine was 22lbs. It still is, somewhere in a trashpile....
3.Misc. metal parts on the car. I had a few parts that if I crash, aren't going to help structure. Out they go. About 10lbs I lost there.
4.Wiring: holy moly, I stripped mine down, removed 35lbs in copper wiring. Who would have thought?
5.Power steering. Lots get by without it, its worth looking into at the least.
6.Single ply sidewall tires, short tread, etc. Good tire selection can save a lot of weight. Study the tires you want, and compare weights. Makes a difference.
6.Driver. Seriously. Lose weight if you can. I can't, I'm already a twig.
7.Keep it clean inside, don't haul anything more than you need, bare minimum.
8.I went even crazier and took a dremel to any small tabs or weld nuts of metal that weren't needed. All the little plastic tabs holding the wiring in place, all the tape wrap. It adds up.

MT is pretty slack on vehicle laws, so I removed my dash, every bit of it. No heater, no ducting, no big clunky plastic dash. Just the metal support bar, with gauges custom mounted to it. My backup car is the definition of stripped. I don't know if photobucket supports user searching, but if it does search for "almightybeamer" and you'll find some pics of my car in various stages. Search for "almightybmw" on picasa (the google pic thing) as well, a few pics up there.

Mind you, I DO NOT daily drive this car, it is strictly for rally and off road fun. The Grand Prix is for daily driving.

just remember the pay off for those numbers. 1% of lets say 50 MPG is only 0.5MPG so to get 1 MPG better, you have to take out 200 pounds (and I know it is just a rule of thumb).

the taking stuff out is free though it does take away from the versatility of the vehicle (no seats = no passengers) but what about all that carbon fiber material. it gets expensive. I know this is a site devoted to saving gas but you have to look at overall cost as well. if you spend a couple hundred for the hood and a couple hundred on the fenders maybe a trunk lid. it is going to add up fast. will you ever see enough of a savings to pay for your upgrades? depends on how long you have the car but usually not.

there is a cool factor in this that many people don't even think of. if you want to do this to have a different look or because you think that it is cool to have a really light car, then go for it. if it is just for the FE involved, I would look into other things like grill block or aero mods, maybe even a WAI. those will pay off faster than weight reduction mostly because of the low (if any) initial cost.

*edit* also the safety factor. I don't need my spare or my jack all the time but one time when I get a flat is going to kill all my savings in gas because of the hassle of having to get it taken care of and depending on where I get the flat, it may put my life in danger too.

Drag racers go off the deep end and do things like cross drill every nut.

I know this isn't the question you asked, but I have to put in my two cents worth. I don't think the results will materialize. I don't know where that rule of thumb came from, but in my study and observations it doesn't seem to actually work.

It certainly could work for someone who drive the opposite of the way any hypermiler would drive -- hard acceleration, never coasting, accelerating right up until it's necessary to stop short for a red light. Even then, it will only affect city driving...and even then, the "100lb = 1-2%" numbers would actually vary depending on the existing weight and FE of the car. For heavier cars you'd probably have to remove way more than 100lbs to get 1-2%, even under those driving conditions.

For people who have even very mild hypermiling practices, I believe that merely reducing weight won't help. It seems to me that the only way a lighter car would benefit such a person is if they can get a more efficient, less powerful engine to go with the lighter weight. Basic entry-level hypermiling strategies (coasting to red lights and accelerating at mild to moderate rates) really help to reduce the effect of existing weight.

Ive driven with my spare tire, jack at home for a few years. its great for the small fuel savings, but you will wind up paying more for

1) calling your friend or family to go to your house, get the stuff, and come to you. it will waste them gas, and in the end you probably have to treat them to dinner or something (20 bucks and up)

2)you will waste more time, since you friend/family member couldnt do it right away, since you cant change the flat within 10 minutes at the side of the road


the other stuff taken out is ok, as long as you do the math. taking out the passenger seat would be good, since its about 35 lbs, seats 1 person. the back seats weigh about the same, but seats 3. so you will still be capable of sitting 4 in a civic

ya i highly doubt just taking out the spare tire and jack are goign to help anything but hinder you when you get a flat (most likely be when snowing, snowy road, rainy, bad area, etc... its never bright and sunny on the side of an empty country road...

like someone said up there your going to have to really strip your car of everything that makes it comfy/looks nice/quiet inside and then some...
so if your really ready to be driving around a demo derby car be my guest

I always carry a small 12volt compressor and a tire plug kit. I have found that I can plug a hole in my tire and refill it with air faster than I can change to my spare. Everyone tells me that they have heard that the plugs are dangerous, but I have done a dozen of them over the years and they have always lasted the life of the tire.

I still carry the spare in the event of a blow out (that happened once too- no plugs in this one).

If you choose to drive without a spare, a plug kit and a foot operated air pump might cost 2 extra pounds but be a little insurance. Oh- don't forget the pliers to pull out nails/screws, glass etc..

yea plug kits work, as logn as its a puncture hole and not a slice or a torn hole. also cant work for sidewall punctures

Plugs work fine for me, and are quicker/easier than changing the tire. They're not dangerous, though to be 100% proper you should get the tire patched too; US DOT standard (and law everywhere in the US, AFAIK) is to plug + patch, not just one or the other.

If you roll into the average local tire place with a puncture they're probably just going to plug it and leave it at that, so you might as well save $15 and DIY.

Still carry the spare anyway, there's a lot of non-puncture tire failure modes.

I have thought about swiss cheesing my car but i don't want to weaken the frame. I use my car for estimations and carrying light equipment. I have gutted it and it seams to help with fe. I have been using 2nd to start then to 4th, skipping 1st and 3rd. I am on my way for my best tank yet. Was also thinking about putting solid motor mounts....anyway its fun to see just what i can squeeze out of my Mazda.

All this is interesting, but...I'd rather have my spare tire, jack, tools, 80-40-20-15 meter CW transceiver, 2 meter radio, several days worth of canned food, several days worth of water, and a couple changes of clothing in the car than not. Carrying all that extra stuff, I am still getting (as of the date I am writing this) 40.57 mpg average over the last three months. So far, modification of driving habits seems to be the best way to increase mileage. Sure, my Auto Club card weighs a lot less. However, when I was growing up, a friend of my brothers' (one of those 'extra' kids every family has) was a tow truck driver. He would tell stories about things he'd do to able-bodied men who called him to fix a tire. Sometimes ended up with somebody being hurt. And it was never him.

I often carry a passenger who weighs 350 lbs. I've never seen a difference in mileage with or without this passenger.

I've plugged sidewalls and driven on those tires for years afterward!

Of course, nowadays I just get the road-hazard insurance...usually about five bucks a tire...

OMFG...just remembered the time a couple years ago driving down the freeway and hearing a BANG! from the trunk of the car...yep, the SPARE blew out! This was about 2005 or so, a 1984 car and I believe it was the original spare...

In theory it does increase mileage, even if it doesn't seem like it and it's a very very small amount. all I hear is how x modification only increases mileage by .5 or something percent. but a combination of a bunch of small stuff like this adds up. with the addition of a multitude of driving techniques.

like said earlier about the cost of a modification, verse how long you'd have to drive the car to actually be saving money is something to really think about. I just bought a bike for $500 and now I have to put another 200 into it to get it running, but It'll still take over a year to save money on gas. unless your an eco modder :-)

but on the subject:
lose weight yourself
fix a flat
all random stuff in the car
I'm not into going to extremes like I was in the past like taking out interior and such. but a lot of parts could be removed or replaced with lighter parts from other models and still not significantly compromise comfort. I know that older hondas have a brake drum that lighter then the other and there's doors that are lighter then others without the seat belt in the door panel. power steering and a/c then switching to the crank pulley without those accessories. ligher battery, but again to see money saved on that would take a while.

I would think that reducing weight would help on hilly terrain; whatever "techniques" you use, you will still need less engine power to move less weight uphill.

a cf hood will save around 14-16lbs which is the same savings as a lightweight battery, this of course depends on brand in both cases.

lightweight fenders are not much lighter. That aluminum is pressed pretty thin. Also the passenger seat is more like 30lbs. if you are taking out all the seats, you might as well take out the seatbelts which total just under 15lbs.

My all time favorite is the bumper supports because they are on the outmost edge (front and rear) of the car. this improves the cars stability as well as shaving off 20lbs.

i have found that less weight doesnt really help mpg that much. it does help acceleration though.

I think that kinda evens out as you have more weight pulling you down the other side...

-Jay

But if you DFCO you really don't use any gas downhill anyway. I might do some tinkering later if time permits. See what it does.

But, if you have more weight behind that DFCO, you have more speed at the bottom of the hill, and more inertia to carry you up the next hill...

When it's all said and done, if you have a net elevation gain (your destination is higher), removing weight will probably help; if you have a net elevation loss (your destination is lower), adding weight may help; and if your destination is the same as your origination (you're eventually going to go back home) then trying to adjust your weight probably won't matter.

In an ideal road, yes. However, there are stops and starts, places where you have to change speed, bumps, etc. While driving technique can help negate the ill effects of extra weight, removing weight cannot hurt. At least, you might not have to downshift as often on steep incline.

My driving is also mostly hilly city driving, so it would have a more significant effect.

Also, gas will be saved on those occasions where you cannot drive efficiently, such as stop and go traffic.

Agreed, those conditions describe when weight can have an effect -- though even then, the amount must be significant to produce measurable results. Removing a 40 pound spare tire and 30 pounds of backseat (commonly discussed items when someone considers weight removal) from a 2,500 pound vehicle won't do the job.

I'm actually going to add weight to my car. Mostly it needs more aero, but I need to increase the coastability. There's a couple downhills I'm used to linking and having to restarted the engine sucks. As long as I don't ever use my brakes though, I feel like extra weight isn't hurting me because I'm regaining that inertia somewhere.

How much weight are you going to add? It would probably have to be a significant amount to help your coast distance as much as you need, and you'll pay in acceleration. It could still help if you really are as good at avoiding brake usage as you suggest; it's probably more efficient to run the engine harder while accelerating and store that energy in ballast than it is to start and run the engine twice when you could have done it once.

It should be easy to test. Take a drive and record the numbers. Throw some heavy stuff in the car and drive it again. Record the numbers.

In my experience, the weight difference between a full tank and an empty one calculates to about 1% per 1% weight reduced. This is averaged from over 800 daily commute data points.

Reducing the weight is going to increase mpg if you keep your driving style the same. It will also lessen the wear on you ball joints/brakes/tires so you reap other benefits as well. It can even help cornering so that will help hypermiling technique of carrying speed thru corners...higher rate.

Look at it this way, less weight means you get up to target speed quicker, and can thus cut your engine earlier and glide. ;)

it also means you will slow down faster.

Only because your car is storing less energy, and thus has less to give up to aerodynamic drag. If you're driving slow enough that aero drag isn't the primary loss, I'd say that less weight definately wins.

And, less weight means less drag from the bearings, which is a loss of energy.

in theory it is less. but i believe the difference is negligible compared to other causes of friction like the tires and aerodynamics even at 35mph.

people always say that aerodynamics dont really take effect until higher speeds, but that is not necissarily true. ever ride a bicycle at 20mph? i believe people confuse the generation of downforce with the generation of drag.

True, tires/rolling resistance being the primary source of energy loss at constant speed before aerodynamics supercede it, at what speed that occurs being a function of drag area v weight/rolling resistance.

I like an earlier posted idea of lets all toss a couple hundred extra pounds in our vehicles and see. ;)

I've been driving with ~300 pounds extra for a couple months now. My FE has gone down mainly with the weather and driving changes I've had to make; I don't think I can blame the slight decrease on weight, though I can't prove that (and I can't get rid of the weight to test it, either).

I have observed the same thing, and wondered that too; I think the fundamental underpoweredness of a bicyclist's power source is to blame for extreme sensitivity to wind resistance (and to drafting).

speak for yourself, I'm not underpowered! ;) To work, slight downhill, I can maintain an average, over 3.2miles, of 18mph on my bike. Going home, it's 12mph. That's with the snow tires, heavier, bigger. The summer tires I was 2-3mph faster average.
Anyways.

The valley I live in is flat, so there are no hills on any local commutes. But when leaving, I cross mountain passes, and having the extra 500lbs (exaggeration) of weight only heats up my brakes when I have to slow down the passes. By coasting, I know I'll hit 90-100mph downhill, with a possibility of a ticket; not something I want. So the extra weight actually fails me on both accords for my extreme "hills" up and down. I'll need a SG to prove this of course, with 5 people in the car, and just me.

I do agree that aero drag starts as soon as you move. Property of physics doods. Didn't someone create a wind tunnel that placed the car on a treadmill, so they could incorporate frictional losses into the total drag cd? Yes someone did, for F1 racing though.
Man I'm on tangent today.

I'm sure baasjoos can coast further than I can, even though his car weighs 1000lbs+ less than mine. His drag < mine and that property outweighs frictional rolling losses and mass differences.

Consider it from a ballistic point of view. Sectional density, the amount of mass of a vehicle in relation to its aero drag will make the glide portion extend to a greater distance. Of course the pulse phase will require more power but the additional power is created at the highest BSFC point of the engine as long as that is properly used by the driver.

I think there would not be much difference, especially in situations where elevation changes do not cause losses due to excess downhill speeds. Where elevation changes are severe weight becomes a much more relevant factor.

In my VX with maximum load it makes some difference, and there are no detrimental elevation changes.

Of course with 4 passengers at 51 MPG each person is using only 1/4 of the total fuel, so you could argue that the per passenger mileage would be 204 MPG in this situation.

regards
gary

Generally engine displacement and gearing are far more important than weight, but they kind of go hand in hand. If a car weighs more you have to have a larger displacement engine and/or shorter gearing to make the car not seem like a dog when getting up to speed. By taking a lot of weight out, you will reap some benefits, but you could magnify those gains by going with different gearing and a smaller displacement engine, but that is a lot of work. At that point you would be better of trading in for a lighter, smaller vehicle to use unless you are really attached to the one you have.

thats still more power than a car with the engine off. note i said power, not stored energy(weight);)

I do agree with the whole "weight doesn't make a big difference so leave your extra seats and spare in the car" thing

here is a theory though. my car usually runs between 30 and 40 percent load. if you had a car that ran higher (maybe 50-60 percent load) you would see more benefits from weight reduction. I still think it would take a few hundred pounds to really show any significant gains.

I could get by with a much smaller engine but that is just my opinion.

Adding weight for increasing gas mileage is foolishness I am sorry to say.

Yes it may increase your coasting distance, but there is no free lunch. You invested energy into your car earlier when you accelerated, and since nothing in a car even comes close to 100% efficient you MUST be losing energy.

Additionally, someone mentioned rolling resistance. Rolling resistance is a unitless value and this becomes obvious when calculating the force caused by this. To calculate force due to rolling resistance you do this: Rolling resistance X weight. So if you increase weight, you must be increasing the force of resistance related to rolling resistance.


It is ALWAYs beneficial to reduce weight in vehicle for performance. Only reason weight is useful at all is for downforce so your tires stick, which coincedently the less mass your car has, the less downforce you need.

that is mighty ironic

everything I have done to my car (for better mileage) has added weight to it. grill block, warm air intake, even the scangauge.

most aero mods add some weight just from the materials used. if you are simply adding dead weight in the back seat, then that statement is true. I don't know too many people that do that though.

there is also a guy on here (basjoos) that has added at leas a couple of hundred pounds to his car to get him up to the 70MPG range. his car is " keeps on rollin' " . Oh did I mention that his coefficient drag is 0.17 it makes a difference how you apply that weight.

your use of the word PERFORMANCE is interesting. we care about fuel efficiency which I guess can be called performance but that word is more often used with guys getting around a track as fast as they possibly can which is pretty much none of us (at least not monday through friday).

interesting first post and welcome to the site

*edit* I don't like absolute statements. it is never always anything. but I guess that is an absolute statement within itself.

also, if I wanted more power out of my cavalier, couldn't I add a turbo for more power? that won't work, it's adding weight to the car.

Good point BEEF. Lowering Cd is probably the best you can do to your vehicle. All that weight reduction means nothing if you are still trying to send a 4x8 sheet of plywood through the wind - what it weighs has little bearing on it's Cd.

basjoos is a good example of what lowering the Cd does to FE, even though he has increased the weight with mods.

Size and horsepower of the engine IS a factor, but not so much as how much horsepower you use to get it up to speed. If you have a 55 hp engine, you might use 35 to get to speed, whereas someone with a 555hp engine might use 400hp to get to speed. Who used to most gas? My math has gotten bad over the years.

My left-handed thought is, if you have a 55hp engine or a 555hp engine, it will still take "x" horsepower to maintain given speed with a given vehicle. It's how efficient and how much fuel it uses at that specific horsepower that matters. Somewhere along the line, I'd think there would be an engine to match the vehicle when moving it at 55mph with the least amount of fuel matters, taking in to account Cd, weight, etc. So if you reduce Cd, then it takes less horsepower to maintain given speed with given vehicle - thus increasing FE. My brain hurts...I think I pulled a muscle...need coffee...wife's got me on decaf...just bumped into a wall...