Cd or weight?

[M_a_t_t]

I wouldn't bother making the final decision based on those 2 facts. I want to know reliability of the drivetrain, etc. I'd consider the cd and weight to be byproducts of the vehicle. No reason to try to save gas if you're buying a different car early because of the drivetrain.

That being said, if they truly are the same but with those being the only 2 differences I'd probably go with the heavier, but aero one. Utility reasons mostly. Good technique can trump specs. Looks at funkhoss's caprice.

[Taylor95]

Originally Posted by M_a_t_t

I wouldn't bother making the final decision based on those 2 facts. I want to know reliability of the drivetrain, etc. I'd consider the cd and weight to be byproducts of the vehicle. No reason to try to save gas if you're buying a different car early because of the drivetrain.

That being said, if they truly are the same but with those being the only 2 differences I'd probably go with the heavier, but aero one. Utility reasons mostly. Good technique can trump specs. Looks at funkhoss's caprice.

I've read his build thread. That car really is one of a kind.

There are two vehicles that fit the description of the OP, actually. The drivetrain is very similar between the two. I was just wondering if most people here would prefer aero over weight.

[Stubby79]

I do 50/50 driving, by distance, every day. The 50 in town takes 5x as long as the 50 on the highway, and averages a dozen stop/starts. There is a long hill on the highway to boot. Lighter weight will win every time.

I'd assume the bigger car would need a bigger engine too, so it would have a hell of a time catching up to the lighter. Would need to be 1:2 ratio or higher to ever make it worth it. And, as point out, aero can be worked on...you'll never be able to take 1000lbs out of the bigger car, and it would be a pain to shrink the engine size.

All of this assuming a plain old gasser. Hybrid or diesel and things would narrow a fair bit. Also gotta assume the heavier car can carry more (people) and be more comfortable. I rather like a comfortable ride...it's worth a few bucks a week in extra fuel.

[kach22i]

Originally Posted by Stubby79

I do 50/50 driving, by distance, every day. The 50 in town takes 5x as long as the 50 on the highway, and averages a dozen stop/starts. There is a long hill on the highway to boot. Lighter weight will win every time..............

Similar to what I was about to post.

That city driving time is a real killer.

Will never make up for it on the highway.

I mean my S10 probably gets 10mpg in the city, and 20 mpg on the hwy.

No improvement in Cd is ever going to tilt the scales back.

In the real world changing out my spark plugs has had the greatest affect.

Therefore if given a third choice to vote on would say "engine efficiency" is most important.

Going further I's say drivetrain efficiency overall is most important because putting the S10 into 4WD is like throwing out a boat anchor with large chain attached.

In short, everything is important, and the ratios of this or that are moving targets at best.

[Ecky]

My intuition says the lower Cd vehicle will be considerably more efficient from the factory, but I'd still rather own the lighter one.

In the real world I picked "both" of course.

[Charlie Cheap]

I vote lighter weight. The CD value hurts economy as the car goes faster, while weight must always be moved by the power source. Around town weight is a bigger concern but CD has little effect at in-town speeds. YES, I understand CD is always a consideration, but slower driving is a large portion of daily use. On a long-haul vehicle CD is much more of a concern...but so is weight. Weight is always a concern on long-haul or in town. An old adage heard at Bonneville is, it takes twice as much power to go from 200 mph to 250 mph as it does to get to 200 mph. Drag becomes a major factor as speed increases. Most of us never go 200 mph. I once went 140 mph in a Ford powered Cobra, and I believe that is my fastest ride.

[aerohead]

I'm already running around a 900-pound weight liability with the crude aero package on the Toyota pickup, however, the HWY mpg is so significantly improved, it has dragged the average mpg upwards in spite of the inertial penalty. So I voted for aero.
When I increased the weight of my Honda CRX to that of a Ford Taurus, and added a 3rd axle, I only lost 2-mpg on the open road ( 50-mpg vs 52 ).

[oldtamiyaphile]

Take the CD, my 'full size' van weighs 2.2 tons, and gets over 30mpg in all city driving (20mph avg speed).

In previous testing (over two years), I've found the weight of a trailer makes no difference to city fuel economy, it can all be accounted for in the aero drag penalty.

Don't brake and weight won't hurt you, and a heavier vehicle that glides further is actually much nicer to hypermile.

In short you can drive a heavy vehicle appropriately, with a draggy vehicle your only choice is to drive slower.

[Charlie Cheap]

Drive ANY vehicle at 20 MPH average and your MPG will be great. In Texas 20 MPH speed signs are only seen in school zones. Also, a 2.2 ton vehicle is NOT a good comparison to a daily driver weighing 1500 pounds less. DRAG is not a force to be dealt with until the vehicle goes faster. In fact, the faster one goes the more CD impacts economy. You are correct about stopping and starting. As the science says, A MASS IN MOTION TENDS TO STAY IN MOTION, AND A MASS AT REST TENDS TO STAY AT REST. One must use energy to move a vehicle off a static position, and use more energy to stop it. Stop-and-go in town is probably the single biggest drain on MPG. Your 2.2 ton vehicle seems to be set up perfectly for the task at hand. Congratulations.

[oldtamiyaphile]

Why in the world would you assume that a 20 mph average means 20mph speed limits? 20mph average means lots of stop and go (average 1 traffic light per km). Weight should kill my mpg but it doesn't, I simply drive around the fact that I've got a 1.6l engine out of a hatchback pulling a train.

Drive any (ICE) vehicle at 20mph (3rd gear in my tall gearbox) and you get abysmal fuel economy. I see about 25mpg - same as I get at 70mph in 6th. At 40mph I get 60mpg.

At 40-45mph (the typical 'city' speed limit here) more than half your energy goes into over coming aerodrag, so that's why I'd take lower drag. In theory you could drive slower, but in reality that would mean using a lower gear killing the benefit of slowing down.