Cd or weight? - Fuel Economy, Hypermiling, EcoModding News and Forum

Taylor95 · 10-26-2020, 05:47 PM

Imagine that you are buying a new vehicle to modify for fuel economy. You plan on using this vehicle for 50/50 city and highway driving. You have narrowed your choices down to two vehicles which are virtually identical except for the following:

Vehicle A has a 10.0 Cd advantage over Vehicle B.

Vehicle B weighs 1000 lbs less than Vehicle A.

Which one would you choose, and why?

CigaR007 · 10-26-2020, 06:28 PM

I would be inclined to say that it is easier to reduce the Cd.

1000 lbs is a lot of added weight and you would be making sacrifices to shed a portion of it.

jakobnev · 10-26-2020, 06:44 PM

This man has a dog and a mother in law that don't like each other!
How do I know?
Elementary my dear Watson, the dog likes to have it's head out of the window, and the mother in law is a bit on the heavy side.
And he has to choose only one to bring on the vacation trip!

freebeard · 10-26-2020, 07:27 PM

Quote:

Vehicle A has a 10 point Cd advantage over Vehicle B.

Vehicle B weighs 1000 lbs less than Vehicle A.

IIRC 10 points is 0.10 Cd.

It's all relative. Beginning Cds and weights are...?

Taylor95 · 10-26-2020, 08:28 PM

Quote:

Originally Posted by freebeard

IIRC 10 points is 0.10 Cd.

It's all relative. Beginning Cds and weights are...?

The question is purely hypothetical so actual values do not matter.

However, Vehicle A could have a Cd of 0.25 and weight in at 4000 lbs.
Vehicle B could have a Cd of 0.35 and weigh 3000 lbs.

freebeard · 10-26-2020, 08:54 PM

Quote:

The question is purely hypothetical so actual values do not matter.

Yes, but relative values do.

Thanks for describing the size of the ball-park. Power to weight? (not trying to be a troll)

Taylor95 · 10-26-2020, 09:54 PM

Quote:

Originally Posted by freebeard

Yes, but relative values do.

Thanks for describing the size of the ball-park. Power to weight? (not trying to be a troll)

Assume both vehicles have the same engine. An average car can put out around 180 horsepower to the crankshaft.

freebeard · 10-26-2020, 10:19 PM

Quote:

50/50 city and highway driving

I going to go ahead and side with JulianEdgar: testing.

aardvarcus · 10-26-2020, 10:29 PM

I would vote lower cD. Careful driving to minimize brake use can minimalize weight penalty. Inertia isn't the enemy until you convert it to heat.

I would also assume in real life that weight could buy you extra utility.

freebeard · 10-26-2020, 10:59 PM

I can't choose. You have one vote each right now.

Less weight means better 60-foot times but better Cd is going to look better.

Intangibles.