Carbon Fiber Hood for FEH - GreenHybrid

EricWil76 · #1 (**permalink**) 10-05-2008, 10:56 PM

I have found carbon fiber hoods for my FEH and wondered if it would make a measurable MPG gain. Some have suggested dropping the spare tire for a 1-2 MPG gain I am assuming based on the weight savings. A carbon fiber hood could save quite a few pounds. Is there any formula to help correlate weight saved to MPG gained?

08hybridok · #2 (**permalink**) 10-06-2008, 02:58 AM

I thought I read 1-2mpg per 100# ???

Still hasn't made me lose any weight yet tho!

From GPS Man:

Quote:

I was at the Dearbon Event in October 2005 and here is what I had written down:

1. A/C on full time in the city equals a 40% loss! At a highway speed A/C = a 10% loss.

2. Expect 25% lower MPG in winter ( all winters are not created equal, of course )

3. Radio drops you 0.1 MPG, Rear Defrost 0.8 MPG,
Headlights 0.9 MPG, and Fan on High, no A/C drops you 1.3 MPG

4. Every 300 pound increase in weight drops FE by 1 MPG.

5. Windows down gives better MPG than A/C use at all speeds.

6. 1.4 mpg loss if tire pressures are 10psi low.

*Note: Figures are for 2005 model year. Models in 2006 and 2007 should be the same. 2008???

--------------------------------------------------------------------------------

http://www.greenhybrid.com/discuss/f...ssories-16464/

So that's the reason I haven't taken a serious diet, I can't lose 300 #'s!

EricWil76 · #3 (**permalink**) 10-06-2008, 06:45 PM

Here is the link I found I thought I had run across another one but forgot to bookmark it. I wonder what the weight difference is compared to the steal. I bet if it were possible to replace the entire front end with carbon fiber hood, fenders and bumper it might be considerable.

http://www.andysautosport.com/ford/2...o00128177.html

Brady · #4 (**permalink**) 10-06-2008, 11:01 PM

After clicking that link, I saw this from the manufacturer: "carbon fiber hoods are almost always lighter than factory hoods."

If they are "almost always" lighter, that makes it sound like the cost-to-weight savings ratio isn't in your favor.

It would be much better if it said they are "always significantly lighter"

gpsman1 · #5 (**permalink**) 10-08-2008, 09:38 PM

I own an Insight... the lightest Hybrid available. 1850 pounds
I own an Escape... one of the heavier hybrids, 3850 pounds ( double the Insight's weight )

The Escape coasts ( in Neutral ) almost forever... like a puck on an air hockey table.
The Insight coasts poorlyl... it slows quickly when your foot is off the gas.
I feel like the Insight is dragging a parachute by comparison when I switch back and forth between cars.

Are the tires and bearings that much better on the Escape, or is it the weight keeping the momentum rolling? I suspect it is the second.

So lighter is not always better. It depends on your situation.
If you are driving mostly highway, and have few chances to "coast"...
Then lighter is better.

If you have lots of chances to coast, heavier is actually better.

Take a light FEH with a Cd of .40 and a heavy FEH with a Cd of .40.
Which will coast through the air for a longer distance?
Which will roll the longest after an elevation drop ( hill )?

The Insight has a Cd of .25 and coasts half as well as the Escape.
-John

TeeSter · #6 (**permalink**) 10-09-2008, 06:52 AM

Quote:

Originally Posted by gpsman1

I own an Insight... the lightest Hybrid available. 1850 pounds
I own an Escape... one of the heavier hybrids, 3850 pounds ( double the Insight's weight )

The Escape coasts ( in Neutral ) almost forever... like a puck on an air hockey table.
The Insight coasts poorlyl... it slows quickly when your foot is off the gas.
I feel like the Insight is dragging a parachute by comparison when I switch back and forth between cars.

Are the tires and bearings that much better on the Escape, or is it the weight keeping the momentum rolling? I suspect it is the second.

So lighter is not always better. It depends on your situation.
If you are driving mostly highway, and have few chances to "coast"...
Then lighter is better.

If you have lots of chances to coast, heavier is actually better.

Take a light FEH with a Cd of .40 and a heavy FEH with a Cd of .40.
Which will coast through the air for a longer distance?
Which will roll the longest after an elevation drop ( hill )?

The Insight has a Cd of .25 and coasts half as well as the Escape.
-John

If you are coasting downhill... yes.... but if you have to lug that weight back up the other side of the hill and push it on level ground I'm guessing the lighter car will always come out better in the long run....

DesertDog · #7 (**permalink**) 10-19-2008, 02:30 PM

Quote:

Originally Posted by TeeSter

If you are coasting downhill... yes.... but if you have to lug that weight back up the other side of the hill and push it on level ground I'm guessing the lighter car will always come out better in the long run....

Yes, lighter is always better. Obviously kinetic energy is linearly proportional to mass, while coasting distance is more or less proportional to the square-root of mass. An Insight won't coast for as long or as far from a given speed as an FEH, but it will convert relatively more of its kinetic energy into distance. Hills are even worse than flat roads because the potential wants to convert to kinetic by increasing speed which increases the aerodynamic drag. Not to mention pesky things like speed limits...

For those more technically inclined, for a vehicle with mass m, aerodynamic drag coefficient of k (.5*rho*Cd*Af) and rolling resistance r, the equation for speed as a function of time when coasting down on a flat road from an initial velocity v0 is given by:

v(t)=sqrt(mrg/k)tan(sqrt(krg/m)(c-t))

where c is the time to coast to a stop, given by:

c=sqrt(m/rkg)arctan(v0*sqrt(k/rmg))