Last updated Sunday March 25, 2012

Under Carriage Cover

Friction is ultimate energy waster and contributor of finite range.  

If you can reduce or maybe even eliminate the friction, a vehicle could travel for any distance, forever on its own momentum.

Air friction (at freeway speeds) accounts for 30-60% of all friction. The faster you drive, the air friction becomes a bigger and bigger waster of energy.

A pickup truck is a great vehicle to convert to electric simply because it can safely carry a lot of heavy batteries. A pickup truck is not a very aerodynamic vehicle though.

The other day, I was walking out to my EV truck when I caught the silhouette of a Toyota Prius parked next to it. This image came to mind: The shape of things to come for my EV truck.

If I could somehow round the front and back of the truck, making it more streamlined, it would make my vehicle 30-60% more efficient at highway speeds, which comprises most of my daily commute.

I was searching on the internet for information about aerodynamic mods when I stumbled across a website about recumbent bicycles that has some of the best tips on aeromods that I have ever found.

It got me re-thinking about the air dam I put on the front of the truck. 

With the air dam on, I am able to measure a 5-10 amp drop in current while going 60mph.  "OK, so the air dam was definitely helping matters."

While an air dam is good, a full undercarriage cover with side fairings is better.  It turns out it is not only better, it is amazingly better.  At 60mph, with a full under cover and fairings in place, my EV truck pulls about 20-30 amps less than it did with no cover and fairings.

Rear view of undercarriage cover.  

Front view of undercarriage cover with side fairings

Undercarriage cover 60mph 100Amps

No undercarriage cover 60mph ~120-130 amps

Air dam 60mph ~115-125 amps

Wow! That is really surprising that a simple cover like that would make that much difference. I have driven back and forth in head-winds, tail-winds and no wind. My new 60mph average current draw is indeed only 100Amps.

I used to drive 40 miles at 55mph and my average energy consumption was 325Wh-Hr/mile. Now if I drive 55mph for 40 miles, my consumption is only 290Wh-Hr/mile.

I can now drive 60-65mph and it only draws the same amount of energy as I used to draw going 50-55mph. 

My cover has a few holes in it. In front of the front wheels and in back of the back wheels. I want to cover those place up next.

I also left room for the leaf springs to flex around and open places under the supports used during vehicle maintenance.

For the first time, I feel like I can drive my EV truck at above-normal highway speeds without fear of loosing too much range.  

The other day, traffic was cruising at 80mph on north-bound I-215. Usually I stay in the right-hand lane and take it easy at 55-60mph, leaving all the other diarrhea rat-racers to their own folly.  This day, I floored it just for fun and got up to 87mph fairly easily before I had to show down for the Legacy Highway exit.  Wow, that's a new speed record for my EV truck.  

 HeadingWind Speed Modification Amp Draw
 North060mph bed cover, tailgate, spare 110-120
 South060mphremoved front air dam 120-140
 North-1060mphremoved front air dam 100-120
 North060mphremoved rear bumper 100-105
 South1060mphremoved rear bumper 120-130
 South1060mphmiddle undercarriage cover piece 100-110
 South 060mphmiddle and back undercarriage cover 110
 North 060mphmiddle and back undercarriage cover 95-110
 South 1560mphfull undercarriage cover 100

Future Possible Improvements:

Increase undercarriage cover from 80% to 90% coverage.

  • Wheel fairings –Used to reduce drag caused by the frontal area of the wheels themselves.  
  • Better rounding of the front of the truck – More streamlined.
  • Headlight covers
  • Hood fairing

Next Article:  Aerodynamic Cover