Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - View Single Post - Does a traditional square pickup camper shell topper help or hurt drag & mileage?

aerohead · 01-12-2010, 05:00 PM

Brett,my data is all dated now and since pickup design has evolved over time,the goal-posts have moved.
Here are some random thoughts from a failing memory:
A pickup, according to the Big-Three,is no more than a body-on-frame two-door sedan without a trunklid,with separate trunk,and rear bulkhead cut away to allow the tailgate.Sounds scary!
Back when pickup Cds were on the order of 0.50,adding a traditional topper would cut the drag of a pickup to that of a station wagon or Carry-all,Suburban,etc.,at around Cd 0.45.With this you might expect a 5% mpg improvement( HWY).
Full tonneau covers were also figured at about a 5% mpg improvement.They basically added back the 'trunklid.'
Ford discovered that a 2-foot wide section of plywood laid across the frame rails ahead of the tailgate would cut drag enough to show at the gas pump.
Later GM noodled around with this theme and arrived at their 1/2-tonneau,for which they received a US Utility Patent,with the claim that it cut drag even better than a full tonneau.The Gale Banks turbo-powered GMC S-15 used this 1/2-tonneau in part,to set a LSR at Bonneville at over 210-mph.
When the Ford guys at Texas Tech published their results of model and full-scale testing of covers in 1988,they had concentrated on the wing-1/2 cover because of "utility" issues for truck owners.
But from the table of results that they published,which did eventually make it into Sport Truck Magazine,the "aeroshell" was clearly the winner as far as drag reduction,with a 20% reduction which would translate to a 10% mpg increase at 55-mpg,even higher percentage at faster velocity.
Modern pickups have higher rails now which changes the camber line over the top and the relative "drop" from the cab roof to the rail/tailgate top is less pronounced.So from everything learned about passenger car aero since Hucho was working on the first VW Rabbit,is working it's way into trucks.
I don't know what kind of numbers the new trucks would generate with mods.Their weight and frontal areas have grown to negate much of the improved aero they've seen,and mpg benefits they might have realized.
It's a tougher call.
But clearly,the aeroshell design appears to be the undisputed heavyweight champion for low drag in pickups.
There is nothing published in the public domain to suggest an architecture which exists,that will do more for reducing drag in a pickup.
And there is nothing in Fluid Dynamics which suggests an architecture which could.

01-12-2010, 05:00 PM	#29 (permalink)
aerohead Master EcoModder Join Date: Jan 2008 Location: Sanger,Texas,U.S.A. Posts: 16,218 Thanks: 24,368 Thanked 7,351 Times in 4,752 Posts	traditional Brett,my data is all dated now and since pickup design has evolved over time,the goal-posts have moved. Here are some random thoughts from a failing memory: A pickup, according to the Big-Three,is no more than a body-on-frame two-door sedan without a trunklid,with separate trunk,and rear bulkhead cut away to allow the tailgate.Sounds scary! Back when pickup Cds were on the order of 0.50,adding a traditional topper would cut the drag of a pickup to that of a station wagon or Carry-all,Suburban,etc.,at around Cd 0.45.With this you might expect a 5% mpg improvement( HWY). Full tonneau covers were also figured at about a 5% mpg improvement.They basically added back the 'trunklid.' Ford discovered that a 2-foot wide section of plywood laid across the frame rails ahead of the tailgate would cut drag enough to show at the gas pump. Later GM noodled around with this theme and arrived at their 1/2-tonneau,for which they received a US Utility Patent,with the claim that it cut drag even better than a full tonneau.The Gale Banks turbo-powered GMC S-15 used this 1/2-tonneau in part,to set a LSR at Bonneville at over 210-mph. When the Ford guys at Texas Tech published their results of model and full-scale testing of covers in 1988,they had concentrated on the wing-1/2 cover because of "utility" issues for truck owners. But from the table of results that they published,which did eventually make it into Sport Truck Magazine,the "aeroshell" was clearly the winner as far as drag reduction,with a 20% reduction which would translate to a 10% mpg increase at 55-mpg,even higher percentage at faster velocity. Modern pickups have higher rails now which changes the camber line over the top and the relative "drop" from the cab roof to the rail/tailgate top is less pronounced.So from everything learned about passenger car aero since Hucho was working on the first VW Rabbit,is working it's way into trucks. I don't know what kind of numbers the new trucks would generate with mods.Their weight and frontal areas have grown to negate much of the improved aero they've seen,and mpg benefits they might have realized. It's a tougher call. But clearly,the aeroshell design appears to be the undisputed heavyweight champion for low drag in pickups. There is nothing published in the public domain to suggest an architecture which exists,that will do more for reducing drag in a pickup. And there is nothing in Fluid Dynamics which suggests an architecture which could.