Aerodynamic Trucks
Posted on Oct 29, 2007 - 9:42pm by Wayne Weisser in Trucks
With record fuel prices ( $3.157 National Average this week) owners and fleets are looking for more then fuel surcharges to help them in their war against the cost of expenses in running a business. Aerodynamics may not be the holy grail for fuel savings, but it’s a good foundation to build on. During our first Roadcast we discussed aerodynamics for trucks and our conclusion was that it’s a great idea if you’re pulling a van trailer and with other fuel saving techniques it’s a good start.
There appears to be a little controversy going on between International and Freightliner about who has the most aerodynamic truck. International has gone as far as putting their Prostar on their front page at International Trucks.com and going to an independent third party for head to head testing between Cascadia and Prostar to refute Cascadia claims that they have the most aerodynamic and fuel efficient truck.
I put the poll back online and after reading both sides, Cascadia’s page and Prostar’s page, try and get past the hype and choose which truck you believe is the most aerodynamic and could be the most fuel efficient.
I’d like to hear from you in the comments how important Aerodynamics are to you. Is it something you’re looking for in your next truck? Is it top on the list of features, nice to have or not-so-much? Even if you don’t pull a van trailer are aerodynamics a choice you want to have in your truck?
Are Longer and Heavier Trucks in Your Future?
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1987 volvo, old road way truck with all the arodynamics u need
I work for an engine maker. I work with a lot of fleets to get them to spec trucks with our engines. Here is a tip sheet you should consider and aerodynamics play an important part the faster you go. (difference between a square nose and an aero truck can be up to 15% improvement in fuel economy!)
The one thing I see over and over is gearing problems. Many times diferences in one truck vs another is one is geared for power and one for fuel efficiency. Never spec one engine the same as another. Use the engine manufacturers gearing recommendations. A C-15 uses different gears than a Series 60 than an ISX. You gear a Cat like a Cummins and it will get horrible fuel economy. Gear a Cummins like a Cat and the drivers will complain about power. Each has its sweet spot. Also, if you buy a used truck, keep in mind the speed the original owner drove at. You buy a 379 and more than likely the owner let it run over 72 mph. Don’t expect to drive it at 55 and feel all the power. They probably geared it tall for the high speed and sacrificed drivability at 55 in top gear. Also, stay in top gear 90% of the time and use cruise 70% or more. Cruise is alway .2-.4 mpg better than pedaling on long trips.
Rock-Solid Rules
§ Every 2% reduction in aerodynamic drag results in approximately 1% improvement in fuel economy.
§ Above 55 mph, each 1 mph increase in vehicle speed decreases fuel economy by 0.1 mpg. (Drive 65 vs 75 and save 1 mpg regardless of the truck you drive. Thats about $10,000 a year if you drive 100,000 miles)
§ Worn tires provide better fuel economy than new tires, up to 7% better fuel economy.(Brand new vs. end of life)
§ Used lug drive tires can get up to 0.4 mpg better than new lug tires. (used means broken in)
§ Ribbed tires on the drive axles provide 2–4% better fuel economy than lugged tires. (new vs new)
§ Every 10 psi that a tire is underinflated reduces fuel economy by 1%.
§ The break-in period for tires is between 35,000 and 50,000 miles.
§ Tires make biggest difference in mpg below around 50 mph; aerodynamics is the most important factor over around 50 mph.
§ The most efficient drivers get about 30% better fuel economy than the least efficient drivers.
§ Idle time is costly. Every hour of idle time in a long-haul operation can decrease fuel efficiency by 1%.
Regarding the comments by Pete. You could not be more right! There are no standards in vehicle configuration or in parameters for testing. Yes, they are playing with numbers. Bottom line, you want better mileage- Gotta do something about the trailer. Sounds easy enough until you consider the guy who owns the truck usually doesn’t own the trailer, and the guy who owns the trailer doesn’t directly pay for fuel. So now what? You’re left with doing it all on the tractor. Which would be fine if the tractor actually could do it all, but it can’t. Here’s how to get the best mileage…..don’t pull van trailers. Stick with flatbeds and your aerodynamic worries are over (as long as you don’t have a condo with a 13′ high roof!).
I would like to clarify a couple of things. First, truck manufacturers design cabs to direct the airflow over the vehicle like a car. The air must travel 13′6″ to go OVER the cab and trailer. With our patented design, airflow is directed AROUND the vehicle, hence it only has to travel 4′0″ +/- in each direction to go AROUND the cab. I have done extensive wind tunnel testing to prove this. I find it very difficult to believe that these trucks turn anything around .6 Cd unless those tests were conducted WITHOUT a trailer.
Secondly, lets look at the testing standards for these type of vehicles. There are none. There is nothing to say that a Class 8 Semi Truck MUST be tested with a 13′6″ +/- tall trailer behind it. So lets ask, were all of these trucks tested with the same parameters or are we just playing with figures?
When I tested my truck design at a major University, the head professor did not think that it would break 1.0 Cd. It turned a .4Cd and that was with a trailer. By the way, my design came about thru extensive
interviews with over the road drivers to find out what they required. Most trucks are designed based on how a “stylist” perceives they should look. Thats why they design them like cars. With the air going OVER the vehicle. http://www.alateinc.com “old news” page also check out my pickup truck products on “products page 2″
Quite frankly tractor aerodynamics was perfected a long time ago. The little tweaks on the tractors of today are just minor changes that are blown out of proportion by the marketing department. I know truckers with blunt nosed Pete’s that get better mileage than a Cascadia. In order to improve on what we see on the road today major changes are in order. Convex windshields, sleepers under the driver, and by all means integration with the trailer. I see your design has merit, but the Germans designed an aerodynamic tractor 35 years ago too and actually built a full scale prototype. People who really know aerodynamics are still 30+ years ahead of their time. Things won’t change until the ownership and logistics change. Until then it’s all about the truck……and that’s hard on the engineers that want to do it right.
Take a look at my design that I delivered to PACCAR 25 years ago. These new trucks are turds.
http://www.alateinc.com
Where did you get that 13% number from? They were too scared to test 387
But thanks for interesting input on math basics.
I just read the note on Pete 387 fuel economy…it’s a laugh. The ProStar has been tested to be about 13% more aerodynamic than the 387. The aero drag force accounts for 1/2 the force on the vehicle at 65 mph, thus the ProStar will achieve approximately 6.5% better fuel efficiency as compared to the 387. This difference will save you $4,500 in fuel per year on average with fuel at $3.50 per gallon and traveling 120,000 miles per year averaging 6 mpg (20,000 gallons of fuel at $3.50 per gallon is $70,000). WOW, fuel cost is really driving competition in the Industry.
I have heard of several companies that are running identically spec’d ProStars and Cascadias. The ProStars are getting 5%-10% better fuel economy. International’s results and advertising is right on. Who is Freightliner trying to fool with their advertising? Maybe, Freightliner’s engineers and marketing groups don’t know how to test a truck.
387 is the most aerodynamic truck since about 9 years already. It also has widest, most comfortable cab and sleeper. It rides like a king because it is 379 with new cab indeed. You guys at IH better start really working (making real progress that is) because its a SHAME, that after 9 years since 387 inception you still are not able to apply ANY new aspect of pro-aerodynamic design except lowering the side-fairings (which is actually great but not practical idea)
i hear ya. but if I can add a couple of grand to my bottom line each year i’ld select fuel efficiency. the other part of the equationis how much of this is real and how much is crap