I am a retired engineer /physicist. I fill my time these days by working on ideas that I think might have some practical value. My strengths are in understanding the science behind things and applying math to problems.
Six years ago, about, I decided to work on some ideas for improving automotive fuel economy. I bought a 2003 Beetle TDI diesel for my "test bed." Frankly, I haven't accomplished nearly as much as I would have liked--which means I have a ton of things yet to try. To start off, I made some small adjustments to the Beetle to improve its mileage.
1) I designed a drag reducer for my car. You can see pictures at
www.ernsblog.com and at
Welcome to www.max-mpg.com Basically, it's a large "wing" on the back to correct the downflow on the backside of the beatle. My drag coefficient is thought to be about Cd = 0.31. The result is an increase of 3 mpg, roughly independent of speed.
2) Tire diameter was increased by 3/4-inch, going from 205/55-16 to 205/60-16. I also raised tire pressure, using 40 to 44 psi depending on conditions and how serious my mileage goal is.
3) I tested a wide range of motor oils and found that some synthetic oils do improve mileage by quite a lot. Bottom line: lowest factory-approved viscosity gives best mileage.
4) I add lubricity enhancers to my diesel fuel: bout 3% biodiesel, and 1/4-bottle of Power Service (silver bottle) to a tank of fuel. I think there is a modest improvement in mileage from this, and a definite extending of engine life. In highway driving, I think my engine is about 35% efficient. (This is based largely on theoretical calculations.)
From the factory, my car would get about 49 mpg at 60 mph. I now get 65 mpg at 60 mph, driving here at 5000 ft elevation with good summer fuel.
My special interests are tire and wheel design and development of a more efficient engine. I am also involved in aerodynamics, having worked in that field before.
I have been working on the theoretical side of engine efficiency for about five years. I think I know how to build a clean-burning engine that is 60% efficient; a patent was filed in December. I hope to find a source of funding to build the engine and try it out.
As for tires, I am still working on ideas here. Some rules I believe to be true--
1) Soft rubber makes more efficient tires
2) Big wheels with low-profile tires are really bad for fuel economy
3) Narrow, large-diameter tires are best
4) The second number on the tire (profile) should be 60 or higher
5) High tire pressure improves fuel economy AND tire life
6) Pavement matters. Smooth (or lightly grooved) concrete can raise mileage by as much as 10% over smooth asphalt, 15% for rough asphalt.
By the way, larger-diameter tires allow your engine to run at lower RPM where it's more efficient, but I think most of you already knew that. Be careful to correct all data for the change in tire diameter. Watch your speed.
My best mileage ever on one tankful was obtained in a friendly competition within the TDI Club. (
Fred's TDI Page. TDIClub.com. VW TDI Enthusiast Community ) I filled my tank at Park City, Utah and headed east on I-80, driving about 55 mph. I reached Davenport, Iowa, before getting fuel-- a distance of 1,209 miles on 15.5 gallons of biodiesel blend.
When people ask how to get better mileage, my standard answer is, "drive slower and keep your foot off the pedals as much as possible."
Ernie Rogers