The Search for Fuel Economy

Pages from a Designer's Notebook

Freedom Machine
The goal: 100 mpg at 70 mph, into a 30 mph headwind, with four bags of groceries.
Chap. 31: A visit with Allert Jacobs Doing it with 9 horsepower

Dec 24, 2009

My 17 hp is too much. But Allert's 9 hp may not be enough.

We are beginning to dial in this horsepower thing.

Should we begin with a bigger engine and run it slower? Should we begin with a smaller engine and run it faster? Opinions are all over the place.

Here is a big clue: A stock Helix gets 64 mpg average as a commuter. But it won't meet the "Vetter Conditions"* In powerful headwinds, a standard Helix will barely go 65 mph and gets 53 mpg at that speed. My streamlined Helix goes 75 mph into the winds and the mileage does not drop. The answer may be as simple as:

"To get 100 mpg, begin with a 100mpg machine and streamline it to go 70 mph"

Does this sound obvious? It just might be true.

Did you think you were going to take a machine that gets 60 mpg around town, streamline it and somehow get 100 mpg at speed?

I don't think so.

What kind of machine gets 100 mpg?

125s get 100 mpg. But 125s won't go 70 mph, into a 30 mph wind, sitting up tall and comfortable.

With proper streamlining I believe they will.

Fortunately, Allert Jacobs, a fellow enthusiast in the Netherlands has begun with a 9 hp 125. He knows things we don't know. I am so impressed with his work that I asked him these questions:

Dec. 9, 2009, Good morning Allert. I have been following your progress with admiration. Your work is great! Your web page is great! Thanks for putting this up. I have been tied up with other responsibilities and have not been able to work in my shop so much. But I am heading back. After I finish up my tooling, I must start over with new running gear.

My question is this: Do you think that 9 hp is enough to go 70 mph into a 30 mph headwind?

This is a crucial question to be answering.

We know that the 17 hp Helix has more power than needed. If I could gear it up, I suspect it would top out at 90 mph. We cannot drive that fast in the US. Besides, we cannot gear it up.

So, somewhere between 9 and 17 hp seems to be the magic number.

My first choice, the Honda CBR 125 *(13.4 hp @10,000 rpm). But, it is not even sold in the US.

What is your educated guess? You have been riding on 9 hp. You have a better idea than anybody in the world! Will it even go 70 mph into a 30 mph headwind? If not, how fast will it go in such conditions?

Every little bit of information helps.

Thanks and don't give up.


Very revealing picture of Allert's 9 hp Honda ANF 125i. Note the sliders to move the fairing forward, out of the way.
Allert's reply: "Hello Craig: My streamlined ANF125i will do 80mph on a flat road, no wind. I think it will do 70mph with a 30mph head wind, full throttle in third gear, but no more than that. I’ve geared it up for maximum mpg so at 80mph it gets to 6000rpm where it should have maximum power at 7000rpm. It might go slightly faster and would surely accelerate faster if I would gear it down a bit at the cost of fuel economy. It’s got only a 4 speed gearbox and it is not easy to add a extra gear, to me this is the major drawback of this bike. Fortunately the engine puts out maximum torque at only 3000rpm and with 9hp it is designed more for power at low rpm than performance at high rpm. And it has good fuel economy, the fuel injection contributes to these features and the catalytic converter cleans the exhaust gasses.

Apart from the engine I chose it for it’s single sloping frame tube which will easily allow for a low seat and recumbent seating position. And of course for the gearbox chain drive instead of the belt drive that most scooters have which makes them less fuel efficient. Last but not least; it is sold in Europe.

But, if I would live in a hilly area, I would like to have a bit more power and more gears. One of your goals is to carry three bags of groceries; my bike will not do that. If your bike has to be bigger and heavier to meet your goals it will also need more power.

The engine and gearbox of the CBR125 seems a good choice to me. It will use a bit more fuel than my streamlined (200mpg) ANF, but I’m sure that it will easily get the 100mpg you’re aiming for, even so with a bigger streamline. But it’s not sold in the US, and it has an air cooled engine. A bike that is very popular in Thailand is Honda Sonic:

this one’s got the same five speed engine as the CBR125 but has it water cooled and the latest models have fuel injection too. And it does have a single sloping frame tube. But I guess it’s not sold in the US. It’s a pity these small engined light bikes are not sold in our country’s. I am quite pleased that I have been able to buy a ANF125i in Belgium, Honda Netherlands doesn’t think it’s worthwhile selling it here."

Best regards, Allert

I encourage you to study Allert's web page . See how he thinks and how he built this thing.
* "Vetter Conditions" are riding at 70 mph, into a 30 mph headwind, with a useful load ( like 4 bags of grocerie). Such a machine must be so comfortable and easy to use that it is the first choice among all vehicles in the garage.
Honda's 13 horsepower CBR125: The best machine to begin again with?
This just may be the perfect powerplant for 100 mpg at 70 mph - a 125 with 6 speeds and just a little more power than Allert's AFN125i.

It needs to be in a scooter frame and streamlined.

Of course, the real problem is that I cannot ride one legally in California. Honda doesn't sell them in the US. I guess they think we don't want them. I will ask my friends at Honda to make it available here. You never know... sometimes they say yes. Look at what the FIM did about my streamlining requests.

8-10 horsepower at Bonneville

Speedweek folks have a class for everything. If you bring it, they will figure out a name and class for it. This is called a "vintage partially streamlined moped'"

Jean Kayou's 8-10 hp, 61 mph "Moped" at Bonneville

Jean guesses he has about 8-10 hp @ 10,500 rpm which gives him an official maximum average speed of 61.4 mph at Bonneville in 2009. If Jean's 8-10 hp was in Allert's streamlining, he would go faster. And he would have been sitting up and comfortable. On the other hand, Bonneville speed is certified. Our indicated "road speeds" may not be so accurate. But, it does make you wonder:

"Why don't we all go directly to real streamlining?"

Page posted Dec 24, 2009
Chap. 3: Road Testing the Long Tail Mar 28, 08
Chap. 1: Streamlining Saves Fuel Feb 20, 08
Chap.2: CAD Streamlined Body Mar 8, 08
Chap. 4: Planking with Foam Apl. 5, 09
Chap. 5: More Wind Testing Apl. 7, 08
Chap. 6: The Final Shape Apl. 17, 08
Chap. 7: Decisions about Details May 10, 08
Page 8: Making the Center Bulkhead June 1, 08
Chap. 9: Rear Bulkhead and Truck bed June 8, 08
Chap. 10: Finish Rear and go for ride June 17, 08

If you have not yet watched my DVD, How they Got 470 mpg it is time to get it for the basic foundation for what we are doing here

Chap. 11: Finish the Tail June 29, 08
Chap. 12: Heading for Ohio, July 13-23, 08
Introduction to Fuel Economy
Chap. 13: Riding in the Midwest July 24, 08
Chap. 14: Vintage Days Ohio, July 25-7, 08
Chap. 15: Summary to date Aug 12, 08
Chap. 16: Adding Weight to the Front Sep. 1, 08
Chap. 17: Truth and Motorcycle Design Sep 4, 08
Chap. 18: Where should the weight be? Sep 25, 08
Chapter 19: Finishing the Streamlining Oct 14, 08
Chapter 20: Streamlining the Handlebars Nov 4, 08
Chapter 21: Unexpected Problems Nov 11, 08
Chapter 23: Getting my feet in and out Dec 19, 08
Chapter 22: Streamlining is working Nov 25, 08
Chapter 24: Streamlining is beginning to work! Jan 1, 09
Chapter 25: Tuft Testing Mar 2, 2009
Chapter 26: Starting Over April 9, 09
Chapter 27: More Ideas for Starting over April 20, 09
Chapter 28: Show time! Aug 1, 2009
Chapter 29: Getting the big parts right Dec 10, 2009
Chapter 30: First evaluation from an outsider Dec 20, 2009
Chapter 31: Visit with Allert Jacobs Dec 24, 2009
Chapter 32: Prius Headlights Jan 18, 2010
Chapter 33: New Gears Feb 17, 2010
Chapter 34: New Mileage Records April 25, 2010
Chapter 35: The Quail Gathering of Motorcycles May 9, 2010
Chapter 36: End of the line with the Helix June 19, 2010
Chapter 37: Vetter Challenge Oct. 9, 2010
Chapter 38: John Keogh helps out Dec 8, 2010
Chapter 39: Working with Keogh Dec 17, 2010
Chapter 40 and up (Work continuing in 2011)
Designing the Last Vetter Fairing

Chapters 1 thru 39 (2007-2010)

Chapters: 40 thru 51 (2011)

Chapters: 52 thru 61 (2012)

Chapters 62 thru 68 (2013)

Chapters 69-up (2014)