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?"

Master Index to the Last Vetter Fairing Story

Page posted Dec 24, 2009