The Search for Fuel Economy

Pages from a Designers' Notebook

The goal: 100 mpg at 70 mph, into a 30 mph headwind, with four bags of groceries.
Chap. 26: Starting Over

(Be sure to hit refresh as I am adding your comments)

My trusty Honda Helix is at the end of its road. It has no business at 75mph, which the streamlining has allowed.

At Alices'
How should we begin again?
It is time to start over with bigger wheels. Should it have a small engine spinning up fast? Or should it have a big engine turning slowly?

Is it better to begin with a motorcycle that really gets 100mpg, but at slower speeds, like a 125cc and streamline it so it will go 70 mph?

Or should we begin with a 65mpg machine, like a BMW GS650, and streamline it, expecting the mileage will get better?

The fact is, I don't know.

Removing the rear body for the first time
After one last high speed run, the engine began running poorly and I had to remove the body. I found that the carb had flapped up and down, causing a big split in its rubber mounting spigot. It is amazing it would run at all. New parts and an upgrade support from Honda will get us back on the road. I am re-designing the rear section so only 5 bolts will hold it in place. It will be easy to remove next time.

The Helix really is a sturdy machine. It is just not up to running 75 mph. It will be just fine until I build the next one.

Therefore, I ask you: What machine should I begin again with?

Send me your ideas and I will post them below. We can figure this out together.

April 10, 2009, Gene says: I think you have already designed the vehicle you want. Something like the Harley Automatic scooter from back when. Of course the engine should be a 12 horsepower or so and the wheels should be 16 inch alloys, at least.
A centrifical clutch driving a motorcycle chain to the rear wheel seems about right for the ratio changes you need. I think the time is right for a machine like this. If you design it, you can sell kits until one of the big motorscooter/cycle companies sees the light and buys the rights from you.
Well, you know where my heart is, Gene. This was a scooter I designed in 2003. I made it before I came to my senses; before I realized just how important it is to live better while consuming less fuel.
April 9, 09, William says:

"I can't think of a specific machine to use, but I have a suggestion: Design the kit to fit the most popular models sold.
I suspect that's going to be a medium-displacement Honda "cruiser" motorcycle.

Or a Honda Silverwing.

I'm definitely of the larger displacement school of thought. A bigger motor turning over at a slower speed won't generate the internal heat or friction of a small engine turning fast. I've noticed the best economy usually comes from an engine turning between 2000 and 3000 rpm at 60 mph. The most important (IMHO) metric is torque, not horsepower; bigger engines have torque in abundance, small ones don't, all else being equal. I'm thinking 450+ cc as a minimum, maybe even up to 1200cc.

With the flap doors for the feet, (inspired by the NSU/Baumm?) you might want to consider installing a minivan-style sliding door to help streamlining. You could also think about installing a real roof for a completely dry riding experience.

What would be really fascinating would be a treatment of the Vectrix electric maxiscooter, or its closest competitor, sold as the Xtreme XM 3500. With the Vectrix costing around $12,000 and the XM 3500 around $4,500 you might want to ask the manufacturers for a little assist, like donating the test mule? I'm suspecting the XM 3500 distributor might be a bit more receptive; if streamlining can get another 10 mph from their machine they'd compete nose-to-nose with the far more expensive Vectrix- until the Vectrix adopts streamlining..."

You like the Suzuki 400 Burgman
April 10, 09, Julian suggests: Suzuki AN400K3 for the win! The K3 is almost perfect. K3-4-5 are 200-3-4-5 and virtually identical. K3 and up are EFI with a Cat in the exhaust and a 3 bolt rear wheel which is much better. Same with K6-7-8-9 K6 was redesigned with a double over head cam motor and new bodywork, but is otherwise pretty much identical.
April 10, 09, Mike suggests:
Well, as per earlier emails, I’d take my Suzuki Burgman 400 over a Helix any day – I get 55 mpg running full blast on the interstate (70-85 actual miles per hour), average 60-65mpg normal, and have gotten 70mpg cruising 40-50 mph on secondary roads with few stops. Out of all the maxi-scooters, Suzuki seems to have the most efficient machine (gets considerably better mpg than Yamaha or Honda’s machines).

I think the upright position is more pronounced on it than the Helix though, and you would consider it too powerful as well – mine tops out between 90-100 mph on the speedo, or 80-90 actual. And I don’t think you could easily up the gearing…

Otherwise, the older single cylinder 650 BMW is a nice machine, I always got 60+mpg on mine, and some guys reported near 80 mpg babying the throttle on secondary roads. Lots of oomph too, easily over 100mph. If you geared that one up, and did some fairing improvements, who knows…. and lots of them have ABS too, which is nice. A single cylinder chain driven machine is probably your best bet, regardless, too bad there isn’t a scooter built with a manual tranny.
April 15, 09, Fabrizio adds: The Burgman 400 will be good (it also is very LOW as shape, the Scarabeo is not....). I agree also with the guy proposing a mid size engine used at low rpm. In this case, having some hp more, will make the bike more safe, (overpassing situation, etc.). Maghenzani

PS: Everyday I also think to my project: a fast vehicle (similar to the Monotracer by Wagner) with high maximum speed and low consumption if used at normal speed. In this case my engine preference will be for the 500cc kawasaki, it has low comsumption, it doesn't suffer at high rpm, it is very little, it is light... and you can buy it with few money.
You like electric:
April 10, 09, Bo asks: Why not go with an electric scooter? It may be interesting to see if you could get more mileage out of the batteries with the fairings on a long haul.
April 11, 09, Josh suggests: But if I were you I'd simply rip the guts out of your helix and convert it to electric...that way you can make whatever gearing you want and you wouldn't have to deal with a transmission. Plus you'd save yourself a lot of time trying to fit that body onto another motorcycle.
April 10, 09, Brian suggests: Electric power. Everybody’s doing it…
Craig responds: I sure hope that you are being intentionally flippant, Brian.

I like electric. But to get a horsepower of energy from the wall to charge up our battery, don't we have to burn a couple of horsepower worth of fuel somewhere else?

Does this make sense to you?

Electric would make sense if we harvested it directly from the sun, say, from our roof tops.

Can't afford all those solar panels, you say?

Lets do "more with less"

If we designed vehicles that consumed the least power, we would need the fewest solar panels. We would be able to power our vehicles from our roof tops.

It all begins with streamlining.

Streamlining is what this web page is all about.

April 10, 09, Eric suggests: Craig, The issue with the Helix was you could never take advantage of the aero improvements by changing gearing, lowering the power output of the drivetrain at a given speed. Aero improvements have to be accompanied by changes in gearing IE the most efficient setting for a vehicle is wide open throttle at a given RPM. When you make a vehicle more aero efficient, you cause the throttle to close more which lowers the power of the drivetrain, lowering efficiency. Instead, when you go for more aero, you should be able to change sprockets to lower the overall power output of the drivetrain by raising the final drive ratio. So that’s why the Helix never did what you would have liked.

My suggestions:

-A small cc’ motorcycle, maybe even an unrestricted moped. Has to have chain drive, allowing easy changes in gearing that will be required to realize benefits of decreased drag.

-If you end up getting an air cooled, the aero mods will take a bit of air off of the engine. Close off air=increased efficiency but decreased cooling. You can counteract this by having a wise engineering type person tap the oil galleys and install an aftermarket oil cooler. I know a guy that did this with an old Honda CAFÉ racer. Also, recommend an oil temp gauge so you can measure how much air you can cut off before you start to cook the oil and, in turn, the engine. A temp gauge on the head would be helpful as well.

-Shoot for low engine vacuum at cruising speed. Ideally, you want to have to pull the bike out of high gear to even make it up a hill.

Outside of that, the sky’s the limit.
Craig responds: I want to sit up and be comfortable. From my Helix work, I know that I need something like 17 horsepower. A moped ain't going to do it.
April 10, 09, David suggests: Craig, as I suggested in my column (Cycle World) a 230 Honda. Since then, they’ve introduced a street-motard version, the CRF230M. Like our dual-sport version, it’s probably right at 100 mpg out of the box. Gear it up, fit a small windscreen, wont’ll she do?
Craig responds: Well, it won't do it with a small windscreen, I am certain. It will need real streamlining to go 70 mph, into a 20 mph headwind and get 100 mpg. Look at the actual results two Honda Helix scooters in Chapter 24... 52 mpg vs 64 mpg streamlined. A cycle configuration is harder to streamline. The frontal area is much greater because we sit taller and the tail makes it awkward to get on and off because we must put our leg where the tail is. The tail is absoultely necessary. A scooter starts out much lower and allows me to streamline the rear because I don't have to throw my leg over anything. We just "sit" on a scooter. That said, I'd like to try. Could Honda be persuaded to give us a CRF to find out?

Two CRFs. One to streamline and one left alone... for comparison.

April 11, 09, Buzz asks: Does it have to be limited to a traditional 4-stroke gas burner?

Would you consider a hybrid electric/gas powered machine and then make it's body slippery?

Tradition? We don't need no stinking tradition. If such a gen-set exists, it might be a good start. Do you know of any correctly sized unit? It has to have the regenerative brakes which seem to be the primary asset.
You like the Honda 250 Rebel: April 10, 09, Gil suggests: I'm thinking a Honda Rebel, they are abundant and their 250cc engines get 70mpg and above, up to 100mpg, but depends on driving style. With a change of sprockets they cruise at 80 quite easily. It has big wheels and cruiser seating position like the helix, only thing is the engine and gas tank are positioned where the helix has nothing in the way. U could more the gas tank. It also resembles the motorcycle u used in your Fuel Economy Contests of the eighties.
April 11, 09, Jack comments: My only thought would be to look into the new small block Moto Guzzi's, the 750 Breva or Nevada. They make about 48HP, handle well, get good gas milage, and could probably do better faired.. but I don't think they'd be the ideal platform.

Other ideas would be cheaper low tech main stream bikes like the Honda Rebel or a Kawi Ninja... but none of these other than maybe the Guzzi Nevada give you that laid back ride, the Rebel is tiny for us tall people.

I wish I could be of more use but somehow my knowledge of motorcycles and scooters still caps off at about 1980 which does you no good what so ever.

Personally I'd like to streamline an Enfield at some point, they get excellent mpg already and are quite simple, but you'd want something that doesn't have to be tinkered with so often, which leads me back to that small block Guzzi.

You will note that high mileage machines have lower horsepower. 16-17 hp is all we need. My question is: Should it be a small engine running fast or a big engine running slow?
April 11, 09, Mark comments: If it was to be easy, there'd be no point.
You like big thumpers,too:
April 11, 09, April 11, 09, Ron comments: I know it's Third World, but there is a brand new Enfield engine, all alloy, I think a 500 cc single, that will give close to 100 mpg in its straight-from-the-store form; and by dint of the cubic capacity, that sort of engine should have the grunt to handle the gearing needed to cruise at sane speeds. Dial in streamlining, and you might be on a new track?
April 11, 09, Danny comments: You should have enough clout that ANY Mfg. would give you the test model you select. My suggestion for a new donated bike would be a 250cc water cooled thumper. Plenty of power, built in heater, electric start and selection of gears. If you choose to scrounge the parts, 230cc suzuki quadsport motor with reverse, grafted into a stretched dirt bike frame.
April 10, 09, Q wrote: My suggestion is to use a small diesel engine driving a 5 speed transmission via primary chain, then chain drive to rear wheel. Use 18" wheels with skinny, hard tires. Use a long wheel base so you could sit low in order to reduce overall height. Make the body of 1/2" surfboard foam bent over a tubular aluminum ribs covered on the outside with thin plastic wrap, perhaps shrink wrap.

If you want to use a gas engine I would suggest a single cylinder low RPM engine in the 200cc to 250cc range. One of the Chinese Lifan 200cc OHV engines would probably work fine. Stick with a 428 non O ring chain.

April 17, 09, Pete C. threatens to build a feet-first B31. I have long held the view that there has been no deliberate improvement in engine design for the sake of economy. Vehicles use fuel and governments tax fuel so there has been no incentive.
However there was a recent period of history where economical, simple transport was essential and that was in the post WW2 years. My father used a BSA B31, an all iron 350cc single, it did 60 miles per gallon, he would have had to walk if it didn't. It also did this with him sitting bolt upright wearing his ex army great-coat!
Craig asks: Did your father get 60 mpg at 70 mph into a big headwind? Isn't it important to qualify the conditions of the mileage? The B31, am sure, got the mileage you remember, but probably not at today's speeds. Right? Streamlining just might make it happen, though.

I agree with you about lack of incentives. Who makes more money doing more with less? Nobody. Take a look at my "Freedom Machine" for incentives that would mean something to people today.

April 11, 09, Rich suggests: I know you want to ride upright, but look at Dan Gurney’s Alligator motorcycles, and the Feet Forward sites on the web. I think you can cut drag and still have a comfortable, utilitarian position. You don’t have to be as high above the ground to be seen as you currently prefer; a small reduction in height will give improved MPG without hurting your visibility significantly.

I love the big thumpers because they seem to sip fuel. But their cylinder sticks up really high. We would have to develop a whole new frame in order to sit low and keep the frontal area small. Or would we? I had the opportunity recently to ask Dan Gurney about fitting one of Fred Hayes' Diesels into an Alligator frame:
Vetter, Gurney and Fred Hayes' Diesel engine superimposed onto an Alligator frame.

It looks like it would fit. Pretty cool, huh? With my streamlining, this combination offers the most promising formula for 100 mpg at 70 mph into a 20 mph headwind. But this combination presents the greatest amount of work, too. I would like to get to this. But, what will I ride around this summer?

Ed votes for the 500 cc Scarabeo
April 11, 2009: Ed brings some real life experience: SUGGESTION ONE
I have taken a close look at the F650 BMW single
Belt drive / simple gearbox / easy to raise final drive ratio
Already relatively low seat, could lose three to four inches by swapping the rear unit, minor changes to the seat, and even a lower-profile tyre!
SUGGESTION TWO Aprilia Scarabeo 500: Injection 500 single, big wheels, good handling, good standard mileage, and good standard distance on a tankful of gas
The seat can be lowered, (a lot, very easily!) the rear units can be swapped, AND it handles very well out of the box, (possibly due to Italian design)
Already somewhat Feet - Forward, it wins over an AN400 due to bigger wheels (the "Roll-Over-Effect" on highway irregularities, etc)
Twin front discs and Fuel-injection economy and low-weight. I have ridden both a modified AN400 and a seriously modified Scarabeo. I like the Scarabeo. A lot.
Finally, I have just done my first annual gas mileage check on my present Yamaha XP500 scooter.....
49mpg!!! NOT good enough (especially as I keep everything right up to "blueprint" state)
April 11, 09, Arnold says: All current designs with shapely front ends and blunt rears are backwards.
Vetter says: Amen
April 11, 09, Tony comments: I‘ve been reading your progress on your project with interest and applaud you for what you attempted to do. It seems however, that it *might* be better to concentrate your creativity on something that is more adaptive, something that can improve a broader range of vehicles rather than something like the Helix? The Helix (and vehicles like it) were never meant to be a real road machine. I’ve had thoughts of a three-wheeled high-mileage vehicle since college, based on (at that time) a Honda 350-4 or 400-4, I thought that would be a really sweet set up with a two wheels in the front and the existing rear wheel driving the vehicle. Something like that could easily sit two people side by side.

These days I think the better power plant to work around would be the already high-mileage, efficient Kawasaki twins: the 250 or the 500 from the Ninjas. These are proven power plants.

I agree with some of the posts regarding keeping RPMs low and the importance of torque over horsepower. Low revs improve ride-ability (less buzz) and increase engine longevity.

My KLR650 is in the shop for a re-bore to take it to a 685 for reduced vibration (lighter piston) and greater low-end torque. What happened to your super KLR fairing project? I already get 52 MPG with a 250 lb rider and full luggage. Getting 65 would be WONDERFUL. Could mileage be increased that much? The 250 Ninja already gets over 80 MPG, but that’s a kid’s crotch-rocket… How could current motorcycles be adapted (fairings?) to yield better fuel performance?

I’m 52. I don’t want to ride a kid’s bike. I tried a Honda Pacific Coast and felt cramped by comparison with the KLR. I want to be able to ride in a comfortable, upright, relaxed posture. Motorcycles are inherently less safe than cars. My posture on the KLR (or any dual sport) give me an edge in traffic: I can see OVER the cars ahead of me, and hence, more safety. Any prone vehicle will be lower and less visible to cars and also have less visibility.

Sorry this has rambled so much. Thanks for being there. >From one industrial designer to another: good luck and God bless…
Three wheeler? All the width of a car with the carrying capacity of a motorcycle. When I cannot hold up my 2 wheeler - and that day may come - I might consider 3 wheels.
Interesting that you bring up my KLR Fairing. I was well on my way to developing it when I encountered the "Truth Project" from Focus on the Family.


The truth is streamlining is round at the front and pointed at the rear.

See: No point at the rear. Since I did not know how to put a tail on a cycle, (because I could not get on or off with a tail) I abandoned the project. Instead, I began with a scooter that would allow me to employ a tail. (I think I know how to put a tail on a cycle now but we still would sit pretty high on the KLR)
April 11, 2009, Kevan wrote: am sorry but not suprised at your conclusions. I had hoped that you may have found some way of tuning the motor and altering the gearing thus allowing the new bodywork to be taken advantage of. I kept a Helix in my garage just in case.
I see that people are throwing ideas at you already but before throwing in my two penny worth I would like to ask you where you are going with this project and what do you ultimately want to acheive? Are you just looking to modify a doner vehicle with a view to producing a kit or is a "clean sheet" design now in the equation?
Regarding engine choice I wrote to Kevin Cameron of Cycle World about the factors involved in creating an economic two wheeler, mentioning your project and his reply is in the May 09 issue,page 106 headed "Candid Cameron". Significantly, he writes, " Ideally, you would provide an engine that was about twice as powerful as needed for the desired cruising speed." If I understand his reply correctly he is saying that the engine should be sized and geared so that it runs at its point of minimum specific fuel consumption when at the desired cruising speed.
I have some suggestions regarding this project but need to know which way you are looking to go with it .
This is the last answer for the night. Actually, Kevan's questions are very good. I will try to give thoughtful answers.

I have a couple of problems I am trying to solve. One is to have something better to ride for this summer. The other is to be making progress in the long haul.

To solve this summer's problem, I need to begin with something I can build quickly to replace the Helix. It will probably be one of the machines mentioned on this page... a 400 Burgman, Scarabeo, Honda Rebel, or BMW GS 650.

At the same time, I am working to finish the streamline tooling. Since the streamlining is for the rider, not necessarily the machine, the streamlined bodywork parts will work on any machine.

In the long term, I want to build a Diesel - for cross country travel - and an electric vehicle for local travel. To build these machines, I will need the expertise of others.

It would be pointless, however, to make an electric vehicle unless I put solar panels up and used the sun for power directly.

All these machines will need the streamlining I am developing. All will be absolutely dependent upon streamlining, which brings me in a big circle, back to my roots as a fairing designer.

Nuff for now...

I do thank you for your comments

Master Index to the Last Vetter Fairing Story

This page posted April 9, 2009

Updated August 25, 2010