Designing for efficiency
 

Just as a design exercise, I would like to design a single-seater commuter vehicle. I would like to keep it relatively simple, so it would be in the realm of the home builder. In essence a 'green' version of the Locost home-built sportscars. (Because I am new here, I can not yet post links to websites. If you are curious, search for Locost Builders in Google) Obviously, the design would be geared entirely towards fuel efficiency rather than performance.

What I had in mind was a single seater, three wheeled vehicle. Two wheels at the front, one at the rear. The easiest way to build it would be by using the engine and swingarm from a light motorcycle. The body of the machine would be teardrop shapedfiberglass, with a clear canopy.

I would really like some input on a few design choises I have to make.

Starting with the engine. The whole vehicle would be as light as possible, aiming for under 300kgs (660lbs) including fuel, excluding the driver. Since it will be designed as a commuter vehicle, and part of my commute includes a highway I can not avoid, it has to be able to cruise at 100kph or 60mph. For the engines, I am looking at these options: 125cc, 4spd semi-auto / 250cc, 5spd manual clutch / 250cc CVT -power output for all these engines would be in the 10 to 20Hp range, with the smaller displacement engine being on the lower side of that figure. Of these engines, which would be preferable? I'm thinking the 125 could reach the best fuel economy, but I am worried the weight might be a little too much for the little motor to pull.

Next are the tires. Most low-rolling resistance tires are for 14 or 15 inch wheels. Would smaller wheels be even more efficient? For example, the classic Mini uses 145/80R10, pretty much the smallest tires a street-legal vehicle could run. Would these be preferable over the larger LRR tires I wonder?

There is much more, but I will try not to bore you guys with an enormous wall of text and instead take this design process step by step.

Any input would be greatly appreciated!.

Your vision sounds a lot like the HyperRocket that's featured on the front page of this website.

HyperRocket: 125 mpg, 100+ mph 3-wheel motorcycle | Hypermiling, Fuel Economy, and EcoModding News - EcoModder.com

Welcome to ecomodder, noorderbuur ;)

I'd use 4 wheels.
While 3 wheels have less drag and weight, the vehicle will also be less stable.

I'd use a manual transmission.
They're far easier to re-gear using different sprockets, than adapting a CVT.
When adding a streamlined fairing, you'll need to re-gear the drivetrain to lower rpm @ your most used speeds.

i dont think a 125cc engine will be enough...

shoot for a 250cc engine from a Kawi EX250.

By design exercise, do you mean you are not going to actually build a car?

I'm not 100% sure, but think the taller the tire the less rolling resistance (all else being equal).

I'd love to, at some point. Right now it's a matter of time and money though. It'll be a while before I'm in a position to tackle such a project. In the meantime, I can sketch, doodle and think, before moving on to a CAD design. Hopefully by the time I am ready to build it, I'll have a full set of plans to work with.

Stability shouldn't be much of an issue - I won't be racing it, and the center of gravity would be pretty low. Besides, there's something else a 4th wheel adds: complexity. Driving a rear axle means I'd also need to use a differential, adding even more weight and design issues. I'd like to use the entire drive section from a light motorcycle. it keeps things light and simple, plus it would get me closer to a real teardrop shape.

Excellent point on the gearing. Looks like a 250cc motorcycle engine will be the ticket then.. anyone know of particular models that get good fuel economy?

Similar in concept, yes. Though I hope to take more design cues from the Peraves Monotracer - only in three wheeled form. A tilting trike would be ideal, but needlessly complex I'm afraid..

Valid points.

Be sure to keep an eye on the CoG and the weight distribution.
Shifting weight aft will give more traction, but can result in the CoG going outside the triangular wheelbase more easily - thus rolling the vehicle.
It happens on velomobiles.


Search the database at Advanced search - Spritmonitor.de
Use very few search factors - say just vehicle type : two-wheeler - gets you a list of vehicles with low fuel consumption.

One of the types that keeps popping up frequently in that list is the Honda Innova / ANF 125i engine.
It should put you solidly below 2.0 L/100km / above 115 MPG.

Of beter dan 1 op 50 , zoals jullie het in Nederland graag uitdrukken ;)

If you keep the weight down, a 125cc shouldn't struggle too hard when the vehicle is really well streamlined.
I wouldn't rule out the 125cc.

See what's possible with a Honda 125i :
Home
1L/100km or 235 mpg


You might want to replace the heavy fiberglass with Zote foam
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