eta: super efficient 3 wheeled car (project thread)

[eta]

Hi, I'm new. "eta" is the Greek letter for efficiency; I want to build a very efficient, super lightweight 3 wheeled car. My design: a side by side 2 seater using the Suzuki 3 cylinder 5 spd drive train.

2 powered wheels in front and a single rear wheel, using as many OEM pieces as possible, front struts, brakes, steering, with a fabricated swing arm rear suspension with a coil-over shock. A steel tube space frame with bonded-on ("stressed") honeycomb aluminum body panels.

I want to make a "bare-bones" running prototype first, with minimal body panels and just a lexan windshield, no doors or other windows. Later I intend to add aerodynamic body panels and weather protection, removable "gullwing" doors, etc.

This will legally be a motorcycle, which makes all the government hassles more manageable; it will have a full roll cage and 4 point racing harnesses, helmets will be worn.

I hope to keep the curb weight down near 800 lbs and so it should be fun to drive, have excellent performance with truly outstanding economy. This 3 wheel layout gives fantastic aerodynamics, a perfect teardrop shape, less weight, rolling resistance, etc.

Your first question, will it tip over? A 3 wheeler of this "tadpole" 2F, 1R layout can be just as stable as a good 4 wheeler, if it has a wider front track, low cg, and proper weight distribution. I plan to use the right-side axles from the 4 cylinder manual trans Suzuki on both sides, as they are longer, to increase the front track from 52.3" up to 60-66".

I also want to experiment with propane. It burns cleaner, the equipment is simpler and I can use an 11:1 compression ratio possible with the 100+ octane rating to get very good efficiency. Yes propane doesn't have the energy/gal of gasoline, but it has HIGHER energy/lb.

I hope eventually this will be a universal frame design that can utilize different drive trains such as VW diesel, or electric, or even hydrogen. I have some rough drawings and notes, including a static stability calculation I can post here if there is interest.

At this point I need feed back and a real engineer to help finish the design. I have shown my sketches to Dave Norton, see his Shrike design online. So, any comments about my little project?

[newtonsfirstlaw]

How big is the engine? And could you go smaller?

[MetroMPG]

I believe the Suzuki drivetrain he's referring to is the 993cc version from the Geo Metro (& various clones). Could he go smaller? Yes, but that's the smallest most commonly available automobile engine in North America. (Though there's always the motorcycle fleet to pick through for smaller engines...)

I did a quick search for "Shrike", and this is what I found:

Norton "Shrike"

My goal for the Shrike was to achieve a unique balance of competing factors, suitable to my own tastes with almost no thought of mass market appeal.

[...]

Here is a rough listing of my priorities, with 5 being most important, 0 least: Crash Safety: 5. Accident Avoidance: 4. Lateral acceleration: 5. Acceleration: 3. Cost to Produce: 4. Individuality: 5. Convenience: 1. Appearance: 1. Operating Economy: 2. Ease of Manufacture: 4. Simplicity: 4. Passenger(s) Accommodation: 1.

Source: http://pages.zoom.co.uk/elvis/shrike.html

[eta]

Yes I like the 1 liter 3 cylinder Suzuki engine. It is very efficient, reliable, cheap, readily available and only weighs 140 lbs! I have had Geo Metros and they get 50 to 60 mpg, and with "eta" I hope to cut the weight of the vehicle in half. I like the idea of using a automotive engine and drive train, as it will be very lightly loaded in this application. It will have plenty of torque, and over-engineered brakes, etc. A motorcycle would be more heavily loaded than it was designed for, might have cooling problems, doesn't have enough electrical output, and most do not have reverse. Dave Norton's Shrike is based on a motorcycle and it goes through tires very rapidly, has clutch problems, and has no reverse gear. I intend to get a Geo Metro donor car for cheap and rebuild the parts I need, I suspect a motorcycle might cost me just as much or more. I also think motorcycles are not tuned for economy, but power.

[SVOboy]

Sounds the a great project, I can't wait to see what it turns into,

[MetroMPG]

Originally Posted by eta

I like the idea of using a automotive engine and drive train, as it will be very lightly loaded in this application. It will have plenty of torque

Good point, which causes me to suggest you also aim for taller gearing than will come with the 3-cyl motor & original drivetrain.

might have cooling problems, doesn't have enough electrical output, and most do not have reverse. Dave Norton's Shrike is based on a motorcycle and it goes through tires very rapidly, has clutch problems, and has no reverse gear.

Those are good points.

It's an interesting idea. All of the 3-wheelers I know of have been built for speed, not fuel economy (like the T-Rex).

[roflwaffle]

Motorcycle engines have crap BSFC compared to larger car engines due to their power to weight ratios. No reverse gear isn't a big deal since we can always just use an electric motor for that, but it still may weigh more than a reverse gear in a manual trans.

[eta]

Yes higher gearing makes a lot of sense with a car this light. I'm going to research the gearing options on the TeamSwift website. As I remember some Suzuki manual transaxles do have higher (lower numerical ) final drives, I think the 4 cylinder models and the XFI economy 3 cylinder version? And I could also go up to bigger diameter wheels as well. That way I might have the choice of some nice light alloy wheels and high pressure LRR tires, although it is hard to find wheels and tires that are skinny enough! The stock steel wheels are 12" diameter and just 4" wide, with a 145/80 tire, which is plenty for this light little car, it will just be driven mildly. I can just use the OEM wheels and get Yokohama Y372 tires, which are (marginally) available in 145/12 and are a good all season tire. They weigh just 11 pounds, but unfortunately are only rated up to 32 psi. Not very exciting, but adequate. And I'm not ready to run space saver spares. Any suggestions?

[eta]

The Vortex 3 wheeler: http://www.vortexplans.com/ is based on a motorcycle. Go to Dan Lenox's link off that website for a discussion about building an electric reverse for his Vortex.

[MetroMPG]

Originally Posted by eta

As I remember some Suzuki manual transaxles do have higher (lower numerical ) final drives, I think the 4 cylinder models and the XFI economy 3 cylinder version?

The non-GT 4-cyl transaxle has the tallest final drive. It's what I put in my 3-cyl car.

light alloy wheels and high pressure LRR tires, although it is hard to find wheels and tires that are skinny enough!

I think most people who know about LRR would instinctively suggest the Bridgestone P165/65R14 RE92’s that were used on the Insight as a great LRR tire.