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Old 08-30-2012, 03:00 PM   #234 (permalink)
EcoModding Apprentice
Join Date: May 2012
Location: Vallentuna, Sweden
Posts: 129

Phantom Blot (Spökplumpen in swedish) - '75 Saab 96 V4
90 day: 52.77 mpg (US)
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Interesting project! As a comparison for small lightweight enclosed vehicles I have a 1959 Heinkel Kabine 3-wheeler: Heinkel Kabine - Wikipedia, the free encyclopedia
It weighs about 250Kg/550lbs, have a single cylinder 4-stroke 10hp/200cc engine with 4-speed gearbox. It can carry two persons in about 80km/h or 50mph in flat ground without too much wind. The slightest inclination will make the speed drop a lot. A fifth gear would be nice as first gear is to high and the difference between gears is a bit to long.

The body may seem streamlined but the side-by-side configuration and the steeply rounded tail makes the Heinkel slower than it could be. The Messerschmitt KR200 with the same engine performance can reach almost 100km/h or 60mph under the same conditions. Messerschmitt KR200 - Wikipedia, the free encyclopedia

Both these vehicles have small 10" wheels and i guess bigger wheels means less rolling resistance.

I´ve been driving small under-motorised cars and 3-wheelers for many years. One thing they seems to have in common is that it may take very long time to reach high speed and the smallest inclination or opposite wind will make it impossible. But while once reached high speed the vehicle seems to be able to keep it for a long time even if I have to go uphill for a shorter distance.

Gear ratio and number of gears are an important factor. The fewer cylinders the peakier engine. Fem cylinders can be compensated for only by more gears. With too few gears the engine can´t reach the revs where it produces the power needed for acceleration. Once at high speed the engine can produce power not only to keep speed but also to continue accelerating! To be honest I´m afraid a 100cc single cylinder engine in a 200kg/400lbs vehicle would need at least five gears to reach highway speed unless a downslope appears.

What I also have learned from my three-wheeler and two tiny fiats is that low weight isn´t always the best. To maintain speed it can actually help to have some extra weight that acts like a kind of "linear flywheel", at least when the vehicle have to few gears. What is the best depends on what type of road you mostly travel. For city traffic, low weight is mostly a winner.
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