[JohnAh]

If you want to experiment with hybrid systems, extra ICE's etc easily, one major problem may be how to transfer power mechanically. I've been thinking a long time for a spring-loaded 5:th wheel behind the car, but then it must not only transfer enough power to (from) the road, it must also follow in every pot-hole and bump. It the 5:th wheel should double as a clutch, the swing arm travel must be even longer.

So why not press that 5:th wheel against one (or both) rear wheels of the car instead of the street? If placed right behind the rear wheel, it will be almost independent of how the car's suspension moves. If the 5:th wheel is to double as a clutch (by an electric motor or mechanical link) the movement only needs to be a few centimeters or an inch.

This kind of friction drive will probably slip a lot easier than a 5:th wheel directly to the ground, but fir longer distances in higher speeds the power is transfered more by speed than by torque, so perhaps it can work great?

The 5:th wheel can also be smaller without need for a sophisticated suspension. A smaller wheel means less torque transfer and/or perhaps more deformation/friction losses?

Will there be a hopeless slip in the slightest of rain, mud and snow?
Will there be more friction heat than with a 5:th wheel directly to the street?
Will there be increased and strange tyre wear or even damage? (something chemical with rubber against rubber perhaps)

If this sort of friction drive can be used it will make experimenting a bit easier, and the 5:th wheel may even be hidded inside the fender discretely. It can make a front-drive car a 4x4 (or 4x3) that MAY not get stucked just as easily in the winters.

I intend to use this type of drive system for a tiny Kubota diesel engine with barely enough power to keep my car at a steady cruising speed. My idea is that such an engine kan be kept perfectly within the BSFC sweet-spot for long distances. (brake specific fuel consumption), being way more efficient than a larger engine at part-load. If the tyre-tyre friction drive can have marginal losses, the rest of the transmission can be kept very simple. The soft friction drive will also help reducing vibrations from the quite rough diesel engine.

With a second friction wheel, a 6:th wheel to the car's other rear wheel and a lower gear ration, I can also get a simple backup system that will get my car back home after a main engine failure. Perhaps I'll waste some extra weitht on installing a hydraulic CVT on that 6:th wheel, then I may get a perfect drivetrain for rush hour traffic as well.

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I've been doing this insane Burn & Glide (burn & coast, pulse & glide) driving for two years now, saving incredible ammounts of fuel. This efficiency comes with a price though, in shape of starting/stopping the engine, accelerations and coasting, in cycles of about a minute. Since there is so much variations in speed, I have to stay away from other traffic as much as possible, or someone may kill me in pure road rage one day... This benefits of this crazy driving comes from the fact that most car engines are way oversized for keeping the cruising speed but the extra power is surely needed quite often in short bursts. By covering the two needs by two separate ICE's I think it may be possible to get the best of both.