He says that both the 4.40 and 4.80 x 10 inch size tire manufacturers recommend a 3 inch wide rim.
Less certain of a recommendation for a 5.20 x 10 inch, as they do not stock that size and therefore had no info on it. My Zeta Sport Prototype has this size tire on only a 3 inch wheel. Nearest comparisons that I could come up with call for a 3.5 inch with for a 5.20 x 12 inch tire, and somewhat less explicably a recommendation of a 4 inch rim width for a 5.20 by 12 inch tire manufacturer.
Have you indeed found a source for these?
I suspect a radial tire on a single rear wheeled vehicle with both the engine and trans mass dampening road irregularities would make lower profile less of an issue. Radials have lower rolling resistance, higher powered lightweight race cars benefit from wide tires, and aerodynamic resistance of a tire at the rear of a microcar at speeds of 45mph are usually considered to be insignificant.
4.40 by 10 is nigh on obsolete in the UK, I think only Trelleburg were offering a tyre, at a huge price and its not the best rubber. When I last messed with a Treinkel you could buy a Kings tyre 4.00 by 10 that bulked up well. Likewise 4.80 by 10 is limbo land though Uwe Staufenberg offers both, I believe. With the Goggo I was using the Coupe rims to run 145 by 10 Mini tyres, They pinched in a little. So I assume they were 3.5J rims.
Cannot comment on Frisky/Zeta but 3J sounds a bit skinny for a Mini. I seem to remember Frisky using 4.80 by 10 but without looking in my stack of stashed info I could be wrong.
Is a 145 by 10 not the same section as a 5.20 by 10 crossply?
If the above is true then I repeat Falken do 145 by 10. Do not know of a cross ply manufacturer that size, talk to the Isetta trike boys.
Not sure I follow your logic on fitting bigger tyres. The weight of the car does not alter but the unsprung weight of the wheel might. The less give in the tyre the less it offers to the suspension. A common error of fitment and why so many modern whizzo wonders are so uncomfortable.
Lightweight racing cars are just that, lightweight racing cars. They are designed with the idea of fitting large specialist tyres. They have fully adjustable suspension. Tyre wear is not an issue over performance. Most humble small cars do not have fully adjustable suspension nor were designed to have wider tyres. It is not a bolt on and go solution. It needs testing to see if the result is satisfactory.
What I will agree is that a wider profile in common use provide better compounds of rubber and more choice. As a for instance I suspect the best set up for a Messerschmitt will be some good scooter tyres on the front and a widened panzer wheel on the back with a reasonably low profile wide tyre on it. However to get the best from this would require the engine to be tweaked to give of its best to make up for the slightly increased drag on the rear and the front tyres would be worn pretty fast being driven into the bends. The very reason that in fact 4.40 by 8 inch tyres were found to be the pick as they offered the compromise in grip, handling and longevity in normal use. I believe it is even quoted in later literature in Germany for the cars.
Isettas in the UK used 4.80 by 10 to the front and 5.20 by 10 to the rear, I think. The four wheelers were 4.80 all round? The early car had split rims and might have had narrower but were not trikes. I believe the BMW 600 and Isetta have three none split rim offset version between them and its all got a bit mixed up in some places.
Back to the thread. As I said there is a scooter rim that is like the Trienkel and I suspect its for a 4.00 by 10 so it will be narrower. The Tourist went on to a fixed rim, none split, with a welded centre before becoming a 5 stud split rim wheel with the Eahrles forks. Dunlop where a wheel manufacturer as well as a tyre manufacturer - see Bond Bug alloys. I have no idea why wheels are still imperial in a metric world, save our dear chums, the French, but maybe Britain claims to have invented them! Certainly many wheels for many cars were, and still are, made in Britain.
I still have many spare Treinkel rims so gaining an additional one is not a problem over and above logistics.