Can I jump in with a related question on the tubed vs tubeless - what makes a tyre need to be tubed?
I have 125 x 12s on mine and one is leaking very very slowly. I took it to the tyre experts and they said it is leaking around the rim, and there's no tube in there.
Do I need a tube in there and is there any way of telling if the other three tyres do have tubes?
If I may I'll add a little to what Hobo1960 has said.
There are specifications for wheel/rim design. One source of info is in the various series of 'Automotive Handbooks' published by Bosch, Germany.
You might find one in a larger bookshop or library.
When tubeless tyres were introduced, the wheel rim design was changed to include a safety 'hump' This is visible on the outside of steel wheels, on the outer and inner flat sections of the rim as a slight depression or groove running all around the rim. On alloy wheels you'd need to remove the tyre to see the 'safety' hump.
There is also typically a 2.5 degree taper to the bead seat. (this angle can vary depending on application).
Tubeless tyres also have a layer of softer rubber at the beads to help sealing at the bead seat. Iirc, this layer of softer rubber may also moulded into the entire inner surface of the tyre to help seal around anything that penetrates the tyre and so avoid/slow deflation.
As Hobo1960 has said it's permissible to fit a tube of the correct size in a tubeless tyre if fitting to a tube- type wheel. You need to use French/tyre chalk and ensure no air pockets exist between tube and tyre inner. This isn't likely to cause any problems on a Fiat 500 but is a concern on cars driven at high sustained speed. As someone else has said you need to remove any labels and any moulded ribs/ridges etc. inside the tyre. If left in place, these will abrade the tube causing deflation. I found this out the hard way in the past, only took less than a couple of 1000 mls to happen.
Remember that you won't be getting the full safety benefits of a tubeless tyre if fitted to a tube-type rim - no safety hump to retain bead in place if tyre deflates, possibly no taper angle on the bead seat. Bear this in mind if running tyres at low pressure, think Fiat 500 front tyres!!
Fitting a tubeless tyre to a tube-type rim without using an inner tube? I've never heard of anyone doing this. I'd imagine it's not a good idea....
How to tell if a tube is fitted? Look at the valve stem, if it's a plain taper from where it exits the rim up to the valve cap then it's a tube that's fitted. If the valve stem has a slight bulge where it exits the rim then reduces in diameter before tapering to where the valve cap is fitted, then it's a tubeless valve (no tube).
As an aside, Am I correct in thinking that the Fiat 126 was available fitted with Dunlop Denovo Run-Flat tyres and used possibly a split rim design?
(or is my memory concocting fiction again!).
Al.