My opinion is that for racing/extremely hard road riding, tubeless is the automatic choice. Whilst I would not use ‘non centreing’ tubeless rims, many people do. I bought into SIP rims years ago, but the tubeless split rims now available appear to be a good product.
However, for as complete a scenario as I can give, the top racer Charlie persevered with split alloy rims which he would have procured via your friends CamLam. They are a lovely product & if fitted properly by somebody with your obvious competence should be relatively safe, even in the event of a puncture. I reckon that a Lambretta will normally be controllable to get to the side of the road in the event of air loss as they don’t have a tendency for the tyre to go all out of shape. So, despite what I have said above, my road SX still has OEM rims fitted with the correct tubes. If that appears to be a contradiction, I apologise, but I just haven’t got around to changing the format, even though I have a set of Ressurection Scooter split alloy rims earmarked for the bike. Not enough hours in the day…..
Before the tubeless rims were allowed in racing, I looked at what the bikers do that had to race using their OEM wheels. They went tubeless by sealing up all the spoke holes with - I think - a silicone type sealant. Despite having no beads to stop the tyre wandering in the event of a puncture, such tubeless set-ups were safer as tube-to-tyre creep/heat build up was eliminated. So, there is yet another option & something I would have implemented had the SIP rims not become available at a good discount to me
Finally, for complete ‘completeness’ be aware that the alloy tubeless rims do tend to be offset due to their design, so they ideally should be used in pairs. Ha! Would any variance in offset of a machine with scaffold tubing & a swinging engine as rear suspension be noticeable by the rider, I am unaware
