I compared with another rim which has the same external width of <>19mm and the orange one fits snugly in perpendicular to the rim. It's a crappy old rim I'd be reluctant to commit the tyre to, but I gave it five minutes of trying to lever one part of the tyre inside the rim but there was no way it was fitting. The flat part on the inside of the tyre is <>16mm and it doesn't compress very much so I think this is probably the minimum inside rim measurement necessary for this tyre. It's a pity this is the hardest measurement to actually take.
Absolute best case scenario is that the 23 tyre would fit with the red clips, and I 'only' lose 40 pounds on delivery if they allow an exchange but I have my doubts and could easily end up 200 quid in the hole with nothing but tears to show for it. Trading in the rims seems like the best solution if I can find a place willing to do it.
They go through the tyre and hold it in place on the rim. There are holes every few cms for a pin. Each end of the pin sits under the "overhang" on the rim.
I've found someone selling a pair of Mavic cxp33 622x15c which would suit my needs. They originally and with a 9 speed set of cogs. Would a 7 speed set likely fit and is it difficult to switch them over?
(I have 'retired' several sets of wheels that were otherwise working perfectly but have what I think are well worn rims. Problem is I don't really know if I'm being over-cautious.)
'These airless bike tyres could put an end to punctures':