Hope it's alright for me to jump in before Gareth . . .
On a related note, I recently stripped the tires off my factory original steel Plus 2S wheels. The car is a February 1970 unit and presumably the wheels from around then, too.
Did the job myself, on a conventional tire machine and wow . . . they did NOT want to come off. More specifically, the "bead" of the tire was so tight on the rim's seat that it seemed welded on. In other words, the Kuhmo tires' inner diameter was too small for the rim. To break the bead (slide the bead off the seat of the rim and into the drop center), I had to repeatedly reuse the machine's bead breaker and rotate the tire around to different positions (normally never necessary) and the machine wanted to simply fold over the sidewall of the tire instead of sliding the bead off.
Personally never seen anything like it. Which leads me to believe that Lotus wheels of this period have bead seat diameters that are a little oversized. If my wheels where the cast ones, I would definitely put them on a lathe and take off just a little to ease this problem. As it is, I'm not sure the steel is of sufficient thickness to safely take off enough material to make a difference.
Question is: are there more owners with similar experiences? Perhaps the tire mounters are not telling owners about the problem with oversized rim diameters . . . ? And interesting to see that at least some of the cast Lotus wheels seem to have exactly the same issue.
Randy