From a time when Citroën led the way – and, of course, nobody followed
The standard wheels for the Citroen SM were heavy steel items, clad with hubcaps. These are made from stamped stainless steel, held firmly to the wheel by a centre bolt. The centre section is painted satin black and the sections between the outer fins are painted in satin silver-grey. There are holes in the hubcaps that allow the actual wheel bolts to show. Although that might not have been the intent, there is the distinct feeling that they were trying to ape the fancy US wheels fitted to any US muscle car of the period. As such, I have never found these hubcaps entirely convincing and, although time has made me more tolerant of them, at the time I even found them a bit tacky. As I know, they are also a pain to restore, since paint never likes sticking to stainless steel.
But there was an alternative, that looked much better. The Michelin RR wheel, clad of course with a Michelin XWX tyre, is the holy grail of many Citroen SM owners. When I bought my SM in 1996, I toyed with the idea of finding a set of RRs, and there was talk of unused wheels being available for under £1,000 a set. This seemed an unjustifiable indulgence. Now, you will pay well over £1,000 for a single, used wheel.
Like the SM name itself, there are at least two interpretations of the initials, either “roues en résine” or “résine renforcée”. Either way, these were developed by Citroen’s then owners, Michelin, with the intention that they would provide a lightweight wheel for the SM to go rallying with, which they did with some success.
Apparently derived from a NASA patent (used on moon buggy wheels) the wheel is a one piece, technologically advanced, reinforced resin casting, being almost 1/3 of the weight of the equivalent steel wheel and much stronger. Since carbon plays a part in the reinforcement, you will come across rash claims that RR wheels are, in fact, carbonfibre. That has some justification, but only if you believe that scrambled eggs are a souflée. Nevertheless, the wheels seemed to be of great technical merit and Michelin proposed them to various carmakers. In the early 70s, Lincoln even tested them on a Continental.
Why they didn’t go further is probably due to the industry’s conservatism, rather than an inherent flaw. The RR wheels come from a time when Citroen were truly innovative, and time has shown Michelin’s manufacturing process to be excellent, considerably more high-tech than that of kit car body laminate and, unlike, say, 60s Minilite alloys, there are no horror stories of drastic degradation. But nothing lasts forever and there are maybe legitimate concerns about relying on a 45 year old composite for your contact with the road. Or maybe I’m just writing that to justify my still having those iffy hubcaps, now in need of yet another renovation, on my car.
There is, however, now a third alternative. SM tuning legend, Regembeau, have released a set of RR lookalike alloys. Damn.