We have ridden tandem for about 25 years and have gone thro' all the stages of super light to rugged and comfortable. This has lead over the years to a stable of tandems with 26 inch, 40 spoke wheels. For the sort of riding we do, 3000 miles per year made up of fast club runs and 1000 mile self supporting tours we have found 26 in wheels to be strong and reliable with a really good mix of available tyres for all types of surface.
However, it is becoming very difficult, in North America al least, to obtain rims with 40 holes. Mavic have stopped supporting 40 holes, leaving Sun with the Rhinolite and Mamoth, and Velocity Aero, all of which are difficult to get at short notice. FIR rims also support 40 holes but are not a serious alternative in any size at the moment, being much too light construction for tandems.
The long term I'm sure is that I will be faced with having to buy new hubs with 36 holes to overcome lack of availability of rims, a propect which does not appeal. Anyone got any advice?