1) Frame. Beefy enough? YES; teams weighing over 500lbs own and ride the same frame used on your Speedster.
2) C/F Fork. Strength is not an issue and the W/U fork will handle the same size tires that Co-Mo's Cromo forks will: can't confirm if that would include a knobby 35mm so you'd need to ask one of the folks at Co-Mo for that bit of info. My only consternation would be chip and nick damage from gravel but that is more of an issue of aesthetics than durability and will pertain to any type of fork, downtube, and boomtube.
3) S&S couplers. The couplers are easily many times stronger than the tubing they are bonded to. In fact, there are several teams who own full suspension off-road tandems with S&S couplers that are ridden on very technical terrain.
4) Low spoke count Rolf wheels. Uh, no. A set of conventionally spoked wheels would probably be required for a couple reasons: rim width compability with your suggested 35mm knobbies, overall durability given the abrubt side loads that wheels encounter off-road, and reduced reliabilty / longevity for road riding.
Comment: If I could only have one tandem and expected to ride it off-road on a regular basis as well as on paved surfaces it would be built to work with 26" wheels. There are few if any real disadvantages to 26" wheeled tandems, but they just aren't as sexy as a 700c model which remains the more popular choice. In fact, in my mind, the "uber-tandem" would be a 26" compatible model with S&S couplers for maximum flexibilty and international servicabilty (almost every bike shop in the world will carry 26" rims, tires, and tubes, not always the case with 700c). But, if you really want to go over the deep end, the real trick would be having a tandem built that has dual disc brakes and two forks; one for use with 700c wheels and one for the 26" wheels so you can have your cake and eat it too.
Less I digress further, you can pretty much have anything done when you're having a tandem made. The trick is keeping your requirements realistic, practical, and executable within your available budget and the capabilities/experience of your builder. Thus, if you really want an enduro that can be used on and off-road with off-road accounting for more than 10% of your riding, a 26" model might be the better choice. If you're pondering the occassional dirt road adventure, a set of larger tires is probably all you need IF you stick with a conventional wheelset for your tandem. If you get into the Rolf Vigor rims and start contemplating a second set of wheels for "some" off-road riding you might want to divert the funds for those special upgrades (several hundred dollars) and see if you can't find a second hand Cannondale MT or other enduro/off-road tandem for around $1,500 to put them towards. IMHO, if you like to venture onto the dirt now and again and enjoy riding a tandem, there's nothing as cool as having a dedicated off-road tandem at your disposal to go play on. It allows you to keep your road machine in pristine shape for road riding (it's intended purpose anyway) and eliminates reconfiguration issues, e.g., chain ring size / gearing, wheel changes and brake adjustments, and of course the accelerated wear & tear that dust, grit and grime have on your drive train and other moving/rotating parts.
Oh well, I guess I didn't stop digressing....
Last edited by livngood; 06-29-04 at 10:26 AM.