Question: “When choosing the components for our tandem, one of the controversial topics was the question about the best fork to use on a mountain bike tandem. What is the best fork to use?”
Response: There are very few mountain bike tandems sold let alone ridden and of those ridden very few are ridden very hard. It is not worth the money or time for manufacturers to test and certify a fork for tandem bikes. While there may be warranty problems if a fork fails while mounted to a tandem there is no real liability issues because of an assumption of risk. If a part fails on any bike an attorney is going to have to prove negligence by the manufacturer towards a known flaw before that company could ever be found financially responsible. The reality is there are not enough tandems to even worry about marketing to and manufacturing parts for that audience.
A tandem team and tandem mountain bike stresses each component in ways not directly conceived by manufacturers. Most tandem teams currently select components designed for downhill or freeride mountain bike applications. These components are designed for and tested under conditions including severe obstacles, large jumps, and the occasional crash.
For our tandems there is a different reality; we don’t jump the bikes, we don’t really target large obstacles, and we rarely crash (at least too hard). Our biggest stressor on a fork will be found in the steering/ headtube section when we wrench the handlebar to maneuver a course and around the brake mounts where severe rotational stresses will be applied.
A downhill specific or freeride specific mountain bike fork will handle most anything a tandem mountain bike team can throw at it. That being said there is due diligence required of the tandem team in maintaining and monitoring the structural integrity of the fork. In all likelihood you will go through several headsets before that fork even starts to show signs of aging. As good practice you should regularly inspect the fork for signs of structural failure and fatigue.
In the end select a fork for your tandem from models designed and marketed to downhill riders and freeriders with the appropriate spring and dampening adjustments to allow you to fine tune to your ride.Disclaimer: the above is a statement of opinion and should be utilized as such in your decision making process. As with all tandem components users should utilize common sense when selecting and using various pieces of equipment.