Originally Posted by
unikid
Agreed - converting to disc in front will cost you a lot more than simply buying that Orbit fork and swapping it right in.
I guess you could check with Orbit to see if they sell the same fork but in Disc option to see what the cost difference is. Or perhaps they have one with both Disc and Brake posts on it? That way you could upgrade to disc in future if needed.
Or bring a higher resale value should you choose to sell the bike in future...
Others on this forum might express concern about adding disc brakes to a bike that was never built with a disc fork in mind. Since adding a 180 or 203 rotor at the end of a long lever can put a lot of force on the frame.
Especially if the frame designer wasn't expecting this. I bet if you ask Trek, their answer would be no.
However I can see from pictures the T900 has an extremely long head tube to accommodate a range of rider heights and appears to be nicely welded to the frame tubes. Hence it appears the risk of adding a disc in front might be a bit lower than other tandems I've seen people do this to. Maybe others who have done this mod already can chime in.
I'd guess the braking forces on the frame aren't that much different. Panic stop with properly set up self-energizing cantilevers or v-brakes creates a TON of frontal load on the fork crown/steerer and head tubes. Plus, compare those potential braking forces to the impact forces the front end experiences when smashing through a pothole. The weight of two people hitting a pothole without the ability or skill to bunny hop it creates major force on the fork, headset and steer tube (among other things). I can't imagine the difference between rim and disc brakes would make a hoot of difference, considering all of the design parameters a tandem frame must already meet.
That said, the one concern I have riding my '97 Cannondale with Fox 34 and 5" of travel is the increased lever arm of the fork and the forces generated when THAT hits ruts, roots and rocks. Then again, the massive welds created around the three tubes as they meet at the head tube tells me the head tube will probably ovalize before it fails catastrophically. And at least off road, front braking forces are limited by traction and don't peak nearly as high as panic braking on asphalt.
So I wouldn't worry at all about using a front disc brake on a tandem with a tandem disc brake fork. It's the fork undergoing the higher loads that is of most concern, and it has been designed with disc brake use in mind.