cajunpedaler

Ok. I have two tandem frames. One is aluminum, one is steel. Both are decent bikes. Both presently have only rim brakes. 26" wheels.
I have some single bikes with disc brakes and my touring coupled Surly has a disc in the front. I like the idea of disc on a tandem, even if only on the front.
I have found a front fork, steel. Threadless, made by Origin 8. It is not specifically for tandems.
Tell me the mechanics of the difference of what stresses that are above and beyond on a tandem fork, vs a single bike. I know weight of course is an issue.
I'm curious about braking...will the fork hold up to a quick stop? Is there a fear that the fork will fold?
What else should I be concerned about?
I'm not looking for fear monger in...just the reasons that I need to be aware of..mechanical, etc.
Thanks.
Perry

OneIsAllYouNeed

I've bought two aftermarket disc forks for tandems: 1 Co-Motion and 1 R+E Cycles. Both are "tandem rated". You can buy direct from Santana, too -- just call them.

I asked Whisky components about that same topic here's what they had to say:

"Thanks for the email. We have not tested our forks for tandem use and so cannot condone their use on a tandem bike. Even though we do not have weight limits on our forks, tandem bikes can put forces on a fork that are impossible to achieve on a normal bike regardless of the rider weight. This has to do with weight being so far behind fork and how a tandem bike is virtually impossible to endo. Using one of our forks on a tandem bike would indeed void the warranty."

Here's a good article by tandem frame builder Dan Towle of R+E Cycles:
The lightest fork for a tandem bicycle - carbon fiber tandem forks

pdlpsher

Given a choice, the rear of a tandem is a much better place to have a disk brake. The rear wheel is already built strong enough to handle the extra torque generated by the disk braking force. The rear triangle doesn't need special reinforcement like a front disk fork needs. On a tandem one cannot lock up a rear wheel like on a single bike. On a tandem with a front disk brake, you would need an extra heavy duty fork to handle the extra load of a tandem and the extra bending force from a disk brake (the braking force is generated near the fork end versus at the fork crown on a rim brake). The front wheel will also require extra reinforcement as the spokes now transfer the braking forces from the hub. On a rim brake setup the spokes transfer zero braking forces. The main benefit of a disk brake on a tandem is no risk of overheating the rim on a steep descent. If you don't do steep descends I think it's not worth the trouble of getting a new fork and front wheel.

OneIsAllYouNeed

Back to the OP's question... Under tandem use, stresses are higher at the steerer, crown, brake mount, fork legs, and dropouts. If you're decelerating at the same rate on a single vs tandem, those stresses increase proportionally with total weight. For a tandem fork to see the same deflection and strain (therefore the same fatigue life) as a single bike fork, it also needs proportionally more material in those areas. To be fair, many areas of the single bike forks are likely stronger than necessary (for manufacturability mostly), so only small amounts of reinforcement are needed to handle tandem loads. Looking at the Origin8 Cromo-Lite disc fork compared to my tandem forks, I'd be worried about the dropouts, crown, and brake mount.

It's also worth noting that most tandem forks have more rake (typically 50mm) than most single forks (typically 43mm).