Yup, the weight is only an issue if you are comparing discs to rim brakes, e.g., ~180 g. / ea for rim brakes = 360 g. vs. 734 g. for a pair of Avid's + ~80 g. for the added weight of disc hubs = 814 g.

But, the Avids are usually looked at as a way to eliminate the 906 g Arai drum brake and that's where the weight "benefit" comes in, e.g., 1,266 g. for rim brakes + Arai vs. 814 g. for Avids = 1lb of weight savings. Now, if you look at the hybrid set-up where you run a rim brake in front & Avid in the rear you're looking at almost 1.5lbs of weight savings.

Of course, if you accept that disc brakes belong on tandems you can then begin to look towards the use of disc-specific rims that can be made lighter because the rim no longer needs to work as a brake rotor, so there are even some additional areas where disc brakes could further reduce weight on a tandem in a very meaningful place -- rototating mass.


Maybe and maybe not. There is a lot of weight variability in forks. For example, a standard 1 1/8" Co-Motion chromo fork weighs about 1,230 g., whereas the older 1 1/8" standard Santana fork weighs about 1,020 g. The custom 1 1/8" steel fork made for our Erickson weighs about 920 g. Erickson has the advantage of knowing how much his clients weigh, whereas the Santana & Co-Motion forks are made for worst case scenario and likely overbuilt. So, there is a lot of margin in those numbers, even for steel.

Let's look at carbon forks. A True Temper Alpha Q X2 is the lightest at around 450 g. The Reynolds Ouzo Pro tandem is closer to 650 g. The Wound-Up fork sold by Co-Motion weighs in at a bit over 900 g. Again, different designs and material approaches can yield significantly different weights that may or may not be indicative of a strength or durability issue, unless there are weight limits attached to the products.

Now, just how much additional braking force does a hub mounted disc exert on a wheel and is it really the energy going into the brake that stresses a fork the most or is it the tire? After all, does the brake stop the bike or does the brake stop the wheel from turning which really means the tire's contact patch with the road is the fulcrum for the greatest stopping energy? Frankly, I don't believe the fork's crown knows if a disc brake or rim brake is increasing friction under the front tire and, after all, that friction with the road is what is responsible for slowing and stopping the wheel's rotation.

As for where the braking action occurs, you're now looking at the geometry, distance, and loads that are transmitted between the brake pad contact patch with the rim (which is just a really big disc rotor) or disc rotor. Frankly, the only place I see an increase in the need for fork strength is in the lower 1/4 of the leg, at and below the caliper mount where, in most cases, a fork is already pretty durable. Given that most of the fork's mass resides in the crown and steerer -- which is where the lion's share of fork and front wheel loads end up -- you could easily beef-up a fork's tips & lower legs -- making them nearly solid if you wanted -- without increasing the fork's overall weight by much more than 10%: chromo or carbon. Anyway, that's my armchair assessment.

My Humble Opinions:

Discs are a sexy-looking way to get an Arai drum brake and perhaps up to 1.5 lbs of it's net weight contribution off of a tandem and to simplify braking on steep descents (i.e., eliminates third control). However, discs aren't drag brakes... so if a team really needs or wants a drag brake, a rear disc isn't a good choice as it precludes the installation of an Arai drum brake.

If a team doesn't need a drag brake, discs might still be attractive and their extra weight may be a non-issue if they routinely find themselves on wet roads, encounter a very steep descent every now and again where for that one day of the year an Arai brake would be a welcome addition, or if they just want better stopping power than is currently available from the various rim brake options.

Discs probably require more maintenance that rim brakes and at present seem to go through brake pads at a much faster rate. However, mechanical disc brakes such as the Avid BB are as easy or in some cases easier to install, adjust, and service as some cantilever and linear-pull brakes. Moreover, if a tandem owner doesn't do their own brake maintenance to begin with, then it really doesn't matter which brakes are easier to install, adjust, or service. If they do do their own work, the Avid's are quickly mastered and they can be improved upon.

Bottom Line: Discs aren't for everyone but, at the same time, they aren't necessarily a bad thing. They can't cause a tire blow-off, aren't likely to fail (at least the mechanical ones if properly serviced and maintained), and if one does fail, the failure mode isn't catastropic (again, we're talking Avid not hydraulic) -- and even a single Avid BB is better than the best single rim brake.