Talbot Frameworks Tandem - Sik Fadez Family Chariot

The major component of this would be kinetic energy (rather than the component of gravitational potential energy you are resisting by going down a slope), so lets estimate this.

Good science but let's try and account for GPE (neglecting air resistance first, but then trying to approximate that).

175kg going down a 10% hill at 35mph (v=15m/s), so they are losing elevation at a rate of 1.5m/s.

So the GPE difference for 1.5m elevation difference is 175 * 1.5 * 9.8 = 2572J, since this is per second it's a healthy 2572W.

Of course, some of the energy 'gained' from GPE is eaten up by air resistance and rolling resistance.

A quick play with http://www.kreuzotter.de/english/espeed.htm shows that you'd need 520W to power a tandem with a total weight of 175kg along at 54kph (15m/s), so that is a reasonable approximation as to how much power will be sapped by air resistance and rolling resistance at 15m/s.

This leaves ~2000W that needs to be constantly dissipated (without overheating) in order to keep the speed at a constant 35mph down a 10% hill for a 175kg tandem. Oof.

you'd need 520W to power a tandem with a total weight of 175kg along at 54kph (15m/s)

I think it's a bit more than that, otherwise our tandem 10 PB would be around 18 minutes, not just under 21. It took Wiggo something like 450W on his super-aero solo track bike, after all. You're not an order of magnitude out, though, so that 10% hill is still going to need over 1.5kW of braking to hold that speed.

Good point, didn't think of that as a sanity check on the figures from Kreuzotter.

Thought about using carbon/ceramic rotors like they do on some cars? Allegedly handles heat a lot better but might cost a fortune

Won't help the problem of the fluid in the brakes getting too hot.

Hadn't heard of these and need to read some more but they look hawt!

If they absorb the majority of the heat and dont go above 100 degrees themselves then the fluid wont get any hotter than that

http://youtu.be/8k26qLQMdv0

So is the objection to the drag brake purely and aesthetic/weight choice?
If I was building a tandem it'd be a no brainer.

On that note I might put in a cheeky offer on the tandem owned by one of my clients that's been sat idle for 10yrs or more.

I think they're a good solution to the problem, but there's no denying that they are heavy.

They also limit hub choice, I believe.

Was this set out to prove anything? They couldve used any material and the fire coming through the rotor wouldve cooked the bacon. Or was it to show they dont melt at high temperatures?

If they absorb the majority of the heat and dont go above 100 degrees themselves

...then they will be defying the laws of physics.

It's water that doesn't go above 100 degrees until it's steam (or pressurised). It sits at 100 while the water molecules take it in turn to fly away. This is latent heat of evaporation.

Mineral oil in Shimano/Magura disc brakes boils at 310 degrees, so it'll all heat up steadily to 310 deg before it plateaus and starts boiling. But I'm guessing some part of the brake system will probably fail before it gets to 310 degrees and would spew hot oil all over you, as if you were attempting to invade a medieval castle.

True on the weight, tandems always gonna have some bulk but worth saving it wherever you can I guess. Presume the mdd version is a touch lighter than the old arai model.
Phil wood still make 145mm tandem hubs right? Again, not exactly a featherweight choice...

Featherweight hubs will just die. Weight weenie on some bits, but tandem wheels get a thrashing and anything lightweight won't last.

You knows it. My tarck bike has the 30+ yr old campag/summit wheels I pulled off the braklessloprotracktandem. Utterly bombproof.

My dream tandem has phil, mdd and hs33 on 650b. Would work lovely and last several generations.
The pug had Mafac cantis which were equally amazing and better than plenty of discs I've ridden.

Saw a couple on a bright orange tandem today, drop bars etc, using hope v-twin cable to hydro converters.

They had clearly just done the ride 100 so it appears people are using hydro brakes for tandems.

They had clearly just done the ride 100 so it appears people are using hydro brakes for tandems.

On mildly lumpy British rides. 7VEN is talking about 20 minutes descents in mountainous forrin places.

My tandem has steel rims and centre pull canti brakes, plus a drag hub brake. I ride it round here, but probably wouldn't fancy it down an Alp.

I shouldve used a science word like dissipate instead of absorb.

My vote is for cable discs and the largest rotors you can fit/find. Coming to a stop and rubbing snow on the rotors also wouldnt be impossible on a 30 minute alpine descent

7VEN is talking about 20 minutes descents in mountainous forrin places.

That's the one. Large Col descents are what I was thinking of however reckon that I could always get a second wheel built up and all the braze ons put on now for every eventuality.

cable discs and the largest rotors you can fit/find

This is what coMotion do with theirs. Need to see what other hot tandem manufacturers are doing OTP.

I didn't notice anything about tubing in the first post, @7VEN

How limited is the range of steel when it come to building a beast like this?

If you look at how most are put together it's just the bottom(?) tube that's different from normal bikes.

Reynolds do the drainpipe tube in round or oval in 525.
My Claud uswb has an absolutely huge diameter base tube, same with my pug. The braklessloprotracktandem had a really neat and tasty looking ovalized number so guess there's a few options out there. No doubt Talbot has already looked into that stuff.

Red this:
http://www.bikeforums.net/tandem-cycling/754272-11-inch-brake-rotor.html
Apparently getting the Hope V2 in the BB7 is fiddly, but works.