plus a drum brake on the hub...

Wouldn't it be easier just to jam your air pump into the rear spokes? That'll stop the wheel in a jiffy.

That's what the extra spokes are for!

Sorry, I'm totally not following you. Can you explain how the setup pictured in the OP is different from a single sidepull in the sense that, even if the calipers are unequally spaced from the rim, upon brake application, one by one, they first contact the rim, before any appreciable braking force develops? Assuming return springs and pivot bolt friction is the same on both sets of brakes, the braking force on each pad will also be approximately the same.

i meant both calipers need to be adjusted so the travel is about the same per caliper.

once one set of calipers closes all of the way, the cable will not move any more. so you need to get both sets of calipers to close all of the way at the same time to get the best results

This is what I needed to do to make the drum and caliper brakes engage at the same time.

Found this once online. Thought it would be clearer to explain how it would function.

precisely, the cable is not anchored to the first caliper, the cable must travel through the caliper and it is the cable housing that closes the first brake, the cable closes the second caliper.
meaning the amount of cable to pull both brakes closed (because the length of housing is constant) must be twice the normal length of cable pull, but given a standard pull brake lever the with the same amount of travel we can assume that caliper travel will be cut in half.
As long as the pads are close enough to still reach the rims both will actuate with equal force (provided identical calipers) and since the force between the two brakes is equal we can ascertain that to reach nominal braking pressure twice the force would have to be applied to the brake lever.
Not to equate braking force with stopping power as the amount of braking area has doubled as well.

Wouldn't it work the equally if the mechanic had merely installed brake shoes of double length?

we can't really tell if the first brake is "anchored" or not in the pic. but if you do anchor both brakes to the cable, it will not require twice as much travel to close both of them

I would've have told the owner to ride slower and avoid hills.

Hows it go???

You can say badass, you know....

The bottom one is the parking brake

If the cable is anchored at the first caliper then how does it still move after leaving the caliper?
For this arrangement to function we must conclude that the cable is only anchored at the end of the second caliper. Imagine if there was no cable housing between the first and second caliper. The cable would still span the same loop but clearly not be pulling the second caliper closed. So if the cable is anchored in two places, even with any arrangement of brakes in between the length between those two anchors will not change.
Don't look at the cable position moving but instead the distance of cable between the two brakes. It can only change if the first brake is positioned with a cable stop (in this case it appears to be a barrel adjuster) allowing the cable to travel independent of the housing.

Maybe better heat dissipation this way.
If one brake caliper had significantly firmer springs you could setup a 2-stage brake.

cause the caliper moves.. if the caliper didn't move, the cable wouldn't move. though after looking at my bike, it does seem the cable only travels about half the distance, because once the cable pulls the 1st arm against the wheel, then it stops moving, though you can still pull the lever more which makes the 2nd arm touch

so you're right, and in the picture it does looks like only the end brake is anchored

It isn't that hard to picture in your mind. The cable and the brakes are in series so the cable travel with be double that of a single caliper. It has to pull both of them closed in series before they contact the rim. It'll have 2x the travel of just one cable and also 2x the leverage ratio. But it will have 2x the swept braking area so it'll have approximately 4x the braking power (if the lever has enough travel). One could change the lever ratio slightly to overcome the travel issue and the fact that they might be a bit grabby.

yes of course. i wonder if v-brake levers would be a good choice for that

what i was imaging was both anchored to the cable, just like two people hanging onto a rope during tug of war.. both of them move by the same amount. but after going and looking at a set of brake, I saw that isn't the case.. When the caliper arm that is anchored to the cable hits the rim, the cable stops moving and it's actually the housing which is getting "pushed" to make the other arm clamp down

Come to think of it, if someone had a mixte with under the chainstay canti studs you could use a tandem brake lever with two cables to actuate three rear brakes.


Or just get disc brakes.

PDXaero and I have the same idea.

My Burley Tandem has both rim and drum brakes on the rear. The rim brakes, front and rear are run off the right hand lever which has fittings for two cables to exit. The rear drum brake is run off the left brake lever. Technically that kind of lever could be used to operate these mixte brakes in tandem (not series).

The empirical model of friction says no. Double the contact area with the same pull (normal) force and you half the contact pressure (per unit area), and hence, the net friction remains more or less constant. In nature, it is not quite as simple as that, but observations show that it is a reasonable model for most sliding friction cases, within a fairly broad ratio of normal force to contact area. Be aware that some brake designs can be self-energizing, like the old automobile drum brakes, so the normal force at the brake pads can have a non-linear relationship with the operator-applied force.

Those Weinmann sidepulls flex quite a bit and don't take kindly to long cable runs (such as on the back of a mixte). Looks like a flipper's ingenious (nutty?) method of getting decent braking power at the back.

-Kurt