> > front disk, during a hard stop from 35kmh, while commuting and regularly
> > send up little puffs of steam, I'm doubtful that drum brakes would suffice.
If you warp a rotor, you have over-heated it and it will never be the same. The very best disc rotors I know of (and use) are from Dirty Dog MTB. Many rotors are not even heat treated like Dirty Dog.
8" rotors are recommended for any kind of cargo bike. Many Longjohn style bikes being made now use 6" rotors. Some even use cross country MTB rotors with all the cut-outs and thin from the start 1.8mm rotors. It is a disaster waiting to happen. Discs that wear thin or get too hot can collapse or tear. The addition of an elecric assist is asking for even more trouble. I personally ride a Bakfiets with a Stokemonkey with Hope vented disc brakes and even those are not enough sometimes. It is my experimental test bike. I am taking my own risks here but would never sell one to a customer. No current brake made for bicycles is good enough for a serious heavy hauler with the exeption of the new Sturmey-Archer 90mm drums, which I will test on my Bakfiets next. Magura BIG discs are used by Frankentrikes.com. They are for a moped. The rotors are 1/4" thick!
Drum brakes are easily 10 times more durable than discs.
With the current renaissance in cargo bikes (CETMA, Metrofiets, Bakfiets, Joe Bike, etc) you would think someone would come up with a better brake!
Hauling kids down a hill and not being able to stop due to brake failure......
The reason it has not happened yet is that everything is still too new and most cargo bikes are less than 5 years old. I got my Bakfiets from my friend Todd at Clever Cycles on his first shipment.
I tried 70mm drums and sometimes could not stop. I switched to 8" discs and was surprised that the brakes were having problems. They would fade and make noise from being too hot. I warped the rear rotor and had to replace it. Modern bicycle disc brakes do not like to be held on. But you have to when decending a Seattle hill! Also it is very easy to lock up the front wheel on an empty Longjohn. A disc up front is perhaps too much brake, especially on a wet hill.
Another problem with a heavy hauler with discs is that everything comes loose. the rotor bolts, the brake adaptor bolts and the axle nuts. Everything needs to be re-torqued regulary. Shimano makes motocycle style brake bolts with holes for a wire and special triangular rotor bolts with metal plates you bend in to prevent them from loosening, however the real problem is the fasteners are just too small for a cargo bike.
I will let ya'll know my experience with the 90mm front drum. I am also considering the Shimano large roller brake for the rear.
> With drum brakes the amount of metal there is to absorb the heat is
> huge compared with the amount of metal in a disk so they shouldn't
> heat up so quickly, and the pads are huge too so they very rarely need
> changing. I've only had mine three years or so and not changed a pad
> yet. I've not heard of a drum warping either.