fietsbob

Drum brakes are cable operated, Not back pedal engaged like Coaster Brakes.

Andy_K 

Plus, you could have contests to see who could leave the longest skid mark on the sidewalk.

As an adult I'm less interested in demonstrating how far I can travel before my brakes actually stop me.

cale

A couple years back my neighbor brought me his kids bike to repair. (I'm always happy to help.) The coaster brake had worn out. I'd never heard of anyone ever fixing one and suggested he throw the bike (originally my son's and now his...so about 6 years of abuse) away.

Now, on the subject of disc brakes. Nobody shops for disc brakes because they want to "lighten" their bike. You buy disc brakes because you want to use them.

habilis

Plus, you sometimes got a nice loud BANG! at the end of the skid mark. With no front brake, everybody was down to the cord on the back tire.

rmfnla

Sounds like you didn't have to pay for new tires...

habilis

It's not that we were rich (hell no). It's just that we were very slow to learn cause and effect.

rmfnla

Or in other words, you were kids...

700

I discovered a tire saving trick. I would steal roofing shingles from the trash piles of new construction. Lay a shingle on the street and get a running start to it and hit the brake when the back tire was on the shingle. The tar would leave better, longer skid marks than the tires would. The trick was to let off if you got too much sideways. Good memories!

habilis

So many ways to have fun that didn't involve buying more and more stuff! No electronics, no $200 sneakers. How did we survive long enough to become old farts?

dabac

OWell, no.
I'm talking about the differences in mechanical advantage between disc brakes of whatever mode of force transfer and rim brakes.
Both start with the same amount of lever travel, but a disc brake needs maybe 2-3 mm of total pad travel to engage well while a rim brake will need a lot more.
A set amount of lever travel turned into 3 mm of pad travel will yield a lot more pinch force than the same amount of lever travel turned into 8-10 mm (or more) of pad travel.

Less slack makes it possible to use tighter tolerances, which makes it possible to design a system with a higher mechanical advantage.

dabac

PwOne should consider not only brake power, but also brake efficiency.
Disc brakes will give wheel lock/lift braking at a considerable smaller amount of hand effort.
For MTBers doing bumpy rides, this mean they can have all the braking they need from only 1-2 fingers at the lever, freeing up some fingers to leave curled around the bar for a better grip.
Or for a foul-weather rider, maintaining braking ability even when you've begun losing hand strength due to cold and rain.

Then there's the reduced weather influence on the braking itself etc.

dabac

Order of priority may differ from rider to rider, but:
- less force needed at the lever for a certain amount of braking force
- less influence on braking characteristics due to weather
- some do ride hard enough to appreciate that brake characteristics are a separate entity from rim conditions. Flares, flat spots, out of true no longer influence braking.
And at the far end of advantages, no rim wear from braking.

habilis

Okay, these are all pluses. Difficulty of adjustment, and the resulting drag, are the minuses. Do disc brakes have a return mechanism that draws the piston back after pressure is released? It seems that they must, since some people report zero drag.

rmfnla

Agreed on the first part (since it's pretty much what I said before ) but not on the second.

Slack is simply slack; once it is taken up it is no longer a factor. The result may be less available lever travel but it does not affect the inherent characteristics of the system...

cale

Only Mom or Dad worked, unlike today when Mom and Dad both work. That's how.

dabac

Well, there you go. With less available lever travel, you need to use less mechanical advantage to avoid bottoming out

dabac

Mine run free. Had to shim the mounting bracket out on one bike first. But after that, no issues.
And while always annoying and by definition "bad", I've yet to find a bike where the drag would actually be significant. Easily tested. Lift wheel off the ground. Spin it by hand. time it. Repeat 10 times to get an average.
Flip wheel and repeat. Compare averages.

I've never had a caliper apart yet, so I can't say what's lurking inside. Only obvious thing on mine is a really flimsy spring that push the pads apart.
I don't think there is one though. Since the pads self-adjust on wear, and the pistons are simply pushed back on pad replacement, I'm rather struggling to visualize how one would work.

rmfnla

That makes absolutely no sense...

ragnar.jensen 

It's the piston seal that retracts the piston. The seal, which most often is a square cross section, sits loosely in a recess in the caliper bore but fits tightly around the piston. As the piston moves out of the caliper body it drags the rubber seal with it, deforming it. When the pressure is released, the seal springs back to its original shape, pulling the piston back a small amount.

The seal can only deform so much, so if the piston has to move further to press the pad onto the disc, it slides in the seal. The piston will always be pushed out until the pad touches the rotor, but will only spring back a fixed amount. That's what makes it self-adjusting. The spring is there to push the pads apart when the pistons retract.

--
Ragnar

Bearhawker

I run 2 bikes both from 2012 with mechanical disc brakes. A bikesdirect Motobecane Turino in the summer and a Trek 3700 disc all winter (hoping to hold off on the studded tires for a few more weeks... we'll see).

Neither has high-end components; particularly the disc brakes. Neither drag or rub - both always stop me when asked to do so no matter what weather I have.

I can only imagine that newer, and better-equipped, bikes would have even better brakes - not worse.