ljsense

Right, they have more mechanical advantage, meaning that at the lever, you'll pull lighter and at the caliper end, it'll clamp harder. Disc brakes have a tiny amount of pad travel.

If you're trying to just lightly graze the braking surface, it's easier to do when you have less mechanical advantage. Disc brakes are great for applying a lot of hard force to the rotor, and you can modulate hard braking well with them, but if your goal is just to touch off a little speed, a rim brake's design makes that easier.

Don't blame me, everyone, when you're all arguing the merits of the road dropper post someday.

RChung

I have a friend who rides: a road bike with mechanical rim brakes, a road bike with hydraulic rim brakes, a MTB with mechanical disk brakes, and a MTB with hydraulic disk brakes. He says the hydraulic bikes have very similar "feel" and modulation; he says the road bike with mechanical rim brakes is smoother than the MTB with mechanical disk brakes.

He says that much of the argument about rim vs. disks is really an argument about mechanical vs. hydraulic.

MoAlpha

Having some experience with cable and hydraulic systems for other applications, that would not surprise me.

Seattle Forrest

We have a lot of volcanos, and a lot of glaciers. Saint Helens went off during our lifetimes, but you can tell when others blew and which way the winds were blowing, from the ash that got deposited in the soil. That ash is rich in particulate matter, stuff like pumice. That's why the soil is so productive here, you should see the wildflowers on Baker. But some if it winds up on the pavement and gets kicked up when you ride in the slop. The glaciers are retreating, used to cover much of the area, they'd grind the stones they passed over down to something like flour, fine enough to float in water. It's why the lakes have that amazing color. It's why some of our ground is so unstable, part of the reason for the Oso disaster, one of the worst landslides in history. Glacial silt is just what a lot of the ground is made of.

Everywhere, it's not the water it's the crap in the water. I guess that's our flavor of crap.

I get 2 to 3 years out of rims. But then I'm a climber, and heavy by road standards. For sure, I waited for discs before buying fancy carbon rims.

Kapusta

I find the exact opposite to be true. In fact, it is one of the main benefits for use on mountain bikes where traction can be poor. It is easier to scrub a little bit of speed in poor traction conditions without locking up the wheels.

It is not that simple, and the last part of that statement is where the problem is.

Sure, IF the leverage over pad movement (the ratio of lever pull to pad movement) was the same on a 160mm disc vs a rim, you would have much better braking on the rim. However, that is not the case. The leverage (lever movement vs pad movement) is MUCH greater on disc brakes. Just look at how far disc pads move compared to rim brakes for the same lever throw.

Three factors allow disc to have higher leverage over the pads and higher clamping force: First, you can set disc pads much closer to the disc then rim pads to a rim, which lets you set the leverage of the brake lever over the pads much higher (if you tried to set up levers with similar leverage over rim brake pads, you would have to pull them incredibly far just to get them to contact the rim). Second, the caliper only needs to clear a 2mm wide disc with a baking surface right at the edge. This allows the caliper itself to be made MUCH stiffer than any rim brake setup that needs to clear around the whole tire. Third, (and this is admittedly conjecture) I kind of doubt most rims could even withstand the clamping force of disc brakes without being beefed up quite a lot.

But these armchair physics discussions are really only useful for explaining what is observed. The proof is in the actual usage, and I guess that is subjective. In in my experience, discs are generally a better performing setup.

Dean V

Still wrong.
How many modern road disc bikes have you ridden?
Discs have better control and modulation all the way from being lightly feathered to an all out panic stop.

prj71

Trust me...within the next 5 years you'll be hard pressed to buy a new road bike without disc brakes.

Kapusta

Except it does not actually work that way. What you are leaving out is that the disc pads/caliper have LESS mechanical advantage over the disc than rim pads over the rim.

Also think about what it takes to "lightly graze the surface". The slower the pad moves, the easier it is to control that.

Another thing to take into account is that disc pads and rim pads are made of completely different materials and have different frictional properties.

Chi_Z

the new shimano di2 hydro shifters looks pretty good

tyrion

I agree with everything you said in your complete post, and I would characterize the part I quoted as contributing to less slop in the system. More precision, more control.

ljsense

This is probably a tough point to make, because it seems like I'm arguing past people who are saying things I agree with. Imagine a turntable, you know, a record player. And you're a DJ. You want to slow the record down from 45 rpm to 44 rpm. Where do you touch the record? Your answer should be right on its edge -- a light touch, right on the edge. That's like a rim brake. If your goal is just to take the angular speed of the wheel down a hair, a rim brake touches the wheel at the right spot, and it has a lot lighter touch than a disc brake caliper.

I get what you're saying about the advantages about disc brakes. I fully understand that their calipers exert much more force, travel less distance, and modulate better under pressure to keep a rear wheel from skidding when you're going down a bumpy trail. What I'm talking about is an alternative to sitting up in the wind. Just the tiniest of brake that moves you 3 inches off a wheel instead of 6. Disc brakes' initial bite is more powerful than a rim brakes. Most people appreciate this phenomenon, because they hit the brakes with the intention to slow down, not make a subtle change in position amid a pack taking a corner.

WhyFi

I love how he edited your post upon quoting it. I guess that's one way of answering the question.

Psimet2001 

I already run into all sorts of big box bikes that are already disc. Mongoose out of Walmart has been for years. Also they are 27.5" wheels too.

Bikesplendor

Safety.

Psimet2001 

*sigh*

I love watching this forum dissolve into chaos over something like this.

Like I said before - everyone's opinions are pretty much useless. No one in the industry cares what you think. Disc are here and aren't going away. It is simply a matter of time before they become ubiquitous.

Those that talk about any sort of real benefit of disc on a road bike: sorry - you're stretching. Rim brakes are amazing and have come a long way just in this century alone. We easily have enough braking power with the rim brakes available now to skid. When you skid your braking power has overcome your contact patch. It doesn't take much to overcome the contact patch of a road tire.

Yes everyone is drunk with going with wider tires. This is nothing new and will also return to narrower tires in the future under some new generally accepted marketing crap "backed up" by all sorts of biased data again. "Well due to new tire technology and compounds we have in fact found that riding narrower tires at pressure x results in a lower rolling resistance and aids in aerodynamic drag reduction.....blah blah blah" Wide tires make it harder to run with the rim brakes we have but there's over a century of rim brake design that is more than capable of handling it.

There will come a time int he future where leading edge niche of riders and certain racers will stray from the herd and field rim brake bikes again. They will cite the feel of the ride, the low weight, having to learn how to carry more speed through corners, etc all as reasons why they have gone that way. As long as they carry with them a Rapha-esque aesthetic pertinent to that time then the minions of recreational forum users will follow suit.

hell I'm already seeing a surge in riders going back to polished silver hubs, rims and spokes.....just because no one else is running them. "Everyone's bikes are all matte finish and murdered out. They're boring"

Sorry just enjoying a bit of this wild ass guessing from everyone and attempts to rationalize what really isn't that difficult of a question.

tyrion

This analogy doesn't account for the greater precision of disc brakes.

Kapusta

Sorry but I have to ask how much actual experience you have with discs? Because in my two years of experience with my road discs, they don't work the way you are describing them. They are not grabby and they are just as good as rim brakes at doing exactly what you are talking about.... scrubbing a little bit of speed.

ljsense

There are two mechanical advantages at play here. One is the distance between the brake and the axis of rotation. The farther a brake is from the axis, the greater mechanical advantage it has. The other is between the lever and the caliper -- for a given pull of the lever, the caliper that travels less has more mechanical advantage.

So, rim brakes operate in a position, relative to the axle, where they have more mechanical advantage, but disc brake calipers have more mechanical advantage in relationship to lever pull.

The complications are materials, speed and tolerances, and how they change coefficients of frictions.

I grant all of you, and have agreed all along, that disc brakes' advantages are plain for stopping or seriously slowing a bike in a wide range of situations. But just trust me, cork on a true carbon fiber rim has less coefficient of friction than disc brake pad (sintered or organic) has on steel, and it does a better job of feather dusting off a little speed. A disc brake will grab a little more speed right from the nanosecond it touches.

I've ridden disc brake everything, except a disc brake track bike (not ready for release until 2021). Don't make me die on this hill.

Maelochs

Really? I learned bike mechanics myself, from literally the ground up---picking up junk bikes off the roadside. I learned about different brake systems when I first saw the,

Sorry, but it ain't rocket science. A lever pulls a cable which in some way pulls actuator arms---or compressed fluid does it. A "bike mechanic" who can't cope with center-pull, side-pull, dual-pivot, cantis, and Vs is just lame.

As for discs, I had to ... read some instructions. Can i still be a mechanic ... after learning to be a better mechanic? I am nto sure of the Mechanic's Guild rules.

Why? Why is that?

If that were the case, shouldn't most riders be best served by single-speed and coaster brakes?

When it comes to brakes, most riders are best served by brakes which stop the bike with the least demand on the rider. A coaster-brake bike demands a weight shift. A bike with weak brakes demands a lot of pressure. A bike with weak rim brakes in the wet has longer stopping distances, demanding greater rider attentiveness and quicker reaction. Brakes that respond very quickly with not a lot of force are best---regardless of what some other person considers to be "tried and true," which is a vague enough phrase that it could mean anything, including Flintstone stops.

A new rider on a bike for the first time learns immediately how the brakes works. if that rider rides a different bike, s/he learns the particulars of that bike' s brakes and adapts---whether they be the same sort or different.

I have driven all kinds of motor vehicles, with air brakes, vacuum-assisted brakes, drum and disc brakes, and with varying levels brake boost. After the first couple stops i .... just drove.

It never took me even a few overly abrupt stops to learn the different braking characteristics of any bicycle I have ever ridden.

Bikesplendor

Sorry, just not buying this feathering stuff. The distance from the hub matters too. So do hydraulics and hydraulic design factors.

You can ask me to trust you all you want. It just reminds me of Hammer saying, "Trust me, I know what I'm doing."

indyfabz

I enjoy your BF commentary immensely.

WhyFi

No.

mgopack42 

I am trying to avoid disks for the same reason i am trying to avoid press fit BBs... I'm a semi-Luddite!
At least Im honest with myself! I just like things the "old" way. until they take away the option of rim brakes, people will choose what they like, and if they dont have an opinion, they will buy what they are sold.

Maelochs

@ljsense ---- you keep saying that rim brakes are so much easier to use with extrme precision for the most minimal applications. My question would be, how much have you practiced.

All your analogies mean nothing. Reality is where i ride, in a concrete, not conceptual world. it sounds like you have figured out a way to explain why a thing won't work---but refuse to accept the fact that it does. (the Catholic Church had to give in to Galileo ... hope it doesn't take 400 years for you to learn to ride discs.)

Fact is, plenty of people find riding on discs to be just as easy as riding on rim brakes. if You cannot, then practice more. Stop inventing weird excuses based on turntables etc. ... it can be done, learn to do it.

I personally don't care what kind of brakes anyone uses or favors. But i do want to keep at least some of the discussion on this site honest and fact-based. You are essentially complaining that you can't make discs work with precision----though that might be your theory rather than your experience. Several others say they have---which makes me think you need to develop a finer touch.

I use Ultegra rim brakes on my "fast" bike (that describes its set-up, its weight relative to other bikes, and its potential---no bike I ride is fast unless going down hill (or on a rack on a car being taken somewhere to ride)) and after a few panic stops left me fishtailing and flat-spotting rear tires ... I gapped the rear brakes a little wider. Because I am right-hand dominant, in emergencies I was over-squeezing the rear brake lever. A simple adjustment has eliminated the problem.

Not suggesting that you look to solve your own issues as opposed to telling everyone that their own experiences are invalid .... at least not directly.

Bikesplendor

On a fast downhill run, on only slightly rough or irregular pavement, during a right hand turn the front tire blew off the rim. It forced me into the opposing lane because I couldn't hold the turn without the tire. Lucky I wasn't seriously injured. There was a gap between cars, otherwise it would have forced a collision. Unpleasant.

Upon inspection, a section of the rim had blown out due to weakening, due to thinning, due to rim brake pads and abrasion. The rim was not obviously or easily noticeably or dramatically thinner, but thinner enough to fail under the stress of the psi spikes from the speed and the bumps.

I find that good hydro discs have a very satisfying feel that no rim brakes can match. Well designed hydraulics make cables seem like Flintstone tech.