roadgator

not so. braking exerts much greater force than pedaling. how long does it take you to pedal up to 30mph, and compare that to how lang it takes you to stop as fast as possible from that speed. you can stop much faster and thus much more force is being exerted.

in total work you are corect, you can never do more work with your brakes than you have done with the pedals since some energy will be lost to drag etc, but in term of instantanious force and thus wheel torque, braking will be substantialy larger.

now if a comon lightweight roadwheel can handle the load of a disk, iduno...

chipcom 

Why not? Doesn't the Specialized Sirrus have a model with disk brakes? Slap on a set of drop bars, and there ya go. Or maybe build up a Surly Karate Monkey frame? Granted I don't know of any disk brake compatible carbon frames, but I don't see why one could not build up an aluminum or steel framed bike. Do you?

Edit: you might also want to see post #25

SDRider

Please, enlighten me. What do disk brakes have over rim brakes in the wet? The limits of braking are the tire to the road and not the rim to brake surface. I could be in a downpour with sheets of water cascading off me and my bike and still apply enough force to lock up both wheels so what benefit could disk brakes possibly give me in that situation?

DannoXYZ 

Due to the extra leverage required to apply braking-force near the center of the wheel, disc-brakes uses a significant amount of force on the pads. Something like 5-10x more than what's applied to the rim in order to get the same leverage. So that extra pressure effectively squeezes out any water.

I'm not sure what the big deal with disc brakes on a road-bike is anyway. I've done a tonne of crits in the rain, close to 100 and I've never had any problems with brakes. If anything, they're less important in the rain because there's less traction between the tyre and the road, so less total friction available. The brakes only have to generate enough to lock up the tyres and that's it.

af895

What SDRider and Danno said.

I add: on all the bikes I've ridden with cantilever brakes, I've been able to lock both front and rear wheels in all weather conditions, winter and summer, wet & dry. I live in relatively flat land though - descents aren't more than a few minutes and don't involve a lot of braking.

I could see discs as advantageous to avoid rim wear (road grit does a number on my rims in wet weather) and brake fade if you had thousands of feet of descending to do.

I'd be into discs to avoid rim wear alone but isn't there added drag from the pads touching the rotor?
It's never going to be completely drag free, right?

Savas

My disc brakes are drag free. When they are properly adjusted, there is only contact when you apply the brake. The disc is flexible and accomodates the shape imparted when one moveable pad presses the disc against the one fixed pad.

DXchulo

You know a bunch of wimpy roadies.

Someone had to say it.

chipcom 

+1 - here in Ohio, not riding in the rain would really limit our riding, wouldn't it!

FarHorizon

MTB disc brakes will NEVER become standard on road bikes. Why? They're heavier, they have more stopping power than road bikes need, they're harder to adjust & more prone to drag, and current rim brakes are "adequate."

When disc brakes are designed FOR ROAD BIKES, they'll be lighter than MTB brakes, integrated with the fork blades for aerodynamics, smaller in diameter than MTB brakes, won't be adjustment-sensitive or prone to drag, and they'll be used BY RACERS for their advantages in descents.

Once ROAD-SPECIFIC discs are invented and become popular, rim brakes will become absolutely extinct (as they deserve to be)!

chipcom 

Yet the first disk brakes were on road bikes, then adapted to mountain bikes, which begs the question, why didn't the road bike manufacturers actively pursue an improved road bike disk brake system over the last 30 years?

FarHorizon

Clairvoyance costs extra!

chipcom 

Put it on my bill!

patentcad

I'm not worried about stopping my 17lb. racing bike in a criterium, even in the rain. But yesterday I was riding down a local descent @ 42mph on a wet road, and I realized that if I had to haul down to a stop with my wet rims - let's just say THOSE are the situations that cry out for better braking on road bikes than rim brakes can provide. I do agree that the tiny tire contact patch limits the braking capability of a road bicycle - but I still think the wet weather braking would be significantly enhanced. But in fairness it IS a relativley tiny percentage of braking situations for roadies. Unfortunately when you're in one of thoes scenarios that extra 10-20' of stopping mojo could save your life- or cost it if your brakes don't perform.

All that being said, the new (10speed) Dura Ace rim brakes seem FAR superior in braking performance (wet OR dry) to the old 9 speed brakes I road for a decade. Anyone else notice this??

Joe Schmoe

Agree with patentcad. I love to have disk brakes on my road bike for that reason. They can really make the difference on a descent. One of the bike trails I ride has a steep descent (getting up to 45 mph is no problem) that ends in an almost 90-degree turn to the right. If you keep going straight you hit a fence and fall into a concrete drainage basin (if the fence doesn't stop you). On this descent, you simply have to slow down about half the way through. I would love to push it a little farther, but rim brakes just don't provide the stopping power. This same descent is much easier on my MTB.

Also, sometimes disk brakes are a real advantage in automobile traffic. Even if you are careful, sometimes the others on the road with you are stupid. The extra stopping power of fisk brakes could wasily prevent you from doing an endo over a car.

For those who have not ridden disk brakes, they are REALLY powerful, especially the hydraulic kind. I have never measured, but I am sure that a stop from 25 mph can be accomplished in @10-15 ft. The most dangerous part is modulating your stop so you don't go over the bars -- they are that powerful.

Trev Doyle

Well, Duh. That's my point. How many people have a Specialized Sirius? And are those brake parts compatible with a normal raod frame and fork. NO. I have never even heard of this model of Specialized. What I wanted to know was if new frames start appearing on the market with disc brake bosses on them will people use them, not will they buy a Specialized mid level bike that has discs on it. I have a Pinarello, Merckx, and a LeMond and I CANNOT put discs on them at this time.

chipcom 

Well duh, that sounds like a personal problem. Frames and bikes ARE available with disk brakes and/or IS mounts. Perhaps you might consider saying what you mean next time, since, to paraphrase a rather cute country song, 'that ain't what you said'.

Woz

Theres a European company that will release an internal kit for DA 10 levers next month. It will replace the internals with a master cylinder for hydraulics.

mingsta

Er...yeah about 2 hybrid frames by the sounds of it. I think the OP's point was quite clear, road frames 99.9% of road frames out there can't take discs. Jeez, some people will argue over anything!

The Carpenter

All road bikes already have "Disc Breaks"!!
Your calipers are the calipers and your rims are the discs.

The Carpenter

You should ALWAYS ride in a manner that is safe for the conditions. If you know that you can't stop as fast in the wet, why the hell would you go flying down a hill that was a wet road? That's just stupid!
The kind of disc breaks that are being talked about here would lock up so fast on a road bike in wet conditions, you wouldn't even know what hit you 'till you got the ER bill. Next would be computer controlled anti-lock disc breaks for your road bike. Oooooooo I know, how about dual discs in the front?
Wait! The second disc on the rear, on the drive side, could double as the dork disc.

chipcom 

Kona Sutra looks like a road frame to me, as does the Specialized Sirrus and Raleigh Route 24. Is there something about flat bars on the latter two that make them NOT road frames? Or do you think a frame has to be drop-barred, carbon and full of bling to be a road frame, or perhaps you think all road bikes are racing bikes? Geeze, some people's kids are pretty stubborn when caught talking BS.

Fact: There are road frames available with disk brakes, not to mention that any decent framebuilder could build one up. Just because disk brakes are new to you, don't mean they are new. The issue isn't availablity, the issue is that, for some reason, there hasn't been any demand by racers and wannabe racers for disk equipped bikes.

mingsta

Wow, you can name a handful of 'road' frames that can take discs, it doesn't stop the fact that they are outnumbered about 100:1 by road frames that CAN'T take discs. What's your point?

And lets not confuse the definition of a road bike, eh? A 'Road Bike', as opposed to a touring, hybrid, cross or mountain bike etc, is a term which the vast majority of posters on this forum would understand to mean 700c, skinny tyred, drop barred bike with a lightweight frameset. There are very few road bikes, as described above, built to take discs. This is what the OP alluded to in his original post, so yes, there is an issue of availablility and I don't think there's a single person who'd disagree with that appart from you.

P.S. Yes, I'm so scared of this new fangled disc thingy that I already have two bikes running Hope Mono Mini's.

chipcom 

From the OP: "When Disc brakes become available for road bikes do you think you will use them? " You must read minds better than I to determine what that little statement 'alludes' too. I stated, correctly, that they already are, which seems to have got your panties in a bunch.

As far as your definition of a road bike - the Kona Sutra meets it...oops! My touring bike meets it - oops! Now perhaps you'd like to rethink your definition of a road bike, since it seems confusing to you. Hint - you might start with frame geometry.

SDRider

The same descent is much easier on your mtb because you aren't going as fast. I'd say that your mtb brakes feel more effective because you have more surface area contacting the road.

Fact: Stopping distance is more a factor of tire to road than brakes...especially in the wet. Disc brakes are no more effective in the wet than rim brakes on a skinny road tire. You might as well argue about the virtues of fat mtb tires on a road bike. You'll be barking up the same stupid tree. Good luck with that.

I'm sure my Dura-Ace rim brakes could send me over the handlebars if I were stupid enough to apply the force necessary to send me into such a ridiculous position. Your point is moot.

FarHorizon

You are completely correct, chipcom. However, the disc brakes that are currently available on road bikes are MTB-standard discs (whether Avid road cable actuators or hydraulics). Although these MTB discs are superior for specific conditions (wet/icy/dirty stops and heavily loaded descents), these MTB discs are NOT yet standard on the majority of road bikes, nor will they ever be in their present form.

To become standard on road bikes, disc brakes will need to be re-engineered for road needs. The disc rotor diameters should be smaller, the caliper actuators should be smaller and lighter, and the entire mechanism will need to become more aerodynamic.

These changes WILL come to road bikes. When a "road bike disc brake standard" is developed and accepted by the marketplace, discs will completely replace rim brakes on all (new) road bikes. Why will this change occur? Because the technology is superior. Disc brakes don't overheat rims and blow out tires. Disc brakes work better in wet/icy weather. Disc brakes work even when the rim is warped or damaged. Disc brakes don't wear out the rim. Disc brakes (being attached to the hub) can dissipate heat well. Disc brakes can be designed, manufactured, and maintenanced more easily than rim brakes.

The superiority of disc brakes is the reason discs are standard on everything from autos to aircraft to motorcycles. The future of ALL bicycle brakes is disc. It is only a matter of time and design.