Disc Brakes



stevegreer

Member
Sep 4, 2008
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I guess I'm a bit of an old school purist. I love rim brakes and doubt I will ever have anything else on my road bikes. Now, my mountain bike is a different story. I have disc brakes, and feel they are necessary as I ride in mud, dirt, water puddles, etc., and the stopping power they offer in those conditions can't be surpassed. The only issue I have with them is the metallic grinding /squealing sound they make when wet.
 

swampy1970

Well-Known Member
Feb 3, 2008
10,079
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CAMPYBOB said:
I like the guy that said, "A racing bike with disc brakes is...not a racing bike.".

Less aero.
Heavier.
Wheels are heavier with more spokes and longer, crossed spokes.
Wheels are less aero with more and longer crossed spokes.

Brake fluid still boils.
Rotors still warp and sandwich construction rotors can come undone.
Organic disc pads can wear away in ridiculously short periods of time. Like one race or one day of descending.
Pads can have the backing pad glue let go.

Cyclo-Cross racers are killing pads in two laps on muddy courses. Two. Laps.

Leonard Zinn states:


Dear Lennard,
If the peloton would switch to disc brakes, the heat would not be a problem anymore!
— Todd
Dear Todd,
That is not entirely true. Yes, the overheated rims and tires we saw in Oman would cease to be a problem with disc brakes. In those conditions, I believe the heat at the caliper and rotor would be a problem, however, and, as I said in my column about Oman, could lead to total brake failure.
Even if the UCI were to allow disc brakes in road racing, for them to gain wide acceptance, road racers would insist on superlight versions that are also low in profile. Racers are not going to be interested in brakes that render their $10,000 aero road bike less aerodynamic than road bikes of the 1970s. Calipers and rotors sticking out in the air create drag, as do the crossed spoking patterns and more spokes required with disc brakes.
But answering some of these demands by reducing the size and weight of the calipers and rotors means there will be very little thermal mass in the system, making them subject to overheating. Too much heat in the caliper can boil the fluid and can burn through the resin pads that good performance with tiny rotors requires.
If hydraulic fluid boils in a brake system, the brakes do not work. Hydraulic brakes work because fluids are essentially non-compressible, so pushing on one end of a column of fluid will result in just as much push at the other end of the column of fluid. Gases, however, are compressible. That’s why we ride on pneumatic tires. So if the fluid boils, gas bubbles will appear in the fluid, and the push from the master cylinder piston in the lever will not push the pistons in the calipers out hard enough to stop the bike.
We’ve discussed this here in the past. Different brake fluids have different boiling points, but all of them do have a boiling point.
As for the pads, resin pads get a stronger initial bite on the rotor than do metallic, a.k.a. sintered, pads. And if the rotor size is going to be tiny, like 140mm (or smaller yet) in order to satisfy the desires of road riders for low weight and low wind drag, you will need a lot of brake bite. But resin pads will rapidly be destroyed with the kind of heat that slowing down a road bike on a steep, fast descent in high ambient temperatures requires.
As an example of the issues involved, I can point to experience with a super strong, super-tall, 330-pound customer of mine who owns five custom Zinn titanium bikes we’ve built for him here in Boulder. The last two have been with hydraulic disc brakes, because he had so many brake and tire problems with rim brakes similar to the ones I discussed in my article about Oman.
This man rides a lot, all over the world, and he does things like back-to-back six-week riding camps in the Alps in summertime. (He gets stronger and stronger, but, contrary to what you might expect, his weight does not change significantly.)
With Shimano hydraulic road disc brakes, he was getting just one day (!) out of organic (a.k.a. resin) pads, even on cool days, and that’s using XTR rotors, 180mm front, 160mm rear, not the 140mm rotors that come with the Shimano Di2 road disc brakes. Yes, his disc brakes work way better for him than rim brakes ever did, and they eliminated the tire problems he was having, but daily pad replacement was overly burdensome for him. So he switched to sintered pads, and on his trips to the Alps, he now goes six days between pad changes. He’s not overjoyed about the hassle, but he can deal with weekly, rather than daily, pad replacement. He also has to forgo the nice initial bite of a resin pad.
Despite Shimano’s insistence that he should need neither the large rotors nor the sintered pads, that is what he ended up with, because he could not stop with 140mm rotors. Imagine the braking power it takes to slow his bike down while descending the Col du Tourmalet. He and his bike weigh 350 pounds, the same as a 175-pound man and his 135-pound wife on a 40-pound tandem. If you’ve ever ridden a tandem down a steep descent (like the Tourmalet!), you know how fast it picks up speed. I know from personal experience how terrifying exactly this circumstance can be. Now imagine the minimal sense of security you would feel if all that stood between you and your partner and flying off a cliff in the Alps were a pair of road disc brakes with 140mm rotors.
It is my opinion that prolonged braking in 120-degree Fahrenheit (49C) temperatures would bring about similar brake problems for a rider of a more average weight.
Cable-actuated disc brakes could solve some of these problems, but they are not likely to be used by road racers. When coupled with sintered pads, cable-actuated disc brakes would eliminate most heat problems at the rim and at the caliper, other than perhaps warped rotors (or even melted sandwich-style rotors). But they are bulkier, heavier, and less aerodynamic than hydraulic discs can be, and they have less power and modulation.
My point is that I don’t think a magic bullet yet exists for being able to do prolonged braking on a steep descent at 120-degree temperatures. The best thing you can do in the meantime is not hold onto the brakes but instead brake harder and let off for a few seconds in between, rather than letting them continue to heat up. Or alternate front and rear braking to let one cool at a time if you have to maintain a slow speed, like in a neutralized descent.
― Lennard
Read more at http://velonews.competitor.com/2015/03/bikes-and-tech/technical-faq/technical-faq-di2-options-hot-brakes_362056#gkVoPdwuOfV1xAer.99


For some types of riding and for some riders there are benefits to using disc brakes. There are also drawbacks that are significant for other types of riding.
I call ******** on the boiling point of hydraulic fluid on a road bicycle - what the hell are they using, recycled vegetable oil? I worried about my brake fluid getting toasty once but that was on a Yahama FZR1000 EXUP that was going from full on the gas at one-hundred-and-plenty miles per hour and then jamming on the anchors every 15 seconds or so on a track. That'll get disk brakes toasty. If you're over heating a 140mm or 160mm disk on a sub 20lb bicycle then you need to take lessons from the local 5 year old girl on how to go around corners on a bike.

The Tour of Oman. There was one unfortunate team riding run of the mill bargain basement carbon tubular rims that had three riders have tires explode on one corner of a descent. There's no coincidence there. Even with tubs, heat is an issue. Either the glue melts and tires roll or the pressure increases and tires go bang. Better rims handle heat better but unless you're riding Zipp Firestrike 404's then you ain't matching braking on alloy rims. Period. End of story. In the heat even Enve's are not the same. In the wet then even Firecrest's are not the same. I've not had the pleasure of riding Firestrikes but I hear good things.

You can say what you want about wheel weight but even with my PowerTap that supposedly measures to +/- 1.5% I can't tell the difference on a 10 minute climb between a light front wheel and a 36 hole behemoth with Campag Omega rims, Campag Victory hubs and DT plain gauge 3X spokes build date circa 1986 with the same tires and tubes on both wheels.

Volnix rides like a 3 year old girl. Dura Ace pads are the absolute business. Stoppers par excellence.

As an example of the issues involved, I can point to experience with a super strong, super-tall, 330-pound customer of mine who owns five custom Zinn titanium bikes we’ve built for him here in Boulder. The last two have been with hydraulic disc brakes, because he had so many brake and tire problems with rim brakes similar to the ones I discussed in my article about Oman.
This man rides a lot, all over the world, and he does things like back-to-back six-week riding camps in the Alps in summertime. (He gets stronger and stronger, but, contrary to what you might expect, his weight does not change significantly.)
With Shimano hydraulic road disc brakes, he was getting just one day (!) out of organic (a.k.a. resin) pads, even on cool days, and that’s using XTR rotors, 180mm front, 160mm rear, not the 140mm rotors that come with the Shimano Di2 road disc brakes. Yes, his disc brakes work way better for him than rim brakes ever did, and they eliminated the tire problems he was having
It says it all really. Big guy rides regular alloy rims and blows up tires. Rides disk brakes and **** don't blow up. I'd rather take spare pads than a spare face and band aids.
 

ABNPFDR

Active Member
Sep 24, 2014
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0
On a MTB bike, disk brakes make total sense.

On a commuter or touring bike which may see lots of bad road conditions they make sense as well.

I just don't understand them on a road bike.
 

swampy1970

Well-Known Member
Feb 3, 2008
10,079
389
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Henri Desgrange didn't see the point of multiple gears on a bicycle. He called riders that used them weak and even went as far as banning them from the Tour de France for a while...

All I see more of with carbon rims and caliper brakes is more crashes in Pro races. Roads are better, tyres are better the only thing that isnt better is the braking. Looking at the average speed of races, they certainly ain't going a lot, if any, faster than before. Read into that what you will.
 

CAMPYBOB

Well-Known Member
Sep 12, 2005
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Quote by swami:
"... but that was on a Yahama FZR1000 EXUP..."

You've managed to splat motorbikes with disc brakes just as well as you pasted your face all over some dude's house with a bicycle.


"I'd rather take spare pads than a spare face and band aids."

I'ld rather you just learn how to ride a bicycle and a motorcycle and stop blaming the machine. Your history tells me it's not the type of brake that's questionable, but rather your lack of good judgment and skill.

As for the spare face...you'ld need that in any event.

And make sure you stop and swap in new pads half way down the huge hill. Be careful you don't burn your fingers and have fun with your new quick release thru axle.

https://www.youtube.com/watch?v=RxXqQqAc2pA
 

aziraphale77

New Member
Mar 22, 2015
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I tried either on a similar bike setup recently.
It's a road bike used both for commuting and cycling.
The extra weight was not worth the advantage of slightly more responsive breaks.
 

vespid49

Member
Apr 11, 2015
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I think disk brakes are more versatile. For instance, if you bike in the rain with rims, you're going to have a fun time bumping into cars and sliding through red lights. With disk brakes, you'll stop a lot faster, even in the rain, although if your wheels lock you might skid a bit. In terms of road safety, I think disk brakes are better because they allow for a much faster response which is always useful when traversing the volatile pavement that is the road.
 

Gelsemium

Active Member
Feb 17, 2015
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I feel they are more safe for the casual rider, but when we are doing competition the weight might make the difference in the negative direction. So, as for me, I am really happy with mine as these days I mostly ride with my kid. :)
 

oldbobcat

Well-Known Member
Aug 31, 2003
3,233
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aziraphale77 said:
I tried either on a similar bike setup recently.
It's a road bike used both for commuting and cycling.
The extra weight was not worth the advantage of slightly more responsive breaks.
Somebody is talking sense here.

If you feel as though disc brakes will enhance your road biking experience, buy them. If you don't, don't worry, you aren't going to die.
 

schwinnhund

New Member
Jul 20, 2013
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63
Chatsworth, Ga.
I guess they are OK, but I never saw anything wrong with plain old properly-adjusted and maintained caliper breaks. I really love cantilever brakes. They are easy to work on, adjust and maintain. Disc-brakes...well, I live 30-45 miles from the nearest bike shop, so I am not crazy about anything I need to have done at a shop.

Any brakes, disc, or otherwise, are only as good as the person using them. Disc brakes will not make up for poor breaking decisions and techniques. No matter how high-tech ....nothing is idiot-proof.

My suggestion is use what you like. It's your bike.
 

egrocket

Member
May 14, 2015
53
8
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Disc brakes are so much better. I get all my wheels replaced in store so they deal with all the considerations there. I hope this helps, and I think that you'll enjoy disc brakes.
 

pinkride

New Member
May 4, 2015
77
2
8
I am not an expert by any means, but from my personal experience I would say disc brakes just feel better. They suit me cause I prefer a tighter grip on my bike, but it is all a matter of taste I guess. Just try them before buying and see what fits you best.
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