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Disc brakes on the road(33 posts)

Disc brakes on the roadtuffnick
Jan 27, 2002 1:52 PM
Do you really think it will happen? There was a post down below where someone said it was just a matter of time and weight. Its kinda an interesting question. In my opinion though caliper brakes have been around for a long time and work great so why would there ever be a need for disc brakes on the road?
re: Disc brakes on the roadVictorChan
Jan 27, 2002 2:14 PM
How about drag???? Not going to happen because it does not look "cool" and "clean."
there's no real needcyclopathic
Jan 27, 2002 2:44 PM
so I don't think it'll happen.

Unlike off-road caliper pads last long long time, stopping power is adequate and not affected by wet conditions as much, what else do you need?

there're no pros only cons:
- extra weight
- need for high spoke count wheels
- worse aerodynamics
bad ideaEric16
Jan 27, 2002 4:55 PM
Disc brakes on a road bike is nothing short of a tall bad idea. The modern dual pivot brake design provides more than enough stopping power and the pads have a pretty long life. Besides you wouldn't WANT that much stopping power on a road bike. I've been able to accidentaly lock up my rear wheel with dual pivots while trying to aviod clueless motorists and trust me, you don't want to lock up a 23c.

This whole stupid debate comes down to one simple fact, dual pivots work and if it ain't broke don't fix it!
if it ain't broke, don't fix itbn
Jan 27, 2002 5:01 PM
hasn't stopped the industry so far!
re: Disc brakes on the roadAkirasho
Jan 27, 2002 5:46 PM
... while the headtube angle is very slack... and the top tube can be longish (from a roadie POV)... and it's debatable exactly what niche this type of bike is intended for... it illustrates that it can be done (as it has been by others in the past)... The smaller illustration shows the bike with a 700C wheel option.

maybe for "The Hell of the North"...

We abide.

Remain In Light.
re: Disc brakes on the road?guido
Jan 27, 2002 8:48 PM
What's their advantage? Increased stopping power. Okay, but what about slipping when wet? Rim brakes work very well when wet. They also grab the wheel at the rim, the slowest moving part, so braking force can be modulated over a wide range. Grabbing the wheel closer to the axle would require more power to slow it down as the hub is spinning faster than the rim, and you need a separate disc to provide an adequate braking surface.

Actually, the disc braking action could be smoother and very positive. You can feel rim dirt and grease as rim brakes grab. Disc brakes probably don't grab like rim brakes.

A rim used with a disc brake wheel wouldn't have to be as strong laterally, and therefore lighter in weight, since the brakes aren't squeezing it anymore. But the stopping power would be transmitted from the disc through the spokes to the rim, which would be hard on the spokes, as already mentioned.

Disc brakes are probably not any more difficult to set up or service than any other brake design found on a mountain bike, so they'd be great for mountain bikes, but no brake is easier to maintain than a rim caliper, and road bikers wouldn't like the weight. Unless, of course, they were urban warriors battling city streets and could appreciate the disc brake's response and control. The bike Akirasho pictures no doubt shines in this task.
re: Disc brakes on the road?mduell
Jan 27, 2002 9:01 PM
I agree with the point about spokes, but "They also grab the wheel at the rim, the slowest moving part, so braking force can be modulated over a wide range. Grabbing the wheel closer to the axle would require more power to slow it down as the hub is spinning faster than the rim, and you need a separate disc to provide an adequate braking surface." is just nonsense. Both are moving at the same angular velocity, so the one with the larger diameter (the rim) is moving faster linearly. Some rough numbers (assuming 5 RPM, which is incredbily slow, but its easy to deal with):
Rim: 700(mm) * 3.14 * 2 * 5 = 21.980 meters/min
Disc: 200(mm) * 3.14 * 2 * 5 = 6.280 meters/min
Clearly the disc has a much lower linear velocity.
Also note, that I agree that the braking force is spread out over a greater range with the rim brakes, but the reasons you supplied were backwards.

Mark Duell
Ah, yes, linear velocity!guido
Jan 27, 2002 9:25 PM
Thank you for waking me up! The rim is actually going faster than the hub, rather than the reverse.

So if the disc has a much lower linear velocity, wouldn't it make a smoother, more positive brake? This seems to me another argument in it's favor.
Ah, yes, linear velocity!Woof the dog
Jan 27, 2002 10:00 PM
ok thats what i thought too
Are you people insaneEric16
Jan 27, 2002 10:01 PM
What's wrong with all you people, are you seriously considering disc brakes on a road bike?!?! Dual pivots work great, why change em?! Furthermore, take a quick look at your road bike's fork, I'm looking at mine right now and noticing that a hub with a big hunkin' disc on it wouldn't even fit on a carbon road fork which usually tapers along the spokes out to the hub rather than coming straight down like a mountain fork! Also, have you ever done any work on hydraulic levers? I've overhauled Hayes levers in the shop I work at and let me tell you, they're a little complicated! Now, try fitting that appartatus in a lever that has to integrate shifting as well, there's a big job for no payoff!

Actually, lets add it up! To change a regular road bike to a road bike with pointless disc brakes you would need to get A) a new wheelset with disc compatible hubs (lets say $300) B) Disc calipers (a dunno $150?) C) a new fork that accomodates the front disc, oh and has disc mounts ($150-200?) D) I just realized, a new frame with disc mounts in the rear (a lot) E) Levers that have both a hydraulic braking device in them and shifting ($300...if they're cheap)....and for WHAT!?! Something that MIGHT work better than calipers?? What's wrong with you people?!?!
Didn't the highwheeler dudes say that about the safety bicycle?Anvil
Jan 28, 2002 10:22 AM
You don't have to be insane to research and consider new designs. Regardless, it's not going to surprise you, it'll take a few years to get it where it needs to be to have any significant impact. Maybe you'll need/want a new bike by then?
re: Disc brakes on the road?Woof the dog
Jan 27, 2002 9:58 PM
wait, wouldn't the rim be moving faster vs. a hub?

howling softly

woof.
Lots of tandems use them already ...tarwheel
Jan 28, 2002 5:10 AM
But I can't imagine why a regular road bike would need a disc. My bikes already could throw me over the handlebars if I locked them down hard enough. Now if you ride an older bike, lots of them didn't stop worth a damn, but I've never even imagined the need for more stopping power than I've got on my new bikes.
We have a rear disc on our Santana, still not completly thrilledMB1
Jan 28, 2002 6:43 AM
by it. On the other hand it does get smoking hot sometimes. Still a half (single seat) bike just isn't going to have the weight and momentum of the tandem to require a disc.

For those that don't know a non rim brake on a tandem keeps the heat built up from braking away from the rim. You really can (I've done it) blow a tire off a rim by getting it too hot.

Feel no need at all for a disc brake on my singles. (Aren't all rim brakes on bikes disks anyway-the caliper is the caliper and the rim is the disk?).
It will never happen...No way, never...Anchorman
Jan 28, 2002 6:13 AM
We just don't need them.

Just like we don't NEED:-

Carbon levers
Carbon Cranks
Carbon Rims
Carbon bars, stems and posts
Carbon frames
Titanium Frames
Titanium nuts and bolts
Titanium bottle cages
10 speed blocks
gore-tex cables
A new/different bike every 2 years

Get the picture?

Smell the coffee - they will sell bikes, so bike makers will make them, so they are coming, like it or not...
Just for a minute I thought we would be denied..John-d
Jan 28, 2002 6:34 AM
an absolutely essential upgrade. Just imagine you have a $5000 bike with dual pivot brakes. In 2003 you absolutely must have disc brakes. This requires special mounts designed into the fork and frame, almost everything is redundant overnight. New wheels, the list is endless. Now how shall we put this across at home?????

"My bike is obsolete, I need a new one". "Well CAAD5 had a different headset to CAAD4 and CAAD 7 had a different...... Now I really need CAAD8". "All the new Litespeeds have them", how will I keep up on the LBS ride?"

I can smell the cofee.

John-d
Can't work out if you are agreeing or not with the post, butAnchorman
Jan 28, 2002 6:49 AM
I would put money on there being disc braked bike in the stores before long. Just look at all the utter cr@p they stick on bottom-range bikes now - you may be addressing the "elite" of the bike-buying public with your reasoning I don't deny, but given that people pay good $ for bikes at 30lb with roller brakes, saddles the size and weight of arm-chairs, suspension posts at nearly 3lbs, racks like scaffolding, 3" thick tyres that inflate to 40lbs max, side stands, musical horns, cell phone mounts, dynamos, bars sized and shaped like they were designed by scribbling on a drawing board, I have no difficulty in seeing disc brakes on road bikes.

Just take a look at courier's hybrids around the place - they are already there. You may not see them on a C40, but see them you will...
A matter of time and design...TJeanloz
Jan 28, 2002 7:19 AM
As soon as they can bring disc brakes down in weight and aero drag, they will be standard issue on road bikes. Why? They work better. We have already begun to see them on cyclo-cross bikes, so it's just a short hop into the road market.

Anybody who claims that calipers work just as well has never descended in wet conditions with calipers vs. discs. (or even in dry conditions) There is a reason that most Shimano sponsored pros use Dura-Ace 7400 brakes instead of 7700- they work better, and better brakes mean faster descents. A disc would further improve braking.

The big picture that people aren't mentioning though, is that the rim could be significantly lightened if it didn't need the braking surface. It would be a revolution in rim design.

I'm not saying I want them (I didn't want integrated headsets...) but disc brakes are coming to a road bike near you- it's just a matter of time.
all carbon rims good application?Dog
Jan 28, 2002 8:05 AM
I was thinking there really is no need for discs, but all carbon rims would be a great application. Carbon braking surfaces can suck, but a disc would allow the rims to get even lighter, and not have to worry about ceramic impregnation or whatever. The trick would be to make the brakes light enough so that the weight savings in the rim is not wasted.

Doug
Au contraireTJeanloz
Jan 28, 2002 8:10 AM
Just think what we always tell people- weight at the rim is far more important than weight at the hub. Even without an overall weight loss, there would be a gain in performance if the weight was moved from the rim to the hub.
Al rims won't get lighter...ohio
Jan 28, 2002 10:19 AM
You can decrease the thickness of the wall, and optimize the shape a bit, but you have to thicken the spoke bed, or your discs will rip the nipples right out of your swanky new wheelset. They gains and losses in material here and there pretty much offset themselves. Look at MTB XC rims and you'll see the lightest of the light are rim brake specific.

However, it would make carbon rims more viable, which would mean a significant reduction in weight at the rims...

Current brakes are plenty powerful especially considering how narrow road tires are, but they're squishy and without feel at the lever, relative to even V-brakes, let alone discs. Current mountain discs are down to under 350gms for caliper, disc, lever and line with fluid and mounting bolts. With an even smaller disc, they'd weigh about the same as a current road combo, provide a much firmer smoother lever feel
with more sensitive feedback, no brake fade on descents, adjustable power (either using a smaller rear disc, or adjustment at the lever) and lighter-than-air rims. They'd also allow you to ride with a damaged wheel. And if you're really worried about aerodynamics, remind yourself that your removing an odd shaped object at the head of your bike (front caliper) and can decrease fork crown to tire clearance. With a fairing at the caliper, and smart cable routing there's no disadvantage.

I'm perfectly happy with my single-pivot brakes, but I think you will see disc compatible road bikes (probably from Cannondale) in the next 4 years. I won't buy them, but I ride a steel single-speed/fixie...
I agreeAnvil
Jan 28, 2002 9:32 AM
And it's going to be cool when it happens! Caliper brakes work great, they really do and I know it's hard to imagine getting or needing better performance, but disc brakes give a much more reliable and repeatable braking performance.

The problem is that many manufacturers will just adapt a MTB design and that's not what needs to happen. A completely new design, specific to road bikes, giving full consideration for their unique needs is required. Disc brake technology is well understood, it just needs to be a applied to road bikes. As Avid has demonstrated with their excellent cable actuated disc brakes, we don't need the complexity of hydraulics. What we do need is to make the most out of the technology available, introduce the use of ceramics and CF in road cycling disc brakes. Use the same properties they use in F1, where the brakes work better and the get hotter and without sacrificing low speed modulation. Rims designs will also have to be addressed. Using discs imparts a new set of stresses that current road rims have not addressed. Simple subsitution of existing CF rims may not be optimal and spoking will have to be looked at but I'm confident that while the net weight savings will be slim or non-existent there can be vast improvements in performance and reliability. It's not there yet and I suspect it won't be for a few more years if not more. Manufacturers like to test the waters first and not risk the expense of bringing an all out design to an unproven market.

I can tell you that the few road going or cross bikes that I've built with discs have worked well even though they have not used optimized components (Amp or Rock Shock cable actuated hydraulic calipers and the new Avids which work better). On a cross or touring bike I think it's an excellent application for discs and the existing crossover brakes from MTB's, i.e., Avids for road levers work well. For road bikes, I'm still holding out for an optimized system.
radial spoking?Dog
Jan 28, 2002 9:44 AM
Would we have to do away with radial spoking for disc brakes?
Yeah,TJeanloz
Jan 28, 2002 9:47 AM
Disc brake side radial spoking would pretty much be hosed.

Here's a project for somebody with too much time and money: buy a pair of Ksyriums, and a pair of CrossMax Discs, disassemble both, reassemble the Ksyriums with the CrossMax hubs. Report back to the group on how well it works.
Better yetAnvil
Jan 28, 2002 10:03 AM
Call Shook Designs, get a set of the AM disc hubs laced to a set of the 350 rims. Install some 700c 23's and stick em in your disc brake equipped MTB and you'll be Rockin' like Dokken! That'll give you a taste, but not the whole burrito.

TJean, don't take my word for it, you probably know how smooth the Avids work on MTBs, now find a road bike equipped with them, they're out there already and it's pretty cool and amazing how much smoother the braking is versus calipers on the road. I've talked to Wound Up about building one of their CF forks for discs since their design is the most easily adaptable to disc use. They're expressing interest and we'll see what happens but in the meantime I'm working on a lightweight Tange Switchblade'esque style road fork. Most steel Cross designs (you have to either use a narrowed MTB unicrown blade or a cross blade that has been shaped to clear the disc.) will work too.
beef up the forks, too?Dog
Jan 28, 2002 10:48 AM
With discs, won't you have to beef up the forks a little, too?

That's something that gets overlooked when comparing calipers with v-brakes, too. With calipers, the forks can be quite a bit lighter, as the fork is stressed as much and doesn't have the bolts. For mountain bikes, it doesn't matter as the forks are plenty beefy to begin with; but, with road forks, especially 300 gram carbon forks, it may make a huge difference. I think you'd have to compare weights of the whole system to be fair.

Doug
beef up the forks, too?Anvil
Jan 28, 2002 3:42 PM
Yep, the fork will be subjected to loads not experienced on forks designed for caliper brakes. I alluded to this in the fork portion of a previos post and was what I meant when discussing "net" weight comparisons. I've not really worked out how to do the fork yet, as I said, the current bunch of Wound Ups are the most likely candidates for retrofit. A fork leg will have to be designed to deal with the loads applied by the braking force of the caliper. But, I agree with your assumption that the fork will have to be heavier. Current caliper brakes take excellent advantage of compensating for braking forces at the crown and not the legs. I think there are engineering solutions to this, but again, I think it will be a while before the weights get where they need to be. A smart design might use a torque arm to transfer the braking force from the fork legs to the crown, but again there will be a weight penalty for this however low it will be. I believe that the answer is in the use of better materials. We must remember that caliper brakes for bicycles have been evolving for a century or more. Cycling disc brakes aren't even out of their diapers. Of course I do remember seeing a Phil disc brake around 1980 or so.
beef up the forks, too?David Feldman
Jan 28, 2002 7:51 PM
Then, how will road forks keep their shock absorbing ability--without a shock function, and then like you said the whole system weight has to be considered. Is it possible that things are at an optimum now re caliper brakes theoretical disadvantages vs. having to redesign the front third of road bikes to make a front disc work. Reading: Bike Culture Quarterly did an article @5 years ago on fork failures due to hub drum brakes; and they were talking about some low-end, low-powered Shimano and Sturmey-Archer drum units.
beef up the forks, too?Anvil
Jan 28, 2002 10:02 PM
"how will road forks keep their shock absorbing ability--without a shock function"

Hey Dave, it's good point but I think it has to be looked at based on how current forks work. Most modern forks flex very little in the blades, it generally occurs in the crown and the steerer tube. I don't think discs, on their own, will cause a stiff fork if the crown and steerer stay the same and I see no reason why they couldn't. When forks fail from brake loadings at the axle (disc or drums) it's usually caused by a point load transferred low on the leg that it wasn't designed to resist and typically occurs just around the caliper or torque arm mount. It's the same problem on the rear of the bike, when disc mounts are mounted on the seatstay, the seatstay invaribly fails unless the mount has been braced to the chainstay. The lower leg of the fork will have to be engineered to resist this new load, current forks just aren't suitable. I mention the Wound Up because it's unique (relative) design makes custom/extended dropouts sleeves and easily installed thicker/stiffer legs possible without molding costs. It's not an optimum systemm, but it could be another step in that direction.

The road style forks I've built for disc brakes and rigid forks for disc brake MTBs use heavy MTB or tandem duty units with a welded mount. Personally I think the way to keep the fork weight down is to use a torque arm designed into the fork and not through bulk on the legs but it's just a theory, I haven't tried it yet. I will. Like I said, I think it's still a ways off for disc brakes to equal the overall performance (performance & weight) of a caliper road brake, but it's coming.
re: Disc brakes on the roadAndy M-S
Jan 28, 2002 7:31 AM
I don't know if it will ever happen on ROAD bikes, but there's a lot to be said for such brakes on touring and/or all-around bikes.

Think about being able to pop out your 700c wheels and replace them with 26", fat-tired wheels. The frame would have to be made to accomodate this sort of thing, but no rim brake is going to adjustable enough to deal with it. Only disk brakes would be able to handle this kind of flexibility.

I can see an all-weather heavy touring bike set up this way, but the weight and aero problems will likely keep disk brakes off serious road bikes for some time to come.

OTOH, with the increasing popularity of and road road-like bikes (thanks, Lance!), we may see a resurgence of sport-touring bicycles, which would also be prime candidates for disk brakes.
Merlin NewsboyTJeanloz
Jan 28, 2002 7:57 AM
The Merlin Newsboy has just such a design (both 26" and 700c wheels)- very slick. And a cool $5,500...
re: interchangeable wheels...guido
Jan 28, 2002 1:31 PM
Also look at the "Jekyll" in Akirasho's posting above. One picture it's got MTB wheels, the other 700C road wheels. It that a Cannondale?