Road Cycling - Discs on a road bike - good idea?

im new to road bikes, im a MTB/BMX boy - i still go to bunny hop drain on my road bike lol

P.

http://thepaulius.com/forum/viewtopic.php?p=20

I find that my dual-pivot calipers stop me fine. Some might argue that you only need dual-pivots on the front and can get away with single-pivot in the rear (ala Campy differential brakes). With this in mind, I think most road cyclists don't feel that discs are that necessary. Having said that, I think if you're doing long steep descents and riding a lot in inclement conditions, then discs solve many problems uncluding heat buildup (yes I know they still build up heat but dissipation is better), better modulation, better wet-weather performance, no rim wear, and all the other things that make the disc brakes advocates gloat over in the MTB world. I'm starting to see mechanical discs on touring road bikes and cyclocross bikes. I think it will be quite a while before we start seeing hydros on road bikes (if ever) though because of the weight issue and lever compatibility limitations.

BTW, I'm running V-brakes on my MTB and am still quite satisfied with their stopping abilities.

I think it will come once the weight issue is narrowed down. A disc set up is quite a bit heavier han typical road bike brakes.

DISCS are awesome. Totally sold on the modulation and power and control. The weight for MTB is a non-issue as they are just as light now.

For road, it's coming. There are alot of advantages and only one disadvantage-weight. But where braking conditions are not ideal it's already becoming popular- like cyclocross.
So, discs for road are really here and only going to gain popularity.

As soon as racers use it in Paris-Roubaix or other races, it will be credible and everyone will jump on it. Technology will catch up and weight will be a non-issue very soon.

I think disks are good for roadbikes..

Unfortunately disks are heavy.

If you take a look at road wheelsets, almost all great wheelsets are aero (radial spokes). You can't use aero style wheelsets with disks.. And since this type of arrangement adds to better aerodynamics, i think it would be hard to justify disks over calipers, since roadbikes are being designed for faster speeds, faster stops in my opinion is secondary.

But disks have been used on cyclocross bikes..

i still use V-brakes on my XC FS MTB...

and on a road bike i see no reason for them as the limiting factor is braking is _not_ braking power, but _tire_ contact. wet or dry i can lock up both tires easily. why would you need more braking power?

with skinny tires on a road bike you can lock the tires up with old-style caliper brakes. V-brakes are probably an improvement as you get better feel and are just as light, but to my discs would offer no benefit.

p.s. from my experience on long descents: i have had many friends with discs experience disc fade when the disc heats up too much (it gets HOT and you spit on it or pour water on it and it hisses and streams). my v-brakes have always performed well even on 2000m sustained descents (i just burn up my brake pads and my rims)

anyhow, i'm still not convinced that the weight and complexity is worth it on a MTB where you can actually need lots of stopping and often have muddy conditions... so i would never even think about it on a road bike.

I don't think weight is an issue. If they wanted them on race bikes they would be. The bikes in the Tour don't use them so there must be a reason besides weight. They can make the bike lighter to make up for the extra weight. Remember there is a weight maximum in the Tour. Everything is designed to win the Tour.

Lightweight carbon road forks may need beefing up to handle disk brakes.

one of the issues of wieght is the fact that the wieght is the added wieght is on the wheels, not so much the over all additional wieght.
i'd be interested to see if a really good decender (sp?) could come down a windy mountain road faster with discs, being able to go into turns faster might make a difference. on a race bike if it doesnt get you to the finish faster there may not be a reason for it.

back to the wieght issue. the rotors calipers and pads could all be made from carbon fiber, this could allieviate the wieght issue. F1 cars for one use them, but they are hugely expensive, the manufacturing process takes like 6 months for the pads to be made. some teams might be able to afford them, but it would be tuff on normal people, the brakes would probably 10x the price of the most expensive modern bike.

I don't see it happening. As nathank mentioned, too much braking force could be detrimental on such a narrow tire.

Plus, one of the primary reasons for disc use is muddy conditions. Thus, the use of them on a CX bike, it's a bit of a stretch to put them on a tour bike, however, many tourers ride despite inclement weather and some non-paved roads, so I could understand that.

Road bikes, probably not happen in the near future. It's a solution to a non-exisistant problem. Uh oh, that mean's Shimano will be producing one for 2005.

L8R

I think you don't see them because there isn't much need for them. Look at a race like the TdF, not that much time is made up on a descent, sure there are guys that are fearless, but I don't ever remember a TdF winner who did it by going down the mountains. The next question is would you really save much time, say with a disc you can brake 5ft more into the corner, after 10 or 20 turns maybe you made up 1-2 seconds, but how much do you potentially lose by climbing that weight up the mountain?

Oh and carbon fiber brakes like on F1 will never work on a bike. Those guys use it because of how well it works when it's hot (like over 1,000 degree's hot), at ambient temps carbon/carbon brakes have VERY little stopping power, watch race's here in the US with the IRL and CART, when they go to Super Speedways they run carbon/carbon brakes, when going into the pits it's typical for the driver to "drag" the brakes to put some heat into them.

Andrew

o yeah forgot about the need for heat with CF brakes, good point. and too expensive really, just mentioned for the sake of conversation as much as anything.


but I don't ever remember a TdF winner who did it by going down the mountains.
Eddie Merkxx sort of did it. he was descending like a stone as they say :), and the actual leader was chasing and crashed.
I realize thats not what you mean, just mentioned it for the fun of it.
i agree increased speed on a descent wouldnt be enough to justify discs, i just think it would be a cool experiment to see if there was a difference in speed with a really good bike handler running them.
enjoying this topic it's a good what if subject :)

weight not wieght

Bad idea.

Here's one more vote for not understanding why this idea ever came up. If you can lock the wheels using rim calipers, what's the point of discs?

Look at the stopping force. Effective force is a function of where the force is applied relative to the wheel axis (i.e., the axle). Equivalent force applied 350 mm from the hub (as on a rim caliper) provides more stopping power than applied e.g. 100 mm away (as on a reasonably sized brake disc).

The reason disc brakes are used on mountain bikes is NOT because of dry stopping power. It's because of other factors such as mud interfering with the friction of pad against braking surface. These factors don't typically apply for road bikes ridden in dry weather. Wet weather is another matter, but this problem, it seems to me, might best be solved by using different rims when riding in the wet (like different tires used on race cars in the wet). The wet weather rims might be more textured to enhance friction and help channel water away from the braking surface.