Why no disc breaks on road bikes?

[PaulSecteur]

OK, I realise this may be a stupid question...

But how come road bikes dont have disc breaks? I would have thought that the extra power, especially in the wet over rim breaks would have been worth the extra weight. The only other reason I could think of is that the stress on carbon forks might be too much.

But even with that, I would have thought that the extra ability would have resulted in some sort of answer to allow disc breaks on road bikes. Or rim breaks are better now than I remember them being.

 

[SquareDaff]

I don't ride road bikes - but I can only assume the answer is weight!!

 

[RedBike]

I've got mixed views on this. I had an Uncle John CX bike for a while that had disc brakes on it.
On a utility bike the discs were a god send. The pads lasted much longer, I didn't get black gunk on the rims, and the braking with panniers on in the wet was greatly improved.

However, I wouldn't want any of the current mainstream 'road' disc brakes on my race bike.

No matter how carefully I adjusted mine (BB5's) they rubbed.
Having spent a spent a fortune on light-weight wheels I've got no intention of bolting a heavy steel rotor onto them.
My brakes on the road bike are more than powerfull enough to stop me even in the wet.
I'm not sure I would be allowed to race on the bike?

 

[mgarl10024]

I've often wondered the same...

 

[Kestevan]

Properly set-up and adjusted rim brakes with decent pads can easily lock up both wheels on a road bike even in the wet.

The added weight and complexity of disk brakes simply isn't needed on a lightweight roadie.

That's not to say that disks don't have their place, on a MTB or cross bike where your dealing with thick mud they're pretty much unbeatable, and I can see an argument for their use on heavily loaded touring bikes/tandems where weights not an issue.

 

[2Loose]

There are plenty of road bikes with disk brakes (Croix de Fer, Kona Dew Drop etc.) , increasingly so since the UCI sanctioned them for cyclocross racing, so expect more and more to appear.

Unfortunately though, they haven't yet managed to get hydraulic braking systems onto road bikes due to the brake levers on drop bars. Cable disk brakes only so far, although there are a number of manufacturers looking at hybrid systems - lever pulls brake cable, cable pulls onto a seperate hydraulic system under the bar which can actuate the disk properly.

 

[iAmiAdam]

For the benefit in braking, it outweighs the benefit in weight.

 

[Over The Hill]

Rim brakes are efficient in parts as they use the rim for an additinal use (a braking surface) as well as being a wheel.
Disc brakes by comparison have to add in both braking surfaces by introducing the disc.

Off road and encountering mud, a rim brake gets mud in betweent the two brake surfaces so is not working properly. The solution (discs) simply moves the contact area away from the rim and so away from most of the gunk.

Braking is about two contact areas pad on rim or disc and Tyre on road. A road bike has generally less contact area and less grip than an off road bike so it is useless uprating its brakes beyond the capability of the tyres to grip the road. Make the brakes good and the wheels lock up and off you go!

 

[John the Monkey]

There are also problems with beefing up the forks & stays to handle the extra forces of disc brakes, and heat dissipation. Since MTBs are beefy anyway, it doesn't matter.

Canyon talk a bit about this on their Project 6.8 page;
http://www.canyon.com/_en/technology/project68.html

And Cotic have posted some interesting stuff related to this about their Roadrat frame & fork (by no means a racing frameset).

Regarding cross, competitive cross bikes are used on lapped courses (unlike road racing bikes). This is significant because in racing laps, braking technology improvements tend towards better lap times. I'm not sure the same gain for the weight penalties would happen in road racing.

As other posters point out, properly set up dual pivots with good pads will stop you PDQ in any case.

 

[normskirus]

Hi

To the initial question the answer would probably be that disks add too much weight. Im not a road cyclist just a commuter and part time MTBer but the addition of disc hub and rotor would elimanate any weight gains by super light wheels.

As to their efficency of different brakes my juicy 3's on my MTB will stop me dead. My cantis on my ridgeback can make stopping in the wet an interesting experience. Ive also noted the shocking state of my rims on the ridgeback after 17 months of commuting. I think I'll need some new wheels in 12 months time.

I can see a time when even more road bikes will have a disc option or have them fitted as standard. Also at some point someone will produce a light weight disc setup for those seeking the lightest possible solution.

Give me discs or give me death!

Normskirus

 

[MacB]

Perspective, tradition and aesthetics, it will come, higher end MTBs tend to be disc, increasingly the same is happening for hybrids. It was held back in CycloX by the UCI ruling which is now amended so I'd expect to see an increased uptake there. Road bikes and road orientated hybrids are still rim brake, they also tend to have 130mm rear spacing and there aren't many 130mm disc hubs around. The frames and forks lack the fitting for disc calipers and can't be retrofitted, or at least not cheaply, as the structural strength isn't present.

The weight argument is a bit of a red herring, I did some rough calcs on differences using Avid BB7 with 160mm rotors as a comparison. Including accounting for heavier frame and forks I couldn't get more than about a 700g weight penalty. This is without allowing for weight savings on rims not needing a brake track. Also they claim that pro riders already add weight to their bikes to reach the required limit.

What is valid are the claims that more powerful brakes aren't needed on road bikes. While true this ignores the fact that poor conditions braking would be improved and, most importantly, you'd no longer be grinding away those expensive rims.

I wouldn't be surprised to see disc becoming the norm in higher end tour and cross bikes and gradually creeping in to audax and sportive. I wouldn't hold my breath on all out race machines though.

 

[tyred]

I don't there is really any need for normal road cycling. I can stop my ancient Carlton with equally ancient Weinman brakes from 20mph+ with only one finger. They are easily powerful enough to lock wheels, even in the wet. What more do you want?

 

[Globalti]

I agree. After about 15 years of riding in gritty Lancashire mud and countless worn out rims (I even taught myself how to replace a rim by taping a new one alongside and transferring the spokes over) my first disc brakes came like a ray of sunshine. No longer did I have to endure the noise of the rims grinding away, the cost - I could easily wear out a set of brake blocks on one Polaris trailquest weekend - and the filthy black paste of brake rubber and aluminium. Disc brakes work instantly unless they're soaked and they are smooth, silent and long lasting and I am still riding the same wheels I've had for about seven years.

Since I seldom ride the road bike in the wet the rims should last many years.

 

[John the Monkey]

The weight argument is a bit of a red herring, I did some rough calcs on differences using Avid BB7 with 160mm rotors as a comparison. Including accounting for heavier frame and forks I couldn't get more than about a 700g weight penalty. This is without allowing for weight savings on rims not needing a brake track. Also they claim that pro riders already add weight to their bikes to reach the required limit.

That does assume that the volte face required by the UCI to allow discs on roadies doesn't follow a similar one on bike weight minima!

What is valid are the claims that more powerful brakes aren't needed on road bikes. While true this ignores the fact that poor conditions braking would be improved and, most importantly, you'd no longer be grinding away those expensive rims.

Not a factor for the pros, as they're given the kit. Given that, will it filter into the consumer "race" bike?

I wouldn't be surprised to see disc becoming the norm in higher end tour and cross bikes and gradually creeping in to audax and sportive. I wouldn't hold my breath on all out race machines though.

That's a fair assessment, I think. It makes sense for cross, and I imagine this will be the route into the commuter & tourer market (tourers already use a lot of nominally Cyclocross equipment).

 

[PpPete]

What is valid are the claims that more powerful brakes aren't needed on road bikes. While true this ignores the fact that poor conditions braking would be improved and, most importantly, you'd no longer be grinding away those expensive rims.

No it wouldn't - in poor conditions it would be even easier to lock the wheels up. FFS I can lock my wheels up on a wet road using old-school cantis - let along dual pivots.
Certainly you wouldn't be wearing out the rims, and the other advantage would be no heat induced blow-outs from riding the brakes on long descents.

For me the logical thing on a touring or audax bike would be dual pivot front, and cable operated disc on the rear.

In fact if my "TraumenFahrad" project ever approaches reality I shall be disccusing rear disc options with frame builders.