Disc brakes on road bikes / hybrids.

[simongt]

Ther's been a recent surge in the popularity of factory fitting disc brakes to road and hybrid bikes. An article in the latest issue of the CTC magazine by technical editor Richard Hallett, warns of the potential problems with the laws of physics. With the size if a typical disc which is about a quarter of the size of a typical wheel, apparently the braking forces transmitted to the spokes are about four times that of rim brakes. This can lead to spoke failure and in some instances failure of a front fork during repeated heavy braking e.g., down a long hill. Because mtbs invariably have front suspension, the fork is hefty enough to soak up such forces. Is this a case of a trend crossing disciplines without it being properly thought through - ?

 

[T.M.H.N.E.T]

That is very much a load of nonsense.

 

[mrandmrspoves]

No doubt about it, disc brakes do exert extra forces on the forks - which is why manufacturers specify a maximum safe rotor size that should be fitted. Even on quite substantial MTB forks, manufacturers often specify 130mm as the maximum rotor size - needless to say, they don't want to risk liability claims if a fork snapped in use - and this will be no different for road bikes.
What may change over the next few years is the axle, as many MTB forks have moved over to through axles for extra strength and security. Factors that may influence this are weight and what racing cyclists adopt - which is unlikely to be any kind of through axle that adds to the time needed to change a wheel.

 

[mustang1]

I figured my next road bike will have disks (assume I buy it soon) but I think I'll stick with rims forna few years.

Disks will slowly come into tdf in 2017 and inwant them to be my Guinea pigs before I commit a couple of years later.

The disk brakes on my MTB are stunningly good, and they're just low end shimano.

 

[mythste]

I think this has been logically debunked before now - I'm happy with mine and wouldn't go back to rim brakes. Even starting to find disks sexier than rim brakes! Ho hum.

 

[Drago]

While they're a leap forward I don't think its quite quantum one some folk are preaching. Conversely, I think the CTC article is a bit over-strong in presenting its case.

 

[BigTam]

Is there life on Mars ?

 

[Drago]

Yes, robotic life from Earth.

 

[ianrauk]

4 years of riding road disc braked bikes. And I do more mileage then most. I haven't had a spoke failure in all that time.

 

[RichardB]

I'm not sure I have worked the physics of this out, but my guess is that the force on the spokes from a disc brake is different in its nature, regardless of the size of the force. When you brake with a rim brake, the two points exerting force on the wheel (tyre contact patch and brake/rim contact area) are roughly equidistant from the axle, and the force on the spokes is therefore pretty much radial - the spokes at the rear-facing part of the wheel are under tension, and under tension is when a spoke is at its strongest. With a disc brake, the forces are between the disc/axle assembly trying to stop and the wheel rim trying to turn, so the forces on the spokes are torsional. However, a spoked wheel is so strong that I imagine both of these situations are well within its capabilities. My Ducati had twin 320 mm discs with 4-pot calipers at the front, which could stop a combined 280 kg of bike and rider in a few seconds from 130 mph, and that had spoked wheels. I have hydraulic discs on the Wisper, and I love them. Very powerful and unaffected by rain. I'll be seriously looking at discs for my next road bike, I'm sure.

 

[winjim]

I think Roger Musson says you need to get your push/pull spokes the right way round, but apart from that it's fine.

 

[Cubist]

No doubt about it, disc brakes do exert extra forces on the forks - which is why manufacturers specify a maximum safe rotor size that should be fitted. Even on quite substantial MTB forks, manufacturers often specify 130mm as the maximum rotor size - needless to say, they don't want to risk liability claims if a fork snapped in use - and this will be no different for road bikes.
What may change over the next few years is the axle, as many MTB forks have moved over to through axles for extra strength and security. Factors that may influence this are weight and what racing cyclists adopt - which is unlikely to be any kind of through axle that adds to the time needed to change a wheel.

Presume 130mm is a typo? its a cyclocross standard I believe, and has bled out into road bike territory. Most suspension forks run 180mm, and one of my forks won't fit smaller than 203mm.

 

[clid61]

Discs on cross and mountain bike , but there's nothing like the the thrill of flying by the seat of your pants, right on the edge , on a road bike with rim brakes !!!!

 

[T.M.H.N.E.T]

Discs on cross and mountain bike , but there's nothing like the the thrill of flying by the seat of your pants, right on the edge , on a road bike with rim brakes !!!!

Theres nothing like brakes that work the same way every time you pull the lever either. Nothing like the feeling of riding through muck grime and wet days knowing that usable life of your wheels isnt an issue, when pads/discs are cheaper to replace

 

[CUBE CRD]

I find the disc brakes on my CX bike a lot more reassuring and effective in the wet.I intend to buy a road bike with discs when there is a bit more to choose from (are you reading this CUBE)