Disc brakes on road bikes

[Binky]

The wet makes zero difference to stopping performance.

Have to say I question this. I have Ultegra rim brake bike, (Canyon as it happens and an Endurace). Anyway, Ultegra brakes with Swiss Stop pads are excellent in the dry. No question though in my experience the braking performance is reduced in the wet especially heavy rain.
Of course can still stop, just need more time and distance on a steep descent for sure.

Aluminium rim wheels.

 

[Webbo2]

When I travel normally I take my Scott CR SL rim brake bike, have done for 10+ years, mostly because it weighs 6.5kg but also because the ultegra brakes are amazing, paired with tubeless wheels. The wet makes zero difference to stopping performance.

My best bike a Cervelo R5 is rim brake with carbon wheels, just as good as hydro discs when it’s dry.

My Canyon Ultimate is disc and tbh it’s the worst of all my bikes but then I believe that down to a shoddy build by Canyon.

I’ve just bought/built a new yes new Canyon Endurace rim brake bike with Di2 Ultegra on carbon wheels.

You can still buy rim brake framesets and carbon rim wheelsets, Elite and Hunt to name but two.

View attachment 817308

CAAD12 hydro discs lurking in the background, was very avg braking performance until I swapped out the stock SRAM pads, now it’s mega, it would be my travelling bike if the seat post wasn’t stuck 🤣

What pads are you using. I’ve used the ones that came with my Zipp wheels, Swiss stop and Wiggles life line and I’ve yet find some that work anything like when you are using Aluminium rims.

 

[Punkawallah]

Yet not for this 280lb (as I was then) male.

I can endo my one rim braked bike - the power of the braking exceeds the bikes fundamental ability to handle those forces. More braking power won't translate to shorter stopping distances if the existing braking ability is already sufficient to elevate the rear wheel from the tarmac.

While true, it does not alter the fact that disc brakes have been shown to have a shorter stopping distance than rim brakes?

 

[Dogtrousers]

While true, it does not alter the fact that disc brakes have been shown to have a shorter stopping distance than rim brakes?

Not picking an argument here, because I really don't have any opinions or any point to make but ...

How does this work? What is the mechanism? Naively it would seem to me that if brake X and brake Y both have sufficient stopping power to lock the wheel then surely stopping distance is governed by the tyre-surface interaction, not the brake-wheel interaction.

The only potential answer I can come up with is that disc brakes have some kind of "human-mediated ABS" in them. Perhaps their modulation allows a user to select a pressure just below the point where the wheel locks up but rim brakes are clumsier and don't, thus making it easier to lock the wheel and skid, causing the user to be more cautious. ... Perhaps ... maybe.

I'm just curious. As I've said on here before I'm prepared to accept that discs are better, but I don't find my rim brakes to be noticeably bad. Certainly not bad enough to warrant the enormous hassle and expense of changing over (buying a new bike, considering what to do with all the rim-braked wheels hanging in my garage and so on) which means I'm not considering the change at the moment.

 

[Binky]

Not picking an argument here, because I really don't have any opinions or any point to make but ...

How does this work? What is the mechanism? Naively it would seem to me that if brake X and brake Y both have sufficient stopping power to lock the wheel then surely stopping distance is governed by the tyre-surface interaction, not the brake-wheel interaction.

The only potential answer I can come up with is that disc brakes have some kind of "human-mediated ABS" in them. Perhaps their modulation allows a user to select a pressure just below the point where the wheel locks up but rim brakes are clumsier and don't, thus making it easier to lock the wheel and skid, causing the user to be more cautious. ... Perhaps ... maybe.

I'm just curious. As I've said on here before I'm prepared to accept that discs are better, but I don't find my rim brakes to be noticeably bad. Certainly not bad enough to warrant the enormous hassle of changing over (buying a new bike, considering what to do with all the rim-braked wheels hanging in my garage and so on) means I'm not considering the change at the moment.

GCN amongst others have tested all this and their findings were that in dry the stopping distance pretty similar but it's in the wet there is a significant difference.

Now, I haven't gone back and rewatched video from a a few years ago but pretty sure that was results. Happy to be corrected.

 

[Dogtrousers]

GCN amongst others have tested all this and their findings were that in dry the stopping distance pretty similar but it's in the wet there is a significant difference.

Now, I haven't gone back and rewatched video from a a few years ago but pretty sure that was results. Happy to be corrected.

That would make sense if the wetness sufficiently reduced the effectiveness of the rim brakes so that at maximum pressure they no longer locked the wheel but let it keep turning. My experience - years back - of chrome rims suggests that in that particular case it's true.

Although I would want someone with a wee bit more rigour than GCN to do the tests.

 

[Drago]

While true, it does not alter the fact that disc brakes have been shown to have a shorter stopping distance than rim brakes?

Corredtion. That the disc brakes tested have a shorter stopping distance than the rim brakes they were tested against. That is not the same as all disc brakes stop in a shorter distance than all rim brakes.

In my case discs may well be more powerful, but as on my sole rim braked bike the rim brakes already exceed the bikes ability to transmit that braking force to the ground any additional braking ability is not only pointless, but actually immeasurable.

 

[T4tomo]

In the wet, rim brakes need a couple of revolutions to clear the water off / dry the rim. Once that is done they will lock up just the same disc brakes / as they do in the dry. Its these couple of revolutions that makes disc brakes, which pretty much grip instantly even in the wet, quicker to stop in the wet than rim brakes.

This drying process is even slower on carbon rims with rim brakes, (I can confirm this first hand) which is why I don't often take the Bianchi out when its wet, but it is still manageable with good swiss stop carbon rim pads.

Winter rides I use the gravel bike with semi-slicks. Disc brakes and wider tyres = bigger contact patch -> gives more braking power / confidence.

 

[Drago]

I've found the biggest advantage of discs is a much better feel and modulation.

 

[Dogtrousers]

I have no reference to any research on this but I suspect that the biggest factor in braking effectiveness is the software in the Bicycle Power Input Directional Control and Brake Actuation System (BPIDCBAS) sitting on the bike.

 

[Punkawallah]

Corredtion. That the disc brakes tested have a shorter stopping distance than the rim brakes they were tested against. That is not the same as all disc brakes stop in a shorter distance than all rim brakes.

In my case discs may well be more powerful, but as on my sole rim braked bike the rim brakes already exceed the bikes ability to transmit that braking force to the ground any additional braking ability is not only pointless, but actually immeasurable.

I look forward with interest to your study on which rim brakes stop in a shorter distance than disc brakes, then.

 

[Drago]

I look forward with interest to your study on which rim brakes stop in a shorter distance than disc brakes, then.

Where did I say that?

All I am saying is that the stoppers on my one and only rim brakes bike are already more powerful than the chassis can handle, and can stand it on its front wheel (and could flip it if I gave it a vulcan death grip.)

That being the case, how do you believe a more powerful disc brake would stop me in a shorter distance when the rim brake is already providing retardation in excess of the bikes abilities?

Its a reasonable question, and instead of sarcasm you could try and answer it.

I have little doubt that a decent disc brake (and they are not universally decent) is well capable of providing greater retardation than a decent rim brake, but when both are already providing stopping grunt in excess of that a bike can handle without flipping its a pointless ability. When the bomb drops it won't matter if its 20kt or 20Mt if youre stood right under it - the excess power is similarly wasted.

 

[Ming the Merciless]

Not picking an argument here, because I really don't have any opinions or any point to make but ...

How does this work? What is the mechanism? Naively it would seem to me that if brake X and brake Y both have sufficient stopping power to lock the wheel then surely stopping distance is governed by the tyre-surface interaction, not the brake-wheel interaction.

The only potential answer I can come up with is that disc brakes have some kind of "human-mediated ABS" in them. Perhaps their modulation allows a user to select a pressure just below the point where the wheel locks up but rim brakes are clumsier and don't, thus making it easier to lock the wheel and skid, causing the user to be more cautious. ... Perhaps ... maybe.

I'm just curious. As I've said on here before I'm prepared to accept that discs are better, but I don't find my rim brakes to be noticeably bad. Certainly not bad enough to warrant the enormous hassle and expense of changing over (buying a new bike, considering what to do with all the rim-braked wheels hanging in my garage and so on) which means I'm not considering the change at the moment.

You are making the assumption that rim brakes offer a perfectly smooth, reliable, even braking, with linear proportional force applied to the rim compared to pressure on levers. That is not the case even when new, and gets worse as rims wear out.

 

[Mr Celine]

How does this work? What is the mechanism? Naively it would seem to me that if brake X and brake Y both have sufficient stopping power to lock the wheel then surely stopping distance is governed by the tyre-surface interaction, not the brake-wheel interaction.

The only potential answer I can come up with is that disc brakes have some kind of "human-mediated ABS" in them. Perhaps their modulation allows a user to select a pressure just below the point where the wheel locks up but rim brakes are clumsier and don't, thus making it easier to lock the wheel and skid, causing the user to be more cautious. ... Perhaps ... maybe.

In the dry your front wheel does not lock up before your rear wheel leaves the ground, even with @Drago in the saddle.

And like him I can do an endo on my rim braked road bike, but only from the drops and it takes a large handful of brake lever and a couple of seconds to achieve. On my disc braked road bike I can do an endo from the hoods.

 

[itboffin]

What pads are you using. I’ve used the ones that came with my Zipp wheels, Swiss stop and Wiggles life line and I’ve yet find some that work anything like when you are using Aluminium rims.

Ones that came with a set of prime 50mm carbon rims, made by brakco whoever they are.