Cable operated disc brakes on road bikes?

meanredspider

Manc33 wrote:

This has to be the costliest upgrade if you suddenly thought "I want to replace my rim brakes with disc brakes".

Why on earth don't they just make frames to accommodate both rim and disc?

For rim brakes its one hole in a fork. For disc brakes its two holes on the fork. They are nowhere near each other and wouldn't interfere with each other.

I wouldn't care about riding around with empty IS mounts, or empty rim caliper mounts. To upgrade to disc currently, I would need a whole new frame. Frame code numbers even determine it, calling them "disc framesets" and so on. :roll:

My Volagi has this capability. Never bothered with the rim brakes though: why would you...? In fact, the main reason they did it is so you can fit guards easily but they also fitted the cable guides too

rolf_f

ugo.santalucia wrote:

Rolf F wrote:

But of course, MTBs aren't road bikes. Disc brakes are a no brainer on mountain bikes. The advantages are far less conclusive for road bikes and are affected by more variables.

Yeah, keep adding variables and try to solve the equation... while your peers face extinction all around you...

Not really no. If I was buying a four season road bike now, I might well go for discs. But for a summer bike I can think of no good reason to go for discs and plenty against. It never ceases to amaze me how folk on here go on about how great the wet weather braking of discs are without questioning whether or not some people might never get their bike wet.

Here are reasons why discs might be sh1t,

1) You live in a dry climate
2) You don't ride that particular bike in the rain (for whatever reason)
3) You aren't heavy and don't want overly powerful brakes that just lock or cause the back end to lift too easily.
4) You've previously owned a MTB fitted with Avid hydraulic discs (!!)
5) You don't have a support vehicle to fix the brake in the unlikely event of a failure
6) It isn't hilly where you are
7) You don't accept that stuff is great just because it's new and someone who likes Apple products tells you to.

Reasons why discs might not be sh1t

1) You are heavy
2) You ride a heavy mountain bike
3) You ride a mountain bike in muddy terrain
4) You ride in wet weather in hilly areas a lot.

As you can see, it doesn't require very much intelligence to realise that the case for discs is far from open and shut. If you can give me one convincing reason, without in so doing coming across as smug, why in my circumstances I should replace my Look 585 with a disc braked bike I'd love to hear it. I've never heard one so far.

ugo.santalucia

Rolf F wrote:

ugo.santalucia wrote:

Rolf F wrote:

But of course, MTBs aren't road bikes. Disc brakes are a no brainer on mountain bikes. The advantages are far less conclusive for road bikes and are affected by more variables.

Yeah, keep adding variables and try to solve the equation... while your peers face extinction all around you...

Not really no. If I was buying a four season road bike now, I might well go for discs. But for a summer bike I can think of no good reason to go for discs and plenty against. It never ceases to amaze me how folk on here go on about how great the wet weather braking of discs are without questioning whether or not some people might never get their bike wet.

Here are reasons why discs might be sh1t,

1) You live in a dry climate
2) You don't ride that particular bike in the rain (for whatever reason)
3) You aren't heavy and don't want overly powerful brakes that just lock or cause the back end to lift too easily.
4) You've previously owned a MTB fitted with Avid hydraulic discs (!!)
5) You don't have a support vehicle to fix the brake in the unlikely event of a failure
6) It isn't hilly where you are
7) You don't accept that stuff is great just because it's new and someone who likes Apple products tells you to.

Reasons why discs might not be sh1t

1) You are heavy
2) You ride a heavy mountain bike
3) You ride a mountain bike in muddy terrain
4) You ride in wet weather in hilly areas a lot.

As you can see, it doesn't require very much intelligence to realise that the case for discs is far from open and shut. If you can give me one convincing reason why I should replace my Look 585 with a disc braked bike I'd love to hear it. I've never heard one so far.

I think you got it all wrong...

They are just an alternative braking system, they are no better or worse in terms of dry performance... they are just more reliable in most cases and they don't cause friction on a system kept at 100 PSI, which is a bloody good idea, of course. Virtually every modern vehicle is equipped with disc brakes, except road bikes... you are resisting the obvious... it's coming and within ten years there won't be any more rim calipers around, simply because there is no longer any interesting development for the manufacturers... rim calipers haven't really changed at all over the past decade and if you look at the decade before, the difference is subtle... you can moan, you can stomp your feet on the ground, but ultimately this is going to happen, whether you like it or not... you might as well give it a try and join the majority of people who are happy on them and have given up going on about the all matter.
The same applies to tubeless tyres... you can go on a about the subject, but in ten years you will only see a few bearded Audaxers with a map folded in their rear pocket changing an inner tube...

When a new technology is a bad idea, it disappears within 2-3 years... if it doesn't, then it gets better than the existing and takes over and this is the case

meanredspider

Rolf F wrote:

1) You live in a dry climate
2) You don't ride that particular bike in the rain (for whatever reason)
3) You aren't heavy and don't want overly powerful brakes that just lock or cause the back end to lift too easily.
4) You've previously owned a MTB fitted with Avid hydraulic discs (!!)
5) You don't have a support vehicle to fix the brake in the unlikely event of a failure
6) It isn't hilly where you are
7) You don't accept that stuff is great just because it's new and someone who likes Apple products tells you to.

In other words, you don't actually need brakes. As I've said before, I'm happy with the rim brakes on my Foil because I don't actually ever brake in NL except for red lights.

I'm more or less with Ugo on this (except I do believe that discs are better in the dry too because they more progressive and modulate better). Rim brakes will join downtube shifters as something quaint on old bikes.

Manc33

I thought disc brakes had a lack of modulation over side pulls, or has the tech on discs evolved since then?

I am going back to when disc brakes were a new thing on mountain bikes. :oops:

For long distance touring, its easier to fix a cable disc brake than one with leaking fluid... but surely if you use cable disc brakes you're not getting that much more power than a rim brake?

Maybe people just see "disc" and think "power" without considering there are cable ones and hydraulic ones? I have to admit even the cheap hydraulic ones I had (on a £600 Carrera Halford's MTB around 1999) were ruddy powerful and it was a bike well over 30lbs. Thanks Halford's.

meanredspider

Manc33 wrote:

I thought disc brakes had a lack of modulation over side pulls, or has the tech on discs evolved since then?

Modulation has everything to do with the characteristics of the materials used. The compound of brake pad in disc brakes can be formulated with only minimal thought about wear of the disc. You can also tune the diameter of the disc to give the characteristics you want (hence many bikes have smaller rear discs than front because the rear tyre can only sustain smaller braking loads).

Manc33 wrote:

... but surely if you use cable disc brakes you're not getting that much more power than a rim brake?

Why do you say that? Again, it has everything to do with the design of the disc brake - something over which there are far less compromises than rim brakes where the wheel diameter is fixed and you'd rather not wear the track too much. If you want more power, then use a larger diameter disc and a more aggressive pad compound. The main compromise of cable discs is that they tend not to be self-adjusting for wear - one big advantage that hydraulic calipers have (and why the HyRd is a good cable/hyd hybrid concept). But then, rim brakes don't self adjust either.

cycleclinic

rotor size also has an infact on modulation. the larger the disc the more grabby the brake as braking torque is higher for a given lever displacment.

Why are folks obbessed with braking power. Power refers to work done over a given displacent diveided by time. While that sort of applies here it is the braking torque on the wheel that is important and how well the rider can control it. In the wet the ammount of braking torque applied by a rim brake is alot less, It rain's in sumnmer too you rolf, anyone out august 10th by any chance, I was it was very wet. In the dry a good disc brake set up and a rim brake setup will be able to lock front and rear wheels but shorter stopping distance are achieved not in a skid but keeping the wheel just of locking up, not really possible with a rim brake but possible sort of with a disc brake.

The braking torque on a disc brake is more easily modulated because the rotor is not the size of a wheel. The rotor therefore requires more clamping force from the pads, it is because the force applied by the pads has to be higher there is greater scope for better modulation by varying the imput from the levers. With rim brake given the rotor is so large it take very little imput from the lever to go from little braking to lifting the back wheel of the ground.

So if you want a nmore grabby disc brake go with a larger rotor 140mm on the front will be too small. With cable disc brakes you will need a compressionless (linear strand brake cable) if running full length rear brake. Around the bars sprial wound housing is best. Jagwire seem to do a linear strand brake housing road pro XL but I do wonder if the weight weenie link housing like nokon would do better. Standard housings work O.K but can leave a spongy feeling on the rear although it was not too bad with the transfil outer I used on one build recently.

If I see braking power as a term here again I will stop reading this thread so go on write it!

Manc33

"Rim brakes are enough to send you over the handlebars"
- Every cycling veteran, ever.

(Didn't mention the P word)

I think good performance from rim brakes involves cleaning your rims quite often, if the bike went out in the wet, I pretty much must clean my rims, this affects the brake's erm, efficiency quite a lot I found. So yeah to escape all of that a cable disc is "better" in that regard.

If I could turn back time I would get a disc setup but with those Kool-Stop Salmon pads on, who cares. They are good enough on that 13% decline I go down and they seem to wear well considering their pow... grip. I am using MTB v-brake levers with road calipers though, so I do lose some p***r, but its safe enough to use.

cycleclinic

I used to be a physics teacher so power to me means something very specific and is measured in watts. Braking performance is measured by stopping distance for which the units are metres. Pedantic I know and tell me to shut up if I am annoying any of you!

meanredspider

thecycleclinic wrote:

I used to be a physics teacher so power to me means something very specific and is measured in watts. Braking performance is measured by stopping distance for which the units are metres. Pedantic I know and tell me to shut up if I am annoying any of you!

I've not really thought about it too hard before but power=torque x rpm. If the calipers are applying torque to the wheel via the disc and the wheels are rotating (in fact, more correctly the wheels are applying torque to the disc), then power is probably a correct measure. It's probably not very helpful though. The power is generating heat and some sound as well as some mechanical wear to the pads.

Personally, I think the best measure of braking is retardation force (ie independent of mass) - your distance measure is relative to mass.