Why have disc brakes become so popular?

[reohn2]

It is very hard to improve a bike and make new fangled bikes that are better.Manufacturers are developing newer devices(discbrakes) which may be no better overall........

Have you the experience of using disc brakes on bicycles to back up that claim?

[Brucey]

Disc brakes use STEEL rotors but with special modern pad material which modulates, and works predictably in all conditions. For what reason wouldn't a steel rim, which is a very large diameter rotor, work with the same callipers and pads in the same manner?

We know that modern rim brakes pressing on alloy rims can work well, though not with the same modulation and light hand force as hydro discs, but I fail to see how a steel rim with hydro calliper and pads wouldn't outlast an alloy rim, especially in winter conditions, by a large margin.

when disc brakes are completely, properly, wet the brakes do not work at all well on first application. I decided to abandon the use of disc brakes whilst commuting for this reason; there are better brakes for that purpose, which reliably give less than half the stopping distance when it is tipping down with rain. BTW this issue causes fewer problems when MTBing or leisure cycling simply because unplanned braking in very wet conditions is less likely.

Rubber brake blocks are flexible and that allows small variations in rim width to be tolerated. You need this because
a) it is impossible to make steel rims that are perfectly uniform in width (at a reasonable cost/weight) and
b) rims get knocked about.

If you used a rigid (disc brake) pad compound you would soon come unstuck; the brakes would no longer tolerate tiny variations in width, the brake still wouldn't work when soaking wet, and the (abrasive) pads would wear the rims out.

Steel rims are both thin-walled and rather heavy. It is also difficult to make them with sensible beads etc so that high pressure modern tyres can be fitted to them.

However the basic premise that rim brakes could be greatly improved is one I agree with. There are any number of hard-facing technologies and pad compounds that could be used.

My year plus old Roubaix road bike has hydro disc brakes and they have faultless and superb. Neither do they shriek or squeal, they just satisfyingly shhhs on application. Should they fail (piston trouble or salt corrosion problems) after say two years, I'd simply buy new ones, ready bled to just bolt on for way less price than having to buy two new wheels.....

The discs will probably be worn out (there is very little wear permitted in current shimano road discs BTW), the wheels may break anyway (because they are built light, what with the bike being fitted with heavy brakes and all) and if you are not putting new rims on your wheels then you won't be working on your own bike either, so the bill should include

brake calipers, brake pads + STIs
gear cables
bar tape
discs
hose clips etc
labour

I think that lot will come to at least double your 'about £160' estimate, nearer three times if you pay anywhere near rrp on the parts. Note also that the brakes may start to drive you nuts before they actually fail; just today I heard a TdF rider's bike make some foul noises which I am pretty sure came from the disc brakes....

You can buy workable training wheels (for rim brakes) for about a hundred quid a pair (leave aside that rims are less than this BTW) and at some small fraction of the total cost you can have a bike that is lighter and arguably more pleasant to ride (the rest the time) if it is fitted with rim brakes. Oh, and spare wheels will fit easily, IME, in stark contrast to spare wheels with brake discs on.

To hear some folk carry on about it you would think that disc brakes represent some kind of nirvana for road bikes, a panacea for all ills.... The truth is not at all like that, they are arguably just as much a curate's egg as rim brakes are, just in different ways.

cheers

[Peter W]

I take your comments in part. I do all my own work on my machinery, and Shimano are too pessimistic in their insistance of what will not work, or must be renewed. No steel rotors on any of my three current well used and abused (by conditions) and 'getting on a bit' MTB's (old Stumpy with 3x9 gearing for instance) have yet needed to be replaced, despite several complete CRC cheap offer ready to fit and go brakes of whatever make.

I admit that with the road Roubaix I failed to mention that I wouldn't expect to have to replace the STI lever and master cylinder part after just two years, at least I HOPE not, and that the quoted cost should cover just the callipers and pads, assuming they are available seperately, and that bleeding kits are obtainable. I would be very disappointed if I'm being too optimistic on that matter.

The point is, time will tell if is a genuine advance in logevity over rim brakes. I do not share your view that the wheels will necessarily prematurely fail from the extra brake stresses, especially since the rims are under no attack from brake pad thinning wear. They show no sign of distress after one and a half years use.That alone is worth a lot of saving of cost over the old bike which eats expensive wheel rims in our winter steep hill Yorkshire Dales and Moors.

[Cugel]

I take your comments in part. I do all my own work on my machinery, and Shimano are too pessimistic in their insistance of what will not work, or must be renewed. No steel rotors on any of my three current well used and abused (by conditions) and 'getting on a bit' MTB's (old Stumpy with 3x9 gearing for instance) have yet needed to be replaced, despite several complete CRC cheap offer ready to fit and go brakes of whatever make.

I admit that with the road Roubaix I failed to mention that I wouldn't expect to have to replace the STI lever and master cylinder part after just two years, at least I HOPE not, and that the quoted cost should cover just the callipers and pads, assuming they are available seperately, and that bleeding kits are obtainable. I would be very disappointed if I'm being too optimistic on that matter.

The point is, time will tell if is a genuine advance in logevity over rim brakes. I do not share your view that the wheels will necessarily prematurely fail from the extra brake stresses, especially since the rims are under no attack from brake pad thinning wear. They show no sign of distress after one and a half years use.That alone is worth a lot of saving of cost over the old bike which eats expensive wheel rims in our winter steep hill Yorkshire Dales and Moors.

A sensible summary. There's a degree of ideological spinning & even dogma in brake technology discussions. Humans seem able to take sides on anything and everything!

In the end, experience counts. We should also note that people have different everyday experiences too. The "best" brake technology depends on the kind of riding, bike, conditions and rider. These are all highly variable, as are their permutations.

Personally I find good quality rim brakes more than adequate on the light summer bike, typically ridden in good weather conditions. The winter bike benefits from hydraulic disc brakes because they are easier to modulate for gravel-infested wet & slimy bad road surfaces, especially on those long descents you mention that are prevalent in the back lanes of the Lakes, Dales or similar terrains.

As to the costs of maintenance and replacement ... these too vary enormously depending on the quality of components used up and the degree of bought-in labour costs involved. And does anyone replace brake-worn rims via a rebuild? New wheels are a more likely (and perhaps cost-effective) fix, since a worn rim likely indicates worn hubs and perhaps even degraded spokes; not to mention the labour costs or time of a wheel unbuild-rebuild.

Cugel

[reohn2]

when disc brakes are completely, properly, wet the brakes do not work at all well on first application

That is most definitely not my experience of BB7 cable disc brakes either MTN or Road models.

[robc02]

And does anyone replace brake-worn rims via a rebuild?

I do. Though I replace them more often due to other damage - usually pothole inflicted - than brake track wear. In fact, it has been quite a few years since I managed to get a winter-bike rim to last until its brake track wore out!

I would normally expect a hub dynamo or hub gear wheel to be economical to re-rim.

[reohn2]

......... And does anyone replace brake-worn rims via a rebuild? New wheels are a more likely (and perhaps cost-effective) fix, since a worn rim likely indicates worn hubs and perhaps even degraded spokes; not to mention the labour costs or time of a wheel unbuild-rebuild.

Cugel

Sadly it's getting that way that if a rim is worn the whole wheel is scrapped ,especially the minimum spoke over priced confections currently on the market.
However decent 32 or 36 spoke touring wheels can be rebuilt in an couple of hours by a competent DIY mechanic and in less than an hour by an experienced pro,spokes needn't be replaced and if the new rim is taped to the old it's just a matter of swapping the spokes over then tensioning and trueing up.
Unfortunately 20 and 28 spoke wheels have the spoke at at such a high tension they need a specialist to rebuild and even then it's a difficult task.

Standard Shimano Cro Mo axle hubs are bombproof and last many,many years if serviced regularly.

Sadly we live in a throw away world which is OK for J cloths but one has to question throwing aside pair of £200+ wheels coz the rims are worn ,one also has to question the need for 28 and 20 spoke wheels being ridden by people who are less than svelte and can't appreciate the aero advantages such wheels claim to offer.
Hey ho,the marketeers dream .......

[Cyril Haearn]

Surely the rims could be made thicker so they last longer
Still don't understand why rims wear away, brake blocks can be changed in a moment

I think it has been explained before, mind

[reohn2]

Surely the rims could be made thicker so they last longer

Weight.
In a world where lightweight means more than durability.......

Still don't understand why rims wear away, brake blocks can be changed in a moment

Friction,road grit that becomes embedded into the brake block and peels of shards of all rim which then become embedded in to blocks and were away the braking surface of the rim,this gets much,much worse in wet winter conditions.

[JohnW]

And does anyone replace brake-worn rims via a rebuild?

I do. Though I replace them more often due to other damage ....................

Yes - me too - I've had a well worn rim collapse under me when I applied the brakes - the sounds it made had to be heard to be believed. That was in earlier days of course, and I'm possibly a bit over-cautious now.

[Cugel]

......... And does anyone replace brake-worn rims via a rebuild? New wheels are a more likely (and perhaps cost-effective) fix, since a worn rim likely indicates worn hubs and perhaps even degraded spokes; not to mention the labour costs or time of a wheel unbuild-rebuild.

Cugel

Sadly it's getting that way that if a rim is worn the whole wheel is scrapped ,especially the minimum spoke over priced confections currently on the market.
However decent 32 or 36 spoke touring wheels can be rebuilt in an couple of hours by a competent DIY mechanic and in less than an hour by an experienced pro,spokes needn't be replaced and if the new rim is taped to the old it's just a matter of swapping the spokes over then tensioning and trueing up.
Unfortunately 20 and 28 spoke wheels have the spoke at at such a high tension they need a specialist to rebuild and even then it's a difficult task.

Standard Shimano Cro Mo axle hubs are bombproof and last many,many years if serviced regularly.

Sadly we live in a throw away world which is OK for J cloths but one has to question throwing aside pair of £200+ wheels coz the rims are worn ,one also has to question the need for 28 and 20 spoke wheels being ridden by people who are less than svelte and can't appreciate the aero advantages such wheels claim to offer.
Hey ho,the marketeers dream .......

I have a neighbour who commutes on a mid-price hybrid. He's gone through two sets of rims in the last 5 years as he commutes 12 miles per day in all weathers & seasons, often down the canal towpath; as well as using his bike for general transport (shopping etc.). He gets me to do his maintenance when something goes wrong.

When considering the worn rims (which end up looking like Saturn's rings before I get to see them) I found that the hubs too (Shimano Deore) were knackered, since he does no maintenance himself, they don't get lubricated or adjusted or even cleaned. It was cheaper to buy another comparable wheelset for £69 in the sale.

Myself, I've never worn out a pair of rims or hubs, despite doing 10X the mileage my neighbour does. I suspect this is due to: regular cleaning, lubrication & maintenance; mostly fair weather cycling, not on the canal towpath or similar; better components. I have one pair of wheels now 30 years old that must have done tens of thousands of miles in their time but are still smooth i' the bearings with unworn rims and shiny spokes. They're Mavic ceramic rims on Shimano sealed bearing 600 hubs with 36 DB stainless spokes.

In short, different styles of cycling & bike-use on different qualities of components create different rates of wear and different effective replacement strategies.

I suppose you can make a case for a worn or damaged rim to be replaced if the hubs are good & well maintained and you can competently deconstruct and reconstruct a wheel. In my experience, many cyclists have mediocre wheels & hubs that came with the bike, which they never maintain; and no ability to build a wheel.....

Cugel

[De Sisti]

And does anyone replace brake-worn rims via a rebuild? New wheels are a more likely (and perhaps cost-effective) fix, since a worn rim likely indicates worn hubs and perhaps even degraded spokes; not to mention the labour costs or time of a wheel unbuild-rebuild.
Cugel

Not necessarily. I had a wheel rim replaced (on the advice of someone who checked my bike) and there was no degredation of the hub or spokes (which were used in the re-build).

[horizon]

Not necessarily. I had a wheel rim replaced (on the advice of someone who checked my bike) and there was no degredation of the hub or spokes (which were used in the re-build).

I faced a wheel replacement or rebuild recently but I couldn't see how it would be worth paying someone else to rebuild it plus the cost anyway of the rim and still having a half worn hub. But expensive wheels with good quality hubs and spokes, rebuilt at home - yes that really makes sense I would have thought.

[robc02]

In my experience, many cyclists have mediocre wheels & hubs that came with the bike, which they never maintain; and no ability to build a wheel...

There's that, plus some bike shops preferring to sell a new wheel rather than advise the customer to have the old wheel re-rimmed.

A friend of mine experienced this with an (apparently) damaged rim (not worn brake tracks) on a decent quality Shimano hub. Fortunately he declined their advice and brought it to me. The hub was perfect, the wheel needed truing slightly and the bulging tyre - the real source of his problems(!) - replacing. I wonder if this type of bike shop even has staff with sufficient skill to build wheels?

(I am confident that an alternative and long standing shop in his area would have given very different advice, but they were closed when my friend needed help.)

[Brucey]

I take your comments in part. I do all my own work on my machinery, and Shimano are too pessimistic in their insistance of what will not work, or must be renewed. No steel rotors on any of my three current well used and abused (by conditions) and 'getting on a bit' MTB's (old Stumpy with 3x9 gearing for instance) have yet needed to be replaced, despite several complete CRC cheap offer ready to fit and go brakes of whatever make.

for whatever reason I think the sandwich construction discs used on road bikes wear a bit quicker than those used on MTBs. I think what they have done is maybe specced more abrasive pads so that the pathetically small 140mm or 160mm discs work reasonably well. In combination with the reduced wear available on those discs, I think they wear out more quickly that you might expect them to, based on MTB/solid disc experience.

I admit that with the road Roubaix I failed to mention that I wouldn't expect to have to replace the STI lever and master cylinder part after just two years, at least I HOPE not, and that the quoted cost should cover just the callipers and pads, assuming they are available seperately, and that bleeding kits are obtainable. I would be very disappointed if I'm being too optimistic on that matter.

you mentioned pre-bled units before; until someone comes up with a design that allows the working parts of the MC to come out of the STI unit, you are looking at new STIs or calipers and bleeding as you suggest above. MCs do wear out and fail, but this is (fortunately) less common than caliper failures; just as well, since I don't think you can install new seals in shimano hydro STIs. Bleeding shimano STIs out is easier than some other systems but it is still (in essence) a PITA that may well leave your lever hoods contaminated with oil. Note that with many modern road frames the hoses route through the frame so you need to split and bleed the system anyway.

The point is, time will tell if is a genuine advance in logevity over rim brakes. I do not share your view that the wheels will necessarily prematurely fail from the extra brake stresses, especially since the rims are under no attack from brake pad thinning wear. They show no sign of distress after one and a half years use. That alone is worth a lot of saving of cost over the old bike which eats expensive wheel rims in our winter steep hill Yorkshire Dales and Moors.

All I can relate is the depressingly large number of failed disc brake rims I have seen. Rims quite often crack anyway but disc brake rims are often built/specced lighter yet (to mitigate the effect of the relatively heavy brake) and they seem to be more susceptible to cracking in many cases. Rims also get bent; between this and cracking, they are arguably doing well on our roads/on a light-ish modern bike if they last for two or three sets of tyres, disc brake or not. BTW the 'weight saving' from having no brake track is of the order of 20-30g, something like that. Because they are slightly thicker, rim brake rims are (when new) noticeably stronger than disc brake rims that are based on the same extrusion, where the brake track is deleted in the disc brake version, for 'weight saving'.
Note that disc brake wheels also need more spokes in, to make the wheels similarly strong. There is also hidden weight in the frameset once it is engineered for disc brakes. Albeit heavier thicker rims put weight in a less good place, but in winter use fairly heavy/cheap rims and rim brakes still make a lot of sense to me.

BTW re hub maintenance; IME the most important maintenance you can do is when the hubs are new; even fairly humble Taiwanse cassette hubs can last well if they are set up/greased properly. Similarly, the few minutes it takes to stress-relieve a set of basic OEM wheels is time well spent; it can prolong their life considerably. If you do both, then re-rimming a set of OEM wheels when the rims wear out/crack/get bent becomes viable.

cheers