The Great Disc Brake Swindle?

Hmmm…things just started getting interesting. A recent post on the Cyclist magazine website may just have cracked open Pandora’s box and let the genie out of the bottle (bar-keeper, mix me another metaphor, this one’s gone flat!). Because (whisper it) disc brakes on road bikes may not be all that.

Here are some quotes from Cyclist’s review of the Trek Domane 6.9:

“The Domane 6.9 Disc is the first disc braked bike I’ve ridden with zero brake rub, even when making exaggerated movements to try to induce it. On this point, the thru-axles are a significant benefit, banishing the constant ‘zinging’ of the disc rotors against the pads I’ve experienced on so many other disc bikes.

It’s a matter of opinion, but I think the dropouts and axle arrangement, especially at the front, look ugly and over-built, certainly not befitting of an otherwise stealthy carbon road bike.

In the wet it required an enormous amount of care not to lock a wheel. Some might say powerful, reliable brakes are a great feature for safety, but I would say you can have too much of a good thing. Dialling down the power, perhaps in this case by fitting a smaller 140mm rotor (which would also look considerably neater) would allow a greater opportunity to tap into the modulation and the ‘feel’ that hydraulic disc brakes can undoubtedly provide. With the set-up as it was on this bike I was wary of pulling on the levers hard enough to feel the modulation, for fear of locking and skidding the wheels, even in the dry.”

OMG! Heretic! Blasphemer! Burn him!

So, to be clear, Stu Bowers (an experienced road-tester of bikes) has experienced brake-rub on every other disc-braked bike he has tested. And the brakes on this bike were so fearsome that he feared wheel lock-up even in the dry.

Oh dear…the industry is not going to like this. What about the fabled modulation improvements? What about the performance and safety gains? What about the Emperor’s news clothes? It’s actually a fairly shocking admission when you think about it. Here’s a £6000 bike that could have you chewing tarmac on your first ride. One that could scare the living crap out of you every time it rains. Is it so over-braked as to not be fit for purpose? I haven’t ridden it, so I can’t tell you. But Bowers has, in addition to loads of other bikes, so you have to assume he’s not incompetent (the accusation normally leveled at people who have braking issues).

Interestingly, this is the subject of a really excellent article in Cycle, the magazine that goes out to all CTC members. In the October/November issue is an piece by Richard Hallett, and it’s probably the most interesting and well argued article about disc brakes on bikes that I’ve read. In it he points out the things that no other mags dare, namely that disc brakes may not be suitable for road use.

This is something that has been bugging me for a while…we’re being sold a pup. The industry wants us to buy new stuff, and to buy new stuff that we can’t easily maintain ourselves. If the bike shops aren’t going to make much profit on sales (thanks to the interweb), at least they can make some money on replacing internal cables, bleeding brakes, replacing disc pads, etc.

Hallett, too, has experienced brake rub on many disc-braked bikes he’s ridden. In an industry obsessed with marginal gains, disc brakes seem to offer more marginal losses than gains. The tiny clearances necessary mean that brake rub is almost inevitable, leading to increased pad wear, especially when road grit gets onto the discs.

Heavy use, and tiny components (relative to a motorcycle or car disc brake setup), means the disc and caliper get very hot, even on relatively short descents. Hydraulic brake fluid is hygroscopic (it absorbs water), so when the fluid gets really hot the water molecules within it turn to vapour, the lever comes right back to the handlebar, and the brakes become spongy and fail. Sometimes the bonding agents in the brake pads overheat and release gasses that prevent proper pad-to-disc contact. This results in a very wooden feeling at the lever and greatly reduced braking capacity.

Bowers criticises the Domane 6.9 for looking over-engineered, but the fact is that for safety reasons it needs to be. To cope with the increased braking forces being nearer the end of the fork leg, and to one side, it’s necessary to build a stronger, tangentially-laced wheel and much beefier forks. That adds even more weight, on top of the already weightier disc and caliper. It’s physics, innit.

Unfortunately the cycling press doesn’t want to address any of this. Except for Cycle, which is funded primarily by CTC subs rather than advertising from the bike manufacturers. By all means embrace disc brakes, but how much of the gains from your aero bike, helmet and clothing are being negated by dragging your brakes the whole time? And how much of the savings you’re making on lack of rim wear are being devoured by increased pad wear and replacement costs? I don’t know.

But what I do know if that your favourite cycling magazine is unlikely to tell you any time soon.





8 thoughts on “The Great Disc Brake Swindle?

  1. Weeelll…maybe. In my experience disc rub in normal riding is a setup issue, certainly in hydraulic systems (this is based on a sample of four bikes – two hydro, one cable-operated hydro and one pure cable). Disc rub when sprinting seems to me no worse than pad rub on a rim-braked bike; the remedy being to stiffen the axle (as Trek have done here) in the same way that the remedy with rim brakes is to stiffen the wheel by widening the flange distance or increasing the spoke count.

    As for feel and modulation, this is the same problem car manufacturers experience when trying to provide one braking system for all drivers, from 4’6″ flyweights with short levers and no leg strength through to basketball players. Ultimately we ended up with ABS in automotive applications because you can’t build a sufficiently servo-assisted system for the light-footed and still make it easy to modulate.

    We don’t need servo-assistance on bikes, but we do need to find the right balance of piston ratios and swept area to enable effective braking by the weak-fingered while retaining modulation. There’s also a learning curve if you’re coming to hydraulic disc from cable-operated rim brakes; both the total force requirement and the force to retardation curve are different; I’d want to know how long Mr Bowers spent on the bike, and what he’d been riding just before. I don’t think experience is necessarily a sufficient compensator. I ride a good deal but will defer to his greater exposure to different bikes; however in a former life I was a racing driver, and I can certainly testify that the main challenge in switching between cars was adjusting to the performance characteristics of their brakes.


  2. What? An intelligent, coherent, and well-argued response to the disc brake debate? You, sir, have no business being on the internet! But thanks for your input. For me it’s more about ease of maintenance and simplicity of design, particularly in a hobby where late-breaking isn’t really a thing. On my motorbike, however…huge floating discs, six-piston calipers…I want it all!


    1. I think you should try commuting in London a bit more before deciding that late braking isn’t a thing. It’s totally a thing these days (phrasing copyright your choice of American listicle website). Or did you mean what you said? Late-breaking, it seems to me, is what you’ll end up doing if you brake too late. Well, something-breaking, anyway.


  3. I’m still not sold on disc brakes for road bikes. It seems to be a solution (and not necessarily a good one) to a problem that doesn’t exist. I haven’t ridden enough disc equipped road bikes to draw a solid conclusion though. I know it doesn’t exactly translate to everyday riding and the Sunday cafe smash fest, but I am interested to see how discs fare in the pro peloton in the coming season.


  4. I have Shimano hydro discs on a Merida Ride 7000 I bought a couple of months ago. The plan was it would be my rain bike (I live on the east coast of Australia, so a winter bike is not necessary) as I have a beautiful Ti Merlin with SRAM Force for the dry / racing.
    Long story short, the hydro discs are just better. Comfort, soft-touch, modulation (and no lock-ups)… All the things they are supposed to be, they are. Forget the industry hype. My experiences have been nothing but positive, so much so my Merlin is getting dusty. Admittedly, being able to fit 28’s on the Merida also helps.
    As for looks, the Merlin is a beautiful bike, no doubt, but looks are subjective. If only I could retro-fit discs on it and squeeze bigger tyres on.


  5. I find all of this things really interesting, firstly I am a roadie, and do TTs on my Cervelo S5. My brakes are good campy rim brakes with Swisstop Pro Race pads – alloys, good solid braking, and I’m tall and solidly built 😉 put my carbon wheels on, braking is a completely different story, both types of rim brakes for alloy or carbon, last a long time.
    This is the bit no one told me about with hydraulic brakes.
    I brought a Mtb for some fun off-road, great, hydraulic brakes, really good and happy with them, they work great. And I thought I’ll get a road bike with disc brakes, for the winter, U.K. I have now completely changed my mind, because I am changing disc pads every 3-4 months, 2 sets front and rear at £12-15 per set, and it’s costing me a fortune. Swisstop pads for rim brakes £25 and last me 2 years ??? Or a minimum 3 sets per year front and rear eg: £12 X 2 sets X 3 per year = £72 per year on brakes for 1 year or £144 for 2 years Vs £25 for 2 years, for 1 bike.
    For me that is a no brainer, I can not afford to spend that much on disc pads for a road bike, I don’t like spending it on my Mtb, but I have to. I can stop very well on alloys with Swisstop pads with rim brakes going downhill upto 50mph. I have now decided I will not have disc brakes on road bikes, mainly due to the cost, their are advantages, but their are also disadvantages, and the over riding factor for me is cost. I am heavy on my brakes, I know that, I am not small or lightweight and I need good brakes that will stop me at high speed and will not fail, as have happened on my Mtb brakes, when I wore the discs out.
    My safety and cost, is more important, I have not heard anyone mention cost of pads in the arguments in brakes, and no one told me about that. That’s my 2 pence worth, if no one minds.


  6. I was surprised to read Stu’s comments – maybe the higher-end machines he’s riding are somehow more susceptable to flex and therefore rub, being made from edge-of-the-envelope bits? I’m now on my 6th borrowed / reviewed / purchased disc-equipped bike to ride long-term (i.e. more than a week/100 miles). The only times I’ve struck rub is when setup was wrong, or in one case, a piston was not retracting correctly (to be replaced under warranty). It’s for good reason I’m now provably faster down hills using dics. And no more pant-fillingly-scary moments forgetting to pre-brake in the rain at the end of long rides, approaching intersections. That, to me, is the biggest bonus: Now my wife’s bike has discs I don’t fret having to remind her to dry things off. She’s a relative beginner to drop bars, has ridden disc-equipped MTB’s for years, and her first intro to road rim brakes in the wet didn’t go *that well*. It’s very easy to spout ‘MARKETING’ in the disc discussion, as if you have some insight as to the vendor/customer relationship and it’s all about cash extraction, not real-world performance/safety benefits. No-one’s holding a gun to anyone’s head here folks.


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