Road Disc Brakes; and Why I Won’t Use Them
September 1st, 2017
September 1st, 2017
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As the founder and former Editor of Rouleur, and one who wrote bicycle reviews for 15 years, it's safe to say that Guy has learned a thing or two about bikes. He's also partial to an industry rant here and there, and who are we to stand in his way? So, Guy, what do you say about disc brakes on road bikes?
I won't be using them. Mostly because I have 10+ bikes and about 20 pairs of wheels in the shed already and even if I do say so myself, some are [literally] works of art. As a veteran wheel builder of some twenty years I recognise that disc brake wheels have distinct advantages over non-disc brake ones in that the rim can be lighter, have a stronger profile and be [arguably] more aerodynamic. But are they stronger? Are they ‘better’? I’ve been pondering the idea and these are my thoughts.
Standard wheels are symmetrical at the front and offset (dished) at the rear, this means you need more spokes to cope with the variable tension in the drive and non-drive side of the wheel. Disc brake wheels need space for the rotor, this is why the rear end in a mountain bike is wider (and road bikes will follow here), but the offset creates a set of issues that are yet to be fully resolved. Let me explain…
I suspect that Tour magazine in Germany will get out their huge testing machines to test the bejesus out of disc brake wheels, but experience tells me that disc brake wheels simply can’t be as stiff as a standard pair. The offset in the front wheel will create imbalance in tension. Again, not a problem off-road because the tyre is so huge, but I reckon Cavendish, Greipel, Kittle and co may be able to feel the difference through a pair of light weight sprinter’s tyres. I suspect they will opt for a disc brake bike in the mountains and a non disc brake bike for sprinting, just a hunch.
In wheels this isn’t really applicable. Wheels flex, they don’t ‘give’. Extensive research states that comfortable bicycle wheels are heavier, have fatter tyres and more spokes and less tension. This research also states that any suspension in a spoked wheel comes from deflection as it moves from side to side. Not convinced? well if wheels moved up and down they’d rub on the frame and forks and calliper brakes would never work.
Disc brake wheels will be more likely to experience catastrophic spoke failures. Steel spokes are still the choice of manufacturers - they are now often straight pull and made from very strong materials - and they’re a lot better than they once were. However, because the tension increases with less spokes the likelihood of failure increases too. The disc brake rims are lighter and reinforced at the spoke holes and there’s fewer spokes, but the tension is incredible. In an old 32 spoke wheel a spoke snapping barely mattered and the bike would still ride OK. Current wheel technology means that when one spoke goes the whole wheel pretzels and often stops dead in the frame or forks. I expect that the wheels will have to have more spokes, which adds more weight and less tension – which results in more flex.
Sure they’ll get lighter, but for now a budget disc pair will add around 500g to your bike than a budget non-disc pair, and spoke failures will be more prevalent in those cheaper wheels too. But, whatever, more rotating weight is a terrible idea, light wheels are just better all-round.
Tyres are the limiting factor with braking. Off-road grip is a battle fought with knobbly tyres, but the slicker the better on the road and that will mean (inevitably) skids. Lock up the front and it’s a visit to the dentists and lock up the back wheel and that’s essentially the braking over – on a road bike that’s a big problem, especially in the wet. So if you can’t control a skid, you’ll be treating your road rash.
The Size and that Infernal Noise
These two things are linked, the racket from a disc braked road or cyclocross bike is hard enough to manage, add the smaller rotor size and it seems to magnify the problem tenfold. So the races are going to get really noisy. Check the latest round of the cyclocross world cup on YouTube for a chorus of squealing rotors.
Mostly I feel sorry for the mechanics, because if you think (or you’ve already been told) that they’re maintenance free… think again. Discs take a lot of fettling to get right, and out of sight out of mind means that they can go wrong without warning. The callipers have to be perfectly in line (this helps prevent the noise) and the pads need to be perfectly lined up and spaced away from the disc equally on either side. The rotors are subject to wear and smaller rotors wear out faster than the big ones. When they do wear out and the pads fail, you’re braking ability will, pretty much, end. This is not so much of a problem with rim brakes, because you can see how much life you have left in the pads and the rims can be easily checked. And don’t get me started on brake fluids and bleeding brakes…
Probably the main reason why professional cyclocross racers aren’t yet fully converted, but the mechanics in the pro tour have a hard enough job with the Lawyer tabs that are now pretty much standard on the forks. Disc brake set-up requires a fair bit of standard accuracy between bikes and wheels, having worked on many mountain bike teams I know that swapping wheels between the same bikes with the same equipment can be a massive palaver. If there’s a muddy Paris-Roubaix next year the riders will be delighted with fatter tyres and brakes that actually work, but wheel changes will dramatically slow down and that’s a fact. And I can’t wait to see two team mates trying to swap wheels in a hurry, that’s going to be priceless.
Bad Riders are Bad Riders.
Better braking means that incompetent riders will take more risks, so they have more thinking time before they slam-on. OK, this won’t be much of a problem in the pro peloton, as they can all ride downhill in a relatively straight line, and there is a case to say that Nibali will put minutes into the peloton on a long descent if they’re on different equipment, but mostly they’ll create more risk taking, of that I am sure. So I really don’t fancy the Etape with thousands of swerving dervishes slamming on brakes and locking up at the last minute, it will be like a demolition derby. Crashes always hurt, many mountain bikers I know carry the burn scars from rotors and they are terribly sharp, but that’s another story.
Frame and Fork Design
Whatever your view on whether you need discs in your life or not, I still say wait a while. Mountain bikes took a while to get it right, years to be precise. Currently most road bike manufacturers are basically using an existing frame design and adding the bosses for the brake callipers and this geometry won’t work brilliantly. I suspect they’ll have to lengthen and alter the chain stays to allow quick wheel changes and possibly have bolt-through axles to prevent wheel misalignment (so even slower wheel changes will follow…). The chain stay size may have to alter too, to allow a better brace for the calliper (again the noise is amplified with the vibrations through a lighter rear triangle). So the disc brake bike will eventually get a bit heavier, because the forces will eventually shake your frame, and its parts, to bits.
These guys are yet to be convinced and they’ve been right (and wrong) before. I do think Shimano discs are fantastically engineered, the integration is so good. Campagnolo stick with cables and callipers for now and until they have a decent solution I guess that’s wise.
Maybe it’s a personal thing, but Mountain bikes need to look up to the job, so discs look OK. I’m yet to see an attractive road bike with discs, to me it just looks wrong. Cipollini have made a pretty good looking stab at it, but in the main they’re all pig ugly. Sure they’re versatile and you can swap over and ride gravel and off road if you like, but will that make your cycling better? I don’t think so.
To be fair we’ve been here before. 5,6,7,8,9,10 speed, then 11. Now electric gears, you need those, really you do. Also in Mountain bikes the suspension fork created a whole new industry of it’s own, people looked for cheap alternatives and they just didn’t cut-it… Then the mountain bikers changed the disc brake rotor sizes, the rear triangle hub spacing, the axles, then the cable routing etc. etc. Why? Because they want you to buy a new bike.
Much of the above are the physical reasons why discs are good and bad, but mostly that they aren’t necessary. Like electric gears they are ‘better’ than the cable pulled calliper, but it’s the thin end of the wedge technology-wise. This doesn’t apply if you only want one bike that will do a lot of different things, as discs offer a lot, but for pro riders… As a pro mechanic said to me just recently, “they need to go faster and stopping quickly isn’t even on the radar for most of them, the good ones don’t even need brakes.” But pro riders will, mostly, do and use what they are told to.
For me though the calliper brakes and the mechanical gears on my bike work really well, if I change to electric, that will mean a new bike and if I change to disc, my fantastic wheel collection becomes an expensive wall decoration. My calliper braked bike is ten years old and, to me, it’s still perfect. Yes, given the choice, I'd really ‘want' Di2 or EPS but I certainly don’t ‘need' it to go any faster or enjoy my riding more and I don’t need disc brakes either.