Now, I've said in another post of mine that I am a Luddite (see the bit about Gear Shifting), and this is admittedly true - I do like my bike to be simple and easy to maintain, fix and set-up. However, I do get that progress means emerging technology and fashion will influence the way bicycles are made and the expectations of the market, and it's always been the case that bicycle design and the gear they carry will reflect that. Recently I've been considering a new bike (recently = two years), and when I started to look, one of the 'must haves' that went on the list was disc brakes. Why? Because I commute all year round in all weathers, and when touring I've experienced the irritation (and occasional terror) of brakes that don't actually, you know, stop the bike. So, discs went on the list.
At the time, the only experience I had of a disc brake was my son's Kona hybrid, which came with hydraulic discs. They're good. Very good. The lightness and modulation (the ability to adjust the degree of braking without them going from nothing to full rotational cessation and handlebar flying antics) is great. But, wow are they complicated. Lots of seals, pipes, moving parts and scarily complex rotors and calipers. To fit the disk within the forks, the front wheel has an asymmetric 'dish' to the spokes, which I find off putting, and which makes me wonder if strength is compromised. For the geeky amoung us, here is a few pictures of the hydraulic disc set-up:
Another bike in the family has disk brakes too, but these are cable operated. More simple, yes, but also more basic. They don't work as well as the hydraulic ones - the difference is really noticable when you can compare them as easily as swapping bikes. But the thing that I found off-putting about the cable disc was that fact that the mechanism only operates a caliper on one side of the disc rather than both sides like the hydraulic type. Are they all like this? Maybe someone can tell me. The thing I don't like about this design is that because the mechanism only works on one side (unlike the hydraulic type that has a caliper on both sides of the disc), it squeezes the disc between the pads asymetrically (that word again), actually bending the disc slightly against the static pad. This seems mechanically wrong to me and raises my anxiety about catastrophic disc failure, although I imagine the designers have taken this into account and it's all fine. Here's a picture of the cable disc brakes...
So what else does having a disc brake mean for bike design, and what might you want to consider? Well, discs look nice, sure, and they look modern. And don't cars have disc brakes too, so isn't this a natural progression towards better technology? Well, yes. And no.
Consider stress. Having your braking system located near the hub of the wheel means the braking system has to be relatively more powerful compared to a rim brake (it's all in the 'leverage', or whatever the technical term is), and all that stress is located in the hub, and forks. The disc is also offset to one side of the wheel, meaning that when it is used, it excerts a twisting moment through the forks. This means the forks have to be made stronger, meaning more weight. The increasing use of through-axel bolts in place of quick release is in part in answer to the need for stiffer solutions for wheel fixing becasue of the torque exerted by a disc brake. So it it worth it?
Yes, probably. For some. If you are mountain biking, or regularly riding on muddy tracks, then a disc brake makes sense as it stays clean and works as well in the wet as it does in the dry. Disc brake performance is reliable. But if most of your riding is on clean(ish) metalled roads, do you need disc brakes? Probably not. Rim brakes, like those shown below, have been around for a long time and are well proven.
Traditional calipers and V-brakes like those shown above are simple, reliable and pretty light-weight too. They are easy to adjust and maintain, and if maintained well and set-up right, can work as well as a disc brake.
Okay, so rim brakes don't always work as well in the wet as discs, but to be honest when set up right and with the right pads, that difference isn't really noticeable. Like many, I ignored my brakes for years and cursed the lack of braking performance, which meant disc brakes went on the new bike list. But then, in a fit of money saving pique, I properly serviced my bike and, for the first time in 18 years of ownership, I took the V-brakes totally apart to clean them (the silver ones in the pics above). New pads (cheap ones from the local bike shop that I thought seemed very soft, but which work like magic) and new cables went on too. I set them up carefully. And guess what - they worked well. Unbelievably well. So well in fact, that I can't really tell the difference in performance between the hydraulic discs on my son's bike and my own bike's V-brakes. In fact I prefer the feel of my V-brakes to those of the slightly grabby discs. Using them is a pleasure! And so, my opinion has changed. Why would I want expensive, complex, heavy discs when I can have simple, effective rim brakes? The answer is, I don't. So my next bike, whenever that might be, will have rim brakes - probably V-brake types because I like the ability to fit wide tyres if I want, and they are just so simple. You also won't find me on twitter or facebook asking why my brakes are so noisy either.
Now, 650b or 700c?
