I thought I just had to share this diatribe from an old friend of mine when asked recently about disc brakes. The traditional roadie's response
The most important thing you are missing is the ability of an industry
to invent a solution to a problem that does not exist, in the
furtherance of driving sales.
Disc brakes have existed on mountain bikes for years, and they are
very effective. Speeds on MBs are low, and since they plough through
mud, rims get caked in mud, making rim braking surfaces ineffective.
DBs are very good in this scenario and are pretty much standard on
In the last couple of years, DBs have become common on cyclo-cross
bikes. They are illegal on road racing bikes under UCI (cycling
governing body) rules, for several very good reasons.
However, manufacturers are determined that DBs will be the Next Big
Thing (to drive sales), and they are pressuring the UCI to legalise
In recent years, carbon fibre has been the NBT, and almost every bike
component has been made from carbon, or a large percentage of carbon.
I don't trust carbon because of its mode of failure - sudden and
catastrophic brittle failure, a very worrying issue on a bike,
compared with the ductility of metal and its ability to absorb knocks
and dents and allow the rider to carry on riding.
One of the components that manufacturers have made of carbon is wheel
rims, a notion that scares me to death. However, the right of
manufacturers to sell to sucker cyclists wheels that cost 2 grand a
pair must not be impeded. A major advantage of carbon wheels (for
manufacturers, not for riders) is that, at little weight penalty, they
can make the rims 2-3 inches deep, thereby allowing the manufacturer
to slap 10 frugly logos all over them. Just tell the dumbo cyclists
that such rims are "aero" and laugh all the way to the bank.
In addition to mode of failure, there is one other, somewhat serious
problem with carbon wheel rims - your brakes don't work any more. A
12-yr old with 1st-year physics could work this out, but your average
cyclist is thick as shit, so they fork over the 2 grands instead.
In accordance with the laws of thermodynamics, braking works by
converting kinetic energy to heat energy. In order to be effective,
the braking surface must be able to dissipate this heat quickly, a
task for which aluminium rims are ideally suited. Since carbon doesn't
conduct heat at all well, it is almost useless for this task. Various
brake pad compounds have been developed, but the problem is basically
governed by a law of thermodynamics, and nature cannot be cheated, as
Mr Feynman reminded us after the first space shuttle disaster.
Now, manufacturers are not to be underestimated in cunning and
deviousness. That braking problem they invented all by themselves when
they developed carbon wheels - guess what? They can ride to the rescue
with a perfect solution - disc brakes! Kerrching, kerrching! And they
can use the safety argument to pressurise the UCI into legalising DBs.
But, but, but...
DBs on road bikes present several problems of their own. The only
scenario in which they might be useful is on long descents in the
rain. I have descended alpine mountains in torrential rainstorms, when
water was running off the mountainside and across the road over 1-inch
deep. My rims were totally submerged in water, and I had to keep the
brakes full on for 10km just to try to keep the rims dry, ready for
braking. No fun, believe me, and your arm muscles end up killing you
very quickly. I would dearly have welcomed a disc brake on these rare,
and scary, occasions.
In the dry, modern rim brakes have excellent stopping power, esp.
compared with the rubbish when I was young. DBs have several problems
on a road bike. There are 2 types of road DB - cable operated, which
are no better than rim brakes, and hydraulically operated. Hydraulic
brakes offer excellent modulation, but at a potentially catastrophic
penalty, since they have very small hydraulic reservoirs. Speeds on a
road bike are much higher than on mountain bikes where DBs became
standard. If a road rider "drags" his brakes on a long descent, it is
possible for the hydraulic fluid to vaporise, at which point the rider
has zero brakes and some very uncomfortable choices - not choices that
I would care to be confronted by.
Another serious problem is that the braking action tries to force the
wheel axle axle out of the dropout, so extra measures, such as tabs on
the dropouts or bolted axles instead of quick-release wheel skewers
There are other problems, but I won't go on, as I have already gone on
too long. Basically, manufacturers, having milked the "weight" and
"aero" bandwaggons, have decided that DBs are the NBT. As you know
from your own experiences living in China, the Chinese have perfected
the practice of getting manufacturing techniques down to a
sufficiently low cost to flood the market with goods of a very high
quality. So expect to see a lot more bikes with DBs in the next few