pedals2slowly wrote:If you did a table of pro's and con's, gave value judgements with numbers and added up the scores, disc brakes would beat all other brakes hands down.
I disagree; they have many shortcomings including
- susceptibility to contamination
- lag in the wet (so inconsistent in action, but not in a predictable way(*))
- rapid pad wear in the wet
- vulnerability to accidental damage
- maintenance hungry
- not designed for UK conditions (I have yet to see one that definitely won't fail in a couple of UK winters)
- imposes unnecessary loads on fork, hub bearings, hub, and spokes
- weigh more than rim brakes
- risk of accidental injury from disc in accident
- risk of accidental burns from hot discs when you climb off the bike
- discs make wheel maintenance more difficult
- dished front wheels are necessary with disc brakes, which means weaker/heavier wheels
- huge and pointless variation in pad designs means sourcing spare pads is needlessly difficult (cf rim brake where two brake block fitments would cover >95% of bikes)
- similar proliferation of caliper mount designs leads to even more built-in obsolescence
- lack of spare parts for most disc systems means failure of trivial parts (eg seals) leads to scrappage of the system
- wheel retention problems
- 'quick release' wheels are not 'quick release' any more with disc brakes
- endless problems with disc rub
- wheel changes often cause problems and that is if they work at all, such is the variety of disc sizes and exact alignments
- disc systems have several ways in which they can fail completely and without any warning whatsoever
- disc pad friction coefficients vary with pad temperature such that you have to be able to modulate the brake power in a wide variety of situations.
and that is just off the top of my head; plenty more of that to come..... 'Best'...? I asked 'best for what?' upthread but in any event for many purposes.....discs are best
...? I don't think so! There is plenty of room for improvement and there are other brakes which do not share some of these unwanted attributes. Horses for courses!
(*) Of their many flaws I consider this to be the most serious, in combination with the thing that sells these brakes to those who perhaps have not thought through all the consequences, being brake power. I've mentioned this before but from about 15-20mph you should be aiming to have the brakes on for a little over one second to bring yourself to a halt in an emergency, if you have powerful brakes. And in an emergency this will be 'cold', i.e. you have to be able to put the brakes on 'blind' and get maximum retardation in the first half a second, i.e. before you will have time to react to the actual state of the brakes and be able to usefully modulate them. In this situation brakes that are sometimes massively powerful are nothing but a hinderance; you cannot apply them 'full gas' without risking going over the bars (and you will go over the bars before you can react; I have seen it happen). If you apply at some lower force, react and then modulate up to full power then that is no good either, you won't go over the bars but you will probably exceed the minimum stopping distance before
you even modulate the brakes to full power. Worse than that should the brakes be wet practically nothing will happen for about half a second (or more), with a similar effect on stopping distance. [Wet rim brakes may even come 'on' quicker than some discs because the rim brakes will be applied 'full gas' and the disc brakes not.]
So disc brakes may give an illusion of power, control etc but in a emergency when you really need that power, you can't use it safely/swiftly and they are often worse in actual result to supposedly inferior brakes.
The 'morer is always betterer' mantra is wrong; needs 'morer better' thinking about....
A brake that is sized/specified so that it cannot flip you over the handlebars can usually be applied 'full gas' and will produce better emergency stops. If it is more consistent too then it is even better again.