Hydraulic v Cable

[Shoogle]

I have mechanical disc brakes, TRP Spyres, on my Tour de Fer and bottom of the range Shimano BR-M485 hydraulics on my Scott hardtail. The hydraulics on the Scott are excellent - smooth and powerful, MUCH better than the Spyres. The Spyres get good write-ups and I know, everything else being equal, hydraulics are better, but why is there such a difference when it’s basically just pads pressing on a rotor?

[Brucey]

the cables are fundamentally somewhat inefficient vs hydraulics for this kind of thing.

The cable friction will impair modulation and will also (for any given designed in pad clearance) reduce the power available at the caliper for any given effort vs hydraulics.

If you are absolutely scrupulous about cable maintenance, and use the highest quality cables, you can improve a cable operated disc brake considerably. Using different pads (eg good quality sintered ones, which I am more reluctant to use in hydro systems) or simply larger discs can help a cable operated brake recover some of the power, too.

Because all the cable issues get worse whenever the cable pull is shorter/higher force, Spyres are not as good as Spykes, and similarly the 'road' BB5/BB7 brakes are not quite as good as the MTN ones.

IME the modulation of a (carefully set up) cable disc brake can be quite acceptable, good even; but if you want the tops in modulation, it is probably going to have to be a hydro system. However hydro systems have their own problems, so for me it is Hydros on the MTB, but I'd more likely choose cable operated brakes on (say) a touring bike.

cheers

[Shoogle]

Thanks Brucey. The Spyres came with sintered pads but there was increasing amount of judder with increased braking force so I changed them to resin and this has almost eliminated the judder with no appreciable loss in power.

[Brucey]

it is not uncommon for discs to have a little DTV (disc thickness variation) when new, and with sintered pads especially (which are stiffer in compression than organic ones) then you can get a little more judder for any given amount of DTV. The DTV (which should not be confused with swash or run-out) need only be a few microns to affect braking; it is very difficult to actually measure it. [R2 very kindly sent me some reject discs to examine, and even with a decent micrometer, the DTV was difficult to measure, even though the discs juddered terribly in use.]

DTV manifests itself worse on front discs (because the fork will flex a bit) than rear discs. You may well find that after a period of use with other pads, you can reinstall the sintered ones and they don't judder in the same way any more, because the DTV is reduced by normal wear on the disc. Or that you can swap a 'bad front disc' into the back and suddenly it isn't so bad any more, (or vice versa).

Needless to say any pad that is harder wearing may also take longer to bed in, too, and you may not get full power until they are properly bedded in.

cheers

[CyclingSi]

With cable you need to take more care in both set up and maintenance, that said it can be a good thing as you are more likely to spot any problems before they go wrong.
The Spyres are an excellent brake and very adjustable, I agree with binning the sintered pads for resin, I have just done this with the Spykes on my Caribou which has helped the braking no end. As a cycle mechanic I see a lot of different systems and their pitfalls, the beauty of mechanical discs are that they are easier to work on, but they must be set up correctly in the first place, especially with the single moving piston design (BB5/7, Shimano). A few tips, don't use cheap cables….I have also found using Middleburn cable oilers a real help too plus Shimano rotors seem to work much better than the TRP units, I have seen several bikes suffering with judder issues (mine included) using the TRP rotors.
Right now I think the best mechanical road brakes have to be the Shimano CX77 Ultegra mechanical disc and the TRP Spyres, the HY-RD units are good but they need a lot of care and can be problematic due to their small reservoir.
For ease of use I am in the process of taking the Deore hydraulic brakes off my Troll touring bike and changing to mechanicals (Spykes).

[blackbike]

I had a cable operated disc brake on my Honda CB100N motorbike back in the 80s. That was excellent so I can't see why cable discs brakes on light pushbikes shouldn't be good.

[Dave W]

I have both on my bikes - can't say there's any difference in performance, just different feel. As someone else said cable types need setting up properly - particularly the cam movement at the calliper.

[TonyR]

The difference is, especially on the back brake, cable stretch and housing compression and friction. You can help a bit by getting good quality cables and housings and by paying attention to the cable runs so there are no tight radius bends but you will never get the mechanical effort transfer that your get on hydraulic lines.

[Dave W]

That jogged my memory - thanks. Our tandem had very poor braking from the rear disc even though the rotor was 203mm. Turned out the very long outer cable didn't help matters. I trimmed it on the frame rather than run it full length to the brake and it improved braking no end.

[Mattyfez]

Assuming disks and pads equal, there's some crossover, a well set up good quality cable system can be just as good as hydraulic, different feel, though.

Hydraulic is simply more consistent and requires less maintenance, cable disks require tweaking as the pads wear to keep the pads close to the disks as generally on cable systems you have a static pad in one side of the caliper, and one that is cable operated, which pushes it's pad into the disk, and bends the disc very slightly into the static pad.

So cable disks are more faffy, there's no doubting that.
About 6 months ago I was seriously considering swapping to a hydraulic system, but I've got the knack of tweaking them now, it was frustrating for a while but all of a sudden it just clicked and became easy as opposed to hit and miss.

I'd still have a fully hydraulic system as a preference, but now I know what I'm doing with cable operated systems, im not inclined to pay to upgrade when I'm happy enough as-is.

Pads are always a contentious subject, I did have sintered, now only organic, organic pads wear quicker but I prefer the feel, and a full set of 4 organic pads is cheap from superstar, so replacing them marginally more often doesn't concern me.

[The fat commuter]

With the cable v hydraulic argument, I've often heard that hydraulic brakes shouldn't use sintered pads as they can produce too much heat and boil the hydraulic fluid. First thing, has anyone on here ever had this happen to them? Brake fluid will surely be manufactured to a high boiling point temperature. When I've watched shows like 'Top Gear', I notice that sometimes cars' discs will glow red under braking. Surely some of that heat it going to be transferred into the brake fluid via the callipers so why don't they suffer from overheated brake fluid?

Going back to the 'correct' pads for the type of braking system, I noticed on one supplier website it mentioned that organic pads weren't as good for people who are heavier than average. It also mentioned that organic pads are mainly dry weather pads. Obviously, those statements may not be true.

I'm looking at a new bike. I can either get BB7 cable operated disc brakes or an SRAM Hydraulic Rival 22 system. I'm in two minds as to which system to get - the cable is much cheaper and I can get copy pads for about £3.50. The Hydraulic system bike is more expensive (£699 for cable, £999 for hydro). Also, I can't find 'copy' pads yet so a set of pads is around £20. I'll be using the bike in all weathers and, as my username suggests, I do carry a fair bit of weight around with me (although it is reducing). If it is true that organic pads aren't as good for lard @rses in the wet and one shouldn't use sintered on hydro systems then that may make my decision easier.

[freeflow]

Go Trp Hy/Rd. Hydraulic at the calipers but cable from sti to actuating arm on the calipers. It means you can choose whichever Sti you please. They also get very good write ups. I find them effective for stopping my 105kg.

[Brucey]

you can't really compare car brakes with bike brakes; the car brakes that glow like that are usually carbon-ceramic composite discs and the hot layer may only be a few microns thick. The rest of the brake system is designed to cope with that heat. Typically the brake fluid is an inch or two and several layers of material away from the brake disc.

In a bike brake the brake fluid is usually around 1cm away from the brake disc. Manufacturers use various materials for the pistons that are meant not to conduct the heat into the fluid. I've tried sintered pads in a system that wasn't meant for them and the brake caliper (and the fluid inside it) got much hotter much more quickly than with the organic pads that were meant for the system. This is because the organic pads are better insulators and deter the heat from running through the pad into the caliper. I guess it would have been OK on most hills with new fluid in the system but on bigger hills with fluid that is a few months old... naaah, not for me.

If the brake manufacturer says it is OK to use sintered pads in a hydro system then it probably (up to a point) is, but if they don't and you bung them in you are asking for trouble. In addition to the heat issue not all systems are supplied with discs that are suitable for sintered pads either.

Note that in the shimano blurb that accompanies their hydro brakes they mention that you can get brake fade on long descents; basically they are saying that their brakes may just stop working if you give them a right good thrashing. This can happen because the fluid boils up (easier.... much easier... if there is moisture in the fluid ) or the (organic) pads start to gas out and go away. You may get little or no warning that this is going to happen. Shimano brakes are not much different to others in this respect.

Organic pads - as a catch-all title for anything that isn't sintered- do vary somewhat. But generally you are trading cold bite, wet bite, heat resistance, cost, noise, wear resistance etc against one another and there is no clear winner, just different compromises.

If you are a commuter and you live somewhere dead hilly (you are in Sheffield, right?) you have to figure that your brakes are going to see a lot of hard use, in the wet you want your brakes to work right first time without delay, and you don't want to be changing pads once every few weeks. In addition you want to be able to fix you bike so you can ride it again next day, almost without fail. These things would -if you are going to have discs- point me squarely in the direction of the BB7s, fitted with sintered pads.

To keep yourself on the road, I'd suggest that you aim always to have a couple of spare sets of pads to hand, a spare caliper, spare mounting cup washers (ones from old V-blocks will do at a pinch), spare cables and spare discs. The same caliper body is used front and rear; the difference is in the mounting adaptor. If you have these parts to hand you can be almost 100% sure that you will be on the road the next day, even if you find a fault the previous evening.

Regular maintenance (once every few days) is to check the pads for wear, check the cables for fraying and free movement (a chainstay mounted cable run will let the water into the cable). I'd suggest that it is a good idea if you rotate the spare caliper through the bike once every couple of months in the winter, even if a longer interval than that in the summer is OK. To overhaul the caliper you have just taken off the bike, the whole thing needs to be cleaned, ramps/balls need cleaning and greasing, the body mounting parts need checking for cracks, and perhaps most importantly the fixed pad adjuster screw thread needs to be cleaned and given a light smear of copper-ease, without which it will corrode and seize in daily winter use.

Note that the supplied cup washers on the BB5/BB7 caliper mounting bolts are (IIRC) aluminium. The female (and sometimes male too) parts of these can and do crack especially if they see road salt. I suggest that you find some steel ones (as fitted on some cheap V blocks) and use those instead. If you are feeling spendy, you can buy stainless steel ones which are specifically manufactured to replace these parts on BB5 and BB7 brakes.

Doubtless there are those who would argue that hydraulic systems are less trouble and less likely to go wrong. Maybe. All I know is that in the event of a fault you need to be able to fix them if you want to ride your bike next day; most bike shops won't mess with them; if they leak then often the whole shooting match goes in the bin and they just change the lot. They need to be 100% sure that the brake is going to work OK (as well as it can do anyway) and not cause their customer to have a nasty accident. No-one can inspect your seals etc and say for sure that they system will definitely work perfectly, and no-one who has assembled hundreds of hydraulic systems has a perfect record with them; it is the nature of the beast. Even 'pre-bled assemblies' sometimes leak right out of the box.

Are there any alternatives? Well yes, if you go for 90mm SA drum brakes then I think you will have brakes that are more than good enough for a hilly commute; they are pretty much weatherproof and they will be less trouble than any disc brake in daily use. Just don't use the SA cables out of the box, they are not really very well lubricated.

cheers

[The fat commuter]

^^

Wow, thank you for such a detailed reply. Really much appreciated.

You're correct, I do live in Sheffield and it is hilly - especially on the side that I live on. I've managed to 'flatten' my commute a bit and minimise the brake usage so that my current brakes do last. However, if I do the direct route into work in the wet then I can easily go through a set of 'V' brake blocks in well under a week - two days is my record! Hills, heavy traffic and water don't mix well.

Back to the discs - I think that you've convinced me that for me, cable would be better. Apart from the commute, I will be using the bike for fun and that does mean long, steep descents (and ascents, unfortunately). I used to live close to and cycle in the Lake District and it was less hilly than here.

I have considered drums. I may put them on my current bike when the time comes for new wheels. Keep that bike as a wet weather winter bike.

Again, many thanks for the reply. Oh, and sorry to the OP for hijacking the thread a little.