hydraulic disc brakes

[hamster]

I note that in aircraft they are (rightly or wrongly) getting rid of hydraulic systems and using electric motors instead. I find this vaguely disturbing in several respects.

I take it you have never flown in an A320 or any other Airbus designed since 1986? They are all fly by wire, with completely proven reliability.

Electric motors are way more reliable than hydraulics! For a start you have fewer moving parts.

[Brucey]

I note that in aircraft they are (rightly or wrongly) getting rid of hydraulic systems and using electric motors instead. I find this vaguely disturbing in several respects.

I take it you have never flown in an A320 or any other Airbus designed since 1986? They are all fly by wire, with completely proven reliability....

you can produce a list of air crashes that are directly attributable to systems of that sort. Having said that, despite the fact that the whole arrangement is flawed in conception, execution, and implementation, I'd gauge that it may have (overall) helped to avoid more accidents than it has caused. To make it reliable enough there is up to four-fold redundancy in some systems; the individual parts are not as reliable as you might think (or hope).

FYI I've flown hundreds of thousands of miles on aircraft of all types; some worry me more than others. I've seen things that would turn your hair white too. I avoid flying on commercial aircraft these days; e.g. in the USA if you take a domestic flight it is likely that your pilot will have relatively little flying experience, is being paid less than $25K per annum, and may be knackered from his commute to work before he takes off with you on board. This is not the sort of thing that inspires confidence....

cheers

[hamster]

The crashes were due to inadequate pilot training, not failure of the FBW systems compared to hydraulics. As somebody who designed part of the A320's electrical system, along with FBW fighter aircraft, we looked at it extremely carefully.

Certainly FBW aircraft are different to fly, in particular poorly-trained pilots ended up either fighting the systems or ignoring them. There were indeed a spate of accidents in third world airlines which had just converted to A320 - a direct result of the training issue. Similar accidents occurred with stick shakers and similar aids in the 1960s in western airlines.

The accident statistics don't bear out your pessimism:
http://www.planecrashinfo.com/images/fa ... idents.jpg

[Brucey]

The accident statistics don't bear out your pessimism:
http://www.planecrashinfo.com/images/fa ... idents.jpg

I didn't say we were going backwards, to paraphrase I said we were not going forwards in an entirely sensible fashion.

It may interest you to know that the introduction of FBW (a la 320) was one factor that dissuaded me from a certain career path in aviation; the events of such accidents as Air France 447 were entirely predictable, I'm surprised that it took as long as it did before that scenario played out in that way. I'm sure that you and others would argue that 'the FBW system didn't fail' but the failure was one of conception and execution of those systems (in relation to human skills and attributes) as much as anything else. That circumstance would not have occurred in the same way if it had been a non-FBW aircraft, or perhaps if that one had had a more sensible cockpit layout.

I've had a chance to hear what Richard CdeC had to say about Quantas 32 too; I'm sure that before that incident everyone involved would have said how wonderful the flight control and error message warning systems were on that plane. Afterwards there were extensive changes made, and rightly so. To cap it all, the whole shooting match came within a hair of burning to a crisp on the tarmac, and the plane couldn't have been safely evacuated in short order had such a fire started.

cheers

[phil parker]

The accident statistics don't bear out your pessimism:
http://www.planecrashinfo.com/images/fa ... idents.jpg

I can't access this link?

[recumbentpanda]

Having just come to the world of disc brakes by acquiring a bike with cable-operated Avid BB7s, my experience is limited.

I did notice however, while adjusting these, that the aluminium caliper housings can be seen visibly distorting outwards as I apply maximum brake pressure. -Probably to about the same extent proportionally, as the rear stays or front forks on a rim v-brake setup. Given this fact, I can't really see any useful difference between cable or hydraulic in terms of power: both can obviously exceed the limit of the caliper's ability to transmit force to the disc. The only practical difference is therefore in 'feel'.

I've never seen anything like that on the four bikes,three steel and one Alu(tandem) that I own.
I suspect either I've got the wrong end of the stick or you aren't explaining it very well,would you care to elaborate a little more.

Sure -if I can make myself heard over the noise of all these aircraft taking off and landing and crashing

Consider the case of an old school, chromoly steel framed hard-tail MTB with v-brakes. If, standing next to the bike, I apply, say, the rear brake until the pads are firmly against the rim - and then squeeze some more, there's nowhere left for the pads to go, all the compression in them and any stretch or sponginess in the cable run has been taken up, so something has to give: the rear stays can be seen visibly moving outwards as I squeeze the brake lever harder. Ditto front forks, ( these are not the suspension type with a bridge at the top for this very reason.) Same applies to a range of other bikes in my fleet, from gas pipe to Reynolds 531. I am also talking traditional diamond frame here, not recumbents. I do see it on my aluminium, v-braked 'bent, but that model has a notoriously flexy frame -in spite of a 10mm thick T6 ally welded reinforcing gusset on the rear stays it STILL flexes outwards under heavy brake pressure!

Turning to the BB7 equipped bike, the lateral force of the pads obv doesn't go into the frame, but I was surprised to see, under similar conditions' eg, pads hard up against the disc, testing my set up of the cable by giving the brake lever a few hard squeezes, that the calliper body visibly 'expands' i.e., distorting outwards.

Car disc caliper bodies I believe, tend to be cast iron or steel, which I imagine is much more rigid than aluminum.

My takeaway point from this, is that purely on the question of braking power, a mechanical system reaches the limit of ability to apply greater pressure quite easily, even with v-brakes, so any increased power offered by hydraulics is fairly moot, especially as, in all cases the wheel is likely to have locked long before pressures at which significant frame or caliper distortion begin.

Of course, it would take a real engineer and some strain gauges to verify all this properly.

Hope this isn't too disturbing

[MacBludgeon]

Thank you all for your highly entertaining and mostly helpful replies. I am a somewhat grouchy but enthusiastic bike nut (MTB, Airborne tourer, Raleigh Randonneur tourer and my workhorse Trek Soho. The latter has cable disc brakes, the front one being effective, the rear one defying all my efforts to make it work properly. I have tried new cable, pads and adjustment but nothing seems to improve it. My Trek 6300 MTB has Avid hydrulic brakes which are pretty damn good, hence my steer towards hydraulics. But being a stubborn old sod and a competent amateur bike mechanic I will have one last go and try low-friction cable, organic pads and a complete strip-down. I will keep you lovely people posted.

Agree stopping power with BB7s is fine, benefit of hydraulics to me would be that both pads move and the lack of a need to manually adjust for wear. I don't find adjusting the BB7s any hardship and you can also get mechanical discs with twin pad movement via TRP now. I have no experience of the TRPs but reviews seem positive.

On the rear brake I found setup was critical for the BB7s. The frames I've built up have always used Goodridge compressionless outer cable, no problems. On a bike I bought secondhand with BB7s I got the front brake working fine but couldn't do the same with the rear until I changed the cable outer. I also dremel the ends of the cable outers after cutting to get them as flat/square as possible.

[reohn2]

[

Sure -if I can make myself heard over the noise of all these aircraft taking off and landing and crashing

Consider the case of an old school, chromoly steel framed hard-tail MTB with v-brakes. If, standing next to the bike, I apply, say, the rear brake until the pads are firmly against the rim - and then squeeze some more, there's nowhere left for the pads to go, all the compression in them and any stretch or sponginess in the cable run has been taken up, so something has to give: the rear stays can be seen visibly moving outwards as I squeeze the brake lever harder. Ditto front forks, ( these are not the suspension type with a bridge at the top for this very reason.) Same applies to a range of other bikes in my fleet, from gas pipe to Reynolds 531. I am also talking traditional diamond frame here, not recumbents. I do see it on my aluminium, v-braked 'bent, but that model has a notoriously flexy frame -in spite of a 10mm thick T6 ally welded reinforcing gusset on the rear stays it STILL flexes outwards under heavy brake pressure!

Turning to the BB7 equipped bike, the lateral force of the pads obv doesn't go into the frame, but I was surprised to see, under similar conditions' eg, pads hard up against the disc, testing my set up of the cable by giving the brake lever a few hard squeezes, that the calliper body visibly 'expands' i.e., distorting outwards.

Car disc caliper bodies I believe, tend to be cast iron or steel, which I imagine is much more rigid than aluminum.

My takeaway point from this, is that purely on the question of braking power, a mechanical system reaches the limit of ability to apply greater pressure quite easily, even with v-brakes, so any increased power offered by hydraulics is fairly moot, especially as, in all cases the wheel is likely to have locked long before pressures at which significant frame or caliper distortion begin.

Of course, it would take a real engineer and some strain gauges to verify all this properly.

Hope this isn't too disturbing

You're saying what I thought you were,I've never seen that happening with V's or BB7's,but I take look tomorrow and get back to you on it.

[reohn2]

Agree stopping power with BB7s is fine, benefit of hydraulics to me would be that both pads move and the lack of a need to manually adjust for wear. I don't find adjusting the BB7s any hardship and you can also get mechanical discs with twin pad movement via TRP now. I have no experience of the TRPs but reviews seem positive.

On the rear brake I found setup was critical for the BB7s. The frames I've built up have always used Goodridge compressionless outer cable, no problems. On a bike I bought secondhand with BB7s I got the front brake working fine but couldn't do the same with the rear until I changed the cable outer. I also dremel the ends of the cable outers after cutting to get them as flat/square as possible.

IME(TPR Spykes fitted to my Genesis Longitude,now swopped for BB7's due to the Spykes squealing so much)the twin pad movement didn't add anything to braking power,BB7's are just as good if set up right and kept reasonably adjusted.
I can see a situation where the static inner pad could cause problems if there were too much clearance between it and rotor allowing the rotor to scrape the caliper body by the active outer pad pushing it over into it,but it would need the inner pad to be backed way off and the active outer pad almost touching the rotor for that to happen.Which would amount to really bad adjustment anyway though.

I have compressionless outers on one bike as it came like that from new,the other three (two Vayas and the Cannondale tandem)have ordinary spiral wound outers,I can't say I notice much difference.
The BB7 cable disc brakes on all four bikes are exceptional.

[Rusty Spanner]

In ten years and over many thousand off-road miles, myself and my wife have had one hydraulic brake failure each;
A failed, non serviceable Shimano SLX lever and a leak caused by poor maintenance.
They get a bleed every two or three years, which is pretty simple and easy to do at home.
I'm genuinely amazed by the controllability and precise modulation of their power, much better than cable brakes of any description I've tried.
Yes, you can boil them if you drag them unmercifully on extended, extreme descents.
It's happened to me once on an long track I can barely walk down.
You soon learn to stop and let them cool off for a while every so often.

For mountain-biking, I still think they are the single greatest innovation we've seen so far.
No more arm pump, which previously ruined nearly every steep ride and no more expensive worn out rims.

I think many of the scare stories on here bear little relation to real world use.


However, after saying all that, my new road bike will have BB7 cable discs.
I just fancy the simplicity and I'd like to see how they cope on a tourer.

[reohn2]

recumbentpanda
I've checked both BB7s(Vaya cro mo frame) and V's(KHS Alu tandem)by squeezing the brake lever as hard as I could(I have big hands and a strong grip)whilst leaning on the saddle and attempting to push the bikes forward simultaneously,I can't detect any movement or spreading of seat stays in the case of the V's,or movement of the disc calliper of the BB7's.

[MacBludgeon]

Agree stopping power with BB7s is fine, benefit of hydraulics to me would be that both pads move and the lack of a need to manually adjust for wear. I don't find adjusting the BB7s any hardship and you can also get mechanical discs with twin pad movement via TRP now. I have no experience of the TRPs but reviews seem positive.

On the rear brake I found setup was critical for the BB7s. The frames I've built up have always used Goodridge compressionless outer cable, no problems. On a bike I bought secondhand with BB7s I got the front brake working fine but couldn't do the same with the rear until I changed the cable outer. I also dremel the ends of the cable outers after cutting to get them as flat/square as possible.

IME(TPR Spykes fitted to my Genesis Longitude,now swopped for BB7's due to the Spykes squealing so much)the twin pad movement didn't add anything to braking power,BB7's are just as good if set up right and kept reasonably adjusted.
I can see a situation where the static inner pad could cause problems if there were too much clearance between it and rotor allowing the rotor to scrape the caliper body by the active outer pad pushing it over into it,but it would need the inner pad to be backed way off and the active outer pad almost touching the rotor for that to happen.Which would amount to really bad adjustment anyway though.

I have compressionless outers on one bike as it came like that from new,the other three (two Vayas and the Cannondale tandem)have ordinary spiral wound outers,I can't say I notice much difference.
The BB7 cable disc brakes on all four bikes are exceptional.

Interesting on the Spykes thanks, and agree that BB7s work fine with normal outers but I like them adjusted quite close, very little lever pull to begin actual contact. I couldn't achieve this with normal outers on the rear but the setup was second hand so no idea of mileage. Maybe a switch to any new outer would have done but I only have a big reel box of Goodridge.