[Closed] Road hydraulic discs

Not sure why you would want anything else really

EDIT oh yeah ...and hub

A friend of mine had an offroad tandem just around the time disc's where starting to become available, he claimed that on long descent's the V brakes could get the rims hot enough to burst the inner tubes 😯
He ended up fitting the biggest discs hope made at the time and also had a V brake on the back operated by a thumb lever to use as a drag brake.

Edit: Is that tandem on the Quantocks?

Dibbs - yes - quantocks

Aracer its not an issue at all. We use out tandem on the road as well - its simply wrong to say its harder to lock the back wheel than the front- as you brake you transfer weight onto the front tyre.

the one we overheated was an old 4 pot - now run 6 tis which are more heat resistant - no issue with them

its not an issue at all for us

FTFY

its simply wrong to say its harder to lock the back wheel than the front

Good job nobody is saying that then.

the one we overheated was an old 4 pot - now run 6 tis which are more heat resistant - no issue with them

So you're talking about problems with heat transfer to the fluid? Never heated up disk brakes enough on a descent to get brake fade? I have on twisty road descents in North Wales (when the chap I was riding with overheated his rims enough to blow the tyre), and on non-technical 3000ft off-road descents in the US. That's running 160/140 discs when I was a skinny 65kg. I don't suppose dual 203 discs provide anywhere near twice the amount of cooling or twice the resistance to heating the disc up enough to make the brakes fade. There are tandem crews more than 3 times that weight.

Never had fade other than boiling old fluid. Discs are blued from the heat - we do use sintered pads for that reason tho as they are more resistant to fade although they do transfer more heat to the callipers. big discs have a lot more surface area to loose heat from.

There is no issue at all with disc brakes on tandems if the right kit is specced - or anyway less issue than with rim brakes

Aracer that is what they ( in your link) are saying ( that its harder to lock the back) - if you have a decent stopper on the front you can transfer so much weight to the front tyre you get hardly any rear braking - and I can easily lock the rear on our tandem with the disc on it even with sticky tyres on the road and even without using the front for weight transfer.

i still can't see why it shoukd be harder to change wheels!!!!

Oh yes sorry, shimano's poor manufacturing.

big discs have a lot more surface area to loose heat from.

In pretty much direct proportion to their diameter. You have twice as much energy to dump on a tandem (for some crews 3 times the amount of potential energy I had). You don't use discs which have twice the surface area (only about 30% more than even my little discs). The fact you've not had fading just suggests you've not encountered the conditions where it's an issue. How many twisting steep tarmac descents in North Wales have you done? How many non-technical 3000ft descents?

that is what they ( in your link) are saying ( that its harder to lock the back)

I must be being dim then. Can you help me out by providing the direct quote from that link which suggests it's harder to lock the back wheel than the front on a tandem?

Aracer - its that the brakes I use have plenty of heat resistance and ability to lose heat. Plus technique probably. I have put them under plenty of heat stress - including the4 worst situation - dragging down relativly steep hills relativly slowly - enough heat to blue the discs.
already quoted it. done both steep and tricky road descents and long offroad ones.

it is [b]virtually impossible to lock up the rear wheel[/b] under the most extreme braking- this makes it a wonderful location for such a smooth stopper. (After all, the braking power of an unarticulated V-brake-, one without a parallel-push mechanism-is already strong enough to [b]lock up a tandems front wheel[/b].)

Fairy nuff on the Santana article - that is a load of BS. In my defence I have to point out that I've never suggested I agreed with that (in fact I disagree with an awful lot of the marketing stuff Santana have put out) - just that I'd not noticed that claim. After all, I've locked up the rear wheel on a tandem, and even endoed one!

Still disagree with you about the issue with disc brakes overheating and fading - if I've managed it with my little discs, then it seems very unlikely for it not to happen on a tandem with discs of only 30% more surface area. Maybe you've just not quite reached the point it's an issue - you say long offroad, but 3000ft (that's vertical)?

I have put plenty of heat stress into the brakes - the one time I really cooked the old brakes was only a couple of hundred feet descent - just it was slippy and I only had one working break so rolled down it slowly dragging the brake hard the combination of low speeds so less cooling and hard braking is what builds the heat - it can be done in very short distances. Our discs are blued and they often stink of hot brake

The ti six pots I now have are designed to cope with more heat - the pistons are perforated and TI and there is room for air to circulate between the pistons/ pads and body of the caliper - the pistons stand proud of the caliper even with new pads also a much bigger pad area and a sintered pad.

Yes done big descents on it in the highlands including with full camping kit and in massif central in France- if 1000+ ft won't cook em 3000 will not. its low speed stuff that really cooks em IME and the thorn article suggests that as well.

I am absolutely confident that there would be no heat build up issue on alpine passes even with these brakes - unless I dragged them the whole way down at low speed

if 1000+ ft won't cook em 3000 will not.

On the contrary - my brakes were fine until near the bottom of that.

As its easy to overheat a brake in a short distance if you put a lot of heat stress into it - I cooked the m4 in couple of hundred feet of slow dragging down a steep hill I would have expected them to have reached a steady state well before the bottom of a 3000 ft hill or have overheated much quicker.

Its just something that the brake designers will have to consider for road bikes - and the riders will have to lean not to drag them continuously.

Phenolic or Ti pistons, and airflow management ar ekey I guess. Maybe ventilated rotors like v2s?

and the riders will have to lean not to drag them continuously.

So there is a problem with the brakes then?

Not more so than rim brakes - appropriate technique for the kit. You have so much power there is no need to drag the brakes. You can let speed build and slow when needed.

Your mate blew a tyre with heat build up remember 🙂

The 6 pots I have are very good at dealing with heat - thats why I got them

Hydraulic disks on road frames seems to be trying to solve a problem that doesn't exist and at the same time coming up with lots of engineering trade offs (heat dissipation versus weight).

For the pros they'd have a place and improve performance without the overheating issue as they're featherweights and brake as little as possible.

The average mid life crisis buyer who'll be able to afford them will be where the problem lies. To dissipate the heat generated from trying to stop the powerfully built will require a bigger disk and more weight. Trade off.

Cable disks is the obvious solution in terms of braking performance and reliability, but this doesn't have the same desirability as hydraulics.
This is probably the reason why this has taken so long to come to market in any real sense. I'm sure they'll find a way to market it though.

Not the whole "faster riders brake less" thing again?

NOOOOOOO!

And pros being a different species that weigh substantially less? Not really, and in any event compensated for by the height gain in their mountain rides.

So faster road riders brake more do they? right....

Average weight of pack of pro riders compared to average weight of pack of Sunday club run. Which one is higher in your opinion?

My Dawes Super Galaxy tandem has a drum brake on the rear for dragging purposes. It's connected to an old gripshifter. These were originally designed for mopeds. This is from the age before disks. And yes, rims can easily get hot enough to burst tyres. I think disks have partially solved this problem.

Disks on road bikes surely only make sense for carbon rims, where I can accept that the combined weight could be less than rim and caliper (maybe). Hydraulic as opposed to cable doesn't really make much sense to me.

fourbanger - Member
So faster road riders brake more do they? right....

Average weight of pack of pro riders compared to average weight of pack of Sunday club run. Which one is higher in your opinion?

Can you establish they brake significantly less?

Average pro - 60kg? Average club rider 75kg? 20% difference, easily within the margins of brake design.

I'm with cynic-al.

and even if the "ave" pro weighs 60kg, there are plenty who weigh over 80

^^^^

Thats before you factor in higher pro cycling speeds.....

My thought with disks is some joe public guy ants to make his new disk braked road bike lighter. Fairly simple, stick a set of 140mm disks on, jobs a good un.

Might not stop his 18st on a downhill during a sportif, but hey, his bike is now 100g lighter so it must be better. There's nothing really he can do to rim brakes to make them lighter currently.

Hydraulic as opposed to cable doesn't really make much sense to me.

It's not JUST about the braking. As I've said before, this is about the cable runs and about making everything internal. Hydraulic hoses can be routed any which way you want with 180 degree bends and all sorts with no loss in performance. Everything routed through the tubes, no need to replace cables.

The sensible thing to do is combine hydraulic discs with electronic shifting and put all the gubbins into the lever. Makes all the lines very clean, gives consistent performance for years and the weight issue is neglible given that bikes can already be built way below the UCI weight limit of 6.8kg/15lb without a problem (other than cost).

this is about the cable runs and about making everything internal

Fair points for professional machines.

this is about the cable runs and about making everything internal

The adoption of discs on road bikes is going to push the development (or maybe that should be refinement) of little things, that we didn't know we wanted/needed, that will make tasks like wheel swapping and replacing damaged levers quicker and easier IMHO - if changing wheels with discs turns out to be as time consuming as some seem to think it will it won't take long for the teams to push their sponsors to improve it. I can see disc mount positioning on hubs to be one of the first things that get standardised, either that or quick and reliable caliper re-alignment.

I can see disc mount positioning on hubs to be one of the first things that get standardised, either that or quick and reliable caliper re-alignment.

Is mount does this ( and post mount to a certain extent) - its only that its become accepted for post mount to use slotted mountings to allow for low manufacturing tolerances. Tighten up the manufacturing tolerances and everything just slots together - rear cassettes remain aligned properly when you swap wheels right now

Cable disks is the obvious solution in terms of braking performance and reliability, but this doesn't have the same desirability as hydraulics.
This is probably the reason why this has taken so long to come to market in any real sense. I'm sure they'll find a way to market it though.

I pretty much have to agree, the reason road bikes have mostly stuck to rim acting calipers up to now has very little to do with power or ultimate braking performance, in those respects they are mostly adequate for the application until of course you're ****ting down an alp boiling the glue off of your tubs, there a disc brake may help (assuming it doesn't fade as previously the linked article described)...

Do cable disc fade in the same way? a lack of fluid for them to boil would suggest that isn't an issue simply making all of the mechanical components sufficiently resistant to sustained heating, and of course light enough to build a bike to the weight limit...

The use of a disc brake opens up a few new design options for other areas of the bike wheel profiles/rims, frames and fork crown areas but using a hydraulic disc means the hoods are now going to have to accommodate a master cyclinder obviously wit Di2 less of an issue as the "shifter" is now just a couple of micro switches, but very few non pro's will be riding with leccy shifting, of course if you were to take a current Ultegra STI unit and use it to actuate a cable disc caliper, I can't really see the problem for the average MAMIL, most of the benefits of Disc brakes, without the problems and cost of implementing hydraulics...

Internal routing would be a touch simpler to achieve with mechanical discs than hydraulics so again wheres the benefit to hydraulics on a road machine?

TandemJeremy - Member
Tighten up the manufacturing tolerances and everything just slots together - rear cassettes remain aligned properly when you swap wheels right now

rear cassettes remain aligned properly when you swap wheels right now

Not really, mine needs a little tweak when I swap wheels, and you're not talking about the very small tolerances of discs.

Can't see you'll get a totally 'universal' set up for a long time, if ever.

Can't see you'll get a totally 'universal' set up for a long time, if ever.

The one saving grace with road discs is that they are completely new. None of the issues that MTBs had where they were introduced gradually and a lot of people subsequently upgraded disc ready frames. At the moment road discs do not exist in the market, you can't upgrade an old frame to discs so aftermarket manufacturers aren't going to be on the scene for a few years yet - it'll be restricted to Shimano and SRAM (Avid) and Magura initially.

I hope and pray that everyone sits down and comes up with ONE standard so we don't end up in yet another standards quagmire:
centrelock vs 6-bolt
IS vs post mount

The pros simply won't use it otherwise as it'll make wheel changes too slow and neutral service will be even more of a pain in the arse than it is now.

Internal routing would be a touch simpler to achieve with mechanical discs than hydraulics so again wheres the benefit to hydraulics on a road machine?

No it wouldn't. You can route a hydraulic hose any way you want whereas cables have to have internal guides and stop points to maintain the tension.

Universal standard? Well for pro teams why don't neutral service (or the organisers really I suppose) hand out a jig for setting the brake calliper and a facing tool that makes the hubs fit a caliper fitted with the jig. Teams (and indeed neutral service) then get to face and if necessary shim their hubs until the work in calipers fitted with the jig. Would take long before hubs / wheels were supplied already properly faced.

Just a thought.

crazy-legs - Member
No it wouldn't. You can route a hydraulic hose any way you want whereas cables have to have internal guides and stop points to maintain the tension.

Sorry but all this waffle about needing some new standards...
Utter cobblers the applicable standards exist already and are established, so why reinvent the wheel (pun intended)...
100/135mm axles, IS mounts on frames/forks, with PM calipers and adapters so users can run whatever size rotors they like, and 6 bolt hubs, or centre-lock if you like, (both align with the same calipers so ultimately it makes bugger all difference).

What a load of bollocks this thread has become, you lot have talked yourselves into the need for hydraulics with miniature quick connecters just so some tarts can have more aesthetically pleasing routing, and the needless bling and car park posing factor that come with transferring the input force from the lever to the caliper using fluid as opposed to cables...
Shimano, SRAM, Campagnolo, Formula, Hope, etc must be rubbing their hands with glee...

cookeaa - the problem is that hub widths vary, so as you replace a wheel with a different hub, you have to re-align the caliper. Therefore, there needs to be a tighter standard in this area to allow for fast wheel changes from "neutral" cars.

Actually thinking again, a single tool that simply faces the 6 bolt holes on the hub an accurate distance from the outer end of the end cap is all you need. Provided manufacturers don't make this distance too large that is.

Manufactures to work to tight tolerances is all you need

How many road bikes actually get used for racing where "neutral" or team wheel swaps are likely? I mean really, most will just be used by fatties on the odd club ride really won't they...

And being realistic if you could manage to get all manufacturers to hit +/-0.1mm from the face of the lock nut to the face of the disc mounting on each hub you'd be doing very well, then there's all the other parts to consider: mountings (even a close fit hole will add another 0.1 diametric clearance to the stack up of tolerances), caliper, pad spacings and the actual disc itself, all have an effect...

"Tight Tolerances" means almost unachievable in this context, hence current systems simply provide adjustments to account for this, a stack up of 0.3~0.4mm either side of the nominal position would not be particularly hard to imagine given all the components in the assembly...

And adding a facing operation to every bike would only serve to increase the potential for an even wider tolerance band problem on each bike, Facing only exists for either A) getting a surface nice and perpendicular to the wheels axle, or B) adding a tenner to the LBS bill for monkeying with a bike...

Having said all of that, Rims vary much more significantly in width and true also, so the issue isn't exactly a new one is it?

Wider pad spacing and lead in features might help but there will always be a variation in dimensions...

How many road bikes actually get used for racing where "neutral" or team wheel swaps are likely? I mean really, most will just be used by fatties on the odd club ride really won't they...

Not many, how many bikes have to be approved by the UCI before they can be raced? ALL of them, and i seem to remember the UCI are going to enforce that all bikes must be available to the consumer. So whatever you buy has to be usable in a race situation.

Rims vary much more significantly in width and true also, so the issue isn't exactly a new one is it?

Do they? have a look at road wheels and there is very little variation. and the QR's that exist cope with what little that exists.

Oo, Ooooo !.

An Engineering debate !, regarding hydraulic brakes.
Kinda re-inventing the wheel type thing.

Well, you're all Engineers then by profeesion.
You go to work everyday and earn your living by being an Engineer, right ?.
😉

And for the record.
I have a road format bike.
I have fitted riser bars and hydraulic brakes.
It should be on the road this coming weekend.

You go to work everyday and earn your living by being an Engineer, right ?.

Yep 😀

Although admittedly nothing to do with bicycles...

the point I was failing (and probably still will) to make is that generally the best way to deal with the inevitable problems caused by the stack up of tolerances across different parts and manufacturers, is to design adjustment/accommodation of on-the-piss-ness into any assembly...

And "Tighter Tolerances" means nothing without repeatability, you'd need to be sure that your zero adjustment required, highly accurate and toleranced assembly of brake and hub parts from Shimano/SRAM/Hope/Formula all bought and slotted together flawlessly in say 2013 will all still be directly interchangeable with parts from YM 2014/15/16-etc from every other manufacturer under the sun, far easier said than done...

Also an engineer - at least I was; these days I manage engineers (electrical network types). Though I think what most of the discussion is about is more akin to a fitter's stock in trade than an engineer's. Perhaps some of the manufacturing tolerances stuff.

cokeea - why not? - al you need to do is as IS does define the various spacings and manufacture to that.

most of the various combinations of wheel and frame I own and have tried are interchangable with no issues

How many road bikes actually get used for racing where "neutral" or team wheel swaps are likely?

the best way to deal with the inevitable problems caused by the stack up of tolerances across different parts and manufacturers, is to design adjustment/accommodation of on-the-piss-ness into any assembly...

This is the reason caliper brakes have barrel adjusters and QRs, discs (hydro or cable)would need the same quick easy adjustment.

I agree with mustard and can back up what he says from experience. A good wheel change can the difference between getting back onto the bunch or a ride back to HQ...

I hope and pray that everyone sits down and comes up with ONE standard so we don't end up in yet another standards quagmire:
centrelock vs 6-bolt
IS vs post mount

I can see that meeting happening - Shimano won't admit 6-bolt are better than centrelock. If SRAM decide to use centrelock is saying Shimano are better. Don't even get Campagnolo started!