Questions about purchasing bicycles and parts
They have been dicussed in the disc roadie thread on p49 I think.
I'd give them a go, but to get a 180/160mm pair, its USD $260 odd.
I'll have to make do with what I have at the moment.
There is a chnace that we may be able to get some for a review on BNA soon, but not sure when.
Yeah, the way he talks I almost feel sorry for him. That's the problem with upgradeitis, never satisfied... I'm glad I don't have that horrible affliction much.
The funny thing is that I got to the endof the basket and anlu just didn't pull the trigger ...
Yep , im lucky to be finally enjoying the bike of my dreams
For these rotors, the carbon fibre is effectively the substrate and the silicon carbide is the friction surface.
Can anyone reference some testing information on them?
I'd be interested in them for our tandem but I'm not trying something untested on it.
That's what I thought but a fair ol' read of other sources convinced me otherwise. These are on the list.
...whatever the road rules, self-preservation is the absolute priority for a cyclist when mixing it with motorised traffic.
London Boy 29/12/2011
I don't know much about these specific rotors, but I know a bit about brakes.
In absolutely fundamental terms, brakes work by converting kinetic energy into heat. That heat energy makes something hot. Hot things are able to reject heat to their environment (second law of thermodynamics - heat flows from a hot body to a cold body) - in the case of brakes, the heat is rejected into the air.
The hotter they are (and the more surface area they have, and the more airflow), the faster they can reject heat... so for a given energy input (average, long-ish term), a brake will settle at an equilibrium temperature where it's able to reject the same amount of heat.
So, carbon fibre rotors.
Carbon fibre is, essentially, fibres held together by a polymer resin binder. With or without functional additives (eg the carbide in these). Resins are organic, and don't have much temperature capability. Epoxies and phenolics aren't much good over 200°C (compared to steel which is stable up to 723°C). They're about as good as it gets for thermal stability.
It's true that carbon fibre composites are good thermal insulators. So the heat isn't going to conduct through to the core of the rotor very quickly - most of it will stay at the surface, getting it extremely hot.
This insulation effect is what saves brake pads from breaking down - the resins only burn up at the rubbing surface, leaving the bulk of the pad structurally intact. But brake pads are only under compression and a bit of shear. Brake rotors have to withstand a bunch of tension - the pads trying to rip the section of rotor they're clamping away from the remainder of the rotor trying to pull it through the caliper.
The whole thing leaves me feeling decidedly uneasy.
With all this talk about road bikes with hydro discs potentially boiling their brake fluid on long descents (DOT3 brake fluid has a boiling point of 205°C when new, and it's well isolated from the real thermal action in a brake), I'm in no rush whatsoever to replace my steel rotors with reinforced plastic ones.
There is plenty of discussion re the fluid boiling, but is this REALLY an issue ?
Is it one of these urban myths ?
I understand barefoot's comments, and believe that it is possible, but is there ANY evidence of what fluid/caliper/rotor temps are for bicycle applications ?
The heat issue is one reason why I have opted for the 180mm front rotor (bigger thermal mass and area to reject heat).
To date, haven't had any issues despite braking my bulk from speed for slow hairpins.
I'd give them a go, and gradually build up the confidence in their ability. Looking fwd to Crittski's experience.
I'd instrument my brakes up and go get some real measurements, but I couldn't possibly ride with a the weight of a datalogger on my bike . I mean, there must be hundreds of grams there
More seriously though... it's a good question, and I'd volunteer to collect the data, but it will be seriously difficult to fit thermocouple leads into such a small space in a bike disc caliper (no way to embed a thermocouple in a ~2 mm thick rotor, so pad temp would have to suffice). I'll have a closer look and see if there's anywhere I can do it. Then I just need to find an enthusiastic lab assistant to ferry me up Mt Buninyong a few times for testing
All in the name of science, of course.
Here is the homepage for Kettle
There is also a good Bike Rumour Wells article on them as well
On a road bike or tandem fluid boiling is absolutely a potential issue on steep or long decents.
On a mountain bike, even a down-hill bike you are unlikely to get them hot enough to ever have an issue since you don't have the grip levels you get on the tarmac.
Look at a dirt rally car as an example, they run TINY brakes compared to the road going equilivants - partly due to the higher profile tyres they use but the smaller brakes are sufficient for their purpose.
In terms of carbon rotor technology, I don't know if the bicycle guys are making them the same as the car manufacturers but pretty much all of your high end exotic sports cars either run or have an option to run carbon ceramic rotors. I'm pretty sure they work fine from dead cold. I think the motorbike guys still run steel rotors in the wet but I havn't followed the motorbike racing closely for a few years so that might have changed?
That's my point, there is bpotential, but is there any evidence to show how much potentyial there is ? i.e. realistic or infitessimally small ?
I understand its a big reason why we havn't seen them offered on road bikes in the past. There is at least one well documented catostrophic failure.
I've had the pads so hot on our tandem that they were smoking, fading, rotor warped BUT I still had SOME brakes. I have no doubt that I would have cooked the fluid on that day leaving me with nothing. It was a 1km decent at 10-20% gradient.
Grip on the tarmac has nowt to do with it.
It's all about speed.
Kinetic energy is 0.5 * mass * (velocity)^2 . A track car at 250km/h at the end of a straight has FOUR times the energy of a (same mass) rally car pulling 125km/h.
If you look at cars with carbon or ceramic brakes, they don't just take standard calipers and pads, and slot a same-sized carbon rotor in to the system in place of a cast iron one. The ceramic rotors I've seen are huge - at least an inch and a half thick, and with lots of material bulk (the cooling vents are quite small). The calipers obviously work the same way, but they have to be bigger to fit over the monster-thick rotors. Friction materials are quite different.
I'm still not keen on the idea of using a 2mm piece of carbon-reinforced plastic, with pads that are designed to be used on stainless, to stop my bike. But hey, I tend to be conservative about these thing.
I'll deal with these statements separately, as they are quite different.
If you are referring to the Bike Rumour article (where the Parabox was used with the Ashima rotors), then there are sooooooooooo many holes in taht articles, it has nothing to do with boiling fluid.
If it is a different article, then please let me know, as I am interested.
OK, so a tandem (which weighs more in itself) with TWO people adds considerably higher braking, and therefore energy dissipation requirements compared to me (even at wombat size) on a roadbike.
They are distinctly different situations. Gotta compare apples with apples.
Also, just becuase a rotor/pads are smoking, doesn't mean a lot in itself. Different pad materials operate at different temp ranges.
Again, unless you know the temp of the key parts of the system, you can only theorise what the temp of the fuid is and therefore how close it is to boiling.
As again, I've also had my rotors piping hot, but the alloy spider was just warm to touch.
As far as temp testing goes, I'll volunteer myself for barefoot's testing regime
Sounds like the same as saying that a boeing 737 has the potential to crash. It can crash but the odds of it happening.
Some good discussion here, but a couple of random points to add in:
- Brake sizes on race cars is largely based around the horsepower involved, (which is pretty much what bearfoot is saying).
- For the testing here of temperatures here mounting thermocouples inside pads although would be cool and get lots of hits on the net, is probably over complicating it a little. An infrared or hand-held probe on the rotor as the bike comes to rest should suffice for trying to determine if brake fluids are going to boil or not. We are just testing if it is 100, 200, 300 or 400 deg. C, not trying to design a system here.
- Mt Buninyong isn't really any where near big enough to do a proper heat test.
- Brake fluids are available up to well over 300 deg. C which is going to be very hot at the rotor as in automotive applications rotor temps can be 5 times fluid temps which is going to be well beyond happy working temps of bike rotors. (though vauge physics here, I am trying to suggest that IF the fluid was to boil, it would most likely be a secondary failure)
Though some testing data would be great to see, especially with a couple of different rotor designs.
Some of the elite guys I occasionally ride with have just received their sets from the initial crowd-funded allotment.
No feedback yet.
As for not boiling brakes on DH bikes, ha! Don't count on it. There's a reason they use four-pot calipers and 203mm rotors, as I found out at Winmalee when I rode the DH trail on my endurance racing bike.
I didn't get to boiling point, but I was starting to get concerned. I run a bit of slack in the levers before the pads bite and I was almost completely out of that when I got to the bottom of the trail. The stink of brake burning pads at the regroup point was really strong and nearly all riders' rotors had turned blue. And that was only 1km or so of trail.
The interesting thing for me is these rotors use normal metallic brake pads and are supposed to offer better disc life than normal stainless rotors.
I'd be inclined to run cable discs on a roadie until the jury is in. Option 2 would be the finned and heat sunk Ice Tech Shimano calipers and pads.
Last edited by trailgumby on Tue Mar 12, 2013 9:49 pm, edited 1 time in total.
I am going to stick a 180 front and 160 rear on my mountain bike, and see how they go. I love how these threads fill up with a bunch of piffle about how discs wont work on road bikes though...
Santa Cruz Blur TRc XTR
Volagi Liscio Ultegra
Agree. I'll let someone else do the beta testing first and if they live, I might think about it in the years to come.
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