Carbon Disc rotors

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Re: Carbon Disc rotors

Postby Nobody » Mon Mar 25, 2013 9:10 am

MichaelB wrote:Who knows until someone does some back to back tests, i.e. 5 stops at a series of speeds, and measures the stopping distance as a starting point.

That's what I'd be doing if I got them.
Good to see someone will be doing some testing. :)

I suppose if you ride a drop bar bike, you can't afford to be settling for lower braking performance.
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by BNA » Mon Mar 25, 2013 9:27 am

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Re: Carbon Disc rotors

Postby trailgumby » Mon Mar 25, 2013 9:27 am

Nobody wrote:So as the disc spins anti-clockwise as we are looking at it as per normal disc operation, the brake clamps to prevent the hub rotating. So the force of the hub trying to continue would be pulling the spokes. How is this a design fault?

On the Avid discs I have, the hub spokes are in the other direction. Either Avid has a design flaw or there is something I'm missing. Why would it be better to compress disc spokes rather than stretch them?

Twists the spokes sideways, increased load increases flex both locally and in the whole structure. Stress risers at the point where the spoke meet the hub and the rotor. Remember that unlike spoked wheels, there is no pivot point built in at either end of the spoke.

Reversing the spokes on the rotor (ie, the "conventional" approach) stiffens the structure when force is applied, as the spokes have the forces applied to them more directly in compression. Less peak stress at the points where the spoke joins the hub and rotor, stress is more equally shared.

I had some Avid rotors with the spokes like in the photo. They were early "cleansweep" models. The later ones had them going the other way, but with the rotor slots as in the photo. All the one-piece shimano rotors I have are cut with the spokes going the "conventional" way, ie opposite to the photo.

Is it enough to make a difference? It depends on what sort of extremes you put them to, I suppose. With stainless rotors you'd get fatigue marks that would warn you it's time to replace. Carbon, given it's catastrophic failure mode, where it looks great until it doesn't, I think I'd prefer the reassurance of conventional rotor spoking.

That photo just yells at me that the designer just made/copied what he thinks is a "cool" design and hasn't really thought through the design and "what if" scenarios with any real understanding.
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Re: Carbon Disc rotors

Postby Nobody » Mon Mar 25, 2013 10:13 am

trailgumby wrote:Reversing the spokes on the rotor (ie, the "conventional" approach) stiffens the structure when force is applied, as the spokes have the forces applied to them more directly in compression. Less peak stress at the points where the spoke joins the hub and rotor, stress is more equally shared.

I had some Avid rotors with the spokes like in the photo. They were early "cleansweep" models. The later ones had them going the other way, but with the rotor slots as in the photo. All the one-piece shimano rotors I have are cut with the spokes going the "conventional" way, ie opposite to the photo.
OK thanks. So there is more to it than meets the eye. Good to see it has been tried both ways and settled to the conventional direction.

trailgumby wrote:Is it enough to make a difference? It depends on what sort of extremes you put them to, I suppose. With stainless rotors you'd get fatigue marks that would warn you it's time to replace. Carbon, given it's catastrophic failure mode, where it looks great until it doesn't, I think I'd prefer the reassurance of conventional rotor spoking.
I've heard/read that CF is better under tension than compression. Maybe this is a factor? I see the Kettle spokes are very wide in conventional pattern. Either way, I'll wait to see what happens long term before I try Kettle. At the moment, the one thing I like about them is no slots or holes.

trailgumby wrote:That photo just yells at me that the designer just made/copied what he thinks is a "cool" design and hasn't really thought through the design and "what if" scenarios with any real understanding.
You could be right about that. The inserts in total area seems too small to engender real confidence in the ability of the disc to expel enough heat. Kind of like a disc with too much/many cutaway sections.
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Re: Carbon Disc rotors

Postby jacks1071 » Mon Mar 25, 2013 3:28 pm

trailgumby wrote:That photo just yells at me that the designer just made/copied what he thinks is a "cool" design and hasn't really thought through the design and "what if" scenarios with any real understanding.


The more simple answer is perhaps that they printed the writing on the wrong side of the rotor for the brochure :D

Stuff like this is VERY common. Walking around the bike show, so many products had logo's printed on them upside down. Bikes had items incorrectly assembled in the rush to get things on display.
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Re: Carbon Disc rotors

Postby MichaelB » Mon Mar 25, 2013 3:29 pm

jacks1071 wrote:
trailgumby wrote:That photo just yells at me that the designer just made/copied what he thinks is a "cool" design and hasn't really thought through the design and "what if" scenarios with any real understanding.


The more simple answer is perhaps that they printed the writing on the wrong side of the rotor for the brochure :D

Stuff like this is VERY common. Walking around the bike show, so many products had logo's printed on them upside down. Bikes had items incorrectly assembled in the rush to get things on display.


Confidence inspiring ..... :roll:
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Re: Carbon Disc rotors

Postby trailgumby » Mon Mar 25, 2013 3:50 pm

jacks1071 wrote:
trailgumby wrote:That photo just yells at me that the designer just made/copied what he thinks is a "cool" design and hasn't really thought through the design and "what if" scenarios with any real understanding.


The more simple answer is perhaps that they printed the writing on the wrong side of the rotor for the brochure :D

Stuff like this is VERY common. Walking around the bike show, so many products had logo's printed on them upside down. Bikes had items incorrectly assembled in the rush to get things on display.

Possible, but given that the brake track slots go the right way (that is, to sweep dirt and debris outwards as it passes through the pads,where centrifugal force will throw it off the rotor) it seemed more likely to me they designed the spokes the wrong way when they programmed the laser cutter.

That's just as easy to do as printing things the wrong way, especially when you're in a rush to get things to market and you don't ride a bike and don't know any better.

Quite often stuff like this is released by small engineering and manufacturing companies who know *a lot* about producing stuff using the hardware they've just bought, but very little about using it.
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Re: Carbon Disc rotors

Postby barefoot » Tue Mar 26, 2013 7:59 am

MichaelB wrote:Who knows until someone does some back to back tests, i.e. 5 stops at a series of speeds, and measures the stopping distance as a starting point.


Absolute stopping distance will always be limited by tyre traction and/or over-the-bars moment. There's not many brakes that aren't capable of locking a wheel or sending you OTB.

If you want to measure anything useful about the brake effectiveness, you'll need to measure fluid pressure (or cable tension) and deceleration, and do a series of stops, as you say, at a fixed pressure (and record the decel achieved) or fixed decel (and record the pressure required to achieve it).

That will give you a measure that is proportional to the coefficient of friction between those pads and that rotor.

Next you'll want to know how the CoF changes with respect to other variables - most critically with temperature. Ideally, friction is constant. In reality, it changes with temperature, pressure, speed, and prior conditioning.

Welcome to my world...

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Re: Carbon Disc rotors

Postby lock_ » Tue Mar 26, 2013 10:02 am

barefoot wrote:
MichaelB wrote:Who knows until someone does some back to back tests, i.e. 5 stops at a series of speeds, and measures the stopping distance as a starting point.


Absolute stopping distance will always be limited by tyre traction and/or over-the-bars moment. There's not many brakes that aren't capable of locking a wheel or sending you OTB.

Or the rate at which the brakes are capable of converting your kinetic energy into heat/noise/deformation/etc. Yep, my roadie brakes will see me over the bars when braking hard from 10, 20 even 30km/h. But I'm finding that they lack, significantly, at speeds over 50 while at the same time requiring much force to be applied at the levers (not good for controlling braking effort). It's that pesky v^2 term ...
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Re: Carbon Disc rotors

Postby barefoot » Tue Mar 26, 2013 11:06 am

lock_ wrote:Or the rate at which the brakes are capable of converting your kinetic energy into heat/noise/deformation/etc. Yep, my roadie brakes will see me over the bars when braking hard from 10, 20 even 30km/h. But I'm finding that they lack, significantly, at speeds over 50 while at the same time requiring much force to be applied at the levers (not good for controlling braking effort). It's that pesky v^2 term ...


I reckon you'd find that if you suddenly mashed your lever to your bar at 50 clicks, you'd go flying OTB at 50 clicks.

I reckon you'd also find that your survival instincts would prevent you from doing this :lol:

You might find, though, that a stop from 50km/h ends up being quite a long drag (especially if you're doing 50km/h down a hill so you have the mgh term to deal with as well), so temperature and wear debris build up during the brake application, leading to changes in the brake effectiveness throughout the stop.

In automotive disc brake land, some friction materials ramp up in friction during a stop, some ramp down. They tend to be noisy and f*cking scary respectively.

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Re: Carbon Disc rotors

Postby lock_ » Tue Mar 26, 2013 12:26 pm

Well I do have the upper body strength of a cyclist, so even mashing may not be enough :wink: .

The survival instincts does come into it I guess, there's a maximum amount of force I'm willing to put through the levers. Yeah I could possibly squeeze harder, but I'd lose any control over the braking effort. So in respect to the above, the brakes may get me over the bars while travelling 50, but not with the level of force I am capable/comfortable putting in at the levers. And yeah, downhill gives you the additional mgh, and raises your CG relative to the 'pivot point'.

If I remember back to uni days we ever only dealt with static or dynamic friction co-efficients; much easier to work with on a bit of paper. But I'd assume in reality these are quite variable. Friction material that ramps down has some appeal in that you could possibly apply the same lever force throughout braking and have the braking effect lessened as you slow. Or perhaps that is better left to a AOTBS (Anti OTB System), hurry up Shimano :wink: .
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Re: Carbon Disc rotors

Postby Nobody » Tue Mar 26, 2013 1:04 pm

lock_ wrote:Or perhaps that is better left to a AOTBS (Anti OTB System), hurry up Shimano :wink: .
Already here. All with one lever too. Just don't brake while leaning though a corner. Or break a brake cable.
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Re: Carbon Disc rotors

Postby MichaelB » Tue Mar 26, 2013 1:59 pm

Hi Tim,

Agree with 'proper' testing protocol would be the best, but if given a chance, need to come up with something that could be done by someone without access to all of the right gear, and only a hill and some effort at their disposal.

So what would you suggest ?
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Re: Carbon Disc rotors

Postby lock_ » Tue Mar 26, 2013 3:01 pm

Nobody wrote:
lock_ wrote:Or perhaps that is better left to a AOTBS (Anti OTB System), hurry up Shimano :wink: .
Already here. All with one lever too. Just don't brake while leaning though a corner. Or break a brake cable.

I'll give them points for simplicity, but don't think you'll be finding such a setup on my bikes any time soon. Was thinking something like a motorcycle ABS system, wheel speed sensors, accelerometers and solenoids... Yeah, a little ways off yet.

MichaelB wrote:So what would you suggest ?

If you don't mind me butting in...

Maybe look at increasing the moment of inertia of the wheel so that when up to a typical riding speed the wheel carries as much energy as a bicycle and rider. By doing this you could test the braking without having to ride the bike at the same time. Simply get the wheel up to speed in suitably reinforced bike stand, apply brakes, and record time to stop (you could calculate theoretical distance travelled from this). Now I haven't done the maths, but I reckon the problem may be making your wheel heavy enough.
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Re: Carbon Disc rotors

Postby MichaelB » Tue Mar 26, 2013 3:07 pm

lock_ wrote: ...
MichaelB wrote:So what would you suggest ?

If you don't mind me butting in...

Maybe look at increasing the moment of inertia of the wheel so that when up to a typical riding speed the wheel carries as much energy as a bicycle and rider. By doing this you could test the braking without having to ride the bike at the same time. Simply get the wheel up to speed in suitably reinforced bike stand, apply brakes, and record time to stop (you could calculate theoretical distance travelled from this). Now I haven't done the maths, but I reckon the problem may be making your wheel heavy enough.



Butt away, but that sort of setup is not something I have in the shed, or am likely to. Closest is, like stated previously, a hill and some enthusiasm.

Also, doesn't reflect the real world, such as in-built AOTB sensors and common sense.

Aim is to have some data (be it directly useful or not) of actual stopping distance compared to a steel disc rotors and carbon rotors for the same other variables (rider, bike, tyres pads, calipers etc).

It will not be the same for the next rider, as everything else (potentially) is different except for the rotors.
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Re: Carbon Disc rotors

Postby barefoot » Tue Mar 26, 2013 3:12 pm

MichaelB wrote:So what would you suggest ?


Sitting here with about $6M worth of brake dynamometers at my disposal, there's no substitute for a subjective "squeal-and-feel" evaluation.

Put the bits on your bike, ride the kind of stuff you're looking for an improvement on, and see how it goes.

There will be some placebo / confirmation bias effect, but if there are significant differences between one system and another, it will be obvious.

If you want actual measurements, numbers and graphs... that's when things get a bit difficult without instrumentation.

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Re: Carbon Disc rotors

Postby barefoot » Tue Mar 26, 2013 3:19 pm

MichaelB wrote:Aim is to have some data (be it directly useful or not) of actual stopping distance compared to a steel disc rotors and carbon rotors for the same other variables (rider, bike, tyres pads, calipers etc).


An imperfect way to standardise your brake application without coming up against the skid/OTB limit would be to slacken off the cable (or retract the pads or put a block of wood behind your lever) so you run out of lever travel at a controlled brake application condition.

Then you could compare the stopping distance of pad/rotor combination A at lever position 1, 2, and 3 (different blocks of wood?) against pad/rotor combination B. Just as long as you can be sure that you're starting from the same setup conditions regardless of differences in pad/rotor thickness, for example. Maybe something like winding the pads (on a BB7) in until they can't go any further, then backing each pad adjuster off by 5 clicks.

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Re: Carbon Disc rotors

Postby barefoot » Tue Mar 26, 2013 3:20 pm

Oh yeah... and only to this^^ on the rear brake. Keep the front brake in perfect working order so you have an uncompromised emergency brake.

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Re: Carbon Disc rotors

Postby Mulger bill » Tue Mar 26, 2013 9:45 pm

I like Tims block of wood method to ensure consistent pulls.
Methinks in conjunction with the block of wood, approaching a mark on your downhill test track at x km/h, pulling the lever to the wood at the mark and marking where you stop should add some element of repeatability to the tests. Still have to consider variables like wind speed and direction tho'...
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Re: Carbon Disc rotors

Postby MichaelB » Wed Mar 27, 2013 8:44 am

There is no hope of replicating repeatable undeniable testing for the level of review that id try and do, but doing repeated tests using the I built AOTB method is real world and applicable to most.

Mind you, its all based on actually getting some rotors to test.

Nother problm that appears to be surfacing is that the Kettle rotors are a bit thick, and are causing problems there
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Re: Carbon Disc rotors

Postby jacks1071 » Wed Mar 27, 2013 10:20 am

There is pleanty of brake testing gear available to test bicycle brakes. I must have seen 3x different vendors at the bike show who either had the jig for sale or who'd provide independant testing. I didn't pay a lot of attention but they appeared to have data logging onto a computer and the tests just kept repeating.

Anyone who wants to have their product tested won't have to go to much trouble, they will have to spend the $$ though and they may or may not be happy with the test results.
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Re: Carbon Disc rotors

Postby barefoot » Wed Mar 27, 2013 11:01 am

MichaelB wrote:There is no hope of replicating repeatable undeniable testing for the level of review that id try and do, but doing repeated tests using the I built AOTB method is real world and applicable to most.


Well then, you'll just be doing repeated measurements on the adhesion of your tyres, and/or demonstrating the position of your centre of mass relative to the front tyre contact patch.

Give or take a small effect of how well the brake can be modulated, to closely approach those two failure points without tipping over them, all brake systems should give the same stopping distance at limit of traction or limit of OTB (or, back in my happy comfortable automotive land, ABS threshold [1]).

tim

[1] we have to deal with clueless motoring enthusiast magazines - especially in Asia - doing limit-of-traction (or even worse, ABS active) stopping distance tests to compare one brake pad against another, and publishing the results. And handling the market outrage when some cheap no-name rubbish pads, that probably couldn't stop a car twice in a row, get better stopping distance test results than a expensive pads that would be just as happy on a race track as on the road. *sigh*.
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Re: Carbon Disc rotors

Postby Nobody » Wed Mar 27, 2013 12:43 pm

barefoot wrote:
MichaelB wrote:There is no hope of replicating repeatable undeniable testing for the level of review that id try and do, but doing repeated tests using the I built AOTB method is real world and applicable to most.


Well then, you'll just be doing repeated measurements on the adhesion of your tyres, and/or demonstrating the position of your centre of mass relative to the front tyre contact patch.
I have to agree since I said the same thing on the previous page.
Nobody wrote:
MichaelB wrote:Feel is one thing, but actual stopping distance is one of the key measures.
...As long as it can get the back wheel off the ground, stopping distance is going to come down the road surface, front tyre and weight distribution.
Nobody listens to Nobody. :wink:
viewtopic.php?f=9&t=62276&start=25#p943671
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Re: Carbon Disc rotors

Postby MichaelB » Wed Mar 27, 2013 4:55 pm

Nobody wrote:
barefoot wrote:
MichaelB wrote:There is no hope of replicating repeatable undeniable testing for the level of review that id try and do, but doing repeated tests using the I built AOTB method is real world and applicable to most.


Well then, you'll just be doing repeated measurements on the adhesion of your tyres, and/or demonstrating the position of your centre of mass relative to the front tyre contact patch.
I have to agree since I said the same thing on the previous page.
Nobody wrote:
MichaelB wrote:Feel is one thing, but actual stopping distance is one of the key measures.
...As long as it can get the back wheel off the ground, stopping distance is going to come down the road surface, front tyre and weight distribution.
Nobody listens to Nobody. :wink:
viewtopic.php?f=9&t=62276&start=25#p943671


OK, OK, OK, OK, I give in :!: :!: :!: :!: :!: :!:

You win. :D
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Re: Carbon Disc rotors

Postby Mulger bill » Wed Mar 27, 2013 9:53 pm

Nobody wrote:Nobody listens to Nobody. :wink:

Must make for some interestingly one sided conversations... :P
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Re: Carbon Disc rotors

Postby MichaelB » Thu Mar 28, 2013 7:30 am

Similar stuff being developed for road MOTORbikes ...

Carbon m/cycle rotors

Will be interesting to find out more about their stuff
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