merlinextraligh

^ I'm not questioning the setup of 2 caliper brakes, and a rear disc. I am questioning using the rear disc constantly as a drag brake.

Does Ercikson advocate using the disc as a drag brake?

It would seem a better management of the heat issue to use the disc either in conjunction with the calipers, or alternating with the calipers, and not dragging it the whole way down.

2frmMI

I'm not sure I'm following you. Is it your thinking that the drag brake is being used alone? That isn't the point of a drag brake.
How else would you use a drag brake? Have you used one in some other way?
Application of a drag brake is not a static thing any more than is the use of the calipers. The drag is used to scrub a bit of the speed while fine tuning with the calipers. I suppose that if the descent was a uniform grade start to finish, one could "drag it the whole way down", but I've never done a descent like that. We add and subtract drag as the grade varies and as we approach or exit curves and switchbacks. And again, the main point is to keep from overheating the rims and blowing a tire. We don't feather it as much as one would with calipers, but it isn't set-and-forget, either.

merlinextraligh

the distinction in my mind is using a drag brake for extended periods to scrub speed, as oppossed to using the brake to slow for turns, then off the brake till the next turn or need to slow.

Carbonfiberboy 

I use an Arai drum as a drag brake when touring. I set it and seldom change the setting. It's purpose is to change potential energy into heat, so I just let it do that. I might adjust it for changes in gradient, but if I use it on a descent, it's on pretty much the whole time. I set it so that I also have to use the V-brakes (plural) to reduce speed enough for safety in the corners. Basically, it reduces 50-60 or more mph speeds to 35-40 mph speeds. That's a drag brake. I think it's important to note that I have to take my hands off one of the brake levers to adjust the drag. I don't want to do that very often in conditions where I judge that a drag brake is required.

A couple of times we've done a descent, after which I couldn't figure out what was wrong with the bike. I'd forgotten I had the drag on.

I wouldn't mind having dual discs, especially with these new rotors and calipers, but OTOH I don't want to spend the money. The Arai wheel weighs 2 lbs. more than my sport wheel. I doubt I'd get much weight saving going to dual discs. I would get rim savings, however, so in the very long run I'd come out on the money. But not at 68 I won't.

2frmMI

I just have to ask if you have actual experience with a drag brake, because you are sort of arguing for how they actually work.

2frmMI

I originally thought I could do that, but it doesn't work for us. Set, and pretty soon the grade decreases, and we slow to a crawl: "let up, honey!"
Yes! Though we find we need more manipulation to keep our speed where we like it.
Well, all I have to do is call out to stoke-person to add/subtract, on/off, etc., since she has the drag controller. That allows us finer control. I agree that on an epic descent, I'd fear messing with another lever or whatever if I had to control it myself. Stoker is my friend in that circumstance!
Well... I've never done THAT. ;^)
But I do love the drag brake as a parking brake (requires that it be controlled by a bar-end or other set-and-hold mechanism).

Carbonfiberboy 

Yes, that's one of the wonderful things about our touring rig. Set the brake, lean it against a wall, and life is good. I like to find a lunch spot with an outdoor terrace now. That's common in the Czech and Bundesrepublik. Ran across one in Canada on our last tour. Feels great to eat and drink with your bike right there. I know you can rubber band your levers, too, but the drag is really cool. I'll use it at long lights too, when it's not flat.

I think the right disc would work fine if used as a drag. Just have to keep an eye on it. No need to make the drag do all the work by a long shot. It's just to keep the speed down to where wind resistance and the rims can handle it without worrying about blowing a tire off.

merlinextraligh

14 years using an aria drum brake on a Burley.

I think you're still missing my point. A drum brag is designed to be used as a drag brake, i.e., on at some level for an extended period.

The arai has fins designed to dissapate the heat that comes from this.

Discs are designed to be used on and off, not in continuos use. The heat generated from braking dissipates between braking events. Dragging it, there's no opportunity for it to cool

Hence the advice that you routinely see not to drag a disc brake.

Carbonfiberboy 

There's a thing I don't understand about this conversation. The radiation coefficient of a body is usually estimated as:

hr = e*s*(Tsurf4 –Tamb4)/(Tsurf–Tamb)
where:
e = emittance of the surface
s = Stephen-Boltzmann constant (=0.1714 x 10-8 Btu/(hft2̊R4)
Tx = Temperature, ̊R
The numerals "4" are supposed to be superscript, but I can't seem to do that in this editor.

So obviously radiative heat loss increases proportional to the 4th power of the temperature of the radiative object, in this case a disc. Therefore, a hot object will dissipate heat (and potential energy) much faster than a cooler object. Hence it seems obvious to me that using a disc as a drag should keep the peak temperature of the disc down, rather than increasing it, as long as said disc is not overused. I guess my question is: what is the governing philosophy of disc use? It is that the peak temperature should be kept down, which is what it would seem to me, or is it that the overall time of use should be kept down, which it seems to me Merlin is saying. Or maybe it comes down to the team's desire, or lack of it, to keep potential energy loss from atmospheric turbulence to a maximum. IOW, how much speed they can tolerate and thus how much energy they will try to dissipate through wind resistance rather than the brakes. But supposing that the tolerance for maximum speed is low, like on a steep winding descent, which is then better? It seems to me in that case that careful use of the disc as a drag would be most successful, bearing in mind that 4th power term.

Edit: in a for-instance, we have a steep winding descent which is frequently done, though no longer by this team, having blown tires off the rim twice. It ends in a sharp right hander. We just had a guy on a single get killed on that corner. On our tandem, I have to keep the rim brakes on the whole way down. Braking and letting it run is like a joke. No way could we allow enough speed to build up for atmospheric braking with being killed ourselves. So everyone who does this descent successfully rides the brakes the whole way down.

Dean V

A disc brake can out perform a drum brake. This has been shown for their use in anything performance orientated for over 50 years. However bicycle discs are typically so thin and light they simply can't cope with dissipating much energy. A drum brake like an Arai, whilst being technically not as efficient as a disc, there is so much more of it that it that it can cope with dissipating more heat. If you were to put a good disc brake system on your tandem that weighed as much as an Arai drum brake I am sure you could use it as a drag brake, stopping brake, whatever, and it would cope just fine.

Carbonfiberboy 

Stefan-Boltzmann Law:
q = σ T[SUP]4[/SUP] A
where
q = heat transfer per unit time (W)
σ = 5.6703 10[SUP]-8[/SUP] (W/m[SUP]2[/SUP]K[SUP]4[/SUP]) - The Stefan-Boltzmann Constant
T = absolute temperature Kelvin (K)
A = area of the emitting body (m[SUP]2[/SUP])

Note that there is no term for mass. Those of us who've used drag brakes much realize that they come to a constant operating temperature fairly quickly. Once there, heat dissipation is governed by the Stefan-Boltzmann Law. Note that area is a term in this equation. That's why larger discs work better - not because they have more mass, but because they dissipate heat more quickly.

waynesulak

I like Dean V's comment. A big disk should perform well. Also it seems to me the cut outs on light weight bike disks serve to lower the surface area moving heat into the air. While it would add weight, an almost solid disk would throw off more heat.

It is my understanding that the venerable Arai can take so much heat because of its construction. Few if any parts that will melt or boil. It also has an inherent limit to the amount of energy it can absorb, and therefore needs to throw off, due to its poor braking performance compared to a disk. I have never heard of anyone using a drum as their primary brake to save their rim brakes. If you use a drum it appears you still must use rim brakes spreading the heat to three brakes.

Dean V

You are right. So to be more technically accurate most bicycle discs have insufficient area to cope with the heat dissipation required. As the area is increased they will usually get heavier though. You could have a 200mm/2mm thick disc and a 250mm/1mm thick disc of equal weight. The bigger one will dissipate more heat but not be structurally sound.

reburns

Heat is dissipated in three ways: radiation, convection and conduction. Radiation is the least significant of the three in bicycle brakes including discs.

Abram

In most cases that is true, but in the extreme -- where people have their discs glowing red and are melting aluminum (600C I believe) -- I could see radiation becoming very significant. Conduction and convection are driven by the temperature differential (linearly), while radiation has that ^4 factor. Doing a rough calculation (assuming 500C and a 200mm diameter rotor of a 20mm wide ring), I get 375W cooling from radiation. Given the length of the conduction path, and the cross sectional area of the rotor to airflow, I would bet that radiation dominates if the temperature really gets that high.

PMK

AKExpress, curious if you have a photo of the failed discs.

Not doubting your description, but did the aluminum actually melt or the bonding agent / adhesive melt?

The math is getting very techy, and focused on materials science and heat dissipation properties. Just curious if the disc failure is that intense or other issues of the design.

Not doubting the failure or seriousness. Just now wondering what the failure looks like.

PK

akexpress 

I will post a picture when I get home. The bike is still in the cases. I could have finished the trip on the disc if I had not carried a spare. The braking would have pulsed and probably been noisy. The team with the melted saint did ride the last to days with theirs as he did not have a spare.

Abram

Please do! I've been wanting to do that ride for years, but keep forgetting about it until it's too late. I just decided yesterday that I'll do it next year. Hopefully on the tandem.

2frmMI

So, I want to engage a twist in this conversation. The main argument against the Ice rotors comes from akexpress' first response to the OP. Suppose akex had posted something like:
"We did this big descent and my rim/caliper brakes overheated and blew the tire off the rim!! There must be something wrong with [brand] brakes/rims/pads!"

Various and sundry sage voices would counsel:
"Dude, you can't just jam your brakes for a long time, you need to alternate front/back, and you need to scrub and release/ scrub and release, rather than hold steady resistance. No brake/rim/pad can handle the momentum>>heat buildup of a tandem hurtling down hill at that grade!"

In this fanciful scenario, blaming the [brand] equipment would be dismissed, and rather, fault would be attributed to a matter of technique. Is it fair, then, to fault Ice rotors, because the operator did essentially the equivalent of what would be roundly criticized if it had been a rim brake?
[The irony of contraposition of overheated discussion and melting disks is not lost on this discussant.]

PMK

I guess, but overall, it is widely known about overheating with rim brakes and possible failures. So far, there is nothing but huge praise and no negative comments until now about failures of these disks. How would a team deal with purchasing an Ice rotor based on good feedback here, had a failure resulting in injuries, only to have AKExpress or others come in after the fact and state, we had failures also but deemed it not needed to mention since it must have been our technique or a fluke.

So far, it seems the best brake is either no longer available or not yet available. We have seen the proven huge diameter Formula rotor with vents and a modified caliper width to be well proven. As for what is not yet available, overall, it seems that new offerings tend to have lighter weight and possibly less ability to control heat or boiling of the fluid / melting parts, with the exception being the new double acting caliper.

I patiently wait to see the failed rotor, if it melted the aluminum, I'm impressed from AK's courage to descend, if the adhesive or whatever laminates this stack failed, I am still impressed with the test pilot attitude from AK.

While most teams have complaints about hearing a slight brake rub that annoys them, it took melting a rotor to annoy AKExpress.

PK

bikeinxs

For those who are interested, I started a new thread in the tandem forum with my complete D2R2 ride report, including how the ice tech rotor performed.

Coles notes version is that it was flawless. It got very hot but not so hot as to blister the paint on the fork or warp the disc.

https://www.bikeforums.net/showthread...0#post15998500

Abram

Colotandem posted a photo of a failed IceTech rotor last month.

akexpress 

here are pics of the both side of the rotor. It is clear that the Alu melted not the bond. If you look at the rotor from the edge it is clearly warped. Apparently 2frMI thinks it is all my technique that is at fault. I live in Alaska, ride in the mountains. We have descended Mt Ventoux, Authers Pass in New Zealand, numerous descents in Turkey, Oregon, Colorado,Callfornia and Arizona.. Many big descents on our mountain tandems, we ride with the faster teams in big events I am pretty sure I know how to use my brakes to get down the mountains. It is a fine line on using the front brake enough to allow the disc to cool yet not overheat the rim and risk a blow out. I have no desire to add a 3 lb drag drumbrake to my Calfee. 2frMI setup of three brakes is not the norm today but instead a rim brake on the front and disc on the rear seems to be the new normal build. I liked the Ice rotor until it failed. I would not recommend it to my friends and I would not let my wife descend on a bike with it period. Our friends whom also had this rotor on the trip changed theirs immediately after they saw ours. As I also stated I was not the only one who melted one on the same descent. I would put this other team against any other team for skill and experience on major descents. He is a European distributor of tandems and has a large tandem shop in Bavaria. He had about 1000km on his disc before the failure. All the fancy engineering formulas are great but in the real world it failed. IMHO

akexpress 

I just measured the thickness change at the melted area. The average thickness in the non melted areas is .075inches and in the melted area it is down to .062 inches so it lost almost 18% thickness which is the cause of the severe pulsing that was experienced after the melting. Close examination does not reveal any delamination between the steel and aluminum.

waynesulak

Possibly the normal build is not the best build. I see little reason not to add a little more heat capacity in the rear rim brake.