Author Topic: Brakes with heat capacity  (Read 5394 times)

hendrich

  • Jr. Member
  • **
  • Posts: 78
Brakes with heat capacity
« on: August 14, 2022, 11:45:49 pm »
For some years, I have been a somewhat religious reader of Thorn literature. I more or less find everything Andy has written is spot on for tour bikes. Our new tandem has a Rohloff, sorry, not a Thorn....we considered but we are tall and sizing was difficult. Regarding brakes, we have good cantilevers (Andra rims) and a standard (non-hydraulic) rear disk (3 brakes). We find this is not sufficient for mountains when heavily loaded and walk down >10% grades.  Our old tandem had an Arai drum and we did >15% downhill without problem. I don't wish to mess with hydraulics. Recent posts have suggested Sturmley-Archer drums are good. We could use such a front drum and I suspect that it would have braking heat capacity similar to the Arai. It appears that adoption of a this front drum would not interfere with front panniers (Tubus/Ortlieb).

Clearly, Thorn literature talks about the problem of standard disks and poor heat capacity (I forget the test hill name that set the brakes on fire). Eventually Hope came up with a solution, but this solution is hydraulic. So my question...drum brakes are very reliable, have high heat capacity, and require a less complicated routing setup. Why did Thorn seemingly bypass this lower cost option?

PH

  • Hero Member
  • *****
  • Posts: 2279
Re: Brakes with heat capacity
« Reply #1 on: August 15, 2022, 09:55:26 am »
I've never ridden a tandem so my assumptions may be wrong, but I thought the purpose of a rear drum brake was as a drag brake rather than deceleration?  Wouldn't doing that on the front seriously mess with the steering? 
I don't know what the Hope solution you refer to is? I know that some rotors and pads are better at dispersing heat than others, I'm doubtful that any would be up to being used as a drag brake on a long decent.  I've never had hydraulic brake fade, I've never pushed the system to anything like the point where that might happen.  The reports of it I've read are frightening, almost complete brake loss without warning!

mickeg

  • Hero Member
  • *****
  • Posts: 2688
Re: Brakes with heat capacity
« Reply #2 on: August 15, 2022, 12:53:01 pm »
Can you put on a larger rotor on your disc brake?  Or, are you already at the maximum size?

For your rim brakes, Koolstop Salmon are generally considered the most grippy of the rim brake pads.  I have them on some of my bikes.

I have had brake fade on a disc brake on my light touring bike, I have resin pads on that brake.   Before I do a bike tour with more weight on the bike, I plan to switch to semi-metallic pads.  I put the softer resin pads on for better braking, most of my riding is in areas without much relief so I almost never have to worry about overheating my brake.  Do you have the right type of pads for the best heat dissipation and high temperature performance on your disc brake?

I know you asked about drums and I was silent on that.  My only Sturmey Archer drum brake experience is I am quite sure irrelevant, as it is on a 1966 three speed hub.  And I would have no clue if such a front drum brake would have better performance than adding a disc to the front.

Does the manufacturer think that the fork is strong enough for adding a brake to the hub on that bike?  Does the manufacturer of your tandem have any other ideas? 


hendrich

  • Jr. Member
  • **
  • Posts: 78
Re: Brakes with heat capacity
« Reply #3 on: August 15, 2022, 01:06:05 pm »
Can you put on a larger rotor on your disc brake?  Or, are you already at the maximum size?
For your rim brakes, Koolstop Salmon are generally considered the most grippy of the rim brake pads.
Does the manufacturer think that the fork is strong enough for adding a brake to the hub on that bike? 

Yes, max 200 mm rotor with semi-metallic. Koolstop pads on cantis. I will discuss with the builder, but I am trying to gather information from knowledgeable sources before doing so. Thanks.

hendrich

  • Jr. Member
  • **
  • Posts: 78
Re: Brakes with heat capacity
« Reply #4 on: August 15, 2022, 01:13:21 pm »
I've never ridden a tandem so my assumptions may be wrong, but I thought the purpose of a rear drum brake was as a drag brake rather than deceleration?  Wouldn't doing that on the front seriously mess with the steering? 
I don't know what the Hope solution you refer to is? I know that some rotors and pads are better at dispersing heat than others, I'm doubtful that any would be up to being used as a drag brake on a long decent.  I've never had hydraulic brake fade, I've never pushed the system to anything like the point where that might happen.  The reports of it I've read are frightening, almost complete brake loss without warning!

Your question regarding front steering is good (perhaps?). On a Rohloff, Thorn adopted a Hope hydraulic made for downhill mtb. The rotor has twice the thickness (2x heat capacity) and is ventilated. Thorn's hydraulic cable routing through detachable clips was innovative (I thought). The heat capacity is higher, but I know a drum is far superior (at least an Arai).
« Last Edit: August 15, 2022, 01:15:07 pm by hendrich »

JohnR

  • Hero Member
  • *****
  • Posts: 675
Re: Brakes with heat capacity
« Reply #5 on: August 15, 2022, 01:41:54 pm »
I've got no tandem experience but there is some interesting discussion about tandem brakes at https://santanatandem.com/brake-tech/ and some comments about disc brake heat build-up at https://www.cyclingweekly.com/news/product-news/is-heat-build-up-in-disc-brakes-something-to-worry-about-310878 .

martinf

  • Hero Member
  • *****
  • Posts: 1129
Re: Brakes with heat capacity
« Reply #6 on: August 15, 2022, 08:51:38 pm »
Recent posts have suggested Sturmley-Archer drums are good.

Though I liked their lack of maintenance and their rain-proof features, my own experience using 70 mm Sturmey-Archer drum brakes suggests that they aren't really better for heat dissipation on long hills than other brake systems (except for coaster brakes, which IMO are worse on long hills).

70 mm drums got very hot on short steep descents when I applied the brakes continuously.

The Atom hub brake I had on a tandem was much better at heat dissipation, but it was bigger and heavier. I reckon about twice the weight. I used this as a rear drag brake in combination with cantilevers, but didn't do any mountain riding with it.

Sturmey Archer made (maybe still do) a 90 mm drum brake, this should be better at heat dissipation than the 70 mm version I had. But I don't know if it would be sufficient for mountain descents with a tandem.

hendrich

  • Jr. Member
  • **
  • Posts: 78
Re: Brakes with heat capacity
« Reply #7 on: August 15, 2022, 09:10:58 pm »
Recent posts have suggested Sturmley-Archer drums are good.

Though I liked their lack of maintenance and their rain-proof features, my own experience using 70 mm Sturmey-Archer drum brakes suggests that they aren't really better for heat dissipation on long hills than other brake systems (except for coaster brakes, which IMO are worse on long hills).

Thanks for your comments, I would use the 90 mm version in addition to rim brakes. I would expect the drum to get very hot. Our old tandem had an Arai, many times so hot I could have cooked eggs on it. However, it never failed and required minimal maintenance over more than 70,000 miles.

Is your SA drum on the front, do you have any steering issues while braking? Does the cable interfere with panniers, racks or fender stays?

hendrich

  • Jr. Member
  • **
  • Posts: 78
Re: Brakes with heat capacity
« Reply #8 on: August 15, 2022, 09:17:58 pm »
I've got no tandem experience but there is some interesting discussion about tandem brakes at https://santanatandem.com/brake-tech/ and some comments about disc brake heat build-up at https://www.cyclingweekly.com/news/product-news/is-heat-build-up-in-disc-brakes-something-to-worry-about-310878 .

Thanks, I am aware of these. Santana does not deal with heavy touring considerations, nor Rohloff configurations.

martinf

  • Hero Member
  • *****
  • Posts: 1129
Re: Brakes with heat capacity
« Reply #9 on: August 16, 2022, 11:20:33 am »
Thanks for your comments, I would use the 90 mm version in addition to rim brakes. I would expect the drum to get very hot. Our old tandem had an Arai, many times so hot I could have cooked eggs on it. However, it never failed and required minimal maintenance over more than 70,000 miles.

Is your SA drum on the front, do you have any steering issues while braking? Does the cable interfere with panniers, racks or fender stays?

I no longer have the bike that had the SA 70 mm drum brakes. It had a front drum brake and a rear 3-speed internal gear/drum brake.

On the front, the main issue I can see is the strength of the forks. A hub brake puts more force on the fork than rim brakes do, for the SA drum this is probably slightly less of a problem than with a disc brake as the reaction arm is quite long so puts the force further up the fork. This reaction arm goes on the inside face of the fork blade, it might interfere with the anchor points for a low-loader front rack. I had no problem with fitting mudguards (fenders).

The reaction arm puts all the braking force on one side. So if the forks aren't strong enough they would either deform temporarily, affecting steering, or permanently, in the worst case breaking either at the fork crown or the point where the reaction arm is fixed to the fork blade. This would be more of a problem with the more powerful 90 mm version and I would not want to fit this to a tandem fork not designed for hub brakes. I believe that a fork designed for disc brakes ought to be OK, but it would be better to get advice from a framebuilder.

I had no problems at all with the 70 mm version, but the bike was used mainly for short rides in an urban setting, although I did test it's performance on (short) steep local hills. I would not have considered using my 70 mm hub brakes for a loaded tourer with long mountain descents.

On the back, the force goes to the left chainstay, which is (usually) triangulated so can resist the braking force more effectively than a front fork. The reaction arm for a rear SA hub brake is shorter, and fits under the chainstay, so no interference with rack or mudguard fittings. A possible issue with mine would have been the braking heat melting the grease for the hub gear internal, but this never happened.

On very long, steep descents, these SA hub brakes might get hot enough to cause either brake fade (drums expanding, brake shoes getting too hot) or melting of the wheel bearing grease leading to damage to the bearings. Due to the design of the SA hubs, IMO the latter problem seems more likely than with an Arai, or even the old Atom rear hub brake I had on the tandem.

SJS sell a replacement for the Arai, with 108 mm diameter drum. But it doesn't look as if it would fit a Rohloff hub.

I also use roller brakes, on the rear on my wife's main bike and my "new" utility bike, where they replace respectively an ineffective long reach calliper and a U-brake (this picked up too much road dirt and then sprayed it onto the chain). I don't like roller brakes as much as rim or drum brakes, the braking action is not so good, they tend to "grab". So I wouldn't like to use them on the front. Another disadvantage of roller brakes is that they use a special grease inside the brake itself, so they need more maintenance than drums.

On the rear, they have the advantage of being compatible with the Nexus 8 Premium hubs. It isn't possible to use a drum brake on these, although I could maybe have used the more expensive solution of Alfine 8 plus disc instead.

The rear roller brake is powerful enough to stop my utility bike and loaded trailer with an all-up weight of about 190 kg max.

Although a recent model roller brake should be quite good at heat dissipation (heavy, with cooling fin) it wouldn't be an option on long steep hills with a loaded tourer or tandem. I tested an older version of a roller brake on an old Moulton about 15 years ago using just the rear brake continuosly on a moderately long steep hill and the grease ran down the spokes onto the wheel rim. New versions would be slightly better, but IMO they would do the same when they got hot enough.

________________________________

Maybe the solution for a Rohloff touring tandem would be good rim brakes (cantilever , V-brake or the Magura hydraulics) combined with front and rear discs ? Twice the braking power of a solo for about twice the weight.

JohnR

  • Hero Member
  • *****
  • Posts: 675
Re: Brakes with heat capacity
« Reply #10 on: August 16, 2022, 12:16:24 pm »
Lateral thinking: Would letting some air out of the tyres at the start of a long descent increase the rolling resistance and reduce the load on the brakes?

hendrich

  • Jr. Member
  • **
  • Posts: 78
Re: Brakes with heat capacity
« Reply #11 on: August 16, 2022, 02:09:21 pm »
On the front, the main issue I can see is the strength of the forks.

Thanks for your detailed comments. Our fork is very strong, but I am checking with the bike maker. I agree that heat melting the grease could be a concern. We have very good canti rim brakes.  I suspect that the front drum would add a significant amount of braking capacity to the total braking capacity. Two rim brakes and a SA drum would be significantly better than 2 rim brakes and a standard 200 disk (on Rohloff). Perhaps I will keep the disk, but then 4 brake levers is complicated. The stoker currently controls 1 brake.

PH

  • Hero Member
  • *****
  • Posts: 2279
Re: Brakes with heat capacity
« Reply #12 on: August 16, 2022, 05:28:36 pm »
Lateral thinking: Would letting some air out of the tyres at the start of a long descent increase the rolling resistance and reduce the load on the brakes?
That would be an easy experiment - I'm guessing, I'd but money on it, that the answer is yes, but the amount is tiny, possibly even too small to quantify.

mickeg

  • Hero Member
  • *****
  • Posts: 2688
Re: Brakes with heat capacity
« Reply #13 on: August 16, 2022, 05:57:50 pm »
... Perhaps I will keep the disk, but then 4 brake levers is complicated. The stoker currently controls 1 brake.

The disc is there, nothing wrong with keeping it, and considering your goal was great braking on steep downhills, I would not drop the disc.

There are brake levers that control two cables.  It would take some effort to get your cable adjustment just right, but it is possible.  That said, I have not seen any drop bar levers for some time that can do that, not sure if they are still made.  We do not know if you have drop bars or flat bars.

If I was going to set it up that way, I would put both front brakes on the same lever, as there may be situations like sand on pavement or other poor traction where you would not want to lock up a front wheel, thus you still have two levers on the rear.  That by itself is a good reason to keep the disc, as if you have to occasionally rely on rear braking, best to keep your second brake that you already have.


hendrich

  • Jr. Member
  • **
  • Posts: 78
Re: Brakes with heat capacity
« Reply #14 on: August 16, 2022, 08:27:26 pm »
The disc is there, nothing wrong with keeping it, and considering your goal was great braking on steep downhills, I would not drop the disc.

Thanks, yes, keep the disk. I'm thinking to use a Sunrace M90 Friction Thumbshifter for drum control. The lever would not interfere with other controls. Perhaps I could "set" it on steep grades without my thumb having to hold it.