Disc brakes vs rim brakes on front tandem wheel

[GrumpyBob]

I wouldn't use a rim brake as a drag brake on a tandem. If I'm concerned about rims or discs overheating, I just alternate between the brakes (2 x V-brakes, 1 x disc). And I would not be keen to go tandem touring on a tandem with only two brakes (unless it was in an amazingly flat landscape). I do have a tandem with only two brakes (both cantilevers) but that's not for loaded cycling.

The only problems I've had with rims overheating have been when the Arai drum brake on the Dawes wasn't working - two occasions when the front tyre blew off the rim due to overheating (once near the bottom of Ben Lawers, and once at the bottom of the Chevin near Otley) in both cases at about 25mph. Fortunately we didn't crash either time, but it definitely gets the adrenaline running.

Robert

[frankenthorn]

The second way is to brake hard at the last moment  rather than gradual braking. This applies on the hairpin roads you get in the Alps.

Not riden a tandem (in the Alps or elsewhere) but I used to turn the hub-dynamo powered lights on when descending on my 'bent.  Yes, the SON is probably too efficient for this to make much difference but every little helps! 

Thorn say that front disc brakes on tandems require forks so beefy that they give poor ride quality. Others may disagree.

Can't help thinking the disc-brake solution would be twin discs on the front end (activated off the same lever) and having actual suspension to restore the ride quality missing due to the required beefy fork.  Not massive MTB style suspension obviously, but more Moulton-esque to take the edges off.  Alas no-one makes such a creation ...

[Kim]

The second way is to brake hard at the last moment  rather than gradual braking. This applies on the hairpin roads you get in the Alps.

Not riden a tandem (in the Alps or elsewhere) but I used to turn the hub-dynamo powered lights on when descending on my 'bent.  Yes, the SON is probably too efficient for this to make much difference but every little helps! 

My experiments with a DH-3N80, descending a gentle slope at a steady ~15mph suggest that the drag from the dynamo lighting is equivalent to moving your hands from the tops to the sides of butterfly bars (that is, just about measurable on a bike computer).

OTOH, if you're zooming down a hill, having your lights on might discourage someone from pulling out into you.

[Morat]

I don't know how people feel about resurrecting old threads on here.. but...

My experience is limited, but at the upper reaches of brake abuse. I'm stoker in a tandem crew with a total weight of 220Kg (it pays to be honest when pushing the envelope!) and we run two bikes. A very funky LaPierre mountain tandem from (I think) the early 2000s with hydraulic Formula disk brakes front and rear and a 2014 Cannondale Road Tandem 2 with cable operated Shimano Disks front and back.

We've always managed to stop, even though the captain is a bit nervy and likes to ride the brakes on descents until he gets an earful about brake fade. The hydraulics are definitely stronger than the cable disks and JD Tandems fitted an extra brake to the Cannondale for this season - that bike now has two disks and a backup V-Brake on the front (there was no suitable mount on the back).

I don't usually ride on the LaPierre anymore, the Cannondale was our reward for dropping from 254Kg, and it is mainly used offroad by the Captain and his wife but even when we were at full Lard and cycling round the Yorkshire Moors, the brakes were solid.

Have we had to use the drag brake? Only as a hand-brake so far - but I suspect it isn't too far away. The Shimanos need regular tweaking, where the Formulas just keep on trucking between disk/pad changes.

[321up]

All contributions to this thread are welcome, different people have different experiences riding in different conditions and it's valuable info to know what can work and what problems people have had.

We had an opportunity to test our brakes on three 1:3 descents at the weekend:  Rosedale Chimney Bank, 'Delves' near Egton Bridge and Limber Hill near Glaisdale.  We were fairly lightly loaded on an Audax (medium sized saddle bag and small bar bag).  We descended the steepest sections slowly (~5-8mph) due to hairpins and to allow time for the heat to dissipate.  Our cable operated front rim brake and rear disc (203mm rotor) were fine.

[Morat]

Chimney Bank eh? "Chapeau!"
My captain flat out refused to consider it.
I don't think the friendly ex - tandem rider in the Lion Inn on Blakey Ridge helped when told us how he faded  his brakes on Chimney Bank and hospitalised his wife. One day

[321up]

I had cantilevers fitted as front brakes on our new Landescape tandem but found that they were not as effective as I expected (i.e. required a lot more force on the brake lever than I expected).  I compared the brake lever cable pull and cantilever pivot post position with my other machines and found that the new 10 speed Ultegra levers pulled a bit more cable (compared to 9 speed Tiagra levers) and the cantilever pivot posts are a bit lower on the Landescape (brake blocks fitted higher on the calliper).  Both these factors combine to require significantly more force on the brake lever.  Our Orbit has mini-v-brakes with 80mm arms and I calculated that I would need 95mm arm v-brakes to compensate for the different cable pull and pivot position on the Landescape.  I fitted TRP CX9 direct pull brakes and these work very well.  The longer calliper arms required on the Landescape have the advantage of allowing more mudguard clearance than we have on the Orbit.  So differences between brake levers and the position of the pivot posts will dictate which calliper will be most effective.

Our rear brake on the Landescape is a TRP Spyre with a Hope floating rotor.  The construction of the floating rotor gives little clearance in the calliper but it seems to be ok.  The TRP Spyre is easier to adjust as the pads wear than the Bengal calliper on our Orbit.

Both brakes got thoroughly tested over the weekend including several 1:3 descents and worked very well in the wet and dry.  We are using Swissstop RxPlus GHP II (green) pads on the front brake.

Landescape tandems are usually supplied with front and rear disk brakes but they added cantilever bosses to the forks for us.  So our forks also have a disk mount which is currently unused.  I decided to have the front wheel built with a disc version son28 dynamo hub so I had the option to try a front disc brake in future.  Contra to what I expected the Landescape disc compatible forks give a less harsh ride than the cantilever only forks on our Orbit and it's hard to see by eye if the front wheel is dished at all.  So the comfort and handling don't seem to be affected by the disk forks & hub.

[gavcos]

Hope you don't mind me asking what rear hub and rims did you go for on
Your new build? My spare Phil wood  rear hub is starting to play up.

I too have just change to trp mini v brakes from campagnolo cantis so much
Better.

[Morat]

We found the limit last night! 25% downhill of about half a mile. The disks plain overheated. Luckily there was a t junction and an escape option at an opportune moment or the next half of the hill would have been far too exciting.
The road was quite meandering so we'd had to do 3-4 heavy "brakings" to make it round corners before they gave out.
Later testing on the V brake showed it slows up to about 11-12 mph on a 20% hill on its own, which should be fine if Captain remembers to use it in advance.

[L CC]

We walked down this hill.
If it had been wet I'm not sure we could've stopped!

[321up]

We found the limit last night! 25% downhill of about half a mile. The disks plain overheated.

hydraulic callipers?  what type of brake pads?  Glad that you are ok.  I've not been brave enough to try a front disk brake yet, but we have the fittings on our Landescape and I've got a cable operated TRP Spyre ready to fit for the winter.  I've not yet decided which pad type is best.  Our only experience is with semi-metallic pads on Bengal & Spyre rear disk's which have been ok for us thus far.  The Bengal pads seem to have a greater metal content and wear less quickly than the pads supplied with the Spyre's.

[Morat]

We found the limit last night! 25% downhill of about half a mile. The disks plain overheated.

hydraulic callipers?  what type of brake pads?  Glad that you are ok.  I've not been brave enough to try a front disk brake yet, but we have the fittings on our Landescape and I've got a cable operated TRP Spyre ready to fit for the winter.  I've not yet decided which pad type is best.  Our only experience is with semi-metallic pads on Bengal & Spyre rear disk's which have been ok for us thus far.  The Bengal pads seem to have a greater metal content and wear less quickly than the pads supplied with the Spyre's.

Thanks!
Shimano R515 mechanical, stock pads. The captain swapped from drops to flat bars with Ultegra flat bar shifters/levers. I don't know what the stock pads are actually made of, I'll see if I can find out. I'd certainly be interested to see if there are options which are more resistant to fade!
The rear disk is 200mm, I think the front is the same.

Captain hadn't been using the drag brake (V brake on a sort of ratchet lever), so I think this little incident will change his mind. Annoyingly, the drag brake has to be on the front on this bike (Cannondale RT2) because there's no way to fit a rim brake to the back. I think the captain may have got Bling Brain when he bought this bike

[The French Tandem]

Shimano R515 mechanical, stock pads. The captain swapped from drops to flat bars with Ultegra flat bar shifters/levers. I don't know what the stock pads are actually made of, I'll see if I can find out. I'd certainly be interested to see if there are options which are more resistant to fade!

Mechanical disk brakes are supposed to be more resistant to fade than hydraulic ones, so if you experienced that with mechanicals, I don't think there is a better option.

Annoyingly, the drag brake has to be on the front on this bike (Cannondale RT2) because there's no way to fit a rim brake to the back.

If there is no provision for rear rim brake, you can rely on bolt-on calipers. Google "Bolt on canti bosses" for plenty of suggestions.

[Morat]

Actually the Disks are BB7s, I'm probably going to investigate ceramic pads.
We tried the drag brake on a pretty decent 17% downhill last night (Settringon High Street for anyone near York/Malton). It did very well, but I thought I'd better check the front wheel when we reached the bottom and the front tyre was definitely pumped solid, noticeably even harder than the 110PSI it normally runs at and the rim was untouchably hot.
It's good to know the limits, but with the rim brake and the two disks I think we're pretty well covered now.
Famous Last Words!

[P Walsh]

On the subject of overheated rims (leading to possible blow-outs) with rim brakes, I recently toured Provence with my wife and daughter and my touring bike had very old Rigida Grizzly CSS tungsten carbide impregnated rims, intended to reduce rim wear (which they do, practically to zero) and to dissipate heat. On a few very long descents with lots of braking I had to stop and wait for the others, and I took the opportunity to touch the rims to judge the heat build up. They were barely warm. The wife's ceramic coated Open Pro rims were also quite cool, but my daughter's plain alloy rims were hot.

The CSS Grizzly rims do seem to deal with the heat problem. The drawback (apart from the price) is poor wet weather braking for the first few thousand kilometres of use, even with the recommended Swisstop pads, but I have been told that Koolstop Salmon pads deal with this. My rims are now worn in and work well with any pad. No rim wear, very slow pad wear, and good effective braking with my cantis.

This is all on a tourer, not a tandem, of course.

[The French Tandem]

tungsten carbide impregnated rims, intended to reduce rim wear (which they do, practically to zero) and to dissipate heat.

I'm a bit surprised by this claim. Tungsten carbide is certainly a wear resistant material, but I didn't know about the heat dissipation properties. Are these rims heavier than normal alloy rims? The weight might explain why they are so good!

[Asterix, the former Gaul.]

Has anyone decended Rosedale Chimney on a tandem?  How did your brakes cope, and what brakes did you have?

Going up is far more fun - at the other side, there's a wonderful downhill to Hutton-le-Hole.

Agreed, I always buy myself an ice cream at the bottom and eat it as I walk up. 

[P Walsh]

CSS (tungsten carbide) Grizzly rims (at least, at the time I bought them) are / were lighter than the non-CSS version because the toughness of the braking surface means that the manufacturer does not have to anticipate rim wear. The heat dissipation is a well known attribute and was the main reason I chose them.

The main problem with these otherwise excellent rims is that after the initial period of good braking (sometimes with squeal) they enter a phase of poor wet weather braking. I have since been told (by a reputable source) that Koolstop salmon brake pads are the cure. Later, the rims work well in all conditions with any old pad. And after many thousands of miles of all weather use (20,000 miles is a reasonable guess) my CSS Grizzly rims show no sign of rim wear and have been transferred to new hubs. Yes, the rims have outlasted the hubs and look good for thousands of miles yet. The braking surfaces are still flat. Brake pads also wear less than with normal alloy rims.

I think one of two things will finally finish off these rims. Firstly, accident / impact. And secondly, fatigue.

[The French Tandem]

I must give them a try, as we will soon need a new pair of tandem wheels. Thank you for the info, Mr Walsh!

[DaveJ]

Isn't it to do with the "On a few very long descents with lots of braking I had to stop and wait for the others"?  A slower descent is going to generate more heat.

[mrcharly-YHT]

Do the tungsten carbide surfaces dissipate heat *better* or *worse* than aluminium?

Aluminium is a very good conductor of heat, it could be that tungsten carbide surfaces take a lot more heat energy to reach the same temperature.

Or it could be that they are lousy conductors of heat, so more of the heat energy is being absorbed by the pads.

[P Walsh]

No, those rims have never felt hot after descents. On another bike I have Open Pros which get hot really quickly. I check quite often because in 1996 I succeeded in overheating a rear rim through excessive braking (I now know better) in the French Alps. The tube blew at about 40mph and the tyre wrapped itself around everything except the rim. Bringing the bike to a halt before the next hairpin with the back wheel jammed and sliding on alloy was interesting.

I don't know why the tungsten carbide rims stay cooler, but they do. Probably a bit like the ceramic discs that supercars are fitted with.

[DaveJ]

The discs on some high performance cars are made of composite because they handle high temperatures MUCH better than steel, not because they don't get hot.  They do.  I remember marvelling at the orange glow coming from inside F1 cars wheels in the dim and distant days when they were still to be seen at Brands Hatch.

[The French Tandem]

I got the numbers from my old and dusty heat transfer textbook:

specific heat of aluminum: 903 J/kg*K
specific heat of tungsten carbide: 200 to 480 J/kg*K

These are very perplexing numbers.  What it means is that it takes 2 to 4 times more energy to increase the temperature of a given mass of aluminum, compared to a similar mass of TC, or, in other words, given two rims of equal mass, the TC rim should get 2 to 4 times hotter than the Al rim under similar braking conditions. I do not question your observations, P Walsh, but there must be something else that I don't understand. 

[P Walsh]

Yes, the physics beats me too. Current info on CSS rims makes no mention of heat, but I bought mine after Thorn made claims for CSS rims on their tandems as a way of dealing with heat on long steep descents. But even Thorn are not mentioning this at present. But, as I say, when I touch the rims out of interest after protracted braking (on a tourer, not a tandem) I find them warm at most, never hot. And that was the case during a recent tour in Provence when I was carrying about 24kg of baggage on twisty hairpinned little cols with long stretches of 10% or more. My Open Pros would have been hot on those descents.