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Overheating rim brakes -> discs?

Robert Jamison2021-11-09 11:50:32

We tandemed down to Gibraltar and the Spanish mountains are just that - mountains. On descending the first pass the rim V-brakes overheated, melted the plastic rim tape, thus exposing the spoke holes, which caused the tube to explode and the tyre wall to shred for a 4" section, exposing the wires, and we hit the deck. Thankfully we had been slowing up to take a right turn, so impact speed was 20-25kph and we limit ourselves to 40kph. 80km ambulance ride to hospital ensued for a brain scan and help with unpleasant facial cuts and bruises. Thankfully nothing broken or serious. All healed after a week.

We were riding an Ecosmo folding tandem with 20" wheels, Schwalbe (Road Cruiser) tyres and tubes, with 2 panniers and a Burley luggage trailer in tow. All up about 190kg. The brakes had been fairly full on for 2.2km and an average gradient of 1 in 10 according to the map.

Disc brakes then come up for discussion to avoid this problem and unhappy experience. Does anyone know of when disc brakes fail, perhaps through similar over-heating or some other issue?

Perhaps the more familiar (to me) and possibly more robust rubber rim tapes are the simple answer?

Stephen Snook2021-11-09 12:27:25

Glad you are both OK and were not too badly injured by that incident. We have a Swallow which has been through several upgrades since it was first built for us 27/28 years ago. When we first specified it we said that we would be hoping to do some fully loaded touring and exploding rims due to overheating on long descents came up in those initial discussions. We had 26 inch Sun tandem rims back then with Campag record cantilever brakes and a drag brake on the rear wheel. We were offered the advice that when on long descents to have the drag brake on and then alternate front and rear brakes to feather the speed. Also to keep an eye on rim wear generally. We haven't had any rim issues whilst touring at any speed.

Our last upgrade was to change over to disc brakes (amongst other things) which are light years better than the rim brakes at stopping - we no longer have the drag brake. However, we aren't touring anymore - just day rides with a couple of panniers - so we can't comment on disc brake failure due to overheating, but I still use the practice of alternating front and back brakes when on longer descents.

Dmitrii Pasechnik2021-11-09 12:30:55

Proper rim tape is made of 1mm, or thicker, cloth;  bikeshops carry rolls of self-adhersive cloth rim tape. It also allows for far greater tyre pressure; used by touring cyclists with racing size (and pressure) wheels. See e.g.

https://www.amazon.co.uk/Schwalbe-Fabric-Tape-50mx15mm-Workshop/dp/B00J4JIJ5Q

As to disk breaks, we're riding a Circe tandem with 20" wheels and disk brakes, and regularly do longish descends in Chilterns and Cotswolds, without any overheating trouble (well, my stoker is a 30kg kid, though). 

 

Ian McCall2021-11-09 13:47:51

Hi, 

  Very sorry to hear about your accident.

I would go for belt and braces if touring in Spain. I have recently bought a Landescape from members on here, because my old Dawes tandem gave me concerns with stopping.

Disc brakes are way to go. I have 203mm rotors on our tandem, and it is not "over-braked" by any means at all. We can also stop quickly with less risk of locking the wheel..Safer in wet for braking too.

We have a rear coasting rim brake aswell which I will probably convert to a conventional rim brake, and use with a twin pull lever as I would not want to leave a rim brake on for any length of time.

Even big disc rotors can overheat so I avoid leaving them on continually, on descents but use them on and off, to allow for cooling. You can even get larger 223mm rotors, I think Galfer make them, ironically a Spanish manufacturer. The bigger the disc, the more chance to stay cooler I would think, and the more leverage.

 

Wheel size must be a factor on long descents, the bigger the wheel in diameter and width, the more heat it can take . But in my opinion, rim brakes should be a backup.

203mm disc brake rotors are easy to get and can be braked by cable operated brakes, which may be better for touring than hydraulic. But my hydraulic Magura brakes on my solo have not let me down on a tour, yet.

If you have not got braze ons already on the tandem frame (I.e. for disc brakes) there are people who will fit them I think, and I seem to remember there is someone in Derbyshire offering this service. 

 

Wishing you well

Ian and Sue.

Alan Jones2021-11-09 14:11:35

I'll second the brake 'feathering' or cadence braking. If you put the brakes on fairly hard and then release for a couple of seconds, and/or alternate them it will cause the (jerky) disruption of a rapid plummet downhill.

Also - I'm guessing that 20" rims will get hotter sooner than 26" or 700c as there is a little less time for the rim to travel and cool down before it meets the brake blocks again.

Ted Savoie2021-11-09 14:58:43

My comments may not be welcome, but come from owning more than 10 different tandems, and having been "tandeming" for the last 63 years, using several types and brands of disk brakes, and also drum brakes plus several generations of caliper brakes.  In addition to a lifetime of cycle touring from 2006 until 2020 we had a property in the French alps, and four tandems that lived there with us, we/I have climbed and descended hundreds mountainous roads and have accumulated considerable experience of the "descending" skill set.  Please search the old threads on the TC forum, there are tomes from numerous members including myself re brakes on tandems, covering the points you have raised so I will not repeat myself.

The elephant in the room other responders are skating around is that the machine you are riding is not fit for purpose for laden touring in mountainous regions. A 20 inch wheel tandem with only two rim brakes, laden with crew, panniers plus luggage trailer and no hub mounted brake is not fit for such usage, as you have now sadly experienced yourself.  I am very relieved to hear the outcome was only passing lumps n bumps.

Put simply, riding alpine tours on a 700c or 26 wheel laden tandem without a third brake is do-able by alternating brakes as long as the road surface is dry, and if stopping on longer descents to cool rims.

Your bike has 406mm dia rims, the circumference of which is 53% of that of a 622mm dia "700c" rim, so each cross sectional part of the rim is subject to braking force generating heat almost twice as much as that on rim section on a 700c bike descending alongside you, and the volume of air in the tube  proportionately lower, meaning simply it heats up twice as fast as a full size wheel bike.

I assume, from the information in your initial post, that this is your first tandem but whatever your circumstances please enlighten us as to which tandem specialist shop informed you your machine would be fit for fully laden alpine touring when you purchased it?  I think this information would be worthy of dissemination and follow up, for the safety of other riders. 
I had never heard of Ecosmo before today, a search online reveals that the whole machine can be purchased new direct from Ecosmobike.com for £479.  The sales pitch on the Ecosmo webpage suggests this is really designed as a city folder:
 "Exploring is better when you can share the experience with our fantastic Folding Tandem Bike. Perfect for touring the towns and villages you visit as you travel around the countryside."

Stuart Hibberd2021-11-09 15:10:30

You must remember that whatever type of brake you are using eventually it will fail you given the right/wrong conditions. We have 200mm disc rotors with spyre mechanical calipers and for the most part these are as good a brake as you could hope for on a tandem.

They have only failed to stop us once, this was on a fast down hill run of about a mile on an unknown road with a number of bends where we were slowing from around 50kph 30kph and when we reached the t junction at  the bottom the brakes were doing almost nothing. I think some of the problem was pilot error ie not alternating between the front and rear brakes to allow them a bit of time to cool rather than braking hard with both brakes.

Also I forgot I had a third brake, front wheel V-brake, which I would definitely recommend you fit with your disk brakes as a back up.

Check out the section posted by Matthew Hodges on this post https://tandem-club.org.uk/forum/discussions?id=11268 where he details testing done by Santana on tandem brakes.

 

Graham Wood2021-11-09 15:35:16

Sorry to hear of that - a frightening experience :(

Living in a steeply hilly part of Wales, and having toured with both rim and disc brakes my feeling is that it's not so much the type of brakes you have as carefully managing whatever brakes you have to avoid overheating that is critical.  As has been said, alternating F & R and being prepared to stop and let things cool down periodically if necessary is important. Disc brakes aren't necessarily a panacea - discs and calipers vary widely and can potentially overheat and fade rapidly, warp the discs, vapour lock etc etc.  And whatever brakes, I'd certainly want a third brake on a  thumbshifter as an emergency and parking brake.,

Our previous tandem had rim brakes and an Arai drag brake. Speed control on descents was brilliant, stopping was fine - but rims wore out rapidly.  Our current Thorn has a front V-brake on a CSS rim with a 203mm Hope floating, ventilated disc and four piston caliper on the back which is immensely powerful, confidence inspiring, very easy maintenance, and seems bombproof on even the longest descents. Highly recommended! 

Good luck,

Graham

Martyn Aldis2021-11-10 11:10:10

Lots of good answers already but if you want to look at some numbers Thorn has some here. Tandem braking in mountainous country is a difficult area and when I explain why we cart around an Arai drum brake on our touring tandems some cyclists just don't seem to get it. The Arai used with a ratchet lever is very useful to save wrist strain and rim wear and just a few times we have really needed it on long steep descents.

Any disk rotor has to be large for tandem use (used in rotation with other brakes) but would need to be used very carefully with 406 wheels in normal conditions as it would have huge power. Looking through the Bike Friday forum posts might help. Chain stay clearance can't be taken for granted.

 

Robert Jamison2021-11-10 11:30:56

I am not sure how I managed to create three posts, so I am replying on the one with the most replies.....Thank you for all your contributions, all of them very welcome (Ted!), and for your good wishes. We thank God for the incident being at a 'perfect' time - injuries not serious, but enough to make us pay attention to this issue. It could have been fatal in other circumstances.

Yes we do feather front and back, but on these 9-10km and steep descents both brakes were needed at times. On continuing our journey to Gibraltar we just went down long hills at 10kph and stopped every 30 seconds to check and cool the rims (as this was when the rims generally became too hot to hold a finger to them). Unscientific, but we were super-cautious, and we were then able to enjoy the lovely scenery!

The Ecosmo was indeed our first tandem 4 years ago. We progressed to a 'full size' Simmonsohn after a year, which is a slightly better ride. However, on touring the UK with it, getting hotels to accommodate it each night was very difficult.

This is why we took the folding Ecosmo tandem - modified as to gearing and synchronised pedals btw. City centre hotels (eg. Madrid) can't accommodate a full size tandem. The folding one folds up in 8 -10 minutes and fits (on end) in elevators as small as 1m x 1m floor size for overnight storage in a corner of the room. Our tours of Devon - 1 in 6 hills of 700m into Lyme Regis for example - did mean the rims super-heated, but we were not surprised by this and took it as a fair test. It wasn't, but with no evident problems and never any loss of braking power, the need for researching the issue did not occur to us.

So, in answer to Ted Savoie's very pertinent and helpful request to "please enlighten us as to which tandem specialist shop informed you your machine would be fit for fully laden alpine touring ......for the safety of other riders" you'll be pleased to know the answer is 'no one'.

Thank you Stuart for referral to discussion id 11268 and Matthew Hodges' post, if only for the physics. My initial search for articles before posting this request was clearly faulty. Ted Savoie's further comment therein was also helpful.

Best wishes

Terry Barnaby2021-11-12 08:59:34

On this subject, I did a bit of playing around with the physics/maths and created a simple simulator to show how much heat the brakes on a tandem need to dissipate when braking down a long hill. As above, I also think that having 3 separate brakes on a touring tandem (rim, rim, hub or rim,rim,disk or disk,disk,rim etc but not rim, rim, rim) is essential. The more brakes and larger the braking surface the better so the heat can be dissipated into the air more easily. So large diameter wheels for rim brakes and/or large disks or hub brakes so the heat can be dissipated. I don't think that alternating F & R brakes will have a benefit (can't see a physical reason this would be better apart perhaps from less boiling some hydraulic systems ?).

One thing to note is that your average speed of decent makes quite a difference. Going down at a semi cautious speed is actually the worst for brake temperature. If you see the graphs below, going down slowly or very fast (where the wind resistance is slowing you significantly) looks the best.

The following graph is a rough simulation showing the amount of brake power needed to hold the tandem at a steady speed on the given gradient assuming a very long hill. Based on having 2 brakes that can dissipate this heat at the 2.0 thermal resistance C/W rate, it shows the temperature of each of the bake systems. The thermal resistance C/W rate depends on the type of brakes in use and how well they can dissipate the heat. The initial parameter given is just an idea. Large diameter wheel rim brakes or large area disk brakes will dissipate the heat better and hence run at a cooler temperature. The black arrow indicate the terminal speed with no brakes applied.

Simulator is at: https://tandem-club.org.uk/files/physics

Robert Jamison2021-11-13 11:30:40

Thanks Terry, very very interesting, that's quite a piece of work.

I thought briefly about proposing that we let the tandem and trailer run to the c.96kph equilibrium speed on those long straight / gently curving Spanish mountain descents so that we did not need to use / heat up the brakes, but even I chickened out on that so we'll go for 10-15kph and enjoy the scenery :-)

To get confidence in the coefficients that were used in the model, adjusting our all up weight to 190kg and output to 220W (you flattered us with 400!) does produce the results we experience on the road - ie. about 26-27kph on the flat, 4kph up a 1 in 10 and, removing the luggage to give a weight of 145kg a flat speed of 29kph (done in a 10mile flat TT!).

However, never having had a power meter I have not calibrated (in my mind) effort to watts, so I have no idea if 220W is about right other than TdF riders producing 600-900 and us being no more than a 1/3 rd of their power!

Nevertheless, it was alarming to realise, as you say,, that holding a speed of 40kph was the worse thing to do - and each of 2 brakes reaching 1,000C? Wow! No wonder the plastic rim tape melted.

Moving to 3 brakes, even a descending speed of 15kph seems to produce brake temp of 400C - do you know what the manufacturers of standard disc/pads and rims/pads - and tyres of course - are designed, and hopefully tested, to withstand?

All the best

Graham Wood2021-11-13 12:40:15
The problem to my mind is, though, that unless you are FAR braver than we are the theory of optimum speed / temperature doesn't sit well on the kind of steep lanes that abound across the hillier parts of the UK.  On long main road mountain descents it's fine to let the speed increase and brake short and hard when needed, but on the other hand our North Welsh valley is not uncommon with a descent to our house of a mile and a half down a steep (1 :5 in places) twisting lane rich in blind corners, high hedges, potholes, broken gravelly surface etc etc, and Bwlch y Groes is not too far away!  So plenty of hills where any speed above cautious to semi-cautious risks a different kind of disaster. For all advances in brake technology it sometimes seems that while our current big Hope ventilated rear disc is excellent and confidence inspiring in these condtions it's an expensive and sophisticated thing that doesn't entirely fill the gap left after the demise of Arai drag brakes with their amazing speed control and heat dissipation abilities.
Terry Barnaby2021-11-13 16:55:43

Robert, do note that the brake temperature numbers are based on the thermal resistance C/W number I used which is probably the most random of the default parameters. It is so dependent on the brake type and how well the air cools it etc. so the actual values are likely to be way off. But the trend is still the same, assuming I have the maths right.

Graham, yes on those long steep potholed lanes letting the tandem go is not my idea of fun also (some in the West Country section are braver than me!). However I think my and other peoples tendency would be the semi cautious mid speed rather than go down a fair bit slower in those cases when you don't have huge ventilated disks :)

I agree on the Arai drag brakes, we have those on tandem and tripplet and I find them excellent although I have heard some people have not got on with them.