Canti's or V-brakes for new touring frame

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horizon
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Location: Cornwall

Re: Canti's or V-brakes for new touring frame

Postby horizon » 2 Mar 2018, 4:40pm

Sweep wrote:And of course it is always possible that you might have to replace a front wheel on tour for reasons other than the terrible crime of using rim brakes and having them chew your rims away.

And, I presume, finding a suitable dished front wheel to drop in rather than a bog standard front wheel, might be more of a problem?


When my rear wheel collapsed on tour a kindly local bike rental place fixed me up with an old but normal rim brake wheel. But they had to search around and even swap a wheel off a hire bike (I said they were kind!).

Having said that I only have rim brakes apart from the drum on the tandem. But that leaves 700c versus 26" and maybe a few other subtleties as well.
Let's just get Brexit done so that we can get on with the important job of re-joining the EU!

Brucey
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Re: Canti's or V-brakes for new touring frame

Postby Brucey » 2 Mar 2018, 5:51pm

Sweep wrote:
Brucey wrote:
2) disc brake front wheels are dished (by an amount that is comparable to a rear wheel).



And, I presume, finding a suitable dished front wheel to drop in rather than a bog standard front wheel, might be more of a problem?


the wheel is dished (wrt to the hub flanges which are not symmetrically disposed in most disc brake front hubs) rather than offset.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

MikeDee
Posts: 576
Joined: 11 Dec 2014, 8:36pm

Canti's or V-brakes for new touring frame

Postby MikeDee » 2 Mar 2018, 8:18pm

RickH wrote:
MikeDee wrote:You should look at the Santana website. They take a dim view of disc brakes on tandems because they can't take the heat and there are no tandem approved disc brakes on the market, which should tell you something.


Tells you that no-one has made a disc brake specifically approved for tandems.

Santana seem to be in a small minority.

A quick look at a couple of tandem suppliers websites JD Tandems & The Tandem Shop shows quite a few brands with discs on at least some of the range. I don't think there is one brand with no discs at all. Here's a list of the brands on those sites that have models with discs:-
Orbit
Cannondale
Cyfac ( pricey full carbon fibre)
Hase Pino (semi recumbent tandems)
Landescape
Co-motion
Circe (small wheel tandems & triplets - the brakes probably aren't "approved" for triplet use either! )
Ridgeback
(Dawes - the Galaxy Twin has Vs front & rear plus a rear disk)

I've had a Circe Helios with discs since 2010 - that had me sold on discs. My other 2 regular rides are both disc bike - my regular stoker's Cannondale tandem & my Kona Sutra Ltd. I think the only bike I've ridden in the last 12 months that didn't have disc was a (free) go on a Mobike in Manchester which had hub brakes.

I don't miss rim brakes in this part of the world - steep hills & abrasive grit that will wear out a Mavic Open Pro in around 4000 miles & leave a horrible grey sludge running down the frame every time you ride in the rain. And, before you ask, I'm not a brake dragger - I prefer to let the bike run where I consider it safe to do so.


Do you think you can ride your tandem down Mt. Ventoux and not experience brake problems?

https://tandemgeek.wordpress.com/2011/0 ... ou-prefer/

Brucey
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Re: Canti's or V-brakes for new touring frame

Postby Brucey » 3 Mar 2018, 9:34am

going down big hills is a special case so far as the brakes are concerned and it is one that many bicycle disc brakes struggle with, even on solo bikes. Even a twisty 1000' descent (think of the south downs rather than the alps) is enough to boil the brake fluid in some hydraulic systems and/or get discs hot enough to turn blue-coloured, and that is on a solo bike. On loaded touring bikes and tandem bicycles pretty much anything can happen.

About 20-odd years ago it was proposed that a standard procedure was employed for testing bicycle disc brakes. This was equivalent to dragging the brakes down a descent, and was modelled on a real descent down a real mountain road in the USA. None of the then current brakes were able to pass this test. The result of this testing was not that they then went and made better brakes, but that they arbitrarily revised the test so that it was about half as hard.... :shock: . That brakes might pass this test should be of scant comfort to those who ride up and down mountains; there are real roads that you can ride where your disc brakes will probably not be good enough to allow you to descend in safety. This goes double for loaded solos, tandems, etc.

It might be worth giving some attention to a comparison with other (say motorcycle) brakes. A fully loaded motorcycle might comprise the motorbike itself (~200kg), two passengers (~180kg) plus their luggage (~30kg). The brakes fitted are not much more than 'good enough' to allow a long descent to be negotiated in safety (NB the brakes are usually saved by engine braking but you cannot rely upon that). Thus a realistic target for a loaded tandem bicycle (which weighs a little over half as much, say) might be to have brakes that are half as good in terms of their power and thermal capacity. You don't need to be an engineering genius to see that bicycle brakes are likely to be not much more than ~1/4 as good as motorcycle brakes, i.e. about half as good as they should be for tandem use.

Thus tandem bicycles which are sold with just two disc brakes might stop OK in normal use but they are liable to be under-braked when it comes to any kind of long-ish descent where you are likely to drag the brakes on the way down.

BTW I'm not saying that two rim brakes would be better; it takes real skill to safely negotiate hilly terrain on a tandem with just two brakes of any kind. The saving grace in traditional touring tandems has always been the drag brake; if used correctly this usually gives fair warning when it starts to get too hot (smells, smoke and/or fading) and there should be enough in the other two brakes to safely bring the machine to a halt so that everything can be allowed to cool off for a few minutes. Drag brakes normally recover from such episodes without permanent damage arising. To date I've not seen a tandem with a traditional drum brake fitted as well as a rear disc (which ought to be possible with revised mountings) only a rim brake and a disc brake at the rear. However if a rear disc brake is used as a drag brake then there is (regardless of disc size it seems) a pretty fair chance of parts in the brake overheating and causing problems. Overheating problems in disc brakes may (unlike drag brakes which are drum-based) cause problems of a permanent and/or sudden and unforgiving nature.

So in a nutshell, you cannot take it for granted that your (two) disc brakes are going to work OK on big descents that require brake dragging; on a loaded solo it is of real concern and on a tandem bicycle it is very doubtful that the brakes will be good enough unless special (pre-emptive) care is taken. Unlike drum brakes and even rim brakes, the indications that disc brakes are getting too hot are not as obvious and in some cases (such as hydraulic fluid boiling) the brakes can work normally one pull and there can be nothing the next pull, which is incredibly dangerous.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

mikeymo
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Joined: 27 Sep 2016, 6:23pm

Re: Canti's or V-brakes for new touring frame

Postby mikeymo » 29 May 2018, 1:19am

Freddie wrote:Why not drum brakes? Pads last practically forever and they are completely sealed away, unlike discs. No real need for a beefier fork either.


Are you sure? Beefier fork needed here, it seems:

http://smutpedaller.blogspot.co.uk/2014 ... g-bad.html

Brucey
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Joined: 4 Jan 2012, 6:25pm

Re: Canti's or V-brakes for new touring frame

Postby Brucey » 29 May 2018, 7:47am

mild steel fork (that is known for being easy to cold set), 90mm drum, rider deliberately doing stoppies. Not a combination that I'd recommend.

I have not seen or heard of similar trouble when using a good quality (eg 531) fork, a 70mm drum, in normal use.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

gregoryoftours
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Joined: 22 May 2011, 7:14pm

Re: Canti's or V-brakes for new touring frame

Postby gregoryoftours » 29 May 2018, 6:49pm

mikeymo wrote:
Freddie wrote:Why not drum brakes? Pads last practically forever and they are completely sealed away, unlike discs. No real need for a beefier fork either.


Are you sure? Beefier fork needed here, it seems:

http://smutpedaller.blogspot.co.uk/2014 ... g-bad.html

Ah I think that guy just never noticed he owned a beautiful hetchins fork.

dragonrider
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Location: Harrogate

Re: Canti's or V-brakes for new touring frame

Postby dragonrider » 30 May 2018, 10:13pm

Interesting reading all the conjecture re the use of discs on a tandem. Really the answer is just how hard you go at the descents and anybody can overheat virtually any brake if they try to. Wife and I did a Norway CTCtour on a fully loaded (four panniers and a rack bag) Santana tandem. The brake set up was V brake at front, V brake at rear with stoker operation on a bar end lever and a 203mm BB7 disc operated by the driver as normal rear brake.

We never experienced overheating and I think I am a “brisk” downhiller. Conscious of the consequences of heating up the rims/tyres too much I used the rear disc to cream off most of the speed between hairpins. JD Tandems advised that in extreme circumstances they have known the red adjuster wheels melt on a BB7 but we never experienced that and the brakes had not used a set of pads up after two weeks of Norwegian passes.

I think there is a lot of worry and understandably so with brakes, but honestly in my experience you need to be a competition MTB downhiller to get trouble on cable operated discs.

However, hydraulic discs on a tandem is another story! I did boil the fluid on our tandem and we nearly came a very nasty cropper descending Park Rash down to Kettlewell. I went to cable operated discs after that.

Brucey
Posts: 36116
Joined: 4 Jan 2012, 6:25pm

Re: Canti's or V-brakes for new touring frame

Postby Brucey » 30 May 2018, 11:03pm

arguably it is the more cautious descender who can get into the worst trouble; the reasons for this are

- going slowly you put more of your PE into the brakes and less is dissipated against air resistance

- the cooling effect of airspeed goes as the square or the cube of the speed of the bike, i.e. the brakes are better cooled when you are going faster.

However the brakes also radiate heat, and this is not airspeed dependant; thus if you descend very slowly (5
mph or so) your brakes probably won't overheat as badly either. The worst technique (that makes your brakes hottest) is to drag your brakes down a long descent at some modest speed like 15mph or so.

cheers
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Freddie
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Joined: 12 Jan 2008, 12:01pm

Re: Canti's or V-brakes for new touring frame

Postby Freddie » 31 May 2018, 1:51pm

gregoryoftours wrote:Ah I think that guy just never noticed he owned a beautiful hetchins fork.
That is the Bates fork you are thinking of, Hetchins are curly at the other end.