Canti's or V-brakes for new touring frame

For discussions about bikes and equipment.
User avatar
Sweep
Posts: 5805
Joined: 20 Oct 2011, 4:57pm
Location: London

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

Postby Sweep » 1 Mar 2018, 5:24pm

Colin_P wrote:. If you are out in the wet and and grit and do a few miles then wheels wear out quite quickly, I'd go through a set every 2,000 miles.


I would never pretend to be technical but your wheels used to wewar out after 2,000 miles?

That sounds extreme.

What sort of riding were you doing and with what sort of rims?

Could you wear out a pair of Sputniks in that mileage?

I ask with some concern as I have two bikes with them.
Sweep

AndyK
Posts: 807
Joined: 17 Aug 2007, 2:08pm

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

Postby AndyK » 1 Mar 2018, 8:42pm

Brucey wrote:IIRC in one of his columns Zinn estimated the increased frameset weight alone to allow discs to be fitted would be in the order of 400g or something. That seems a pretty reasonable estimate to me; there are parts of a disc brake frameset that unavoidably see much, much higher stresses than in a rim brake frameset and you cannot withstand those stresses safely without having more material in there, simple as that.


I was curious about this so I just did a quick bit of googling for actual numbers.

Frame & fork: Surly's 2016 catalogue quotes exactly the same frame and fork weights for the disc and non-disc versions of their Long Haul Trucker - though they only go to one decimal place of Kg, so we could infer that they're hiding a difference of up to 100g. I think they're generally regarded as reputable manufacturers and the LHT in both variants has a reputation for reliability.

The Thorn Cycles catalogue has much to say about the different construction of disc and non-disc forks (and how much less comfortable disc forks are) before revealing that its 700C Reynolds Super Tourist disc fork is 113g heavier than the non-disc model. I can't find separate frame weights; however given the rear triangle has to undergo huge forces on any bike, I don't see why it should be much different for a disc frame. But let's add a bit, and say that a disc frameset might be 200g heavier than the non-disc. Or zero if you believe Surly.

Brake callipers, pads, rotors: Surly's LHT models come with Avid BB7 Road disc brake (329g per brake including a 160mm rotor) or Avid Shorty 4 cantilevers (157g per brake - I'm assuming that includes the pads, as it's sold with them.) So that's 171g difference, x 2 for front and back: 342g. Call it 350g.

Brake cables: OK, slightly longer. An uncut inner cable weighs 20-25g (Jagwire catalogue) while outer clocks in at 30-60g per metre (Weight Weenies). Compressionless brake cable might be a little heavier than spiral, of course - I can't find a figure right now. Say an extra metre is needed on a disc-equipped bike. Being generous that's up to an extra 70g.

Hubs: In Surly's 2016 catalogue it specifies Shimano T670 (365g+121g) on the non-disc Trucker, M756 (496g+302g) on the disc: an extra 312g.

Rims: let's assume no difference (Surly specs the same rims on both models).

Total weight penalty for disc over cantilever rim brakes: somewhere from about 730g (using Surly frame figures) through 930g (Thorn) to 1130g (using Zinn's frame estimate, though I can't find his article online so I don't know where he got his number from).

A simpler example: the current model Genesis Equilibrium 20 has a claimed weight of 9.44Kg. The Equilibrium 20 Disc is 10.28Kg: a 760g difference. Both are similarly spec'd, though the disc model has disc-specific rims which you'd expect to be lighter (no need for extra braking surface to wear away).

So I'm calling it down the middle: on average the weight penalty for using disc brakes is probably a bit under 1Kg. You're both wrong. So is Zinn (gasp).

You're welcome. ;-)

Freddie
Posts: 2329
Joined: 12 Jan 2008, 12:01pm

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

Postby Freddie » 1 Mar 2018, 9:03pm

I have only skimmed the thread, but I thought this had been dealt with already.

Surly frames are mass built in the far east and the disc and non-disc frames are the essentially the same, save the braze-ons. Thorn's forks are really heavily built, expedition touring forks, so they start off weighing a fair bit more than the average fork. I think Brucey's argument was that 1" threaded forks are preferable on non-expedition touring bikes. Thorn's forks are 1 1/8" threadless IIRC.

robc02
Posts: 1667
Joined: 23 Apr 2009, 7:12pm
Location: Stafford

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

Postby robc02 » 1 Mar 2018, 9:15pm

Frame & fork: Surly's 2016 catalogue quotes exactly the same frame and fork weights for the disc and non-disc versions of their Long Haul Trucker - though they only go to one decimal place of Kg, so we could infer that they're hiding a difference of up to 100g. I think they're generally regarded as reputable manufacturers and the LHT in both variants has a reputation for reliability.


I'd noticed this as well. As I posted earlier, a few years ago they did acknowledge a difference in the weights of the disc and non disc frames and forks.
(Furthermore, I'm sure the fork weight they quoted back then was greater than in the catalogue you link to - around 1100g for LHT as I recall. When I built my LHT I weighed the frame and forks and they were just a little heavier than the quoted figures). In the meantime they have, presumably, either decided not to bother differentiating between two similar models, or they have changed the material spec. so that both frames use the same tubing (for economy reasons).
Looking at the size of the front disc mount it is implausible that the forks are the same weight even if using the same fork blades, but I suppose they could be within 100g. Likewise, the rear disc ends which are also quite bulky.
I notice they have also taken to quoting the weight of the smallest frames rather than a mid - sized one.

Freddie
Posts: 2329
Joined: 12 Jan 2008, 12:01pm

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

Postby Freddie » 1 Mar 2018, 9:39pm

robc02 wrote:I notice they have also taken to quoting the weight of the smallest frames rather than a mid - sized one.
Which is a bit crafty, to say the least.

Beyond the brakes I wonder how much weight can be saved if, when riding a larger frame, instead of having a horizontal or mildly sloping top tube, a severely sloping one is used. What difference would it make to weight, as compared to a standard horizontal top tube frame, if you had the equivalent of a 25" frame at the head tube and a 21" frame at the seat tube.

Would this be a good way to save weight and are there any negatives associated with such a setup?

PH
Posts: 7663
Joined: 21 Jan 2007, 12:31am
Location: Derby
Contact:

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

Postby PH » 1 Mar 2018, 10:44pm

AndyK wrote:The Thorn Cycles catalogue has much to say about the different construction of disc and non-disc forks (and how much less comfortable disc forks are) before revealing that its 700C Reynolds Super Tourist disc fork is 113g heavier than the non-disc model.

This is true for the reasons Freddie gives. Thorn also offer a rim brake 700c fork that's 350g lighter than the disk fork, it's not comparing apples with apples, but there is no similar disk option for the reasons they give.

Brucey
Posts: 36074
Joined: 4 Jan 2012, 6:25pm

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

Postby Brucey » 2 Mar 2018, 12:13am

In response to Andy K's post; Zinn's estimate (which I might have remembered wrongly) was for the frameset weight only. Comparing weights is tricky; there is no guarantee that disc and non-disc models from any one manufacturer are similarly optimised.

If you start with an expedition bike it already has stiff forks etc on it so the weight penalty of adding disc brake fittings to the frameset is likely to be small. [Even so it might be about the same as riding an round with a 6" adjustable spanner strapped to the forks and another to the frame , with much of the extra metal placed to further stiffen parts that just makes the ride less comfortable.]

If you start with a light tourer with a steel frame and fork, the penalty of adding discs is somewhat larger; basically you are likely to end up with a fork that is more akin to an expedition fork (in weight and stiffness, if not outright strength per se) whether you like it or not.

The vexed subject of wheels has not been touched on, but (if built with rims and spokes of the same weight) disc brake wheels are likely to be relatively weaker than rim brake wheels. This is for two reasons

1) the service loads in a disc brake wheel are higher (a lot higher in some places) than in rim brake wheels, and
2) disc brake front wheels are dished (by an amount that is comparable to a rear wheel).

Similarly the loads in the LH bearings are absurdly high in disc brake hubs; really disc brake hubs ought to have bearings that are about 3x stronger in the left side than in the right; that so many disc hubs use bearings that are little different to other hubs just means they have eaten into (and often beyond) whatever safety margin there might have been in the design.

If you were to say that the weight penalty of adding disc brakes to a touring bike with a steel frameset varied from about 0.5kg to 1 kg I would find that a reasonable estimate (about the same as fitting SA hub brakes, which are arguably better.... :roll: ) . In the grand scheme of things this weight increase isn't the end of the world, but two things are likely to stick in one's craw somewhat;

a) you are likely to be asked to pay more for the privilege of lugging this extra weight around the countryside and
b) more importantly the ride quality suffers with disc brakes fitted, because a good deal of the extra weight goes into stiffening parts of the frame and fork at the expense of comfort.

Right now I'm glad that we have the choice to make between braking systems; doubtless various ones will suit some folk better than others. But in any event it is unlikely that the choice in good quality parts will be maintained in all systems and this is likely to affect touring bikes most adversely; they tend not to have parts specially made for them, and are commonly built using parts that are really meant for something else but just accidentally work OK on a touring bike. A good example is the disc brake itself; if it were only ever fitted to touring bikes, no-one would have ever bothered to make them.

cheers
-------------------------------------------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

User avatar
The utility cyclist
Posts: 2514
Joined: 22 Aug 2016, 12:28pm
Location: The first garden city

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

Postby The utility cyclist » 2 Mar 2018, 8:02am

MikeDee wrote:Seems to me that arguing about the extra little bit of weight that disc brakes add to a touring bike is a bit silly. Touring bikes, by their very nature, are heavy. They have to be to support racks and panniers and luggage. The little bit of weight that disc brakes add to the overall is tiny compared to the hefty weight of the bike, racks, panniers, luggage, and rider weight. There's more to be considered on a touring bike and that is simplicity. Dealing with a dodgy disc brake while on tour can ruin your day.

Yes there's more to consider, one that is ignored is that disc brakes lure the user to go faster and brake later, inevitably just like in cars some folk run out of talent, grip of the tyres and most importantly thinking time with worse consequences than someone having to go slower because ultimate braking power in x conditions is less or percieved to be less.
Watch how the pro road riders will not crash any less if disc brakes increase in use or are the new standard.
Despite discs being popular we don't seem to have any fewer helmet saved my life stories or any reduction in KSIs since introduction.
Discs will offer no palpable safety benefit just allow users to go faster and have less thinking time to react to stuff.

fastpedaller
Posts: 2138
Joined: 10 Jul 2014, 1:12pm
Location: Norfolk

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

Postby fastpedaller » 2 Mar 2018, 11:06am

The utility cyclist wrote:Discs will offer no palpable safety benefit just allow users to go faster and have less thinking time to react to stuff.


Maybe should read " just allow riders to maintain the (lower due to lugging all the extra weight around) speed for slightly longer before they brake. :lol:

User avatar
The utility cyclist
Posts: 2514
Joined: 22 Aug 2016, 12:28pm
Location: The first garden city

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

Postby The utility cyclist » 2 Mar 2018, 11:34am

fastpedaller wrote:
The utility cyclist wrote:Discs will offer no palpable safety benefit just allow users to go faster and have less thinking time to react to stuff.


Maybe should read " just allow riders to maintain the (lower due to lugging all the extra weight around) speed for slightly longer before they brake. :lol:

That is more accurate, thanks, the effect as I described will and does come to pass though.

User avatar
andrew_s
Posts: 4987
Joined: 7 Jan 2007, 9:29pm
Location: Gloucestershire

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

Postby andrew_s » 2 Mar 2018, 12:48pm

The utility cyclist wrote:Discs will offer no palpable safety benefit just allow users to go faster and have less thinking time to react to stuff.
Do I take it you've never ridden in heavy rain, and found that rim brakes go from OK to very poor?

I've seen a tandem loose control on a steep hill because the rims were getting water on as quickly as the rim brakes were clearing it off. They failed to make the bend at the bottom, and hit a wooden fence stout enough that the tandem was a write-off, and the pilot got a broken pelvis.

A more normal situation might be that some SMIDSY pulls out of a side road in front of you, and the second or three before the brakes bite is the difference between impact and no impact.

Brucey
Posts: 36074
Joined: 4 Jan 2012, 6:25pm

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

Postby Brucey » 2 Mar 2018, 12:59pm

sounds nasty; three brakes is best on a tandem for sure.

Re wet anti-smidsy braking, if you want instant 'bite' then SA drum brakes are far better than discs.

When it is properly wet disc brakes take a fraction of a second (at least) to bite; the disc has to clear the water and then the pad compound has to be hot enough to 'come on'. If it takes just one 700C wheel revolution to clear the disc of water, that is about half the stopping distance afforded by decent drum brakes from ~18mph.

cheers
-------------------------------------------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

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

Canti's or V-brakes for new touring frame

Postby MikeDee » 2 Mar 2018, 3:18pm

Deleted

User avatar
Sweep
Posts: 5805
Joined: 20 Oct 2011, 4:57pm
Location: London

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

Postby Sweep » 2 Mar 2018, 3:56pm

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



thanks for this brucey - I had genuinely never thought of this.

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?
Sweep

User avatar
RickH
Posts: 4557
Joined: 5 Mar 2012, 6:39pm
Location: Horwich, Lancs.

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

Postby RickH » 2 Mar 2018, 4:10pm

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. :D

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 ( :shock: 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.