Disc v Rim brakes

General cycling advice ( NOT technical ! )
andrewk
Posts: 354
Joined: 20 May 2011, 3:19pm
Location: SW London

Re: Disc v Rim brakes

Postby andrewk » 26 Aug 2016, 9:28am

531colin wrote:But I think the light tourer is a fashion victim, and dead as a dodo. STI levers are a fashion imperative, which rules out full-size Vee brakes which are the most sensible brakes for a tourer. You can just bung on a bigger tyre for roughstuff, and get a raised bottom bracket. And all the fashionistas know that cantilevers don't work, so you absolutely need disc brakes to get clearance for more than 25mm tyres. What a crock!


May I take this opportunity to ask for advice...I have a nice to ride bike which is laid up following a couple of incidents due to inadequate braking. It is shod with 37mm tyres (though I would be happy to go down to 35mm or possibly 32mm) and has mini v brakes. Therein the problem, they require constant adjustment which I seem to be unable to get right. (Also wheel removal is a pain requiring deinflation of the tyres since even after unclipping the mini vees there is insufficient clearance.) The bike has Tiagra STIs.
I would like to bring the bike back into service but need to solve the brake issue...I need effective braking that does not require constant adjustment.
My LBS (part of a chain) suggests changing to cantilever brakes. Would this solve the problem? How do I figure out which size I need? Or is there another solution that would give even better braking? BTW the bike is a Spa titanuim tourer.
thanks
Andrew

Brucey
Posts: 35610
Joined: 4 Jan 2012, 6:25pm

Re: Disc v Rim brakes

Postby Brucey » 26 Aug 2016, 9:34am

It would help if you say which model tiagra STIs and which mini-Vs (or at least arm length) you have; both can vary somewhat.

The wheel removal problem ought to be solvable; just fit shorter brake blocks that don't foul with the fork blades/seat stays, thus allowing the brake to swing out more.

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

andrewk
Posts: 354
Joined: 20 May 2011, 3:19pm
Location: SW London

Re: Disc v Rim brakes

Postby andrewk » 26 Aug 2016, 10:05am

Brucey,
The Tiagra STIs are 9 speed triples and the mini vees are of indeterminate manufacture having 8cm arms, the bike being Summer 2012 vintage. Hope this helps.
Andrew

Brucey
Posts: 35610
Joined: 4 Jan 2012, 6:25pm

Re: Disc v Rim brakes

Postby Brucey » 26 Aug 2016, 10:32am

9s tiagra is not a unique identifier per se (there are two different models of Tiagra 9s, 4400 and 4500) but both versions share the same brake cable pull/MA (Mechanical Advantage) which is intended for use with DP calipers first introduced between ~1993-2008.

These levers (when used with mini-Vs) tend to give a (potentially slightly spongy feeling) powerful brake that needs frequent readjustment. If the brake arms are short and the brake bosses are set low on the frame, this can improve matters. However with your setup many people (including CJ IIRC) would happily trade away a little mechanical advantage in return for more running clearance, less frequent adjustments etc.

[BTW you may not feel that the brakes are very powerful at present, but this could be because you are used to it, and/or that the cables, brake blocks etc are holding the brakes back.]

So from where you now there are several approaches that you could perhaps try;

- fit harder wearing/less squashy brake blocks
- fit a shorter-armed mini-V (if you can find one and it will fit OK)
- use less compressible cable housing
- move the STIs so that the brake lever can move further before it hits the handlebar
- fit mid-profile cantis (eg BR-CX50/70, but with a standard straddle rather than the unit link if necessary)
- use a later model of STI

3/6 of these things will reduce the brake MA, i.e. if you don't improve the cables or the friction properties of the brake blocks as well, you will have to pull the lever harder to stop OK.

Later model road STIs (most models newly introduced 2008 or later) have a longer cable pull and a lower lever MA. These levers appear to be a very good match for most mini-Vs. Sora 3500 9s would be a suitable choice to match your extant setup; it'll work the rear mech OK for sure and do check, but I think that the front mech will work OK too.

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

reohn2
Posts: 35939
Joined: 26 Jun 2009, 8:21pm

Re: Disc v Rim brakes

Postby reohn2 » 26 Aug 2016, 11:41am

You could also fit cable accelerators(Travel Agents) and full sized V brakes,which will work well with your STI's,though won't eliminate the clearance issues when removing the wheel unless suitable brake block/pads can be found to allow the arms to open wider.
-----------------------------------------------------------
I cycle therefore I am.

PH
Posts: 7500
Joined: 21 Jan 2007, 12:31am
Location: Derby
Contact:

Re: Disc v Rim brakes

Postby PH » 26 Aug 2016, 12:05pm

As in the quote - are you really that wedded to STIs? Or for that matter drop bars?
It's a shame to have such a bike out of use because you're unhappy with the brakes. I'd choose brakes I was happy with and the other components to go with them rather than the other way round.

PH
Posts: 7500
Joined: 21 Jan 2007, 12:31am
Location: Derby
Contact:

Re: Disc v Rim brakes

Postby PH » 26 Aug 2016, 12:30pm

531colin wrote: Ihave been comparing other bikes/forks with my 631 forks....these are on my bike, which is a light tourer, its not a standard Spa bike....perhaps I should have spelled that out?

No, I don't think anything needed spelling out, you believe a lot of the people you ride with chose some of their clothing and components because of poor bicycle design, nothing there to misunderstand. I’m just curious if you believe the same of everyone who makes similar choices. I’m sure there’s an element of that, though I believe most of it is people think they need to conform to the norm, this forum doesn’t do much to dispel that.
STI levers are a fashion imperative, which rules out full-size Vee brakes which are the most sensible brakes for a tourer.

Another example of it: That touring bike = drop bars. No problem with STIs and V brakes, just consider an appropriate bar for them. In countries where touring's more popular it is the norm. This isn't a criticism of anyone who choses a different bar to me, just that assumption that it's the only choice.

andrewk
Posts: 354
Joined: 20 May 2011, 3:19pm
Location: SW London

Re: Disc v Rim brakes

Postby andrewk » 26 Aug 2016, 12:50pm

reohn2 wrote:You could also fit cable accelerators(Travel Agents) and full sized V brakes,which will work well with your STI's,though won't eliminate the clearance issues when removing the wheel unless suitable brake block/pads can be found to allow the arms to open wider.


What are cable accelerators, how do they work and where can I buy them? My internet search for info only gave results for car accelerator cables and some electronic stuff.

andrewk
Posts: 354
Joined: 20 May 2011, 3:19pm
Location: SW London

Re: Disc v Rim brakes

Postby andrewk » 26 Aug 2016, 1:23pm

PH wrote:As in the quote - are you really that wedded to STIs? Or for that matter drop bars?
It's a shame to have such a bike out of use because you're unhappy with the brakes. I'd choose brakes I was happy with and the other components to go with them rather than the other way round.



Yes it is a shame, to my disgrace following 2 incidents due to inadequate braking (a crash (with no ill effects) and worse still (certainly more embarrasing) bumping another rider's rear wheel with my front wheel whilst stopping on a group ride) I've let the issue slip by way of laying up the bike and using a German flat bar tourer instead which has the excellent Magura hydraulic rim brakes.
However the Spa titanium tourer did ride nicely, very nicely in fact apart from the braking and some front derailleur adjustment issues. The braking problem being the significant issue.

I definitely want to keep the drop bars for their aero efficiency when on the drops and also for variety, my other bikes having flat bars.
I'm not wedded to STI's but would prefer to retain them as they are a neater solution than bar end shifters. The down tube shifters of my youth being a definite no no.

So yes it is a shame to have such a nicely riding bike laid up unused hence my desire to resolve the brake issue .

tatanab
Posts: 3768
Joined: 8 Feb 2007, 12:37pm

Re: Disc v Rim brakes

Postby tatanab » 26 Aug 2016, 1:38pm

andrewk wrote:What are cable accelerators, how do they work and where can I buy them?
Amplifier is a better description than accelerator. It increases the cable pulled at the brake versus the brake lever. Cable from the brake lever wraps on a small diameter pulley - cable to brake leaves from a larger diameter.
http://problemsolversbike.com/products/travel_agents/ Available from St John Street cycles and many others. For use with STI, I suggest you buy ones with adjusters built in. https://www.sjscycles.co.uk/cables/trav ... lack-each/

andrewk
Posts: 354
Joined: 20 May 2011, 3:19pm
Location: SW London

Re: Disc v Rim brakes

Postby andrewk » 26 Aug 2016, 1:56pm

tatanab wrote:Amplifier is a better description than accelerator. It increases the cable pulled at the brake versus the brake lever. Cable from the brake lever wraps on a small diameter pulley - cable to brake leaves from a larger diameter.
http://problemsolversbike.com/products/travel_agents/ Available from St John Street cycles and many others. For use with STI, I suggest you buy ones with adjusters built in. https://www.sjscycles.co.uk/cables/trav ... lack-each/
[/quote]

Thank you for the explanation and links.

Now back to my STI equipped bike brake problem.....(please bear with me, I have limited mechanical knowledge or ability).
As I understand it, these "Travel Agents" would allow me to fit full size vee brakes in place of mini vees.
Would this give better brake performance without requiring frequent adjustment?
Would this give better brake performance than cantilever brakes?

PH
Posts: 7500
Joined: 21 Jan 2007, 12:31am
Location: Derby
Contact:

Re: Disc v Rim brakes

Postby PH » 26 Aug 2016, 4:42pm

I've realised that someone in a group I toured Wales with earlier in the year had the same bike with the same levers and brakes (Well mini Vs, can't be sure they were the same model) he didn't seem to be having any problems and there were enough hills to test any brakes.
Before you go changing too much, is it worth getting someone familiar with this set up to make sure you're getting the best from what you already have?

Brucey
Posts: 35610
Joined: 4 Jan 2012, 6:25pm

Re: Disc v Rim brakes

Postby Brucey » 26 Aug 2016, 4:47pm

FWIW I don't like travel agents that much; the cable never sits on the little wheel without springing slightly and this often makes for a brake that has relatively poor running clearance at any given system MA.

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

reohn2
Posts: 35939
Joined: 26 Jun 2009, 8:21pm

Re: Disc v Rim brakes

Postby reohn2 » 26 Aug 2016, 5:02pm

andrewk wrote:
reohn2 wrote:You could also fit cable accelerators(Travel Agents) and full sized V brakes,which will work well with your STI's,though won't eliminate the clearance issues when removing the wheel unless suitable brake block/pads can be found to allow the arms to open wider.


What are cable accelerators, how do they work and where can I buy them? My internet search for info only gave results for car accelerator cables and some electronic stuff.

https://www.sjscycles.co.uk/cables/trav ... lack-each/

They alter the cable pull between lever and brake,in you case the STI's don't pull enough cable to make V's practical, accelerators(TA's)overcome the problem.
We had TA's on our Santana tandem which stopped it PDQ without the pads needing to be grazing the rim and with minimum lever movement if required.
There are those who claim TA's shorten cable life due to the tight radius needed through the TA but I never found that to be a problem in the ten years we owned the bike.
I of course examined the cables regularly, changing them bi-annually and never found a frayed one,in fact I used to reuse the rear one on the front cutting off the excess :) .
Would[T/A's) this give better brake performance without requiring frequent adjustment?
Would[T/A's] this give better brake performance than cantilever brakes?

Yes and yes.

Tatanab beat me to it.

I don't share Bruceys resevations of T/A's,never had a problem with them.
-----------------------------------------------------------
I cycle therefore I am.

User avatar
531colin
Posts: 12491
Joined: 4 Dec 2009, 6:56pm
Location: North Yorkshire

Re: Disc v Rim brakes

Postby 531colin » 27 Aug 2016, 7:03pm

Andrewk....are they perhaps like these?

Image

Thats a May 2012 photo.....we have learned a bit since then

These will be a straight bolt-on fix for your braking woes......

Image

Thats an October 2014 photo, the brakes are Tektro RX6, you need one of those for each wheel and a "noodle" with adjuster for each brake.
The brakes are £20 a wheel and the noodles with adjuster are £3 a wheel....if you would like to PM me your address, I wouldn't be at all surprised if I could talk Spa into sending you some proper brakes.

The problem with the mini-vees which we used early on appears to be a problem of "lost motion" due at least in part to the flexibility of the arms; the RX6 brakes (amongst others) have much more rigid arms so that (counter-intuitively) you can get better clearance with the longer-armed brake.
Spa's brake bosses tend to be positioned quite high in order to get maximum tyre clearance, but even so 37mm tyres with the shorter-armed brakes may be pushing it a bit....is it possible that the mudguards are pushing the brake cable upwards, causing more lost motion?

As Brucey says, you can get very good braking with Shimano CX70 cantilever brakes, but they do need setting up rather than just bolting on, and best results are obtained with straddles other than the ones Shimano supplies. I'm not a fan of CX50 brakes, because its a struggle to get decent aftermarket pads to fit.