Author Topic: How to choose and fit disc brake?  (Read 3752 times)

Genosse Brymbo

  • Ostalgist
How to choose and fit disc brake?
« on: August 07, 2011, 11:37:43 am »
I'm not far from getting through the second rear rim on my commuting BSO.  (Actually I bought a cheap new wheel as I'm not a wheelbuilder.)  It's a 26" wheel and the frame has a rear disc mount (about 50mm between centres, so IS I believe).  I'm considering fitting a cable-operated disc brake so that I'll only have to change pads and rotors.

Can I just buy an Avid BB7, a wheel with a disc hub, a rotor and just fit them?  Or is there more to take into consideration, like compatibility between rotor diameter and caliper and compatibility for lateral position of caliper?  I can think of so many things that could go wrong that I don't really know where to start.

There are photos of the bike at https://picasaweb.google.com/110343324705050016920/DiscBrakes?authkey=Gv1sRgCJa7s_2Xn8iuMQ#5638052734351886178.  I intend to keep the current, cheap Shimano brake/8-speed gear lever combination and I'll make my own standoffs for the rack from bolts and nyloc nuts.  Any advice from forumites will be greatly appreciated.
The present is a foreign country: they do things differently here.

Re: How to choose and fit disc brake?
« Reply #1 on: August 07, 2011, 11:48:23 am »
Can I just buy an Avid BB7, a wheel with a disc hub, a rotor and just fit them?

Yes.  Make sure you get the MTB version of the caliper to suit V-brake levers.  You'll need the correct adaptor for the caliper/disc combo too - there are lots of different types, so get advice from the shop if you can.  Any 6-bolt MTB hub will work just fine - there is some lateral adjustment in the caliper to tweak the position.

Re: How to choose and fit disc brake?
« Reply #2 on: August 07, 2011, 08:15:23 pm »
Can I just buy an Avid BB7, a wheel with a disc hub, a rotor and just fit them?

Yes.
 You'll need the correct adaptor for the caliper/disc combo too

BB7s come with a 160mm rotor and the correct IS adapter for a 160mm rotor (or at least my BB7 Road did)
MTB/V lever BB7 are black, Road/drop lever BB7 are grey.

Steve Kish

  • World's No. 1 moaner about the weather.
Re: How to choose and fit disc brake?
« Reply #3 on: August 07, 2011, 08:53:19 pm »
Check this brand as an alternative to BB7.  They also have a cam device, so that both pads move inwards rather than just the usual one pad situation, as with most cables.  I've used a pair and they are very good!

http://www.ebay.co.uk/itm/KOOKA-CABLE-DISC-BRAKE-160mm-REAR-/260801897469?pt=UK_sportsleisure_cycling_bikeparts_SR&hash=item3cb90123fd

Old enough to know better!

Genosse Brymbo

  • Ostalgist
Re: How to choose and fit disc brake?
« Reply #4 on: August 07, 2011, 09:03:33 pm »
Thanks for the information.  When researching on the forum before the original posting I thought all the talk of adaptors was for proprietary/incompatible mounting tabs, not to accommodate different rotor diameters (I'd wondered how that worked, thinking maybe each caliper was designed for/came in models for different rotors  ::-)).  I now believe I understand and http://www.on-one.co.uk/i/q/BCAVBB7/avid-bb7-mechanical-disc-brake-%28mtb%29 looks like the kiddie for me - the description says it'll do front or rear.  I think I'll go for the 160mm rotor.

Eek, there's been a new reply posted while I'm typing.  Thanks for the alternative suggestion, Steve, but I'll stick with the BB7 as there appears to be a lot of people with experience of it and this is my first foray into the world of discs.
The present is a foreign country: they do things differently here.

Andrij

  • Андрій
  • Ερασιτεχνικός μισάνθρωπος
Re: How to choose and fit disc brake?
« Reply #5 on: August 08, 2011, 01:12:57 pm »
I'm tagging my question on to this thread as it's related, rather than start yet another disc brake thread.

I've been thinking of putting a mechanical disc brake on my commuter, which currently has Vs.  Would I be able to use my current lever if I fit a disc brake on the front?
;D  Andrij.  I pronounce you Complete and Utter GIT   :thumbsup:

Kim

  • Timelord
Re: How to choose and fit disc brake?
« Reply #6 on: August 08, 2011, 01:15:26 pm »
I'm tagging my question on to this thread as it's related, rather than start yet another disc brake thread.

I've been thinking of putting a mechanical disc brake on my commuter, which currently has Vs.  Would I be able to use my current lever if I fit a disc brake on the front?

Yes.  Make sure it's a 'mountain' disc brake (most are, BB7s come in both flavours) rather than a road one.
Careful, Kim. Your sarcasm's showing...

Andrij

  • Андрій
  • Ερασιτεχνικός μισάνθρωπος
Re: How to choose and fit disc brake?
« Reply #7 on: August 08, 2011, 01:21:47 pm »
Thanks!  Now off to OnOne for their deal on disc brakes.  As I'm in no rush* I will now sit back and wait for deals on Shimano disc dyno-hubs.

If anyone knows of any deals please don't tell me until after the 25th of this month - I need to cut back on buying bike stuff so I have money for other things.

* I had planned to see how I feel about disc brakes after I picked up n+1 (I've never used them before).  If I liked, I'd add a disc brake to the commuter.  OTOH, the deal from OnOne is too good to pass up.  Actually, I could probably sort out the commuter - new wheel and all - before I can collect n+1. *sigh*

EDIT: Do larger discs offer better stopping power?  I can get either 160mm or 185mm for the same price - any good reason to choose one over the other?
;D  Andrij.  I pronounce you Complete and Utter GIT   :thumbsup:

PaulF

  • "World's Scariest Barman"
  • It's only impossible if you stop to think about it
Re: How to choose and fit disc brake?
« Reply #8 on: August 08, 2011, 01:41:50 pm »

EDIT: Do larger discs offer better stopping power?  I can get either 160mm or 185mm for the same price - any good reason to choose one over the other?


Yes, but 160mm will be more than enough for a commuter I'd say

Re: How to choose and fit disc brake?
« Reply #9 on: August 08, 2011, 01:45:49 pm »
Some forks have a limit on the max. rotor diameter, check before you buy.  I've got a 160mm brake on the front of my Roadrat (biggest you can fit to the Roadhog fork) and never felt under-braked on the road.

PaulF

  • "World's Scariest Barman"
  • It's only impossible if you stop to think about it
Re: How to choose and fit disc brake?
« Reply #10 on: August 08, 2011, 01:48:38 pm »
Some forks have a limit on the max. rotor diameter, check before you buy.  I've got a 160mm brake on the front of my Roadrat (biggest you can fit to the Roadhog fork) and never felt under-braked on the road.

Had just come back to add the same thing!!

Andrij

  • Андрій
  • Ερασιτεχνικός μισάνθρωπος
Re: How to choose and fit disc brake?
« Reply #11 on: August 08, 2011, 01:55:51 pm »
Thanks, will go with the 160mm.
 
;D  Andrij.  I pronounce you Complete and Utter GIT   :thumbsup:

Kim

  • Timelord
Re: How to choose and fit disc brake?
« Reply #12 on: August 08, 2011, 02:01:59 pm »
EDIT: Do larger discs offer better stopping power?  I can get either 160mm or 185mm for the same price - any good reason to choose one over the other?

I remain unconvinced by the benefit of larger discs in terms of braking force, except perhaps for crazy downhill mountain biking type stuff - 160mm has no problem locking the wheel, so you're limited by the tyre anyway.  What it does give you is a bigger (and heavier) heatsink, which is desirable for serious descending on a loaded tourer or tandem.
Careful, Kim. Your sarcasm's showing...

Re: How to choose and fit disc brake?
« Reply #13 on: August 08, 2011, 02:13:55 pm »
You're planning to do what I did to my Orbit Orion. In addition I had to fit a disc-ready fork. I chose a Pompetamine one that sort of matched the colour scheme of the rest of the bike. I had Tektro v-brake levers.

Fitting the disc was a piece of cake, as I had also upgraded to a non-centerlock, disc-compatible, rather old Shimano dynohub. The caliper fitting was also easy. It's the best upgrade I've made to the bike by far.

One regret? Going for the BB5 & not the BB7.
Haggerty F, Haggerty R, Tomkins, Noble, Carrick, Robson, Crapper, Dewhurst, Macintyre, Treadmore, Davitt.

Genosse Brymbo

  • Ostalgist
Re: How to choose and fit disc brake?
« Reply #14 on: August 08, 2011, 09:21:36 pm »
Just ordered mine from on-one, or at least I think I have.  The website's transaction processing screens are pretty poor and they sent me an email with my chosen password in plain text  :facepalm:  I went for the 160mm rotor because there shouldn't be any problem with it fitting within the dimensions of the frame.
The present is a foreign country: they do things differently here.

Genosse Brymbo

  • Ostalgist
Re: How to choose and fit disc brake?
« Reply #15 on: August 31, 2011, 08:47:24 pm »
I've received my Avid BB7 and I've been trying to figure out how this device works before installing it at the weekend.  The brake cable pulls the actuator arm which causes a piston to push the outer pad onto the rotor.  There does not appear to be anything which actively pushes the inner pad towards the rotor - there is no inner piston and there appears to be no provision for the caliper body itself to move relative to the mounting (the only two ways I can think of the inner pad being actively moved).

The installation instructions say that the inner pad should be closer to the rotor than the outer pad ("Rotor should be offset to the outboard side of the rotor slot. Ideal ratio is 1/3 to 2/3").  Is the inner pad intended to contact the rotor by flexing of the rotor/mounting/caliper body?  Surely I've missed something here.  Can anybody enlighten this bear of little brane?
The present is a foreign country: they do things differently here.

Re: How to choose and fit disc brake?
« Reply #16 on: August 31, 2011, 09:11:49 pm »
The outer pad pushes the rotor onto the inner pad hence why you want the inner pad closer to the rotor as less deflection is required. I followed these setup instructions:-

http://www.twowheelblogs.com/avid-bb7-disc-brake-set-and-tuning
Nuns, no sense of humour

Re: How to choose and fit disc brake?
« Reply #17 on: September 01, 2011, 07:37:56 am »
Yep, the disc bends over to contact the fixed pad.

Kim

  • Timelord
Re: How to choose and fit disc brake?
« Reply #18 on: September 01, 2011, 02:45:13 pm »
...hence the adjustment is a bit of a black art, compared to hydraulics (where both pads move).  You get two stages of braking: firstly as the moving pad presses against and deforms the rotor, then as the rotor contacts the stationary pad and is gripped between them.  Fiddling around with how much space there is between the rotor and the two pads changes how quickly the latter happens.  Make it happen sooner and you get strong, possibly 'grabby' brakes.  Make it happen late and you get nice smooth modulation, but possibly reduced braking force.

The real art is getting really strong braking without excessive rubbing from the stationary pad - if the rotor's out of true, this becomes really difficult.

I've recently upgraded to BB7s from some older Tektros, and found that following the BB7 fitting instructions to the letter gave pretty good results.  They're also much easier to adjust.

My main advice would be not to get too hung up about slight rubbing when you first fit them.  If they're just making noise, but the wheel is spinning freely, and the brakes appear to be working well, don't get hung up by trying to adjust things to eliminate the noise - go for a ride first, preferably incorporating some nice hard braking, and see what happens.  I found that the rubbing noises stopped (and the braking performance improved) once the pads had bedded in a bit.
Careful, Kim. Your sarcasm's showing...

Re: How to choose and fit disc brake?
« Reply #19 on: September 01, 2011, 05:24:09 pm »
My main advice would be not to get too hung up about slight rubbing when you first fit them.  If they're just making noise, but the wheel is spinning freely, and the brakes appear to be working well, don't get hung up by trying to adjust things to eliminate the noise - go for a ride first, preferably incorporating some nice hard braking, and see what happens.  I found that the rubbing noises stopped (and the braking performance improved) once the pads had bedded in a bit.

Oh, that is so true, I tied myself in knots trying to get them perfect first time, the above is what I'd follow now.
Nuns, no sense of humour

Kim

  • Timelord
Re: How to choose and fit disc brake?
« Reply #20 on: September 01, 2011, 05:35:35 pm »
Similarly the pad alignment can go a bit wrong when the brake is used to stop the bike from rolling backwards, setting off the rubbing noises again (though the BB7s don't seem to suffer this to anything like the extent the Tektros did).  Again, don't meddle, it should clear up on its own after a couple of decent stops.
Careful, Kim. Your sarcasm's showing...

Re: How to choose and fit disc brake?
« Reply #21 on: September 01, 2011, 10:20:08 pm »
Thanks!  Now off to OnOne for their deal on disc brakes.  As I'm in no rush* I will now sit back and wait for deals on Shimano disc dyno-hubs.

If anyone knows of any deals please don't tell me until after the 25th of this month - I need to cut back on buying bike stuff so I have money for other things.

* I had planned to see how I feel about disc brakes after I picked up n+1 (I've never used them before).  If I liked, I'd add a disc brake to the commuter.  OTOH, the deal from OnOne is too good to pass up.  Actually, I could probably sort out the commuter - new wheel and all - before I can collect n+1. *sigh*

EDIT: Do larger discs offer better stopping power?  I can get either 160mm or 185mm for the same price - any good reason to choose one over the other?

Better stopping power, but more stress on the frame!

You need to balance the two.

I have never had a problem with the BB7 and 160's



Re: How to choose and fit disc brake?
« Reply #22 on: September 01, 2011, 10:24:12 pm »
Also keep the cable run short and direct.

On the Gekko, they had fitted flexible v brake noodles, and a long run.

Braking was spongy, so I replaced with Nokon cables at half the length and the braking is now crisp, and efficient

Genosse Brymbo

  • Ostalgist
Re: How to choose and fit disc brake?
« Reply #23 on: September 11, 2011, 11:27:43 am »
Fitted a week ago - just followed the instructions provided and had no problem.  Gives good progressive braking and the rim should last a while longer  :).  Thanks to fellow YACFers for replies and information.
The present is a foreign country: they do things differently here.

Genosse Brymbo

  • Ostalgist
Re: How to choose and fit disc brake?
« Reply #24 on: July 15, 2012, 03:22:59 pm »
What with the recent wet weather and constantly muddy tracks (very gritty mud when you're cycling on what was probably once the bed of the Thames, and very mobile due to the daily rainfall) I needed to fit new pads.

While chipping the mud off the BB7 I thought "what if I undo this bolt" and one thing led to another until the caliper was halfway disassembled.  Found the disassembly/reassembly instructions on the WWW.  Now completely serviced.  What an absolute piece of cake!  I am really impressed with this simple, effective device and take my hat off to Avid for providing the instructions.  Might even get one for the front.
The present is a foreign country: they do things differently here.