Disk brakes - the story so far (long)

(Please comment, but quote only the relevant lines from this long post)

There have been two main threads on aus.bicycle this year on disk brakes. The following is my
personal selection of the matters raised and conclusions reached, cutting 18 pages down to 2 1/2. I
have not attributed or dated any quotations; you can locate the originals by accessing aus.bicycle
through Google and searching.

The first thread began on 27 February and the second on 26 March 2003

___Disk brake pros____ I still think that most people get disks for reasons other than their greater
braking power and effectiveness

In the wet and mud they remain consistent all the way thru. Also in the wet the disk gives almost
identical braking effectiveness to what it is in the dry. This is very different from rims.
Performance in wet and muddy conditions is critical to a lot of MTBers, and rims will never compete
with disks in that.

They look awesome/cool

Very good modulation (fine control over braking power). Braking modulation is very important to most
riders; any rim brake can lock a wheel but it's much harder to *not* lock a wheel while still
getting close to maximum braking.

Not being affected by buckles and rim damage can be critical especially in endurance events.

Braking surface further away from puddles, mud, rocks etc.

Don't have to release callipers/V's to remove wheel

Less lever effort (not a big deal for most riders)

Because the braking force is being applied to a disk of steel by a compact calliper unit as opposed
to a hollow rim of aluminium by comparatively spindly callipers, then the braking force applied to a
disk can be massively higher than the force applied to a rim without fear of breaking the brakes /
rim / pads / components.

The holes in brake rotors are there to scrape off pad and foreign material.

Prolonged rim braking on very long descents causes heat dissipation from the rims into the tyres
which can lead to tyre burst.

____Cons____ More expensive initially

More difficult to maintain/repair (not much more). Not so sure: I find adjusting pad position _much_
easier (Avid Mechanicals). Just dial each pad in, rather than gambling with springs etc.

Can't have low spoke count wheels. Nor radial spokes (as opposed to crossed spokes).

Heavier unless at the top end, where the $$$ are, or heavy V-brakes at moment (also factor hub
weight, and stronger spokes, nipples etc)

Limited availability of specialized parts when travelling

Not all frames support disc brakes

On average, non-extreme bikes rim brakes are sufficient to stop the bike adequately and heat
dissipation is not a problem. If you ride a MTB off-road, heat dissipation and brake fade due to
water and mud is a big problem. Disks remove this problem.

I worry about the rotors being whacked on something in the rocky terrain around Townsville and as
for just throwing it into the back of the ute, I have to be more careful.

____Attachment standards____ there are two different attachment standards

____Comments on brands____ **Formula mech: has had a bad rap. Weel, I've got a Formula hydraulic on
the front; love the hydraulic 'cos the fluid pumps up so that irrespective of pad wear the brake
actuation remains the same.

**Avid: IIRC, can definitely recommend Avid mech. You should be able to find plenty of reviews that
say the same. I do like the fact that the Avids are so easy to adjust.

**Hayes - they are great, clear of all the dirt, water and debris, plenty of power and modulation,
pads last for ages and zero maintenance needed in 2 years.

**Shimano - the Shimano Deore mech discs are very fine. Easy one finger braking, no problem with
power or modulation, I can recommend them highly for a good value disc brake.

I've certainly noticed that my Shimanos do stretch the cables a fair bit, now that I'm doing a lot
of offroad with steep descents - I find that I am tweaking the lever adjustment every second or
third ride, and adjusting the cable at the brake housing every 15 to 20 rides.

____Pannier rack and disk brake compatibility____ Don't see why not. The disk sits inside the frame
so will be out of the way. I guess it depends where the pannier attaches, and where the brake bosses
attach. I needed to make two bushes about 1cm thick to ensure the rack did not hit the brake
calliper on the rear.

____Touring bikes____ Try descending a long steep descent from the High Country, in wet conditions
on a rough dirt road, or in very hot conditions and you'll be persuaded about the advantage of discs
for touring.

Not being affected by buckles and rim damage can be critical especially in endurance events.

I haven't tried hydraulic brakes on tours, but I wonder how practical these would be on longish
tours in the backwoods where there may not be any bike shops with extensive stock (unless you carry
hydraulic fluid and repair spares with you).

Hydraulic fluid bleed kits are relatively compact, so it's not impossible.

I wouldn't expect you'd get much service on busted discs in a third world country. Preferable to
take a conventional equipped tourer. Even then there's still plenty of possibilities for stuff-ups.
However if you had hydro discs and they just needed bleeding you should be able to get dot 4 hydro
fluid and someone who could help at a motor mechanics shop.

___Disk brake types____
(1) mechanical (cable actuated) and (2) hydraulic

If hydraulic cables are the most vulnerable part of a hydraulic disc brake system, perhaps cable
discs may be good options.

Every report that I've heard suggests that most cable discs suck, and good V-brakes are much better.

Many of the posts on cable discs make a lot of fuss about the performance "degradation" with the
wearing of the cables. I wouldn't have imagined that it would be worse than the effect of cable wear
on V-brakes.

____Myths____

2. Disk brakes permit greater braking force, unlike rim brakes which are vulnerable to breaking /
crushing rims. Not so.

3. Steel is a better braking surface. Not so: aluminium/alloy is better in terms of both heat
dissipation and friction, but their disadvantage is that they can still overheat

4. Disks are significantly heavier. Not so: for brake sets of a similar price, the difference is
only 100g or so, not significant.

 

Keith:

> (Please comment, but quote only the relevant lines from this long post)
>
> Because the braking force is being applied to a disk of steel by a compact calliper unit as
> opposed to a hollow rim of aluminium by comparatively spindly callipers, then the braking force
> applied to a disk can be massively higher than the force applied to a rim without fear of breaking
> the brakes / rim / pads / components.

For the same braking effort, a much higher caliper force is required on discs than on rim brakes
because of the smaller diameter of the rotors. It's not a consequence.

I suggest you read the recent "more on disc brakes" thread on rec.bicycles.tech and the safety
issues in the combination of standard "vertical" fork dropouts, disc brake caliper placement and
QR skewers.

If you must use disc brakes, ensure the QR is always tightly done and your fork has so-called
"lawyer lips". Best is to use 20mm bolt through axles. Also be aware that Manitou and Fox (at least)
recommend against using 203mm (DH) rotors on their non-DH specific forks (with warranty being
voided). You can find the moment calculations I made on why this is so.

 

Keith wrote:

> In the wet and mud they remain consistent all the way thru. Also in the wet the disk gives almost
> identical braking effectiveness to what it is in the dry. This is very different from rims.
> Performance in wet and muddy conditions is critical to a lot of MTBers, and rims will never
> compete with disks in that.

While this is a valid argument in some parts of the world, such as my native UK, I think it's
irrelevent for most mountain bike use in Australia - people just don't ride in the wet much here, in
my observation. Whereas in places like the UK, not riding in the wet almost means not riding!

> Prolonged rim braking on very long descents causes heat dissipation from the rims into the tyres
> which can lead to tyre burst.

For tandems, yes, but I don't think any of the disk manfacturers warrantees their brakes for tandem
use (if anyone knows different let me know, I'd love disks on my tandem). I've never heard of a solo
blowing a tyre off the rim from rim heating.

>
> ____Cons____

> Can't have low spoke count wheels. Nor radial spokes (as opposed to crossed spokes).

This should be listed under 'Pro' as: "Prevents you from demonstrating that you are a technically
clueless fashion-following muppet who has swallowed wheel maker marketing BS."

 

John Stevenson:

> Keith wrote:

> > Prolonged rim braking on very long descents causes heat dissipation from the rims into the tyres
> > which can lead to tyre burst.
>
> For tandems, yes, but I don't think any of the disk manfacturers warrantees their brakes for
> tandem use (if anyone knows different let me know, I'd love disks on my tandem). I've never heard
> of a solo blowing a tyre off the rim from rim heating.

It's not the disc brakes you have to worry about, but rather your fork and specifically, the
dropouts. Vertical dropouts (especially without the protruding lips) and disc brakes seem to be a
bad combination, with a good argument for this existing in the form of a force analysis on the axle
when disc brake is applied. There also seems to be many anecdotal evidence in one of the sites
posted at rec.bicycles.tech (look under "more on disk brakes...").

 

"John Stevenson" <[email protected]> wrote in message
news:[email protected]...
> Keith wrote:
>
> > In the wet and mud they remain consistent all the way thru. Also in the wet the disk gives
> > almost identical braking effectiveness to what it is in the dry.

<snip>

> I think it's irrelevent for most mountain bike use in Australia - people just don't ride in the
> wet much here, in my observation.

Hello there, from southern Victoria. A different viewpoint. Yes, down here we do ride in plenty of
mud - although last winter was an exception with the worst drought in 100 years. Normal weather
programing will be resumed shortly.

On my old rigid, used off road and for touring, I wore out the rim sidewalls in 5 years of not too
heavy use. Muddy autumn and spring rides in the forests of the Dandenongs and Murrundinidi were a
major cause of the wear.

Cheers Peter

 

"John Stevenson" <[email protected]> wrote in message
news:[email protected]...
> While this is a valid argument in some parts of the world, such as my native UK, I think it's
> irrelevent for most mountain bike use in Australia - people just don't ride in the wet much here,
> in my observation.

Speak for yourself. As a commuter, I ride in the wet quite regularly (Brisbane, so not too cold).
I've been eyeing-off the new flat-bar road bikes with disk brake setup, at least partly for better
wet weather braking.

> > Prolonged rim braking on very long descents causes heat dissipation from the rims into the tyres
> > which can lead to tyre burst.
>

> I've never heard of a solo blowing a tyre off the rim from rim heating.

It happens. A mate was descending the back of Mt Glorious with a light touring load and blew a
decent quality mountain bike slick (specialized fatboy I think).

Ciao,

AndyB

 

Peter Signorini wrote:

> Hello there, from southern Victoria. A different viewpoint. Yes, down here we do ride in plenty of
> mud - although last winter was an exception with the worst drought in 100 years. Normal weather
> programing will be resumed shortly.
>
> On my old rigid, used off road and for touring, I wore out the rim sidewalls in 5 years of not too
> heavy use. Muddy autumn and spring rides in the forests of the Dandenongs and Murrundinidi were a
> major cause of the wear.

Ah, yep, having no experience of Victoria weather I'd forgotten that your rainfall pattern is more
like the UK's (less rain in total than Sydney, but more rainy days, so more likely to be wet). Makes
sense there then.

--
John Stevenson Cyclingnews.com

 

AndyB wrote:
> "John Stevenson" <[email protected]> wrote in message
> news:[email protected]...
>
>>While this is a valid argument in some parts of the world, such as my native UK, I think it's
>>irrelevent for most mountain bike use in Australia - people just don't ride in the wet much here,
>>in my observation.
>
> Speak for yourself.

'I think' and 'in my observation' rather implied I was doing just that... I thought.

> As a commuter, I ride in the wet quite regularly (Brisbane, so not too cold). I've been eyeing-off
> the new flat-bar road bikes with disk brake setup, at least partly for better wet weather braking.

Tempted to go that way for my next commute bike too (though with drops please), but I worry that the
forces a disk puts on the dropouts aren't being thought about by the makers of those bikes. Now, if
I could get a road fork that would take a 20mm though-axle, then you'd be talking...

--
John Stevenson Cyclingnews.com

 

John Stevenson <[email protected]> wrote in message
news:<[email protected]>...

> Now, if I could get a road fork that would take a 20mm though-axle, then you'd be talking...

What's wrong with a Z1?

Dave - who hasn't ridden that bike to work for a while...

--
Dave Hughes [email protected] It typically takes 25-30 gallons of petrol/diesel to
fully-consume an average- sized body under ideal conditions. That I am conversant with this level of
detail should serve as an indication of why the wise man does not ask me questions about
MS-Windows." -Tanuki the Raccoon-dog

 

On 4 Apr 2003 03:49:22 -0800, [email protected] (Keith) wrote:

><snip>
>
>Every report that I've heard suggests that most cable discs suck, and good V-brakes are
>much better.
>
>Many of the posts on cable discs make a lot of fuss about the performance "degradation" with the
>wearing of the cables. I wouldn't have imagined that it would be worse than the effect of cable
>wear on V-brakes.

I have Avid mechanicals. They don't suck, and perform almost as well as hydraulics. whether that's
better than perfectly set up high end Vs is a moot point - they're better than any Vs or cantis I've
ever used, and setup is much easier.

I understand some of the early mechanicals weren't much chop - eg Formulas, eh Dave? Maybe that's
where this belief stems from?

I haven't adjusted my brake *cables* at all in over two years of discs
- all adjustment has been in the pad position only. I have worn out the original pads, but the
aftermarket replacements (EBC) have lasted more than twice as long.

I won't be going back anytime soon.

Tony F

 

tony f:

> I have Avid mechanicals. They don't suck, and perform almost as well as hydraulics. whether that's
> better than perfectly set up high end Vs is a moot point - they're better than any Vs or cantis
> I've ever used, and setup is much easier.
>
> I understand some of the early mechanicals weren't much chop - eg Formulas, eh Dave? Maybe that's
> where this belief stems from?
>
> I haven't adjusted my brake *cables* at all in over two years of discs
> - all adjustment has been in the pad position only. I have worn out the original pads, but the
> aftermarket replacements (EBC) have lasted more than twice as long.
>
> I won't be going back anytime soon.

What kind of fork are you using with your discs? Have you ever had any issues with QRs loosening or
moving on the dropouts?

 

I run disk on a Judy XC with no issues. This seems to be the norm for most ppl who run disks. Not to
say that there are not problems just that the majority of ppl with disks don't experience them. I do
find it interesting that the failure rate seems to be ever so low in comparison to what it should be
if these issues are as serious as some ppl believe. One wonders if the failures are due more to
specific (and isolated) issues than the general problem ?

AJS

"Jose Rizal" <[email protected]_._> wrote in message
news:[email protected]...
> tony f:
>
> > I have Avid mechanicals. They don't suck, and perform almost as well as hydraulics. whether
> > that's better than perfectly set up high end Vs is a moot point - they're better than any Vs or
> > cantis I've ever used, and setup is much easier.
> >
> > I understand some of the early mechanicals weren't much chop - eg Formulas, eh Dave? Maybe
> > that's where this belief stems from?
> >
> > I haven't adjusted my brake *cables* at all in over two years of discs
> > - all adjustment has been in the pad position only. I have worn out the original pads, but the
> > aftermarket replacements (EBC) have lasted more than twice as long.
> >
> > I won't be going back anytime soon.
>
> What kind of fork are you using with your discs? Have you ever had any issues with QRs loosening
> or moving on the dropouts?

 

"Jose Rizal" <[email protected]_._> wrote in message
news:[email protected]...
>
> What kind of fork are you using with your discs? Have you ever had any issues with QRs loosening
> or moving on the dropouts?

Using SID 100 forks with Hayes hydraulic discs with no problems at all. Less adjustment and work
than my old cantilevers as the pads are self-adjusted by the pistons. I have certainnly never
experienced any movements of the wheel in the dropouts like you are referring to. A couple of times
I have actually found that I have not tightened the QRs up enough ([email protected]&se), and there is a bit of
axle movement when I bounce the wheel, but the axle never shifts. This is because of the 'lawyer
lugs' which virtually every bike or fork manufacturer puts on the dropouts now. Some talk of filing
these out, but do this to a suspension fork and bingo! You instantly invalidate any warranty.

Surely the weight of yourself on the bike will over-ride any upwards force caused by the disc
action. If I undo my QRs and loosen them off, then apply the disc with forward force, the wheel
doesn't move out of the dropout - even lifting the wheel of the ground the wheel remains in the
dropout. I really don't see this as a major problem and have never heard of it occurring.

Cheers Peter

 

A - J - S:

>
> I run disk on a Judy XC with no issues. This seems to be the norm for most ppl who run disks. Not
> to say that there are not problems just that the majority of ppl with disks don't experience them.
> I do find it interesting that the failure rate seems to be ever so low in comparison to what it
> should be if these issues are as serious as some ppl believe. One wonders if the failures are due
> more to specific (and isolated) issues than the general problem ?
>
>
> AJS
>

It's probable that wheel dislodgements with discs on "vertical" dropouts happen most when braking
very hard from high speeds such as in steep descents, and when QRs aren't sufficiently tight. Since
most mountain bikes (with discs or not) are only ever used in much milder operations, it may account
for the few instances of this happening.

Apart from a force analysis of the system, the tendency for wheel dislodgement with disc brakes
and vertical dropouts is easily demonstrated by a practical test. Remove the skewer on the front
hub, stand by your bike and apply the brake such that the front wheel is locked. Push the bike
forward and note that the disc side of the axle will slide out of the dropout, while the opposite
side will stay on.

The question then is how tight should the QR be to prevent this from happening. It's practically
very difficult to measure how hard the lever should feel for "sufficiently tight", so I'm curious
whether on average QRs are done up sufficiently for most people such that wheel dislodgements
rarely happen.

> "Jose Rizal" <[email protected]_._> wrote in message
> news:kv6ka.11947$ey1.10[email protected]...
> > tony f:
> >
> > > I have Avid mechanicals. They don't suck, and perform almost as well as hydraulics. whether
> > > that's better than perfectly set up high end Vs is a moot point - they're better than any Vs
> > > or cantis I've ever used, and setup is much easier.
> > >
> > > I understand some of the early mechanicals weren't much chop - eg Formulas, eh Dave? Maybe
> > > that's where this belief stems from?
> > >
> > > I haven't adjusted my brake *cables* at all in over two years of discs
> > > - all adjustment has been in the pad position only. I have worn out the original pads, but the
> > > aftermarket replacements (EBC) have lasted more than twice as long.
> > >
> > > I won't be going back anytime soon.
> >
> > What kind of fork are you using with your discs? Have you ever had any issues with QRs loosening
> > or moving on the dropouts?

 

"Jose Rizal" <[email protected]_._> wrote in message
news:[email protected]...

> It's probable that wheel dislodgements with discs on "vertical" dropouts happen most when braking
> very hard from high speeds such as in steep descents, and when QRs aren't sufficiently tight.
> Since most mountain bikes (with discs or not) are only ever used in much milder operations, it may
> account for the few instances of this happening.

Most of my MTB friends do ride steepish terrain, and pretty quick. I have never heard of any
instances of wheel dislodgements due to any cause. But then it could just be that we are all fussy
with our QRs.
>
> Apart from a force analysis of the system, the tendency for wheel dislodgement with disc brakes
> and vertical dropouts is easily demonstrated by a practical test. Remove the skewer on the front
> hub, stand by your bike and apply the brake such that the front wheel is locked. Push the bike
> forward and note that the disc side of the axle will slide out of the dropout, while the opposite
> side will stay on.

Tried this little number and the LH side of the axle did move about 3 mm, on close observation. It
could only move out of the dropout if the rear of the dropout actually broke off.
>
> The question then is how tight should the QR be to prevent this from happening.

For me it's tight enough that I can still undo the damn QR without too much strain. Mine can easily
be overtightened.

> It's practically very difficult to measure how hard the lever should feel for "sufficiently
> tight", so I'm curious whether on average QRs are done up sufficiently for most people such that
> wheel dislodgements rarely happen.

Correct, I believe. I will of course take your point on board and check the QRs regularly.

Cheers Peter

 

On Mon, 07 Apr 2003 03:45:20 GMT, Jose Rizal <[email protected]_._> wrote:

>tony f:
>
>> I have Avid mechanicals. They don't suck, and perform almost as well as hydraulics. whether
>> that's better than perfectly set up high end Vs is a moot point - they're better than any Vs or
>> cantis I've ever used, and setup is much easier.
>>
<snip>
>>
>> I won't be going back anytime soon.
>
>What kind of fork are you using with your discs? Have you ever had any issues with QRs loosening or
>moving on the dropouts?

I've got Judy XCs. At first I had problems, but only because I was putting the QR in the wrong
position - the forks were so much thicker than my old ones the QR wasn't completely closed if I used
the old position.

Once I got that through my thick skull, never a problem with loosening. I now put the QR almost
upright, just ahead of the fork - it still tucks in well out of the way of any rampaging shrubbery.

Tony F

 

Did no one say anything about Hope disc barkes?? I have been using these for about three years now
and they have been great. Just had the fluid changed and brakes adjusted for $38, not sure if that
is a good deal or not but I am happy with the work.

Nice summary Keith.

rb

[email protected] (Keith) wrote in message news:<[email protected]>...
> ____Comments on brands____ **Formula mech: has had a bad rap. Weel, I've got a Formula hydraulic
> on the front; love the hydraulic 'cos the fluid pumps up so that irrespective of pad wear the
> brake actuation remains the same.
>
> **Avid: IIRC, can definitely recommend Avid mech. You should be able to find plenty of reviews
> that say the same. I do like the fact that the Avids are so easy to adjust.
>
> **Hayes - they are great, clear of all the dirt, water and debris, plenty of power and modulation,
> pads last for ages and zero maintenance needed in 2 years.
>
> **Shimano - the Shimano Deore mech discs are very fine. Easy one finger braking, no problem with
> power or modulation, I can recommend them highly for a good value disc brake.
>
> I've certainly noticed that my Shimanos do stretch the cables a fair bit, now that I'm doing a lot
> of offroad with steep descents - I find that I am tweaking the lever adjustment every second or
> third ride, and adjusting the cable at the brake housing every 15 to 20 rides.

 

Keith wrote:

> (Please comment, but quote only the relevant lines from this long post)
>
> There have been two main threads on aus.bicycle this year on disk brakes.

Sorry to be picky but they are actually disc brakes, disks are what you use with your computer. Just
a pet hate of mine people misspelling disc.

As to the actual subject of discs...I've never ridden a bike with them and for the type of riding I
do (mostly commuting on paths or sealed roads) they would be a waste of money.

 

Ross MacPherson <[email protected]> wrote...
> Keith wrote:

> > There have been two main threads on aus.bicycle this year on disk brakes.
>
> Sorry to be picky but they are actually disc brakes, disks are what you use with your computer.
> Just a pet hate of mine people misspelling disc.

Hmmmm. I was wondering if anyone would raise this. I really didn't know the answer, but now that
it's been raised, I checked a couple of good, recent dictionaries. I find there that the word comes
from the Greek <diskos> which was the weapon thrown for sport in the original Olympic Games 2500
years ago. Then it was picked up by the Romans to cover flat circular objects more generally,
including the appearance of the full moon. It became <disc> for the Romans. You're quite right
about present-day use: disk is the more common spelling in the world of computers (and the most
common form across the US); <disc> is the more common form for brakes (and generally more common
across the UK).

I'll slip into line from now on and will refer to <disc brakes> and <computer disks>.

Keith

 

[email protected] (Keith) wrote in message news:<[email protected]>...
> Ross MacPherson <NOSPAMPLEAS[email protected]> wrote...
> > Keith wrote:
>
> > > There have been two main threads on aus.bicycle this year on disk brakes.
> >
> > Sorry to be picky but they are actually disc brakes, disks are what you use with your computer.
> > Just a pet hate of mine people misspelling disc.

As far as I am concerned I use the English spelling "disc" for both computer components and brake
components. Mr Gates and the rest of the American based computer industry may do as they please! I
suspect that the American automobile industry also uses the word "disk" for brake components.

Mike (I hate the American way of spelling) Ayling