6 or 8 inches front disc?

i was faced with a similar dilemma a while back. /terrible/ brake squeal, pads getting so hot both
they and the disk were turning blue...

the "recommended" solution was 8" rotors, but i was reluctant for the reasons you state, too much
liklihood of endo, etc. effectiveness wasn't the problem - 6" rotors are already /way/ more
effective than any rim brake solution i've ever tried.

i tried "one last thing" before going down the big rotor road - a different brand of pad. all
problems ended! great braking, excellent modulation, no squeal, no overheating... i now use e.b.c.
pads rather than shimano and would never bother with a 6" rotor.

jb

Colin said:

Hi all,

If you are given a choice to choose between a 6" and an 8" disc rotor for your front disc brake on
a single crown fork, on a full-sus XC/epic bike, which would you go for? why? would you also opt
for the 8" rear?

There are people who would say that a 6" will serve the purpose on an XC, and is "more than
enough" braking power, too much braking power will make you endo, lost control on loose
soil, etc...

There are also people who would say that "more is better", better modulation, better heat
transfer, etc.....

What's your thought and comment?

Colin:

Quoted message said:

Hi all,

If you are given a choice to choose between a 6" and an 8" disc rotor for your front disc brake on
a single crown fork, on a full-sus XC/epic bike, which would you go for? why? would you also opt
for the 8" rear?

There are people who would say that a 6" will serve the purpose on an XC, and is "more than
enough" braking power, too much braking power will make you endo, lost control on loose
soil, etc...

There are also people who would say that "more is better", better modulation, better heat
transfer, etc.....

What's your thought and comment?

Make sure your forks are warrantied for an 8" rotor. Most manufacturers limit rotor size on their
particular forks, and void warranties if greater than 6" rotors are used.

An 8" rotor is overkill for most off-road applications; only the steepest downhill courses *may*
justify these.

Hmm. Interesting thread. Let me make sure I've got this straight.

The choices are 6" rotors and 8" rotors. The 8" rotors, it appears, have more stopping power since
they are referred to as being "overkill" amd "more likely to cause endos." Am I with you so far?

Now, if these statements are accurate, then it seems to me that the post powerful braking system
possible for a mountain bike would be the one that uses 22" rotors: rim brakes!

Colin said:

If you are given a choice to choose between a 6" and an 8" disc rotor for your front disc brake on
a single crown fork, on a full-sus XC/epic bike, which would you go for? why? would you also opt
for the 8" rear?

There are people who would say that a 6" will serve the purpose on an XC, and is "more than
enough" braking power, too much braking power will make you endo, lost control on loose
soil, etc...

There are also people who would say that "more is better", better modulation, better heat
transfer, etc.....

The advantage of a bigger rotor is primarily larger cooling surface; the disadvantage is greater
weight. Unless you are doing very long downhill sections at high speed (as in downhill racing) I
find it hard to believe that you need the greater cooling area, and if you're doing an epic you
certainly don't want to carry more weight.

In this case, less is more: less weight to heave up each hill means more distance covered.

--
[email hidden] (Simon Brooke) jasmine.org.uk~simonOpen ↗

;; in faecibus sapiens rheum propagabit

Tim McNamara said:

Hmm. Interesting thread. Let me make sure I've got this straight.

The choices are 6" rotors and 8" rotors. The 8" rotors, it appears, have more stopping power since
they are referred to as being "overkill" amd "more likely to cause endos." Am I with you so far?

What gives more stopping power is, ultimately, ability to dissipate heat, since brakes essentially
convert kinetic energy to heat energy and then dump the heat energy into the environment. Other
things being equal, a larger rotor has a larger radiant surface and is able to dump more heat.

Quoted message said:

Now, if these statements are accurate, then it seems to me that the post powerful braking system
possible for a mountain bike would be the one that uses 22" rotors: rim brakes!

If you dump too much heat into the system which holds your tyres on, you're going to blow tyres.

--
[email hidden] (Simon Brooke) jasmine.org.uk~simonOpen ↗

;; in faecibus sapiens rheum propagabit

Tim McNamara:

Quoted message said:

Hmm. Interesting thread. Let me make sure I've got this straight.

The choices are 6" rotors and 8" rotors. The 8" rotors, it appears, have more stopping power since
they are referred to as being "overkill" amd "more likely to cause endos." Am I with you so far?

No, you're not. I don't know where you got the "more likely to cause endos" bit. "Endos" aren't
solely reliant on brakes (let alone the type of brake) but involve riding position as well, among
other things. The overkill claim comes from the fact that 6" disc rotors provide ample stopping
ability for all but the most demanding incline, eg steep muddy downhills with a relatively heavy
rider/bike *and* very short distance stopping requirements, such as those in some downhill
mountainbiking courses. However, larger disc rotors exert larger bending moments on caliper mounts
despite the smaller stopping force exerted by the calipers (compared to smaller disc rotors), and
therefore require relatively stronger mounts than those designed for smaller disc rotors.

Quoted message said:

Now, if these statements are accurate, then it seems to me that the post powerful braking system
possible for a mountain bike would be the one that uses 22" rotors: rim brakes!

You're over-simplifying to an erroneous extent. You would know by now the main mechanical
differences between rim brakes and disc brakes; if not, Google will come up with many threads and
pages about that in cycling-related newsgroups and websites. By now you must also be aware of the
different features of both types of brakes, as well as the pros and cons of both so there is no need
to rehash all of that here.

If the purpose of your post, however, is to try to dismiss bicycle disc brakes as unnecessary in any
case, you need to come up with a lot better argument than what you've posted, addressing all the
relevant issues that have been discussed and argued for several years now.

Tim McNamara <[email hidden]> wrote in message
news:<[email hidden]>...

Quoted message said:

Hmm. Interesting thread. Let me make sure I've got this straight.

The choices are 6" rotors and 8" rotors. The 8" rotors, it appears, have more stopping power since
they are referred to as being "overkill" amd "more likely to cause endos." Am I with you so far?

Now, if these statements are accurate, then it seems to me that the post powerful braking system
possible for a mountain bike would be the one that uses 22" rotors: rim brakes!

You would have a point IF rim brakes generated as much pressure between the pads as disk brakes do.

The appeal of disk brakes is not that they provide more stopping power than rim brakes, but rather
they the stopping power they provide is almost constant regaurdless of the conditions. Wet, Dry,
Muddy, Icey...disk brakes work more or less the same in all those conditions. That is certainly not
a claim that can be made by rim brakes.

Quoted message said:

Quoted message said:

Now, if these statements are accurate, then it seems to me that the post powerful braking system
possible for a mountain bike would be the one that uses 22" rotors: rim brakes!

You're over-simplifying to an erroneous extent.

I think he was being sarcastic... lol

--
Phil, Squid-in-Training

Simon Brooke said:

Tim McNamara said:

Hmm. Interesting thread. Let me make sure I've got this straight.

The choices are 6" rotors and 8" rotors. The 8" rotors, it appears, have more stopping power
since they are referred to as being "overkill" amd "more likely to cause endos." Am I with you
so far?

What gives more stopping power is, ultimately, ability to dissipate heat, since brakes essentially
convert kinetic energy to heat energy and then dump the heat energy into the environment. Other
things being equal, a larger rotor has a larger radiant surface and is able to dump more heat.

Humm. And a rim would have a much larger surface than a 6" or 8" rotor, which again would indicate
that the rim brake would have greater stopping power than either size disc brake. Thanks for
clarifying that for me.

Quoted message said:

Quoted message said:

Now, if these statements are accurate, then it seems to me that the post powerful braking system
possible for a mountain bike would be the one that uses 22" rotors: rim brakes!

If you dump too much heat into the system which holds your tyres on, you're going to blow tyres.

I've heard of that happening, although in the 30+ years I've been riding bikes as an "enthusiast,"
it's never happened to me. Of course, I've also never lived in mountainous terrain with the long
steep descents necessary to heat a rim up that much. OTOH in my tour in the Alps in 2002, I never
had a problem with rims heating up.

My wife and I have never ridden our tandem in the mountains; that's a situation that I could easily
see resulting in very warm rims and might warrant a hub brake- but since my wife hates climbing,
it's not something I'll ever be likely to test.

"Colin" <[email hidden]> wrote in message news:<[email hidden]>...

Quoted message said:

Hi all,

If you are given a choice to choose between a 6" and an 8" disc rotor for your front disc brake on
a single crown fork, on a full-sus XC/epic bike, which would you go for? why? would you also opt
for the 8" rear?

There are people who would say that a 6" will serve the purpose on an XC, and is "more than
enough" braking power, too much braking power will make you endo, lost control on loose
soil, etc...

There are also people who would say that "more is better", better modulation, better heat
transfer, etc.....

What's your thought and comment?

Dear Colin,

The trails that you ride might be what really matters.

The first Montesa trials motorcycles had huge brakes:

"The brakes are borrowed from Montesa's other dirt models; of 7-inch diameter, they require a
delicate touch." --"Sammy Miller On Trials"

Miller was being unreasonably polite--the damn things were virtually useless in tricky downhill
sections because a single finger's pressure would lock up the front wheel. The next model had much
smaller brakes that allowed real control at low speed instead of the giant on-off switches stolen
from the motocross line.

It would be worth trying to arrange a test ride or two on a familiar trail to see which kind of
brakes appeal to you. If you do fairly fast, smooth riding, then larger brakes are likely to be what
you want. If you do more low-speed riding with switchbacks, awkward rock sections, and so forth,
then smaller brakes may offer the necessary light touch for control.

Keep in mind that brakes are far more important off-road for bicycles than motorcycles. Descending
long bad sections of trail is much harder on a bicycle with nothing but brakes and a useless
freewheel, compared to a motorcycle with brakes and a throttle to provide engine braking. This is
why bicycle rear brakes are more impressive--they're actually used.

Carl Fogel

RE/

Quoted message said:

There are also people who would say that "more is better", better modulation, better heat
transfer, etc.....

What's your thought and comment?

I've got 8" on my front wheels, but with 6":

- Interchangability: If you wind up with a spare somehow, it'll fit any of your wheels instead of
just fronts for just backs.

- Simpler: I had to get an add-on bracket to make Avid mechs fit the 8" rotor.

- More bulletproof (this is a stretch...but it seems logical) because there's less leverage on the
thing when you bang it up against, say, a big rock.

- Safer (another beeeeg stretch....) because there's less area for a stick or something to find it's
way into while you're under way.

Besides fade resistance (which is moot for the kind of riding I do) the only theoretical con I can
come up with is the leverage/front wheel ejection thing. Bigger rotors move the pad further out,
creating less ejection force for a given amount of braking. How much? Does it matter? Dunno.
--
PeteCresswell

Colin' may have said:

Hi all,

If you are given a choice to choose between a 6" and an 8" disc rotor for your front disc brake on
a single crown fork, on a full-sus XC/epic bike, which would you go for?

8"

Quoted message said:

why?

Better mechanical advantage.

Quoted message said:

would you also opt for the 8" rear?

No. In fact, I wouldn't spend the bucks for a disc on the rear at all.

Quoted message said:

There are people who would say that a 6" will serve the purpose on an XC, and is "more than enough"
braking power, too much braking power will make you endo, lost control on loose soil, etc...

There are, and will always be, alarmists for any given piece of new tech, often persisting well
after the new tech has become old.

Quoted message said:

There are also people who would say that "more is better", better modulation, better heat
transfer, etc.....

What's your thought and comment?

In most cases, there is no need for a disc brake on a bicycle. Disc brakes have some small, often
purely subjective and somewhat infrequent advantages in normal use which do not objectively outweigh
the high cost for most people. On the other hand, for a rider who does a lot of prolonged descents,
the disc has some significant advantages in the area of removing the heat buildup from the rims.

There is also a consideration to be weighed in the area of safety, in that on rare occasions,
ejection of the front wheel from the fork has been attributed to the way that the disc brake setups
are designed. In my personal opinion, these reports do not constitute a serious enough cause for
concern to keep me from buying or using a disc brake setup.

I wouldn't disqualify a bike from consideration because it had disc brakes, but I would not
spend a lot of extra money to step up into one, either, unless I was contemplating a lot of
downhill braking.

--
My email address is antispammed; pull WEEDS if replying via e-mail. Yes, I have a killfile. If I
don't respond to something, it's also possible that I'm busy. Words processed in a facility that
contains nuts.

Jose Rizal _@_._ said:

If the purpose of your post, however, is to try to dismiss bicycle disc brakes as unnecessary in
any case, you need to come up with a lot better argument than what you've posted, addressing all
the relevant issues that have been discussed and argued for several years now.

Jose, you need to check your sense of humor. It seems to need a tune-up. You also need to re-read
what was previously written by other posters. The implication was clear that the larger disk rotors
offer more stopping power, which is erroneous.

Also, the math done in other threads addressed the fact that the smaller rotors place a higher
ejection force on the axle, with current fork and caliper designs. I'm afraid I'll have to ask you
to explain how the larger rotors create a larger bending force on the fork leg, since I'm having
trouble perceiving that.

Disk brakes are unnecessary in most cases, as far as that part of your critique goes. I was merely
poking a bit o' fun at some of the logic thus far in the thread. You disk-brakers seem to be kind of
touchy on the subject!

Hi gentlemen,

Thank you very much for all your feedback and comment.

On the other hand, do you think that we should also take into considerations of the tire's traction?
Given the same circumstances, a "grippier" tire would benefit more from the braking as compare to
one with less grip.

Do you think that there's a point where additional braking would be of no use when the tire starts
to loose traction? Especially on mud, loose gravel, etc.

Although I am just a novice, I think the braking power (of any brakes) will best benefit while
riding on asphalt (or optimal traction), other than that, its just too much "waste". Am I right or
there are other issues such as braking technique, etc.?

"(Pete Cresswell)" <[email hidden]> wrote in message news:<[email hidden]>...

Quoted message said:

RE/

Quoted message said:

There are also people who would say that "more is better", better modulation, better heat
transfer, etc.....

What's your thought and comment?

I've got 8" on my front wheels, but with 6":

- Interchangability: If you wind up with a spare somehow, it'll fit any of your wheels instead of
just fronts for just backs.

- Simpler: I had to get an add-on bracket to make Avid mechs fit the 8" rotor.

- More bulletproof (this is a stretch...but it seems logical) because there's less leverage on the
thing when you bang it up against, say, a big rock.

- Safer (another beeeeg stretch....) because there's less area for a stick or something to find
it's way into while you're under way.

Besides fade resistance (which is moot for the kind of riding I do) the only theoretical con I can
come up with is the leverage/front wheel ejection thing. Bigger rotors move the pad further out,
creating less ejection force for a given amount of braking. How much? Does it matter? Dunno.

Dear Pete,

Pardon an innocent's fascination, but I love lists of advantages like this and am intrigued by your
"more bulletproof" idea for the smaller 6" rotor.

I can see that a 6" rotor would hit fewer rocks to start with because it's an inch higher than the
8" rotor, a world of difference in nasty places.

But I'm not sure that I follow your idea of "less leverage when you bang it up"--do you mean that a
smaller rotor is less likely to bend inward toward the spokes when mashed sideways against a rock
because it doesn't stick out as far from its supports? Or am I missing something better?

Carl Fogel

Tim McNamara said:

Simon Brooke said:

Tim McNamara said:

Hmm. Interesting thread. Let me make sure I've got this straight.

The choices are 6" rotors and 8" rotors. The 8" rotors, it appears, have more stopping power
since they are referred to as being "overkill" amd "more likely to cause endos." Am I with you
so far?

What gives more stopping power is, ultimately, ability to dissipate heat, since brakes
essentially convert kinetic energy to heat energy and then dump the heat energy into the
environment. Other things being equal, a larger rotor has a larger radiant surface and is able
to dump more heat.

Humm. And a rim would have a much larger surface than a 6" or 8" rotor, which again would indicate
that the rim brake would have greater stopping power than either size disc brake. Thanks for
clarifying that for me.

Well, you're trying to be smart but in general I would agree that rim brakes have a number of
advantage WRT disks. The chief among these is that they don't impose a torque loading on the wheel.

The primary disadvantages of rim brakes are

(i) it's difficult to keep them out of the dirt, so in muddy conditions the braking surfaces are
contaminated, and

(ii) it's difficult to keep them perfectly true, so the brakes have to work at much less precise
tolerances

However, if you're doing the sort of sustained braking that the true downhill loonies do, and you
dumped that much heat into your rims, you probably would blow tyres.

--
[email hidden] (Simon Brooke) jasmine.org.uk~simonOpen ↗

;; better than your average performing pineapple

Tim McNamara said:

Jose Rizal _@_._ said:

If the purpose of your post, however, is to try to dismiss bicycle disc brakes as unnecessary in
any case, you need to come up with a lot better argument than what you've posted, addressing all
the relevant issues that have been discussed and argued for several years now.

Jose, you need to check your sense of humor. It seems to need a tune-up. You also need to re-read
what was previously written by other posters. The implication was clear that the larger disk
rotors offer more stopping power, which is erroneous.

No, it's not, actually. While the instantaneous stopping power is (other things being equal) may be
the same, the ability to sustain that stopping power over time is greater because the radiant area
is greater.

--
[email hidden] (Simon Brooke) jasmine.org.uk~simonOpen ↗

;; better than your average performing pineapple

"Colin" <[email hidden]> wrote in message "]news:[email hidden]...

Quoted message said:

Hi gentlemen,

Thank you very much for all your feedback and comment.

On the other hand, do you think that we should also take into considerations of the tire's
traction? Given the same circumstances, a "grippier" tire would benefit more from the braking as
compare to one with less grip.

No. Any brake has enough power to either lock the front wheel or flip you over the handlebars.

Quoted message said:

Do you think that there's a point where additional braking would be of no use when the tire starts
to loose traction? Especially on mud, loose gravel, etc.

Exactly, and that's the reality most of the time riding on dirt.

Quoted message said:

Although I am just a novice, I think the braking power (of any brakes) will best benefit while
riding on asphalt (or optimal traction), other than that, its just too much "waste". Am I right or
there are other issues such as braking technique, etc.?

Good technique is everything.

Disks are an advantage in muddy or snowy/icy conditions, but otherwise probably a waste of money.
Some people like the modulation for stunt-type riding. But for normal riding, properly adjusted
standard brakes are more than good enough for most people. Save your money for other stuff that will
make far more difference in your riding experience -- good shoes and clothing, for example. Or a
trip to a great riding area.

Some mid-level mountain bikes come with disks anyway. In that case, take them and be happy. But
don't spend extra for them. With over 15 years experience in the sport, I would still not buy disks
if I were building my "dream bike" today -- unless I lived where the trails were always muddy/snowy.

Matt O.

Mark Hickey <[email hidden]> wrote in message
news:<[email hidden]>...

Quoted message said:

(Carl Fogel) said:

Keep in mind that brakes are far more important off-road for bicycles than motorcycles.
Descending long bad sections of trail is much harder on a bicycle with nothing but brakes and a
useless freewheel, compared to a motorcycle with brakes and a throttle to provide engine braking.
This is why bicycle rear brakes are more impressive--they're actually used.

Carl, if we ever end up riding off-road motorcycles together, I'm going to insist you ride
in front.

Mark Hickey Habanero Cycles habcycles.comhabcycles.comOpen ↗ Home of the $695 ti frame

Dear Mark,

Actually, I almost always ride sweep. No one can stand waiting behind an unreformed trials rider
given to digressions.

But you needn't worry about my inability to find the rear brake pedal (I think it's on the right on
the Honda, but it was on the left on the Bultaco).

After all, chopping the throttle on a four-stroke TL-348 chirps the rear tire on pavement. In fact,
some of the Honda team's RTL machines ran brakeless spool rear wheels to reduce unsprung weight.

As for bicycles, well, anyone stuck riding behind me off-road or on pavement will get a lot of
practice doing trackstands or coasting.

Slowly yours,

Carl Fogel