please tell me all about braking

(Carl Fogel) said:

I asked what the basis is for an assumption of a maximum
braking on a typical disk brake mountain bike of 0.6 g.
That is, can we confirm this figure as significantly low,
reasonably correct, or significantly high?

It sounds like the right ballpark to me. But please don't
ask me to do the math -- my last dynamics course was 11
years ago. :-)

Quoted message said:

Do bicycle-style disk brakes offer better braking than rim-
caliper brakes? Given the same bicycle and front tire, how
far will each kind need to stop from 20 mph on flat dry
pavement?

If you could apply them both smoothly, then they should be
the same, since both offer sufficient braking force to stop
the wheel and go into a skid. If one let you control the
braking better, and avoid a skid (which I hear disk brakes
are good at), then that one might be able to stop sooner.

On the other hand, if your traction is good enough that you
will go over the bars before your front tire will skid
(which should be the case on flat dry pavement) then this is
not an issue. Both brakes have more than enough force to
make you do a faceplant.

Quoted message said:

Do mountain-bikes with disk brakes and knobby tires brake
better, as well, or worse off-road than street bikes with
caliper brakes and thin tires on flat dry pavement?
Imagine two appropriate riders, side by side, one on the
street and the other on the dirt shoulder. Who stops
shortest?

If the dirt was slippery and caused a skid, then the road
rider stops first. If the mountain biker got as good a grip
on the dirt as the road rider does on the road, then they
should be the same.

Quoted message said:

Does a downhill slope affect braking? That is, does it
matter that the bike is already in a slightly tipped-
forward position?

If this means the rider is in a slightly more tipped-forward
position, then yes, this affects braking. By moving the
center of gravity further forward you give the bicycle more
leverage on the bicyclist, meaning less braking force will
be required to cause the rider to go over the bars. If the
bicyclist is able to lean far enough back (such that they
are in the same position as they are on level ground) then
this should not be an issue.

Also, when braking in a downhill the brakes are countering
both the force of gravity on the bike/bicyclist as well as
reducing the momentum of the bike/bicyclist, so you can not
slow down as quickly as on level ground.

Quoted message said:

Does a downhill angle affect traction? Does a bicycle
braking from 20 mph to 0 mph at the same rate require more
braking force and traction descending a slope than it
would on level ground?

To answer this properly you need to strictly define
traction. I am too tired to do this now. :-) My gut feeling
is this: if by "same rate" you mean "constant acceleration",
on a downhill your brake has to both counter the force of
gravity (pulling you down the hill) and reduce your
velocity, which means it has to do more work. So more
braking force is required to slow you down at a fixed rate
on a downhill slope.

Quoted message said:

Does front (or rear) suspension affect braking?

On perfectly flat pavement front suspension could cause
the rider position to shift slightly forward, which would
make braking worse. On rough ground front suspension could
keep your wheel in contact with the ground, which makes
braking better.

Quoted message said:

Do rear brakes work better on downhills?

No -- but if you use rear brakes you reduce the risk of the
front wheel skidding and hence a loss of steering control.

Chris
--
Chris Colohan Email: [email hidden] PGP: finger
[email hidden] Web: www.colohan.com Phone: (412)268-4751

Some miscellaenous ramblings follow..

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

Quoted message said:

I asked what the basis is for an assumption of a maximum
braking on a typical disk brake mountain bike of 0.6 g.
That is, can we confirm this figure as significantly low,
reasonably correct, or significantly high?

I can't say really..I know motorcycles can stop in the 1g
range, so I don't think this number is wildly out of the
question. It might be a little high..1g is about 35km/h to
0km/h in 1 sec, right? (10m/s * 60s * 60m /1000
= km/h). So .6g is about 20km/h to 0 in 1 sec? I think
= that's a pretty
good braking feat..so maybe a bit high but not out of the
question in extreme situations and for brief periods of max
deceleration.

Quoted message said:

First, what do we mean by braking? Stopping distance,
force in terms of g, practical measurements, or
theoretical calculations?

I take braking to mean stopping distance. Decelerative g's
are interesting, but stopping distance decides whether
you're going to hit the car or not! I think you could use
either, but g's, unless measured continuously, are hard to
judge stopping by. There is fade, the g's can vary up and
down according to conditions even within the stop. I'd use
stopping distance.

Quoted message said:

Do bicycle-style disk brakes offer better braking than rim-
caliper brakes? Given the same bicycle and front tire, how
far will each kind need to stop from 20 mph on flat dry
pavement?

I think both are pretty equal in terms of braking force.
Fade and modulation are where the difference are between the
two (ignore the serviceability and wet-braking arguments I
think for this discussion). I can lift the rear wheel of my
MTB when braking with v-brakes (you mentioned "rim-caliper"
but I'll throw v-brakes into that category..) and that's
pretty much max braking on a bicycle. So I don't think v-
brakes are lacking in stopping power. Fade and
modulation..well, arguments could be made to those.
Modulation especially as that's pretty much the "feel" of
the brake.

Quoted message said:

Do mountain-bikes with disk brakes and knobby tires brake
better, as well, or worse off-road than street bikes with
caliper brakes and thin tires on flat dry pavement?
Imagine two appropriate riders, side by side, one on the
street and the other on the dirt shoulder. Who stops
shortest?

Pavement bike. Simply more traction. I personally find it
easier to control my MTB while stopping quickly and that may
mean I stop more quickly on pavement than on a road bike,
but I suspect it's simply due to comfort level.

Quoted message said:

For that matter, would mountain-bikes with disk brakes and
knobby tires brake better on the same flat dry pavement
than thin-tire caliper-brake street bikes?

I think this would be down to the available traction at the
front wheel for both. Brakes I don't think would make a
difference, or not much.

Quoted message said:

Does a downhill slope affect braking? That is, does it
matter that the bike is already in a slightly tipped-
forward position? Does a downhill angle affect traction?
Does a bicycle braking from 20 mph to 0 mph at the same
rate require more braking force and traction descending a
slope than it would on level ground? Does front (or rear)
suspension affect braking?

Downhill would affect braking. How much would be the debate.
If your Cg is already forward and you start braking, you
would be able to use less braking force before the rear
wheel lifts. Therefore, you will have longer stopping
distances. You would actually have more traction at the
front wheel but you would also go over sooner. And since you
are going downhill, you would require more distance to stop
since you're also countering gravity. Suspension affects Cg
and would alter the forward weight transfer and rear wheel
lifting accordingly.

Quoted message said:

Do rear brakes work better on downhills?

No. Not from a braking distance perspective.

Carl Fogel said:

Some questions about braking arose in the disk-brake wheel-
ejection thread that might be deserve their own thread.

I asked what the basis is for an assumption of a maximum
braking on a typical disk brake mountain bike of 0.6 g.
That is, can we confirm this figure as significantly low,
reasonably correct, or significantly high?

That's reasonably correct for bicycles of normal upright
geometry. Has nothing to do with whether it's a mountain
bike nor whether the brakes are discs.

With good brakes of any available type, the minimum braking
distance depends on traction and the angle formed between
the front tire patch and the center of gravity of the
bike/rider.

Quoted message said:

First, what do we mean by braking? Stopping distance,
force in terms of g, practical measurements, or
theoretical calculations?

All of the above.

Quoted message said:

(I think that we're ignoring rider reaction time and just
talking about what happens after we actually drop the
anchor.)

Do bicycle-style disk brakes offer better braking than rim-
caliper brakes? Given the same bicycle and front tire, how
far will each kind need to stop from 20 mph on flat dry
pavement?

No difference.

Quoted message said:

Do mountain-bikes with disk brakes and knobby tires brake
better, as well, or worse off-road than street bikes with
caliper brakes and thin tires on flat dry pavement?
Imagine two appropriate riders, side by side, one on the
street and the other on the dirt shoulder. Who stops
shortest?

Road rider can stop shorter because the traction is better.

Quoted message said:

For that matter, would mountain-bikes with disk brakes and
knobby tires brake better on the same flat dry pavement
than thin-tire caliper-brake street bikes?

The brakes make no difference, assuming they're in good
condition, but knobby tires get worse traction on hard
surfaces, so the mountain bike would have a longer
stopping distance.

Quoted message said:

Does a downhill slope affect braking? That is, does it
matter that the bike is already in a slightly tipped-
forward position?

Yes, because this steepens the angle between the tire-patch/center-of-
gravity.

Quoted message said:

Does a downhill angle affect traction?

It does, it improves front traction and reduces rear
traction.

Quoted message said:

Does a bicycle braking from 20 mph to 0 mph at the same
rate require more braking force and traction descending a
slope than it would on level ground?

Yes, because the brake is working against both momentum
and gravity.

Quoted message said:

Does front (or rear) suspension affect braking?

In some conditions suspension can improve traction, mainly
at higher speeds.

Quoted message said:

Do rear brakes work better on downhills?

No, they work worse.

Quoted message said:

It might be well to test any theories involving slope on
uphills as well as downhills and level roads.

Details about skidding, tipping, tread, tire pressure,
gravel, and anything else to do with braking are welcome.
I only hope that we can avoid any spelling argument about
disk versus disc. As always, any links to tables or
studies would be nice.

You might find my article on Braking and Turning
enlightening:

sheldonbrown.combrakturnOpen ↗

Sheldon "Friction" Brown +-------------------------------------------------
+
| Men and nations behave wisely once they | have
| exhausted all the other alternatives. | -- Abba Eban |
+-------------------------------------------------+ Harris
Cyclery, West Newton, Massachusetts Phone 617-244-9772 FAX
617-244-1041 harriscyclery.comharriscyclery.comOpen ↗ Hard-to-find parts
shipped Worldwide captainbike.comcaptainbike.comOpen ↗
sheldonbrown.comsheldonbrown.comOpen ↗

cut to the chase carl. the calculation of the ejection force
is a reasonable wost-case estimate; it's the
/underestimation/ of pull-out force necessary to cause
ejection that's not being addressed properly.

pull-out is dramatically affected by the serrations
manufacturers put on their axle facings. these create
corresponding indentations on the relatively soft fork
material of the mtb fork - easy to see with the naked eye.
so now, assuming a properly clamped skewer, pull-out has to
overcome not simple friction, but material shear.

the force necessary to shear through only 25mm^2 of
serration engagement, [a conservative estimate given that
a shimano xt mtb disk hub has a minimum outside serrated
face diameter of 17mm & an inside of 13mm - you check the
math] and assuming a very conservative shear stress of
only 200N/mm^2 for the fork material, would be over
5,000N. suddenly, the 1825N pull-out force supposed to be
generated by a disk brake is insufficient to be any major
worry. and that's /before/ any consideration of factors
that would reduce it like lack of traction, blah blah blah
blah blah blah.

it's late. and this debate has a cT of 0.9.

Carl Fogel said:

Some questions about braking arose in the disk-brake wheel-
ejection thread that might be deserve their own thread.

I asked what the basis is for an assumption of a maximum
braking on a typical disk brake mountain bike of 0.6 g.
That is, can we confirm this figure as significantly low,
reasonably correct, or significantly high?

Obviously, the kind of tires, the slope of the ground, the
nature of the surface, and the details of the bike
(suspension, frame geometry, and rider position, for
example) may affect braking.

A clean start might help things, so I'll name no one. Some
early posters are now moving from theory to testing.
Others, like me, are merely waffling hopefully and looking
for answers.

First, what do we mean by braking? Stopping distance,
force in terms of g, practical measurements, or
theoretical calculations?

(I think that we're ignoring rider reaction time and just
talking about what happens after we actually drop the
anchor.)

Do bicycle-style disk brakes offer better braking than rim-
caliper brakes? Given the same bicycle and front tire, how
far will each kind need to stop from 20 mph on flat dry
pavement?

Do mountain-bikes with disk brakes and knobby tires brake
better, as well, or worse off-road than street bikes with
caliper brakes and thin tires on flat dry pavement?
Imagine two appropriate riders, side by side, one on the
street and the other on the dirt shoulder. Who stops
shortest?

For that matter, would mountain-bikes with disk brakes and
knobby tires brake better on the same flat dry pavement
than thin-tire caliper-brake street bikes?

Does a downhill slope affect braking? That is, does it
matter that the bike is already in a slightly tipped-
forward position? Does a downhill angle affect traction?
Does a bicycle braking from 20 mph to 0 mph at the same
rate require more braking force and traction descending a
slope than it would on level ground? Does front (or rear)
suspension affect braking? Do rear brakes work better on
downhills?

It might be well to test any theories involving slope on
uphills as well as downhills and level roads.

Details about skidding, tipping, tread, tire pressure,
gravel, and anything else to do with braking are welcome.
I only hope that we can avoid any spelling argument about
disk versus disc. As always, any links to tables or
studies would be nice.

Thanks,

Carl Fogel

.6 is a slightly high figure, .5-.6 g is the range most bikes fall in.
.56-.57 g is the nominally cited road bike decel rate before endo.

If you lower cg or move the mass backwards on a bike, you don’t see a huge increase because you aren’t that much away from the limits of adhesion for a road bike tire on pavement.
A mountain bike tire would have less adhesion than the road bike. LWB and MWB recumbents and tandems will have higher decel rates since 1endos are removed from the braking limits and adhesion will become the new limiting factor. Lowracers with their low cg resulting in a small moment about the front patch will have a more optimal weight distribution for adhesion.

Unless specified otherwise, decel rate in G’s is the most frequent and practical criterion for comparative measurement because all others are a function of either speed and/or weight.
Decel reate is a near constant, so stopping time is a product of speed and decel rate. Stopping distance is proportional to the square of speed over stopping time. Force is mass times decel rate.
Another measure includes heat dissipation rate (measured in watts) for downhill situations in which you are pressing the BRAKE’S heat dissipation limits, and still another measure heat dissipated.

Disc brakes are more resistant to the effects of the elements than rim brakes such as rain, dirt, mud or snow and for that reason are favored in mountain bike use.
The lighter weight rim brakes are preferred for road bikes. Discs can be more effective whenever brakes become a limiting factor such as long downhills, particularly with tandems or recumbents.

The reason a mountain bike tire has less adhesion on dry pavement that a road tire are: 1) those gaps in the rubber are no longer abutting portions of the road- the flexible rubber conforms to the small dimples and irregularities in the pavement providing additional side resistance in the direction of decel 2) the knobs sometimes add some small bumping of the tire off the road reducing contact and contact forces with the road.

If front and rear tires are identical, optimal braking occurs when the dynamic weight (not the standing weight) on each tire is equal. From a practical standpoint, the further back you get the weight the more even the dynamic tire weight distribution in a high decel condition. The notable exception can be a long wheelbase lowracer recumbent which can actually achieve a static weight distribution far enough back to be beyond optimal in a likely overly optimistic .8 g decel.

On a downhill, front traction is improved less than rear traction is degraded. 3 reasons: the gravity downforce on each the tire is reduced by: 1-cosine (slope angle) so the friction is reduced, with net of the tire pair reduced by this amount even though there will be more front traction on mild downgrades; a rearward force is added to the bike from the slight downgrade equal to the mass times g times the sine (slope angle); weight is transferred to the front tire from the rear tire deviating further in high decel conditions from the optimal equal weight distribution (excepting the long wheelbase lowracer).

Suspension can help braking by maintaining constant force on the tires which in turn maintain a constant footprint when traversing road undulations even small ones thereby eliminating pitching the bike up and down-even if vertical pitching is so slight as to not be humanly perceptible. Suspension can adversely effect braking because: upon initial application, the bike and rider pivot forward relative the tires creating a latency before the bike and rider start slowing down; also the bike-rider combination can start harmonically oscillating on their rotation path adding components in yaw axis and roll axis directions which will reduce braking effectiveness.

Carl Fogel said:

Some questions about braking arose in the disk-brake wheel-
ejection thread that might be deserve their own thread.

I asked what the basis is for an assumption of a maximum
braking on a typical disk brake mountain bike of 0.6 g.
That is, can we confirm this figure as significantly low,
reasonably correct, or significantly high?

Obviously, the kind of tires, the slope of the ground, the
nature of the surface, and the details of the bike
(suspension, frame geometry, and rider position, for
example) may affect braking.

A clean start might help things, so I'll name no one. Some
early posters are now moving from theory to testing.
Others, like me, are merely waffling hopefully and looking
for answers.

First, what do we mean by braking? Stopping distance,
force in terms of g, practical measurements, or
theoretical calculations?

(I think that we're ignoring rider reaction time and just
talking about what happens after we actually drop the
anchor.)

Do bicycle-style disk brakes offer better braking than rim-
caliper brakes? Given the same bicycle and front tire, how
far will each kind need to stop from 20 mph on flat dry
pavement?

Do mountain-bikes with disk brakes and knobby tires brake
better, as well, or worse off-road than street bikes with
caliper brakes and thin tires on flat dry pavement?
Imagine two appropriate riders, side by side, one on the
street and the other on the dirt shoulder. Who stops
shortest?

For that matter, would mountain-bikes with disk brakes and
knobby tires brake better on the same flat dry pavement
than thin-tire caliper-brake street bikes?

Does a downhill slope affect braking? That is, does it
matter that the bike is already in a slightly tipped-
forward position? Does a downhill angle affect traction?
Does a bicycle braking from 20 mph to 0 mph at the same
rate require more braking force and traction descending a
slope than it would on level ground? Does front (or rear)
suspension affect braking? Do rear brakes work better on
downhills?

It might be well to test any theories involving slope on
uphills as well as downhills and level roads.

Details about skidding, tipping, tread, tire pressure,
gravel, and anything else to do with braking are welcome.
I only hope that we can avoid any spelling argument about
disk versus disc. As always, any links to tables or
studies would be nice.

The disc (disk) [1] brake starts off at a disadvantage
because it's such a small diameter. A lot more frictional
force is needed than with rim brakes to get the bike to
slow down at the same rate (open a door by pushing on the
hinge edge and you'll see what I mean). This means the pads
have to be run close to the rim so that an actuation
mechanism with high mechanical advantage can be used. A
good choice of pad and disc material can also add to
friction, but my school physics tells me this can never
exceed the squeezing force applied by the caliper, do the
latter is the limiting factor.

Against this you have the advantage that they stay out of
the mud, are stiffer so they run more true, and allow rim
designs that aren't compromised by the need for a flat
braking track. The latter is, however, rarely exploited on
production bikes.

[1] Did you know that a digital Compact Disc is always spelt
with a "c" even in the US? The spelling is part of the
Philips/Sony "Red Book" standard...

jim beam <[email hidden]> wrote in message news:<[email hidden]>...

Quoted message said:

pull-out is dramatically affected by the serrations
manufacturers put on their axle facings. these create
corresponding indentations on the relatively soft fork
material of the mtb fork - easy to see with the naked eye.
so now, assuming a properly clamped skewer, pull-out has
to overcome not simple friction, but material shear.

the force necessary to shear through only 25mm^2 of
serration engagement, [a conservative estimate given that
a shimano xt mtb disk hub has a minimum outside serrated
face diameter of 17mm & an inside of 13mm - you check the
math] and assuming a very conservative shear stress of
only 200N/mm^2 for the fork material, would be over
5,000N. suddenly, the 1825N pull-out force supposed to be
generated by a disk brake is insufficient to be any major
worry. and that's /before/ any consideration of factors
that would reduce it like lack of traction, blah blah blah
blah blah blah.

Nevertheless, it moves. Not always, but not never either.

James

Zog The Undeniable said:

... The disc (disk) [1] brake starts off at a disadvantage
because it's such a small diameter. A lot more frictional
force is needed than with rim brakes to get the bike to
slow down at the same rate (open a door by pushing on the
hinge edge and you'll see what I mean). This means the
pads have to be run close to the rim so that an actuation
mechanism with high mechanical advantage can be used. A
good choice of pad and disc material can also add to
friction, but my school physics tells me this can never
exceed the squeezing force applied by the caliper, do the
latter is the limiting factor.

However, as the wheel diameter decreases, the effective
braking force available from brakes that act at the hub
(disc and drum) is increases, and the rim diameter/disc
diameter ratio is of course much smaller.

Quoted message said:

Against this you have the advantage that they stay out of
the mud, are stiffer so they run more true, and allow rim
designs that aren't compromised by the need for a flat
braking track. The latter is, however, rarely exploited on
production bikes.

There are now rims being made for trikes that do not have
a rim braking surface. (All but the cheapest trikes use
hub brakes).

--
Tom Sherman - Quad Cities (Illinois Side)

On 26 Mar 2004 18:22:14 -0800, [email hidden] (Carl Fogel)

Quoted message said:

Do bicycle-style disk brakes offer better braking than rim-
caliper brakes? Given the same bicycle and front tire, how
far will each kind need to stop from 20 mph on flat dry
pavement?

Here's the thread I mentioned where I had questioned
braking: groups.google.comgroupsOpen ↗
%40news.chiark.greenend.org.uk

David Damerell does a great job of summing it up in a
single message.
--
Rick Onanian

Zog The Undeniable said:

[1] Did you know that a digital Compact Disc is always
spelt with a "c" even in the US? The spelling is part
of the Philips/Sony "Red Book" standard...

Disc brakes have sometimes been spelled with a 'c' in the US
for 25 years, at least. I remember a 1978 Chevy dumptruck
whose brake pedal said "Disc brakes" on it, and a 1990 GMC
dumptruck that may have said the same. The memory is a bit
fuzzy, me having been a child, but I remember my fascination
with the 'c' spelling.
--
Rick "Fuzzy memories" Onanian

Disc brakes, on mountain bikes, are really no better at
_stopping_ the bike than any other kind, as far as actual
power is concerned. The surface the tires are traveling is
the deciding factor there.

The main advantage is water and mud, because these brakes
are mounted on the hub, away from these contaminants. Also,
they offer a better "feel" than calipers, thereby offering
more precise control. A plus for braking on road/trail
surfaces offering questionable traction.

As for tandems bikes, this is a different story. These
bikes, because of their greater weight to frontal area
ratio, require much more braking on downhills, lest they
get going too fast. Here the main advantage is rim
heating. Again, solved by the mounting f the stopping
surface on the hub.

I have discs on my ATB, and they stop no faster or slower
then my linear pulls on my road tourer.

- - "May you have the wind at your back. And a really low
gear for the hills!"

Chris Zacho ~ "Your Friendly Neighborhood Wheelman"

Chris'Z Corner geocities.comczcornerOpen ↗

"Chris Zacho "The Wheelman"" <[email hidden]> wrote in message
"]news:[email hidden]...

Quoted message said:

Disc brakes, on mountain bikes, are really no better at
_stopping_ the bike than any other kind, as far as actual
power is concerned. The surface the tires are traveling is
the deciding factor there.

The main advantage is water and mud, because these brakes
are mounted on the hub, away from these contaminants.
Also, they offer a better "feel" than calipers, thereby
offering more precise control. A plus for braking on
road/trail surfaces offering questionable traction.

They also take less effort to stop with, I can leave
three fingers and my thumb wrapped around the grip with
discs which is important to relieve hand fatigue on long,
bumpy descents.

Greg

Quoted message said:

serviceability and wet-braking arguments I think for this
discussion). I can lift the rear wheel of my MTB when
braking with v-brakes (you

mentioned

Quoted message said:

"rim-caliper" but I'll throw v-brakes into that
category..) and that's pretty much max braking on a
bicycle.

Absolutely not. You can lift the rear (brake-only) on ANY
properly-maintained bicycle, and yet be nowhere near maximum
braking. You have to lean almost as far back as you can,
almost to the point where the front wheel would rather skid
than hold, before you can reach maximum deceleration.

Sheldon explains it well... body position is absolutely
critical to acheiving optimal braking performance.

--
Phil, Squid-in-Training

Quoted message said:

Details about skidding, tipping, tread, tire pressure,
gravel, and anything else to do with braking are welcome.

Carl, I feel that braking can be summed up easily:

1. More braking power can be effected with a farther-back
handlebar position. Ergo, mountain bikes are inherently
better brakers than road bikes with drop bars. This is
also due to the obviously more perpendicular brake-lever
action of the flat bars. You can get perpendicular in the
drops, but this puts you farther forward over the front
wheel, decreasing your braking effectiveness.

2. All recent brake designs have enough power for either
skidding the front wheel or flipping the rider over the
bars, disc or caliper (don't know about hub brakes)

3. On pavement, the front brake is always the primary brake,
except in wet, sandy, icy conditions. This includes
downhills. Thus, road bikes should primarily use the
front brake.

4. Off-road on MTB, the front brake either tends to take the
backseat or works more so in conjunction with the rear
brake, as front-wheel slideouts while turning are more
common in loose sand, leaves, pine needles, etc. and
often unrecoverable. Sliding the rear, as we all know,
rarely ends in a crash.

5. Straight offroad extreme-angle short downhills (> 70
degrees) on MTBs can be descended initially with both
brakes, and then usually with the rear throughout. It
requires more skill than most have, though.

--
Phil, Squid-in-Training

ZeeExSixAre said:

Quoted message said:

serviceability and wet-braking arguments I think for this
discussion). I can lift the rear wheel of my MTB when
braking with v-brakes (you

mentioned

Quoted message said:

"rim-caliper" but I'll throw v-brakes into that
category..) and that's pretty much max braking on a
bicycle.

Absolutely not. You can lift the rear (brake-only) on ANY
properly-maintained bicycle, and yet be nowhere near
maximum braking. You have to lean almost as far back as
you can, almost to the point where the front wheel would
rather skid than hold, before you can reach maximum
deceleration.

Sheldon explains it well... body position is absolutely
critical to acheiving optimal braking performance.

Or you can ride a bicycle that puts the seat close to the
ground and near the rear wheel, so the angle (relative to
the ground) from the front tire contact patch to the
combined bicycle/rider center of mass is small.

--
Tom Sherman - Quad Cities (Illinois Side)

ZeeExSixAre said:

Quoted message said:

Details about skidding, tipping, tread, tire pressure,
gravel, and anything else to do with braking are welcome.

4. Off-road on MTB, the front brake either tends to take
the backseat or works more so in conjunction with the
rear brake,

That's a bit of a stretch, the front brake is still the
primary brake. If you're using more rear than front you're
not braking very efficiently. The exception is your 2nd
number 4, very steep pitches..

Greg

you're crying wolf.

and if you feel rejected because you're only trying to save
fools from themselves, don't. it's called evoluton.

James Annan wrote: <snip>

Quoted message said:

Nevertheless, it moves. Not always, but not never either.

James

Quoted message said:

That's a bit of a stretch, the front brake is still the
primary brake. If you're using more rear than front you're
not braking very efficiently.

The

Quoted message said:

exception is your 2nd number 4, very steep pitches..

Now that I think about it, I agree. The case with me is that
I don't usually brake unless I'm in a turn, though.
Therefore, most of my braking is with the rear. However,
after a long straight downhill before a turn, then yes, both
the front and rear come into play.

--
Phil, Squid-in-Training

jim beam said:

you're crying wolf.

No, just quoting Lennard Zinn, among others.

Ok, it wasn't a direct quote. But this is:

"I have noticed on my own mountain bikes, all of which have
disc brakes, that if I use a skewer where the lever is
aluminum with an off-center hole at its rounded end to
create the cam, I get downward movement of the axle in the
dropout. After riding, I notice this by flipping the front
skewer open when the bike is standing on its wheels. If the
fork drops down a bit to clunk back down onto the axle, I
know that that hub moved down in the dropout while riding."

Lennard Zinn, author of "Zinn and the art of mountain bike
maintenance" (and other books), and also various technical
Q&A columns in cycling publications.

Shame none of the manufacturers seem to read him.

James