From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: Cornering issues
Date: 16 Aug 2000 20:15:33 GMT

Mike Plawski writes:

> I think my difficulties cornering, particularly on descents, are due
> to the following:

> A Not knowing where I need to enter exit the curve safely
> B Braking excessively
> C Being overly concerned with the surface quality
> D Not wanting anything to do with finding out that I've miscalculated
> any of the above

That sounds like not enough riding in the formative years.  Some of
these things are hard to acquire later in life.  As I said, an active
young person learns how to run around corners leaning into them as
much as traction allows.  The same goes for bicycling and an absolute
fear of falling is a great hindrance to extending that ability.  Not
that it takes falling to get fast in curves, but it must be
calculated in or nothing can be done.

> I am improving--that is, my cornering is improving.  My appearance
> definitely isn't.  I have found that the more I ride a particular
> descent, the better I get, and I feel safe.  However, I am nowhere
> near as good at cornering/descending as other riders who ride at a
> similar overall speed, and I do need to practice more.

It takes a quick CPU to descend an unfamiliar road but just as quick a
one to ride a known one because you cannot depend on what was there
yesterday both on the pavement and traffic.  The old story of "well he
knows the road" doesn't draw much weight because a rider who descends
fast cannot rely on prior experience.  At the limit all roads present
the same hazard, old or new.

> I didn't mention in my earlier post that a couple of cues for my
> improving my cornering is to look further ahead up the road, or
> around the corner, and spreading my fingers out, away from the
> brakes, so that I'm forced to let my bike and body get me through
> the corner.

There are no secrets or secret handshakes and you can't "force"
yourself to be faster by doing hazardous things.  The notion that
everyone who goes faster than I is a fool or at least doing something
risky is false pride.  Fast people are fast in perception and in
analyzing the situation at hand.  Don't ride faster than you feel is
safe or you will possibly strongly reinforce you aversion to fast
cornering.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: Cornering issues
Date: 21 Aug 2000 17:45:36 GMT

Sheldon Brown writes:

>>> If the rear wheel is at the traction limit, any unloading will
>>> induce a skid.  If it isn't at the limit, some rear brake usage is
>>> possible, though it's not clear to me that there's anything to be
>>> gained by it.

>> This is not a binary condition.  Close to the limit of traction is
>> not the limit.

> I was speaking theoretically.  Clearly nobody actually corners _at_
> the limit of traction in practice.

>> Your point of braking with the front wheel only is well placed but
>> it does not explain why using both brakes appears to work better
>> for limited traction.  I learned this from descending dirt roads in
>> the days of yore when many famous descents were unpaved and
>> skidding sounds from the gravel gave good feedback about the
>> benefit of using both brakes.

> I would grant this example, and agree that using both brakes is
> sometimes appropriate in off-road conditions.  The rear brake is
> also a good learning aid in the use of the front brake, because
> skidding gives the clue that the front brake is approaching its
> maximum safe force.  Fixed-gear riding is even better at this.

> Certainly there are degrees of cornering, and few cyclists corner
> close to the max (as in the famous Avocet ad photo of you.)  I would
> maintain that _if cornering near the max_ a rear wheel skid will be
> un-recoverable, and can be induced by even slight use of the rear
> brake, especially if done in combination with the front brake.

> Cornering that is more moderate, where the "centrifugal force" isn't
> close to enough to cause a skid by itself, does permit the use of
> rear-tire skid with recovery, and a cyclist who relies on skid
> sounds as a braking/traction indicator can do so safely.

I gave this some thought as I descended some steep roads this weekend
and am sure that both brakes is the way to do it.  With only a small
margin of traction remaining when banked over steeply, weight transfer
is minimal when braking with about 1/10g and makes front and rear
wheel loading about equal.  Under these conditions, braking load added
to tire traction that is close to its limit, is best distributed to
both wheels.  This results in a traction demand half as great as doing
it with one wheel.

Therefore, I think your comments in the two paragraphs above are not
correct, and this becomes more apparent in practice when on the
bicycle cornering hard.  It is not without reason that all racers in
pictures in hard cornering, descending or in criteriums, are using
both brakes.  This is a pragmatic method that is learned in formative
years by crashing, then when the consequences were taken more lightly.
It is not an optional or style choice such as sticking out the knee in
curves because it is the difference between crashing and not crashing.

I find this easier to visualize by isolating the effects, riding
straight ahead on a 45 degree sloped curb.  This can be done slowly
and the slip distance, if it occurs, is small.  On my daily commute, I
ride along a road that has such an asphalt curb and riding on it gives
a good sense of how to do the braking.  Doing it at downhill speed may
not be everyones cycling enjoyment but it is far more convincing.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jobst.brandt@stanfordalumni.org
Subject: Re: 200mph shimmy, or what makes a bike stay up
Newsgroups: rec.bicycles.tech
Date: Tue, 04 Sep 2001 00:11:01 GMT

Nick Maclaren writes:

> You are wrong, I am afraid.  It requires good middle-ear balance.
> Of the three normal methods of balancing, sight is too slow, touch
> needs at least one hand on the handlebars, and that leaves the
> circular canals.  And 20% of the population have loss of function in
> the middle ear, even ignoring those with heavy colds!

Not so.  Where do you get that.  I suggest you read the FAQ item on
descending and note that I had a middle ear disturbance once that
rotated my sense of down by 90 degrees or so, so that I fell over when
closing my eyes.  In that state, I could descend winding roads as fast
as ever from visual means.  How do you propose the middle ear (like a
plumb bob in moving vehicle) has any idea where "down" is.

> I have serious middle-ear damage, and balance almost by sight and
> touch alone - I cannot ride no hands, and even riding with one
> hand requires a stable bicycle.

You have other problems.  Don't extend that to an explanation of how
people stay upright.

>>> However in my personal experience, riding with no hands leaves one
>>> vulnerable to unseen road debris and road damage.  This is one
>>> lesson I learned the hard way, I have the bad knee to remind me
>>> and I do not intend to repeat my previous mistake.  There is
>>> little to gain and much to lose.

> This is true even riding one-handed.  Few people can control a
> bicycle if they hit anything serious with only one hand on the
> bars, but I agree that riding no hands is far more likely to
> cause a loss of control.

Not true.  One handed causes steering motions while no handed does
not.  I have often let go of the other hand while riding one handed on
encountering a bump in the road to avoid this effect.  I get the
impression that much of this discussion is based on untried
theoretical perceptions.  It takes more than that to analyze such
matters.  I suggest a keen sense of observation and an understanding
of what physical effects apply.

That one chooses to not ride no-hands indicates that the rider feels
there is not enough safety margin to do it safely.  The same goes for
old folks who are afraid to cross the street because they cannot jump
out of the way in an emergency.  I know how that feels from when I had
a sprained ankle and couldn't run.  Crosswalks became danger zones for
me that I had not known before... or after.

When I hurry down a mountain and pass a car that speeds up
inadvertently when I am even with the driver, I don't hesitate to
knock on his window as we enter a curve at speed.  This works miracles
and is not as hazardous as it may appear if you are agile on the
bicycle.  It's all relative to the speed at which one processes events
and is able to respond to them.  I also have neighbors who have AARP
lights along the front walk and garden, even in bushes and trees.
They are terrified of the dark and wouldn't go there at night... or
for that matter ride a bicycle no-hands.

Jobst Brandt    <jobst.brandt@stanfordalumni.org>

From: jobst.brandt@stanfordalumni.org
Subject: Re: Braking while turning
Newsgroups: rec.bicycles.tech
Message-ID: <qMoWa.7304$dk4.324939@typhoon.sonic.net>
Date: Fri, 01 Aug 2003 07:36:54 GMT

Subject: 9.15  Descending II
From:  Jobst Brandt <jobst.brandt@stanfordalumni.org>
Date: Fri, 11 May 2001 16:35:42 PDT

Descending and Fast Cornering

Descending on mountain roads, bicycles can reach speeds that are more
common on motorcycles.  Speeds that are otherwise not attainable, or
at least not continuously.  Criterium racing also presents this
challenge, but not as intensely.  Unlike a motorcycle, the bicycle is
lighter than the rider and power cannot be applied when banked over
when cornering hard.  Because narrow bicycle tires inflated hard have
little traction margin, a slip on pavement is usually unrecoverable.

Drifting a Road Bicycle on Pavement

Riders have claimed they can slide a bicycle on dry pavement in curves
to achieve greater cornering speed, as in drifting through a turn.  A
drift, in contrast to a slide, means that both wheels slip, which is
even more difficult.  This notion may come from observing motorcycles,
that can cause a rear wheel slide by applying power when banked over.
Besides, when questioned about how this is done, the proponent says
that the ability was observed, done by others.

A bicycle can be pedaled only at lean angles far less than the maximum
without grounding a pedal, so hard cornering is always done coasting,
hence, there is no power in hard cornering.  Although bicycles with
high ground clearance have been built, they showed only that pedaling
imbalance has such a disturbing influence on traction, that pedaling
at a greater lean angle than that of a standard road racing bicycles
has no benefit.  That is why road bicycles are built the way they are,
no higher than is useful.

That bicycle tires have no margin for recovering a slip at maximum
lean angle, has been tested in lean-slip tests on roads and testing
machines.  For smooth tires on pavement, slipout occurs at slightly
less than 45 degrees from the road surface and is both precipitous and
unrecoverable.  Although knobby tires have a less sudden slipout and
can be drifted around curves, they begin to side-slip at a more
upright angle as their tread fingers walk rather than slip.  For this
reason, knobby tires cannot achieve lean angles of smooth tires and
offer no cornering advantage on pavement.

How to Corner

Cornering requires estimating the required lean angle before reaching
the apex of the turn where the angle with the road surface is the
critical parameter rather the angle with the vertical, as is evident
from banked curves.  Lean angle is limited by the available traction
that must be assessed from velocity and appearance of the surface.
For good pavement, this angle is about 45 degrees, in the absence of
oil, water, or smooth and slick spots.  Therefore, a curve banked
inward 10 degrees, allows a lean of up to at least 55 degrees from the
vertical, while a crowned road with no banking, where the surface
falls off about 10 degrees, would allow only up to 35 degrees.

Banked curves have a greater effect than just adding to the maximum
lean angle, because with a steeper banking, more of the centripetal
cornering force goes into increasing traction directly into the
banking up to the point of a vertical wall where only the maximum
G-forces limit what speed a bicyclists can attain.  In contrast, an
off banked curve makes cornering progressively more difficult until
the bicycle will slip even at zero speed.  This effect is more
naturally apparent to riders who exceeded these limits early in life
and  have added the experience to expected natural phenomena.

The skill of visualizing effects of speed, traction, braking, and
curvature are complex, but is something humans and other creatures do
regularly in self propulsion.  The difficulty arises in adapting this
to higher speeds.  When running, we anticipate how fast and sharply to
turn on a sidewalk, dirt track, or lawn, to avoid sliding.  The method
is the same on a bicycle although the consequences of error are more
severe.

Cornering requires reflexes to dynamics that are easily developed in
youth, while people who have not exercised this in a long time find
they can no longer summon these skills.  A single fall strongly
reinforces doubt, so cautious practice is advisable if returning to
bicycling after a long time.

Countersteer

Countersteer is a popular subject for people who belatedly discover or
rediscover how to balance.  What is not apparent, is that two wheeled
vehicles can be controlled ONLY by countersteer, there is no other
way.  Unlike a car, a bicycle cannot be diverted from a straight path
by steering the wheel to one side.  The bicycle must first be leaned
in that direction by steering it ever so slightly the other way.  This
is the means by which a broomstick is balanced on the palm of the hand
or a bicycle on the road.  The point of support is moved beneath the
mass, in line with the combined forces of gravity and cornering, and
it requires steering, counter and otherwise.  It is so obvious that
runners never mention it, although football, basketball, and ice
hockey players conspicuously do it.

Braking

Once the basics of getting around a corner are developed, doing it
fast involves careful use of the brakes.  Besides knowing how steeply
to lean in curves, understanding braking makes the difference between
the average and the fast rider.  When approaching a curve with good
traction, the front brake can be used almost exclusively, because it
is capable of slowing the bicycle so rapidly that nearly all weight
transfers to the front wheel, at which point the rear brake is nearly
useless.  Once in the curve, more and more traction is used to resist
lateral slip as the lean angle increases, but that does not mean the
brakes cannot be used.  When banked over, braking should be done with
both brakes, because now neither wheel has much traction to spare and
with lighter braking, weight transfers diminishes.  A feel for how
hard the front brake must be applied for rear wheel lift-off, can be
developed at low speed.

Braking in Corners

Why brake in the turn?  If all braking is done before the turn, speed
will be slower than necessary before the apex.  Anticipating maximum
speed for the apex is difficult, and because the path is not a
circular arc, speed must be trimmed all the way to that point.  Fear
of braking in curves usually comes from an incident of injudicious
braking at a point where braking should have been done with a gentle
touch to match the conditions.

Substantial weight transfer from the rear to the front wheel will
occur with strong use of the front brake on good traction just before
entering the curve.  When traction is poor or the lean angle is great,
deceleration cannot be large and therefore, weight transfer will be
small, so light braking with both wheels is appropriate.  If traction
is miserable, only the rear brake should be used, because although a
rear skid is recoverable, a front skid is generally not.  An exception
to this is in deep snow, where the front wheel can slide and function
as a sled runner while being steered.

Braking at maximum lean

For braking in a curve, take the example of a rider cornering with
good traction, leaning at 45 degrees, the equivalent of 1G centrifugal
acceleration.  Braking with 1/10g increases the traction demand by one
half percent.  The sum of cornering and braking vectors is the square
root of the sum of their squares, SQRT(1^2+0.1^2)=1.005 or an increase
of 0.005.  In other words, there is room to brake substantially during
maximum cornering.  Because the lean angle changes as the square of
the speed, braking can rapidly reduce the angle and allow even more
braking.  For this reason skilled racers nearly always apply both
brakes into the apex of turns.

Suspension

Beyond leaning and braking, suspension helps substantially in
descending.  For bicycles without built-in suspension, this is
furnished by the legs.  Standing up is not necessary on roads with
fine ripples, just taking the weight off the pelvic bones is adequate.
For rougher roads, enough clearance must be used so the saddle carries
no weight.  The reason for this is twofold.  Vision will become
blurred if the saddle is not unloaded, and traction will be
compromised if the tires are not bearing with uniform force on the
road while rolling over bumps.  Ideally the tires should bear on the
road at constant load.  Besides, if the road has whoop-de-doos, the
seated rider will get launched from the saddle and possibly crash.

Lean the Bicycle, the Rider, or Both

Some riders believe that sticking the knee out or leaning the body
away from the bicycle, improves cornering.  Sticking out a knee is the
same thing that riders without cleats do when they stick out a foot in
dirt track motorcycle fashion.  On paved roads this is a useless but
reassuring gesture that, on uneven roads, even degrades control.  Any
body weight that is not centered over the bicycle (leaning the bike or
sticking out a knee) puts a side load on the bicycle, and side loads
cause steering motions over uneven road.  Getting weight off the
saddle is also made more difficult by such maneuvers.

To verify this, coast down a straight but rough road, weight on one
pedal with the bike slanted, and note how the bike follows an erratic
line.  In contrast, if you ride centered on the bike you can ride
no-hands perfectly straight over the same road.  While leaning off the
bike, trail of the front wheel causes steering on rough roads.

Outside Pedal Down

It is often said that putting the outside pedal down in a curve
improves cornering.  Although most experienced riders do this, it is
not because it has anything to do with traction.  The reason is that
it enables the rider to unload the saddle while standing with little
effort on a locked knee, cushioning his weight on his ankle.  This can
only be done on the outside pedal because the inside pedal would hit
the road.  However, standing on one extended leg does not work on
rougher roads, because the ankle cannot absorb large road bumps nor
raise the rider high enough from the saddle to avoid getting bounced.
Rough roads require rising high enough from the saddle to avoid hard
contact while the legs supply shock absorbing knee action, with pedals
and cranks horizontal.

Body Contortions

Most of the "body English" riders display is gratuitous gesturing,
much like the motorcyclists who stick their butt out in curves while
their bikes never get down to 45 degrees (the angle below which hiking
out becomes necessary to keep hardware from dragging on the road).  In
fact, in a series of tight ess bends, there's no time to do any of
this.  It's done by supporting weight on the (horizontally positioned)
pedals, and unless the road is rough, with a light load on the saddle.
On rough roads, the cheeks of the saddle, (the ones that went away
with the Flite like saddles) are used to hold the bicycle stably
between the legs while not sitting.

The path through a curve is not symmetrical for a bicycle, because it
can slow down much faster than it can regain speed.  Thus the
trajectory is naturally asymmetric.  Brakes are generally used to the
apex (that is usually not the middle) of the curve, where pedaling at
that lean angle is not possible, nor does pedaling accelerate as fast
as braking decelerates.

Hairpin Turns

Although the railroad term switchback arises from early mountain
railroading where at the end of a traverse, a switch is turned to back
up the next traverse, after which another switch is turned to head up
the next, on roads these are hairpin turns.  In such turns trajectory
asymmetry is most conspicuous, because braking can be hard enough to
raise the rear wheel when entering but one cannot exit with such
acceleration.  For this reason, riders often find themselves with
extra road on the exit of such turns, having slowed down too much.

Vision

Where to direct vision is critical for fast cornering.  Central vision
should be focused on the pavement where the tire will track, while
allowing peripheral vision, with its low resolution and good
sensitivity to motion, to detect obstacles and possible oncoming
traffic.  Peripheral vision monitors surroundings anyway, so the
presence of a car in that "backdrop" does not require additional
consideration other than its path.

If central vision is directed at the place where an oncoming vehicle
might appear, its appearance presents a new problem of confrontation,
stopping image processing of the road surface for substantial time.
Because the color or model of car is irrelevant, this job can be left
to peripheral vision in high speed primitive processing, while
concentrating on pavement surface and composition.

When following another bicycle or a car downhill, the same technique
is even more important, because by focusing on the leading vehicle,
pavement and road alignment information is being obscured giving a
tendency to mentally become a passenger of that vehicle.  Always look
ahead of the vehicle, observing it only peripherally.

Riders often prefer to keep their head upright in curves, although
leaning the head with the bicycle and body is more natural to the
motion.  Pilots who roll their aircraft do not attempt to keep their
head level during the maneuver, or in curves, for that matter.

The Line

Picking the broadest curve through a corner may be obvious by the time
the preceding skills are mastered, but that may not be the best line,
either for safety or because the road surface is poor.  Sometimes
hitting a bump or a "Bott's dot" is better than altering the line,
especially at high speed.  Tires should be large enough to absorb the
entire height of a lane marker without pinching the tube.  This means
that a minimum of a 25mm actual cross section tire is advisable.  At
times, the crown of the road is sufficient to make broadening the
curve, by taking the curve wide, counterproductive because the crown
on the far side gives a restricted lean angle.

Mental Speed

Mental speed is demanded by all of these.  However, being quick does
not guarantee success, because judgment is even more important.  To
not be daring but rather to ride with a margin that leaves a feeling
of comfort rather than high risk, is more important.  Just the same,
do not be blinded by the age old presumption that everyone who rides
faster than I is crazy.  "He descends like a madman!" is one of the
most common descriptions of fast descenders.  The comment generally
means that the speaker is slower.

Braking Heat on Steep Descents

Although tandems with their higher weight to wind drag ratio have this
problem more often, steep mountain roads, especially ones with poor or
no pavement require so much braking that single bicycles blow off
tires from overheating.  For tubulars the problem is not so much over
pressure than rim glue melting as all pressure sensitive glues do with
heating.  As glue softens, tires slip on the hot rim and pile up on
the valve stem.  This is the usual indicator that tubular tire wheels
are too hot.  The next is that the tire arches off the rim in the area
just before the stem.

This is a serious problem both for tubulars and clinchers because most
clincher tires, given enough time on a hot rim will blow off if
inflated to recommended pressure.  Pressure that gives good rolling
performance (hard) while tubulars roll off from lack of adhesion to
the rim.  The faster the travel, the more descending power goes into
wind drag and the better the rims are cooled.  Going slowly does not
help, unless speed is reduced below walking pace.

On steep descents, where rims stay too hot to touch for more than a
minute, reducing tire inflation pressure is a sure remedy.  However,
tires should be re-inflated once the rims cool to normal.  The
blow-off pressure is the same for small and large tires on the same
rim, it being dependent only on the opening of the rim width.  Also,
tires with a smaller air volume become hot faster than larger ones.

There is no way of descending continuously and steeply without
reducing inflation pressure, unless there is an insulator between the
tube and rim of a clincher.  Insulating rim strips are no longer
offered because they were an artifact of dirt roads that often
required riders to descend so slowly that all potential energy went
into the brakes and almost none into wind drag.  These rim strips were
cloth tubes filled with kapok, their insulating purpose being unknown
to most people when they were last offered.

Jobst Brandt
jobst.brandt@stanfordalumni.org
Palo Alto CA

From: jobst.brandt@stanfordalumni.org
Subject: Re: Downhill speeds...or:  I must be getting old
Newsgroups: rec.bicycles.misc
Message-ID: <fK5Ec.19477$Fo4.257542@typhoon.sonic.net>
Date: Tue, 29 Jun 2004 03:54:51 GMT

Fred Hall writes:

> Background: Just started seriously road riding this year on a Trek
> 1500, after mostly trail (packed stone dust fairly flat) riding on a
> Gary Fisher hybrid.  Got the road bike about 3 weeks ago and have
> been cruising around, a lot of flat roads, but some minor climbs and
> descents.

> Anyway, yesterday I figured I'd change up my route and take a
> certain road I knew had a pretty good hill on it.  Not wanting to
> climb the hill, I made the route so it went down the hill.  Long
> story short, it's a pretty good hill and even with a decent headwind
> according the the ol' computer I was doing about 35 mph down the
> hill for a good three plus minutes.  Needless to say, the knuckles
> were white from hanging on for dear life and all I could picture was
> having a dog (or something) jump out at me, or getting a blow out,
> and me going ass over teakettle down the hill.  Of course, I made it
> to the bottom with no incidents and went about the rest of my ride.

Don't descend any faster than you feel is safe.  Pressing top speed
descents is a good way to get hurt, badly.  Most fast descenders I
know, including myself, took a lot of spills when young and
rebounding.  I don't recommend trying to do that after age 25 or so.
Some people can do it but learning a new mother tongue like a native
is easier than riding close to the limit of traction, something that
is necessary to descend fast.

How it is done is analytical, but the rider must be sure of the limits:

http://draco.acs.uci.edu/rbfaq/FAQ/9.15.html

Jobst Brandt
jobst.brandt@stanfordalumni.org

From: jobst.brandt@stanfordalumni.org
Subject: Re: Downhill speeds...or:  I must be getting old
Newsgroups: rec.bicycles.misc
Message-ID: <WAqEc.19648$Fo4.260485@typhoon.sonic.net>
Date: Wed, 30 Jun 2004 03:38:30 GMT

David Reuteler writes:

>>> If you drag your brakes to keep a speed you're comfortable with
>>> you run the risk of overheating.  That's only applicable on
>>> serious descents but that's where the problem manifests itself
>>> most strongly anyway and 30mph just ain't that fast on a descent.

>> This is all true but doesn't really address what the OP was asking,
>> "Does everyone get used to higher speeds?". That was the question I
>> was addressing, not "What are some of the mechanical aspects of
>> descending at speed?". And no, 30 mph ain't that fast.... :-)

> Well, it's a bit more than just a mechanical aspect of descending at
> speed.  Blindly telling someone to slow to a comfortable speed w/o
> that little bit of info is potentially dangerous.

> Anyway, a little more context from the OP would be useful.  Like,
> for instance does he live in Kansas or western Colorado.

That makes no difference.  The mechanics of it are the same and I am
sure that riding a criterium in Kansas (if you like( is the same as
riding one in Milano (I).

Maybe you can explain what is potentially dangerous about slowing to a
pace that feels safer.

Another point worth mentioning is that I have had enough riders crash
behind me to believe they probably had no idea with how little margin
I was descending nor that I wasn't fully loading the the saddle as I
rolled over poorer traction at the maximum lean angle that I though
possible.  Don't follow a faster rider and assume that because you
think you are doing the same thing and that therefore, you are safe.

Jobst Brandt
jobst.brandt@stanfordalumni.org