Not clear why racers drag their knees

The physics of motorcyle dynamics has to be a complex subject being that
one-track vehicles came on the scene quite late in human history. The
modern bicycle predates the automobile by only a quarter century, or so.

Marilyn Vos Savant and others have attempted to explain how a two wheeler
stays upright and turns. See:

http://www.wiskit.com/marilyn/bicycle.html

My question is directed specificly to the aspect of rider position, as the
physics has to be the same regardless of whether one sits in the usual way
or hangs off to the side of the machine with is knee almost touching the
roadway.

When I want to make a turn, I push on the handle bar and shift my body
weight to the opposite side. For example, if I want to turn right, I push
on the right grip and my body moves to the LEFT while the machine takes a
lean to the RIGHT. In essence, my body stays upright and essentially
vertical to the roadway while the motorcycle assumes a lean underneath me.
I think what happens is a push to the right turns the bar a little to the
left. Gyroscopic precession then causes the bike to fall to the right a
little and assume a circular path with the center approximately at the
intersection of the extended centerlines of the front and rear axles. My
body weight shift must be equal to its centrifigal force and is irrelevant
to the motorcycle otherwise. This would explain the next paragraph.

Racers however, appear to be hanging off their machines. Is there a good
reason? Perhaps it has to do with the knee as a gauge as to how much lean
the bike can stand before it slides out. Certainly there are no
centrifigal forces felt by the rider as there are in a car, because the
lean assumed by the motorcycle resolves all gravity and centrifigal forces
vectorly to a point "down" with respect to the rider's senses. This is
just like flying a coordinated turn in an airplane. You just get "heavier"
but do not have a sensation of side force as you do in car. It also occurs
to me that hanging off the bike cannot change its lean angle for a
particular radius turn because the mechanics are the same: intersection of
radii. Therefore it can make no difference in the resolved forces whether
the rider sits upright during a turn or hangs off the bike. Am I correct?
If so, the bike doesn't care, so there must be another reason why racers do
what they do.

Its interesting to note that when a motorcycle is at walking speed, it has
to be manhandled and steered tiller-wise like a car, but once at any kind
of stable speed, its "steering" is automatic as determined by little pushes
and shifts of body weight as I described. Any attempt to turn the handle
bar as you would a trike will immediately destabilize the bike as every
rider knows. The reason why pushing on the handles is okay must be that
simultaneously the body weight is shifted to the opposite side, maintaining
balance. That makes it all the more difficult to explain why shifting the
body off the bike on the side of the turn and lowering the knee to the
pavement doesn't dump the machine.

 

Gravity pulls the bike toward the center of the turn.

Centrifugal force pushes the bike out.

Hanging in toward the center moves the center of gravity in and down,
allowing for a faster corner speed given the same lean angle.

And if you are really staying upright while your bike leans in the corner,
you're not doing yourself any favors. Lean with the bike, but keep your
head upright.

 

so.

So google up "tony foale" and buy his book and take it to bed and do
whatever it is that you do with the shades closed and wash your hands
afterwards...

(Snip a bunch of trolling text intended to make NN look wiser than he
is...)

Why roadracers hang off motorbikes is a matter of *technique*, not
physics, they could give a *fig* for physics, pro racers use techniques
that WORK to WIN races, and squirrels copy those techniques to
grandstand for other squirrels. It's evolution you see. Darwin.
Squirrels that survive street racing graduate to track racing, some
win, some lose, some sell techniques back to other squirrelly kids,
some superstar racers learn from other pro racers and become
legendary...

Motorbikes and bicycles just *happened*, they developed *accidentally*
from the "Gentleman's Hobbyhorse" of the 18th century. It was nothing
but a wooden beam with a saddle between two wooden spoke wheels and a
dandy could straddle it and walk faster. No rake, no trail, no physic
involved, just the art of wood working and a market for it...

Bicycles developed from that and people in Europe fell in love with
*bicycle racing* because it was a lot cheaper than racing a horse and
they didn't have to feed the horse or shovel horseshit. So far as I
know (or care to know) nobody has ever claimed to have done the
original structural analysis or investigated the dynamics of handling
of the Safety Bicycle with its diamond frame. Bicyles became mass
produced because one small manufacturing shop saw a market and copied
the other shops product...

Motorbikes just *happened* too. Nobody ever thought about moment arms
and centers of gravity and beam torsion, they simply were *tired of
pedalling uphill*. So somebody figured out how to clip a Maytag washing
machine engine into a Safety Bicycle frame and the motorbike was born.
They quickly tired of pedalling on the flat, too, so they kept the
motor running constantly and the pedals became superfluous so they were
omitted...

And owners of motorbikes met and debated about which brand of motorbike
was best at climbing steep hills and whose motorbike was fastest on the
flat or around a flat track and so motorbike racing clubs were born,
just as bicycle racing clubs had multiplied thirty years before...

And some riders liked to go in circles on flat dirt tracks and slide
the tires and they found they fell down a lot on the side toward the
inside of the turns as the back tire skated away and they started
wearing heavier padding on the left or right leg of the leather suits
that they wore to keep from scraping their own hides off when they fell
down on these dirttrack speedways...

They looked like hockey players with one big leg...

And so Speedway Racing was born and the British racers went 'round and
'round on the dirt with one knee on the ground to act as an outrigger,
until some Brit heretic decided that he could control the bike better
by *standing up on one foot* with most his weight OFF THE BIKE...

And it was way back before World War II when the sport of ice racing
was born in northern latitudes, and ice racers went around and around
on their spiked tire ice racers leaning way over and sliding on leather
padding on their inside thigh too...

Fast forward to the 1970's and a young rising star with the initials KR
(if you don't know who KR is you are a danged furriner or an
infidel!)has risen up through the heretical ranks of stand up flat
track racing and is now being mentored by Kel Carruthers (as above, if
you don't know who Kel was, etc...) to become Yamaha's great Grand Prix
hope...

KR sees a young Finnish guy named Saarinen racing around and this
danged Finn is dragging his knee and going fast and winning races on
his TR-350 Yamaha production racer and he's fast enough from his ice
racing experience, KR decides to try it and he goes faster...

So KR says to Kel, "Hey, I'm dragging my knee on the pavement!" And Kel
says,
"Well, *don't* do that!" But KR is wearing holes in the knees of his
leathers and he's repairing his leathers with duct tape and soon
everybody is copying KR's style and a whole knee puck industry was
born...

I explained it above. The knee is not only out to gauge lean angle,
it's there to push the bike back up if the tires momentarily slide
away. In the recent AMA Superstock race at Fontana, California I
watched one Team Yoshimura almost run into the back end of his Yosh
team mate and lose traction at front and rear of the bike, he stomped
the ground *once* with his right foot at about 120 mph to push the bike
vertical again...

As I recall, it was Ben Spies that almost hit Aaron Yates, who'd
suddenly slowed. Maybe Yates missed a shift, Spies hit the brakes too
hard, got his rear wheel off the ground at a buck and change (If you
don't know what a buck and change is, you're a furriner)...

Somebody said that Spies elbows sometimes touch the ground at max lean
angle.
I have heard of riders who've leaned past 60 degrees from the vertical
saving the motorbike by pushing with their shoulder...

If you watch the riders setting up for a high speed corner, you'll see
them stick the inside knee out very early, adjust their speed for the
corner and then flick the motorbike down to maximum lean angle rapidly.
I watched one youngster on 1000cc Superstock machine stick his knee out
one way and lean his body the opposite way lap after lap as he entered
a high speed turn...

He was riding on pointy race tires that are intolerant of transistional
lean angles. Just sticking his knee out was steering his bike toward
the apex of the turn, and he was just increasing his physical work load
by having to lean the wrong way...

Once upon a time, in a galaxy far, far away, we were racing street
bikes with low mufflers and we didn't have pointy racing tires. We hung
off and pushed the motorbike *away* from the direction of travel to
keep from scratching out mufflers. But some Brit riders didn't *care*
if they scratched their mufflers and side stands and center stands and
made the spark fly. They were known as "Scratchers"...

Oh, no kidding? You noticed that *heavy steering feeling* in a
motorbike, and thought it was *unique* to two-wheeled vehicles? Look up
*castor angle*. Compare the castor angle of a car to that of a
motorbike and report back to us. Find somebody who owns an old 1960's
Triumph TR-4A and do some parallel parking and let us know how it feels
to muscle the steering wheel back and forth, and let us know your
theory about why the steering is lighter as you drive the car in
*reverse* than it is going *forward*...

BTW, Nomen, are you that programmer guy who's a hockey goalie, claims
he's an elf, and dresses up in fur suits?

And why have you posted all that encoded stuff to those
alt.anonymous.message
sites? What is somebody with a handle like "Nomen Nescio" trying to
hide?

 

Maybe you should do some more reading before writing
all this, it's rather tireing to read you know.

The basic (there are other minor/secondary ones) reason
to hang of on the inside is to prevent bike hardware
dragging too hard on the pavement, causing a crash by
unloading the wheels.

<snip>

You ride off road style. This has certain advantages
but apply mostly to bikes with light front ends ridden
on low friction surfaces.

If you maintain your weight on the outside, sit
centred or hang of on the inside will affect the
"balance" (lack of better word) of the bike during
the turn. As far as I have managed to understand
it the bike is steered more like a car (by angling
the front wheel into the turn) when hanging of but
when you sit up and let the bike lean more (off
road style) it turns more by the (debated) cone
roll effect where both wheels carve into the turn.
The end result of this is that road racers
preserve more of their precious rear wheel
grip by utilising the front more for steering by
hanging of. Motocross riders in flat sharp turns
avoid front wheel wash out and promote
beneficial rear wheel slides by putting more of
the cornering work on the rear tyre.

Let the endless debate continue!

 

OK, so my simplification eluded someone.
Gravity pulls the bike down to the ground, towards the center of the turn.

Must teach different stuff in the science classes where I grew up.

 

it has to do with the bike's tires being upright. the sidewalls of the tires
are not
as capable of gripping the road as an upright tire.
sammmmm

 

But in north Texas the football team was quite the thing.

A lot to read. I knew I missed out when I didn't take physics.

 

If a rider actually got off the crown of the tire onto the sidewall,
what you say would be true. The motorbike tire manufacturer's go
through some abstruse formula that can probably be found in the conics
section of a math book, but I dunno exactamente what to look for...

Anyway, the manufacturers either design the crown of the tire to give
the same area of rubber (and therefore the same size tire contact
patch) at all angles of lean, or they design the crown of the tire to
actually give *more*
contact patch area at higher lean angles...

The crown of a motorbike tire has a uniform stiffness all the way
across its surface so the contact patch will have a uniform size...

But, as the angle of lean increases, the motorbike tire pushes harder
against the road (41.4% harder at a 45 degree lean angle) and this may
actually increase the size of the contact patch for that reason...

But, it wasn't until the mid-1980's that sportbikes were produced with
high, tucked up exhaust systems and high foot pegs so riders could use
all the lean angle that manufacturer's were designing their tires
for...

Before that, riders had to hang off to avoid scraping the hard parts if
they wanted their motorbike to remain pretty...

Bridgestone published this handy English language document about 20
years ago to educate riders as to what was going on with tires. Too bad
they hid it on a Japanese language site:

http://mc.bridgestone.co.jp/pdf/mcintroe.pdf

 

So I went home and read a little more. I ran across another explanation of
what goes on when a motorcycle turns. This one is taken from the book
Motorcycle Design and Technology - How and Why, written by Gaetano Cocco in
collaboration with Aprilia. I'll transcribe what he wrote so nothing gets
lost in interpretation, even though he uses the dreaded "F" word.

page 31:
"Let us look for a moment at two phenomena that play a very important role
in allowing motorcyclists to corner. they are:

centrifugal force;
gyroscopic effects.

"What is the centrifugal force? It is a pseudo-force that opposes a
rotating motion, acting at te center of gravity of the body under
consideration.Its direction is given by the conjunction between the center
of gravity and the center of curvature of the trajectory of the mass; it is
directed radially toward the outside of the curve.
"The intensity of such a force is expressed in the well known relation;

"Fc( centrifugal force) = Mass times (Velocity squared) / Radius"

then there is a section about gyroscopic effect

"Let us once again take up the concept of gyroscopic effect, introduced in
the previous chapter, and add a few observations to it. With straight arms,
hold up a bicycle-wheel axle, as if you were riding on a bicycle; turn te
weel in front of you, imagining that it's axle is the handlebar.
"As we have seen, raising and lowering this axle parallel to itself, no
extraneous forces are felt on your hands because the sole force to be
opposed is the weight of the wheel itself. Try now to 'steer' firmly
towards your left, as if you were cornering in that direction. The effect
may come as a surprise to you: what you will feel is the action of a couple
on your arms that tends to make them tilt clockwise with respect to the
direction of imagined travel. At this point, keep in mind the concepts of
centrifugal force and gyroscopic effect as they have just been presented,
because we are ready to go around our first corner, for example, to the
right.
"Putting the wheel back onto the bicycle, mount the bike and pedal until
you work up to a good speed. At this point, perform the maneuver just
described above in the section on gyroscopic effects: that is to say, a
rapid but brief turn of the handlebars to the left.
"That's right, we are quite serious: remember that our intention is to
corner to the right, but trust us for a moment and see what happens. Since
the bicycle is changing directions, both a centrifugal force and a
gyroscopic effect are created, with the following consequences:
"- the centrifugal force that acts upon the center of gravity, being
directed outwardly away from the curve, will tend to overturn the bike,
leaning it towards the right;
"- the gyroscopic effect will give rise to a comparable effect, as a
consequence of the pull of the handlebars to the left, creating a couple
that will lean the vehicle ever more towards the right (clockwise with
respect to the direction of travel).
"Unless something else intervenes at this point to create a new state of
equilibrium, the situation will inevitably deteriorate and the bike will
fall over. And yet, it is just as we are losing control of the bike that we
are also about to go around the corner!
"We have said that our bike is leaning towards the right and that the
rider also feels a sensation of falling towards the right. Let us now turn
the steering, making a slow rotation to the right: this places the bicycle
on a circular path (or rather, in a curve towrads the right), giving rise to
a centrifugal force that will bring about a new state of balance.
"The force of the bike's weight, tending to make the motorcycle fall
inwardly, combined with the centrifugal force, will give rise to a resultant
force along the axis that connects the point of contact wheel-to-ground with
the center of gravity.
"What we are describing is a state of balance"

OK, that's how the folks who build bikes describe it. The first time
reading it, I had to get used to European English. It appears the "F" word
(centrifugal) is (mis?)used by people in the industry, and they're writing
books to lead us astray. Kind of like all those people selling "billet"
parts.
As for me, I'm just a lost sheep wondering who's the heretic and who's
right. ;-)

 

Oh, no! The dreaded gyroscopic precession effect again! It has its
greatest effect when you are riding at the motorbike's top speed, yet
you are able to start countersteering the motorbike at 5 or 10 mph, but
you still get the same feeling from the tire's contact patches that you
got from spinning the bicycle wheel when it was OFF THE PAVEMENT...

Wazzup wif dat? Enquiring minds want to know...

Sure, there are gyroscopic effects associated with both front and rear
wheels of any wheeled vehicle, especially if they are spinning rapidly
and you will *feel* the gyroscopic precession effect in the handlebars
if the tire contact patches aren't touching the pavement, as in the
bicycle example you quoted...

Your motorbike will countersteer if the front wheel is on the pavement,
and what you will feel then is the raction of the tire contact patches
against the pavement...

Maybe it's a coincidence that motorbike steering and gyroscopic
precession feel the same. As I mentioned before, motorbikes just
happened, they evolved out of bicycles. (1)

There's a three-finger rule to demonstrate what a gyroscope's rotor
will do if it is free to precess, but, of course, a motorcycle's wheel
isn't free to precess if the tire contact patch is touching the
pavement. That's why we go to all the trouble of employing complicated
high-$$$ suspension systems and strive to keep our tires in contact
with the pavement by careful throttle control on rough pavement...

Here's the three-finger rule as it applies to motorcycles and bicycles.


Hold your right thumb up and tilted at about 25 degrees to the
vertical, back toward you (precession vector and steering axis), point
your index finger away from you, and it will point a little upward
(torque vector and axis), point your middle finger to the left (spin
vector and axis). Imagine that the axis of wheel rotation is your
middle finger, and that the steering axis is your thumb...

Using your left index finger, push your right index finger so your
whole hand has to turn to the left, pivoting around the wrist. You'll
see that your wrist (symbolizing the steering head) has to bend to the
left, but it *twists* to the right...

So the motorbike leans to the right, if I push on the right handlebar,
and I get that weird pleasure from feeling like the handlebars are
alive---alive, I tell you! My handlebars are alive!

Is all that by coincidence, or by design? Enquiring minds want to know
who this "King" guy was, that the tilted kingbolt was named after. What
did he know, and when did he know it? Or was it some guy named "Caster"
that figured it all out? The truth is lost in the mists of time...
----------------------------------------------------------------------------

(1) There's a theory of the natural metamorphosis of the baby paper
clip into the pupal coat hanger state, and on, to the adult bicycle
form...

The theory goes that all bicyles that once coat hangers lying tangled
in a dark closet. And coat hangers evolved out of chains of paper clips
in a messy desk drawer. And every once in awhile the local police
force has a sale to get rid of all those ownerless bikes laying tangled
in their impound yard, but nobody wants 'em, so they get shipped back
to Japan where they are become paper clips again, but nobody is certain
about the role of the Japanese in the life cycle of the bicycle, if
they contribute DNA or what...

This can be proven by the cyclical shortages of paper clips, coat
hangers, or bicycles. You will always seem to have a shortage of clips,
hangers, or bikes, but never seem to have lots clips, hangers or
bicycles at the same time...

 

Gyroscopic precession is real, but the turning force is small
when compared with camber thrust. That is, as speed increases
the resistance to turning is felt, but the contribution of
the effect to turning is at least a decimal order of magnitude
smaller than camber thrust (think of rolling a cone).

Above 150mph, I've noticed that it takes a lot more effort to
turn the bars .... ;-)

 

Seriously? What kind of motorbike? Before I bought my FZR-1000, I was
interested in the GTS-1000 forkless wonder. The owner of Hollywood
Yamaha claimed that as he rode faster, the GTS-1000 got more stable,
unlike forked motorbikes which have a problem with suspension
compliance over smaller bumps.

(He was ready to blow out a new $14K GTS-1000 to me for $8K, but he got
called away to answer a long phone call. I was unconvinced that I
wanted such a big heavy machine anyway, and never rode one...)

The front swing arm of a motorbike with a Funny Front End has a lot of
leverage over the spring, just like the rear swing arm has over the
rear spring, so little bumps start the wheel moving more easily. The
suspension natural frequency is lower...

I would believe that you could feel the gyroscopic effect of the front
wheel at high speed with an FFE-equipped machine...

Motorbikes with telescopic front suspensions compromise ride and
steering feel with a limited travel suspension and the rider has to
accept high spring frequency up to the point of eyeball jiggling if he
wants predictable steering when he's riding hard in the canyons or on
the race track...

An eyeball jiggling stiff front suspension will result in the motorbike
starting to speed weave at a lower speed, explaining why
conventionally-suspended motorbikes feel lighter around 120 mph, while
the flywheel effect of the rapidly spinning front wheel should be
adding *artificially harder steering feel*....

I could tell you my horror story about violent speed weaves and wobbles
on Willow Springs when I didn't know as much about suspension systems
as I knew about engine. But I've told that same story many times...

 

Oh, posh, the 749 gets very stable above 100mph. I think that most
sportbikes with taut (and properly-adjusted) suspensions do.

I rode a Bimota Tesi for a while, and have ridden Beemers with the
paralever/telelever susp. Front swingarm suspensions absorb bumps
like a soft fork and corner like a stiff one -- and don't dive as
much under breaking. The latter property can be a nasty side-effect
without integrated braking and/or ABS -- with less weight transferred
to the front wheel, it becomes easier to lock the front wheel under
heavy braking.

Oh, heck, why not post it again? BTW, having separate adjustments
for high and low speed damping is a good thing. And components that
have that feature tend to be expensive.

 

Because it hurts too much when they drag their peckers.

 

The front of my bicycle broke off, once. I sure was glad I was almost done
with the paper route.