Avoiding headlight bulb failure - suggestions, pls?

Post one please. ;-)

 

You're probably talking about front wheel "tuck". That's what happens
just before the "wahoo!" that either spits the rider off or seriously
damages his underwear...

Professional racers and magazine test riders are cornering with a lot
of lean and a lot of throttle...

The excess power will actually cause the chain to pull on the swing
arm, increasing its angle. If the swing arm angle increases, the swing
arm pivot point has to rise, and this makes the frame rise...

But that action causes weight transfer to the front end of the
machine...

The forks compress a bit under the extra weight, the rake and trail is
reduced, the steering feels a bit lighter, the rider figures that all
is going well, since the motorbike isn't understeering like it was a
second ago...

The rider applies even more throttle, leans the bike a bit more, the
front wheel tucks into pre-wahoo! position, and a photographer snaps
the picture you see in the magazine...

 

I don't know about your bike, but applying power to my bike makes the
swing arm angle (as you describe it above) decrease, and the pivot
descends. The rear squats, the front of the bike rises.

On my bike (and every other one I've ever seen) applying power causes
weight transfer to the rear end of the machine. You can't apply
torque to the rear wheel without this happening - if you figure that
one out, you'll die a very rich man.

If there WAS more weight on the front of the bike, the reduction in
rake and trail would be very miniscule, and somewhat offset by the
deformation of the front tire increasing the contact patch.

As the bike leans more, and as more steering input is applied, the
trail reduces as the tire's contact patch moves toward the steering
axis (line drawn through the head tube to the ground). If and when
this point gets ahead of the steering axis, the bike becomes
inherently unstable, and that photographer gets the photo you mention.

Mark Hickey

 

swing arm angle (as you describe it above) decrease, and the pivot
descends. The rear squats, the front of the bike rises.

Have you read Kevin Cameron's book on sportbike technology? He explains
how the swingarm pivot point rises *during hard cornering* and the
swingarm jacks the chassis up...

Suspension tuners have been interested in swing arm angles for the last
several years and the motomags picked up on that and some mags even
started including swing arm angles in their data panels...

weight transfer to the rear end of the machine. You can't apply torque
to the rear wheel without this happening - if you figure that one out,
you'll die a very rich man.

Power squat is what happens when you accelerate in a straight up
attitude and the front wheel isn't pinned against some solid object...

But, take your motorbike and park the front wheel against a brick wall
and watch what happens as you twist the throttle and slip the clutch as
though you wanted to start moving. The motorbike's seat will rise and
the forks will compress...

In the front wheel tuck scenario I described, the front wheel is pinned
against the pavement by the tire contact patch's *grip*...

The magnitude of the force is over 1.5 times the normal weight on the
tire contact patch, and it gets *worse* as the swingarm jacks the
chassis in the rear...

 

This is completly ridiculous. It's hard to believe people are still unclear
on this concept.
Go ride your bike, bank into a long sweeping turn, notice your handlebars
are straight through the corner, not turned.

 

When you counter steer you're only nudging the bars 1/8 inch at the most.
This is irrelevant as far as the headlight goes.

 

ACTUALLY with the front tire being narrower than the rear one could just as
easily say it was turning away from the turn (Like it IS ;-) Read David
Hough. & mount a big degree wheel on your handlebars on your next ride. And
as you said, it ain't gonna do squat for seeing around a corner. Fairing
mount = HB mount .

 

Fine, but I was replying to your claim that the application of power
causes the swing arm angle to rise and the front end to dive. Just
ain't so. For reference, here's what you said...

There are a lot of complex things going on in a hard corner with a
motorcycle suspension - I was addressing only the concept that adding
power causes the front end to dive.

Which is significant *how*? Explain how you can prevent rearward
weight transfer when applying power. Other than working a deal to
alter the laws of physics or putting the rider on a sliding saddle,
there ain't no way to prevent it.

Heh... I'm trying to picture what would happen if you were in a tight
corner and suddenly had your front tire "pinned" to the pavement in a
way that would even remotely replicate parking the bike against a
brick wall. It would make an interesting video, but you'd want to
have an ambulance there.

OK, I'll bite. What is "pushing back on the front wheel" other than
normal rolling resistance and hysteresis loss in the front tire?

I think you're thinking of what happens in that split second after
something causes the trail to go negative (whether from a rear tire
slip, chassis flex or whatever), and the front tire "digs in". Yes,
at that point, the swingarm pivot goes skyward with the rider, the
rear wheel, and the rider's heart rate. But that has nothing to do
with a corner you actually get to ride through (not fly over).

Mark Hickey

 

Depends on the bike - on my shaftie, the rear end squats. On a bike
with a chain or belt, it depends on the geometry of the driveline and
the pivot point on the swingarm. If the bike has a particularly low
pivot point, it'll probably squat - if it's a very high one, it might
tend to rise (though that doesn't mean that the front wheel sees an
increase in weight transfer, which was why I brought up the point).

Mark Hickey

 

causes the swing arm angle to rise and the front end to dive. Just
ain't so.

It just IS so, Mark, I didn't smoke anything before typing about
chassis jacking under heavy power apprlication at high lean angles...

We're still working with Sir Isaac Newton's laws of physics here, no
forays in the Otherworld or deals with Satan are implied...

corner and suddenly had your front tire "pinned" to the pavement in a
way that would even remotely replicate parking the bike against a brick
wall

The tire doesn't "suddenly" get pinned to the pavement, it's always
held to the pavement by gravity, and the weight of the motorcycle is
multiplied by a factor of about the square root of 2 as you lean the
bike to an angle of 45 degrees or more...

normal rolling resistance and hysteresis loss in the front tire?

Sir Isaac said that for every action there is an opposite and equal
reaction. If the motorcycle tire is pushing against the pavement with
about 450 pounds of force, Newton says that the pavement is pushing
back with an equal force. That's the reaction that engineers use when
they work with Free Body Analysis...

Like, a general aviation aircraft weighs 2000 pounds. The wings must
generate 2000 pounds of lift to sustain the aircraft in flight. The
atmosphere must therefore react, by pushing upward with a ton of force
under the wings...

No, I'm not thinking about 3.5 inches of trail suddenly going negative,
or even neutral. The rear wheel would have to be high off the pavement
for the trail to go negative, but I don't have time to work the trig on
that problem, so you can do it

 

Except that no one applys heavy power at high lean angles, if they know what
they are doing.
At heavy lean angles the suspension is compressed a great deal.
Your argument is of no use and doesn't apply to the real world.

 

know what they are doing. At heavy lean angles the suspension is
compressed a great deal. Your argument is of no use and doesn't apply
to the real world.

Oh! You're right. All motorcycle roadraces take place in an alternate
universe where different rules apply. My bad...

 

You gotta come up with something better than "it just IS"... when you
apply power (assuming rear wheel drive), weight transfers front to
back, not vice versa. Wheelies don't happen because of aerodynamics,
y'know...

Then it shouldn't be hard to explain how you're getting the opposite
effect the rest of us have been getting for the last couple centuries.
;-)

OK, but how does adding power to the rear wheel REDUCE the force on
the front wheel? Explain that one and you'll have me stumped (well,
me and Sir Isaac).

Yep (though that would igore other sources of lift on a GA aircraft,
like negative pressure above the wing, but that's another thread).

It's not a trig problem - it's what you see at the race track when
someone high-sides a bike. You're picturing the rake/trail
relationship with the bike vertical - picture the contact patch with
the bike leaning at 45 degrees (1g cornering) - now picture what
happens to the contact patch if the tire is turned a bit more sharply
into the corner. Until the trail goes negative, the front end of the
bike wants to self-correct. It's when the trail goes negative that
things get really, really ugly (since it's a self-perpetuating
phenomenon - it causes the tire to want to turn in more, which makes
the trail more negative, causing the tire to want to turn in more,
which makes the trail even MORE negative... oh, mama!).

Mark Hickey

 

apply power (assuming rear wheel drive), weight transfers front to
back, not vice versa.

Weight will transfer from front to back even if your vehicle has *front
wheel drive*, and upset suspension geometry, unless you implement some
sort of anti-squat system...

power>

http://www.eurospares.com/tfoale/book/ Click on "anti-squat" and you'll
see that Tony Foale is talking about swing arm arrangements that can
produce 100% antisquat...

You may have noticed that Yamaha, the leading motorcycle company that
Honda, Kawasaki and Suzuuki follow, have been developing their
FZR series into a YZF series over about two decades and that their
most recent public offering, the R1 has a chassis with an unusually
*long* swing arm...

In fact, the desired swingarm length, in the interest of traction and
geometry control along with a certain short wheelbase was paramount in
the design. The managers then instructed the engine department to
design an engine which would fit into the space remaining, and so we
began to see Japanese motorcycles with the transmission shafts stacked
on top of each other to save precious inches of space for that longer
swing arm...

And some folks would claim that the stacked tranny shafts were arranged
that way for "mass centralization" and moving the MC's CG foward a bit
to weight the front wheel more, and, while they wouldn't be wrong, the
new engine design was driven more by the desire to have a comparatively
long swing arm on a short wheel base machine...

Of course some of the drooling squirrels who read motorcycle magazines
and watch motorcycle racing videos are still going out and doing power
wheelies on their R1's, so Yamaha obviously doesn't have
a 100% anti-squat system on their latest greatest machine...

centuries.

Motorcycles haven't been around for 200 years, and I never said that I
personally was overcoming Newton's laws of physics...

But here's what Kevin Cameron had to say about the current problems
with mismatched front and rear tire sizes on the current crop of
sportbikes:

"While autos present 100% of the width of their tires to the pavement,
the motorcycle offers only 1/3 of tread width at a time, severely
limiting cornering grip. To make motorcycles steer well, front tires
must be of modest section, while rears, to apply engine power, must be
large. With the forward CG position necessary for rapid acceleration, a
powerful motorcycle must therefore overload its small front tire in
cornering, while under-using its larger rear. The result is that as a
machine's power increases, its corner speed must decrease." K. Cameron,
introduction to "Motorcycle Handling and Chassis Design" by Tony Foale

So the unknowledgeable rider finds himself in a situation where he
feels like he has a surplus of rear tire grip, with that huge meaty
190mm wide tire on the back, and he *gradually* dials on more and more
power to increase his *forward* speed and simultaneously countersteers
a little more to increase his *lateral* speed toward the inside of the
turn, otherwise he'd be heading off the track, and he washes out his
front tire and goes into a big speed weave, and no laws of physics are
violated...

And it really doesn't matter which way his *headlight* is pointed, he
probably doesn't even have one on board, and all this is a long way
from the question by the OP, who never said another word on this
thread...

 

Those might stop squatting, but they cannot stop rearward weight transfer under
power. To do that you would have to move the center of mass of the machine
below the level of the road or track! It's a simple matter of moment
equilibrium.

Why not? The bike can still wheelie without the *suspension* squatting.
A rigid rear can wheelie, can it not.

 

Exactly. The two phenomenon are (sometimes) related, but there is no
force on earth that will keep the weight transfer to the rear from
happening under acceleration. OK, if you have a reverse gear you can
get it to go the other way I suppose... ;-)

Exactomundo. The "anti-squat" geometry is a simple matter of the way
the chainline and pivot point are configured - doesn't change anything
to do with weight transfer.

Mark Hickey