This is about how the air flows around a motorcycle. If the bike isn’t shaped well, it creates more drag, which makes it harder to go fast and can affect how stable it feels.
Horsepower is a measure of engine power output, often used to compare performance potential. In racing contexts, it also interacts with traction, gearing, and aerodynamic drag—so “more power” doesn’t always translate to faster lap times.
The Lucid Air is an electric car that runs on batteries instead of gasoline. It’s designed to move through the air efficiently, which can help it go farther on a charge. That’s why it may come up when people talk about how air flows around a vehicle.
A wind tunnel is a place where you can blow air past a vehicle in a controlled way. It lets engineers measure how much the air is resisting the vehicle (drag).
MotoGP bikes are prototype-class motorcycles built for racing, where aerodynamic drag and rider position strongly influence top speed and acceleration. The speaker connects high power output to overcoming aerodynamic resistance at extreme speeds.
Near the surface, air doesn’t move smoothly—it forms a thin “sticky” layer. If that layer gets turbulent, it tends to create more resistance, so designers try to control it.
A plug chop is a quick test where you ride in a certain way, then shut the bike down fast. You check the spark plugs afterward to see if the mixture was too rich or too lean. It’s a tuning method used during practice.
A venturi is a tube shape that squeezes air and then lets it expand again. When air speeds up through the narrow part, pressure drops there. The speaker uses this idea to explain how shape can pull or guide airflow.
Vance & Hines is a motorcycle performance brand, especially known for exhaust and racing involvement. Here it’s mentioned because the people behind it also competed in high-speed drag racing.
A fairing is a shaped cover that helps air flow around the bike more smoothly. In this story, adding a front fairing helped the motorcycle go faster by reducing air resistance.
If you leave anything sticking out—like brackets, wheels, or parts of the body—it disrupts the air. That usually makes the bike or car slower because it creates extra drag.
He changes his posture so the air flows more smoothly over his riding suit. When the suit stops flapping and creating messy airflow, it can reduce drag.
Concept
excrescences
In plain terms, “excrescences” are extra bumps or things sticking out. The speaker is saying those are bad for aerodynamics because they mess up the airflow.
Concept
asperities and velaset
These are words for surface roughness or little imperfections. The idea is that even small bumps can make the air flow less smoothly and increase drag.
Term
dipoles
The speaker is talking about a specific airflow effect caused by parts sticking out. They’re saying a small change in airflow can reduce the resistance those effects create.
Frontal area is how much of the bike’s shape air has to hit head-on. If you make that area smaller, the air pushes back less, and the bike can go faster.
Downforce is the “air pushing down” on the bike. More downforce usually means the tires can grip harder, especially when you’re accelerating or cornering.
Ride height is how far the bike is off the ground. Aero parts work best when that gap is in the right range, so ride height changes can make downforce go up or down.
Yamaha is a big motorcycle brand that competes at the highest levels. In this discussion, they’re mentioned as part of the group trying to get better traction at the rear wheel.
Formula One (F1) is referenced as a benchmark for advanced aerodynamic control devices. The speaker implies that similar airflow-management strategies—like devices that can change aerodynamic elements—exist in F1 and may inspire motorcycle aero features.
Concept
stall the rear wing array
“Stalling” here means making the wing stop working the way it normally does because the air can’t flow over it smoothly. That can change how much downforce the rear end makes.
Term
0.7q
“q” is an aerodynamics shorthand for how “energetic” the airflow is. Saying “0.7q” means the speaker thinks the inlet provides some fraction of that airflow strength.
Term
Pratt & Whitney 2800s
Pratt & Whitney made a well-known aircraft engine called the R-2800. The speaker is using it as a real-world example of using exhaust flow to help cooling.
“Out of the box” means you can take the bike to the track with minimal changes. Instead of doing big custom work, you mainly swap wear items like tires and pads.
The front fork dampers are what control the “bounce” of the front suspension. If the bike feels too soft, too bouncy, or unstable, changing dampers can help it feel more controlled.
makes us all seem so cerebral. Well said, P-51, that scoop on the bottom of the P-51 is not
fared. It is not fared into the airframe. The fuselage, it has a gap because it can't use that
air. It wants to be in the not that air. And all that the boundary layer is, is the molecules that
have been slowed down by colliding with the surface of the vehicle. And they form a layer of
relatively stagnant flow. You don't want that trying to weakly push its way through the radiator
core. I'd like to cool, but I'm just going to sit over here. So Laguna Seca, 1988, 1989,
Grand Prix 500s, cresting turn one. We got up at 4 a.m. to get our spot on the fence,
because the hill had not been cut back yet. So it was kind of dangerous, but you were right on
top of those guys going over one, which is that, you know, it's barely a corner at Laguna. And then
big corners turn two, but they would go over particularly on the plug chop, but a two stroke
was so quiet on overrun that when they would, and then plug chops. So they crest the hill and
everybody's doing a plug chop at the end of practice to check their mixture. And the bikes would go
over and the fairings would go, they would be fluttering and there was no other noise except
aero. And then they'd go and they'd stop at the entrance of two. They just put the brakes on.
And there goes Kel Carruthers walking down to pick up Eddie and pushing the bike. And then Kevin's
walking back and his Kevin Schwantz is walking back and his Pepsi Suzuki is being pushed by the
mechanic. We're yelling, but you could hear the turbulent boundary layer on those little potato
chip fairings going, it was a spectacular word of memory to be there. Yes. So an airplane has a
closes its wake with a tail and the tail, a streamlined body like a fish or a bird,
is essentially a venturi turned inside out. A venturi is a duct which starts large, quickly
tapers down to a small diameter and then slowly expands back to the original diameter. And what
happens is this produces a very low pressure at the point of highest velocity. As we observed before,
if the air accelerates, it's gaining kinetic energy, which means it's taking away pressure
energy. The molecules are going in this direction at a tremendous speed and that speed is subtracted
from their random beating on the walls of the duct. So this thing works well. The pressure in
is very close to the pressure out because accelerating down to that small orifice is
quite smooth. The difficult part is expanding the flow to slow it back down to its original velocity,
turning the energy of velocity, kinetic energy, back into the energy of pressure.
Now, what you're trying to do with a tapered tail is air has had to accelerate to go out around
the bow of whatever it is that's moving. It has accelerated. Now what we would like to do
is get that energy back, not let it become drag. We want to taper the back of the vehicle
such that the airflow will adhere to it and apply pressure to it as it slows back down
and finally leaves at the close to the tail. Well, it's interesting, the airframe evolution,
if you look at your, I mean, look at any 60s aircraft, anything that was designed in that era
from your Cessna 150s, your 421s, twins, and then you'd look at the diamond aviation,
they have a DA42 twin star, it's called, it's a diesel piston engine twin. And if you look at
the tail section of that and the difference between, you know, this kind of World War II fighter look
where it's 30s and it just kind of straight lines back, the DA has a very, and most
current design aircraft like a Cirrus, it goes, and it has quite a dramatic taper.
And I'm imagining that's convert, that's, you know, making the pressure that you're talking
about as well. And on the tail of a fish, if you're, if you're trying to grasp a fish, a fish
is slippery. So your dad puts his two fingers into the fish's gills and holds it up. Look
what we did, we're great anglers. You don't take hold of the body of the fish because it's tapered
and the harder you squeeze, the faster it shoots out of there. What we want the tail for is for
the air to squeeze and some of that vector of squeezing points forward. You are recovering
pressure so that it can push the aircraft forward. A motorcycle has no tail.
And that's why. Except for, except for Dennis Manning's land speed stuff. So I interviewed Dennis
Manning like 20 years ago and I asked him about, you know, I asked him about Arrow and he's like,
well, you know, Sam and another fish have been at it a really long time. So that's, that's,
he's like, that's where we, that's kind of where we start. And, you know, they have to,
they have to be careful about the center of pressure, where the pressure is for stability.
You know, there are, there are, there are things to think about at two, three, 400 miles an hour.
So if the back end comes around, you want the natural aerodynamic forces to tend to push it
back straight, not to make it worse. Now think about this. Sorry. One more related. Oh, okay.
Yeah. More related story. Terry Vance was, I interviewed Terry Vance of Vance and Hines. So
he, he got to start in drag racing. He was, you know, he was with Rich Collins, RC engineering,
and they were doing Hondas. And then he and, and Byron Hines started Vance and Hines. And
they made tons of money and they made zillions of exhaust systems. And he was a successful
drag racer and he went to Top Fuel. And they just decided to go Top Fuel racing and they're like,
yeah, let's make some body work. And so they made some body work. And it was like a fiberglass
wedge thing that they were putting. They had a little tiny nose and had a big spoiler on the
back and they were running a huge tire, but they didn't do any aerodynamic work. And he said the
body wasn't even symmetrical. It was just like, yeah, that looks pretty good. And the guy made
the body and it was sort of like maybe a slightly crooked. And he said, when he ran that thing down
the strip, he's doing 200 miles an hour plus. He said, it was like trying to fly a dart backwards.
He said it was incredibly difficult to run. So that's my story.
Yeah, that's my Terry Manette's aerodynamic story.
Seen in gross terms, drag is the difference between the pressure on the front of the motorcycle and
the pressure on the rear of the motorcycle. And if you don't have any tail, the pressure on the rear
of the motorcycle is like the pressure behind a flat piece of plywood that is being crammed through
the air by a motor. And that means that the drag will be very high. When Craig Vetter,
I think he had, I think he did something impromptu with cardboard and duct tape once
to show how easy it would be to increase the top speed of low-powered, get-around-town
motorbikes. And he started cutting out cardboard and made a tail and he made a sort of rounded
fairing for the front. And pretty soon he had the thing going pretty fast. And all he was doing
was trying to increase the pressure on the back of the vehicle by designing a tail to which the
flow would attach itself. And by attaching itself, exert pressure on it just like trying to hold
on to a slippery fish. Yeah, there was the Craig Vetter fuel economy challenge that was part of that.
And the folks were just trying to hypermile and they were building like big, big little wing
things that you would sit in, completely enclosed vehicles and trying to continue the bodywork.
You know, we're limited by the FIM rules. We don't get dust and fairings that have the big
nose that stick way out in front of the front wheel and we can't extend them off the back.
Yeah. So we have an aero limitation by rules alone, but not on the street. If we want to
get into our cigar, we can't. We can live it up. So it turns out that one of the worst things that
you can do is to have junk sticking out of your smooth aerodynamic shape. And the example that I
like the front wheel, the brake discs, the calipers, all of it. It's just sticking out there. Yes,
the rider's elbows. You know, there are some riders who were called Mr. Elbows. And we have
to bear in mind, of course, that the rider's manner of riding the motorcycle is very important.
And if that's the way he or she feels most comfortable, that's fine. Rich Oliver on his 250
at Daytona said he would come off the seat and arch his back until his leathers stopped having
turbulence. Yeah, you could feel them detaching from your back. He was trying to continue that
arch from the fairing to their, you know, those drooped tail sections that they could still be
seen in MotoGP people putting their butts up on the seat back a bit. Because it looks smooth. You
can draw this line, the windscreen, the rider's helmet, the back. Oh, it's going to be the original
active arrow. Yes, but the air looks at it. This stinks. I'm not sticking to that.
Yeah. I'm out of here. So when excrescences, add that one to asperities and velaset, if you will,
when excrescences jut from the smooth salmon-like contour of our creation,
they are especially drag producing because the awful turbulence that streams off of them
flows down the surface of the vehicle and ruins the flow there as well. So here we are in our
B-47 1950s jet bomber, the US first swing or swept wing jet. And we have, we're preparing to land
someplace, unknown AFB. And we extend the undercarriage, as the British say, gear down.
And if we do this at what is it, 225 knots, the maximum at which the gear is permitted to be
extended, the drag of the airplane doubles. And on commercial airliners, it is said that extending
the gear more than doubles the fuel consumption. So just looking at the front of the motorcycle,
of course, we've been seeing the same look since 1958, which was the first year of the FIM rules that
said the front wheel must be completely exposed. There can be no streamlining ahead of a vertical
plane through the front axle. At various times they changed that, they made it 50 millimeters ahead,
then 100, now I think they've come back to 50, I'm not sure about that. But there is this awful thing
sticking out front. And I went to see some MIT Aero guys. I wanted to put my home-built
H2R into their low speed tunnel, low speed meaning 140 miles an hour, as it then was.
And they were telling me that this was a bad idea. They said there isn't even a dynamic model
for motorcycles yet. What do you want to do? It's foolish. But they gave me an example.
It's foolish. Can we just write that down under motorcycle period? That's why it's so great.
Because with motorcycles we're really on our own. So many of the improvements that have come to
motorcycling have come from the users and not from mighty electronic brains in the
employ of the manufacturers. Not that they haven't made their contribution. But at any rate this
mass of stuff out front reminded these two MIT profs of something that happened during World War II.
Usually painted out of photos for publication at the time were radar dipole arrays. World War II
aircraft with airborne radar did not have little dishes that panned and tilted
underneath a fiberglass cover. They were dipole arrays that were just stuck out into the wind.
And they found that if they put a flat surface behind these arrays that the velocity of air passing
through all those dipoles, you know the phrase the wind in the wires, the World War I fighter plane
movies where you hear the bracing wires of the wings singing as our hero dives to what could very
well be his demise. Keep tuned in folks for the outcome. But off of each of those dipole arrays
streaming vortex shedding. And the tone that you hear is the speed with which those little vortices
are being produced. Anyway if they put a flat plate behind that the airflow tended to be pushed
ahead by the flat plate reducing the drag caused by the dipoles to by a useful amount.
And I showed them a picture of the of Kawasaki's what year was it. There was a year that they had
a chin projection that reminded me of Abyssinian the beards of Abyssinian kings. And they said
it could very well be that that flat radiator reduces somewhat the terrible drag of all that
chunk sticking out in front. So it is almost as though those rules makers in at the end of 57
were trying to increase the drag of motorcycles. The front wheel must be exposed.
There can be no stream lining behind XYZ and all of this business. And so
we we just keep adding power. That's how you go faster. And it's strange. Another thing that
used to bother me is people would put fairings on their motorcycle and instead of shaping them
so the fairing ended quite close to your tucked in knees the fairing was made like a plow getting
wider toward the back so that it was throwing air outward. And I'd say is that do you have a reason
for wanting to do that? Yeah, I like the way it looks. Good. I'll remember that. So
such a good looking bike in 13th place didn't you think?
Stylin man. So the front of the fairing
in a lot of those late 60s bikes was just a huge opening so that all that the fairing was
was a hemisphere for the front number to be painted on with a large plastic windscreen
that most riders made come to the top of their helmets. Honda created quite a stir by making
it come to the top of the rider's shoulders. And the sides of the fairing had no streamlining
purpose whatsoever. They were just like flat sheets that were connected by maybe a six inch tongue
on either side that joined the hemisphere. They weren't streamlined at all. They were covers
and that's what I called them covers. And you could put the numbers on the side.
Well, you know, in recent conversations with Steve McLaughlin and John O'Ritch,
Steve was one of the instrumental guys in making his fairings larger so he could fit
more sponsors on them. So there you go. Good stuff. Good business might have helped there
eventually. 1980, I helped one of the early super cart guys.
Super cart meant that you had a six speed, usually a Yamaha engine at that time
on the back of your cart. And he had an enormous
world of outlaws style wing that was tipped up at a jaunty angle. And I kept saying,
John, you got to take that thing off there. I got to have it on there and sponsors. I got
to put all the sponsors on there. Could we just level it off so that we could reduce the drag
somewhat? I kept after him, eventually said, okay, picked up like 30 miles an hour.
Yeah. Well, what he was doing was carrying that sheet of plywood that we were just discussing.
Well, instead of having it absolutely flat, it was tipped back a little bit.
And this was supposed to produce a downforce that could overcome the fantastic
power of the 250 Yamaha, 40 horsepower. Yeah. So
then along comes Harley Davidson. They have their wonderful moment.
Bunch of guys spending the afternoon at XL shop playing with a Harley flathead.
Dick O'Brien, the Harley racing manager comes out because they found something.
And in the course of trying to
gain as much as they could from this, not only did they put on two Tilletsons instead of one,
carburetors, those were, they also went to the Caltech wind tunnel and a fairing was designed
for this motorcycle, which has not subsequent to that time failed to increase the speed of every
motorcycle it was ever put on because it had a limited opening for cooling. It wasn't just
a hemisphere in the front and two plates on the side. And the widest part of the fairing was at
the front and it tapered inward from that point as though it were trying to create a streamlined
tail. And in effect, what it was doing was reducing its wake area.
And this was not so much science at work as a combination of aerodynamic theory
and ours spent in the tunnel. Well, yeah, I'd like another beer. Thank you.
That looked like it was going to work, but it didn't. So now we've got to think about it again.
So Harley comes in 68. Triumph has won the Daytona 200 twice in a row and Harley's looking like a
pretty tired 1930s POS. And suddenly Harley's efforts, including the Caltech tunnel fairing,
made the triumphs obsolete. Just don't bother. Ride a Cushman. You might do as well. Anyway,
streamlining done carefully can result in gains. But they're going to be relative to that flat
plate of plywood because the motorcycle is so constrained by those rules. So much so that John
Britton came to the conclusion that the main variable in motorcycle streamlining was frontal
area. Reduce it. He took the lower fairing off on that 20 miles straight away where all the white
helmet guys go in New Zealand and picked up speed. That was the same. Well, it makes sense. Air's
getting going between the rider's lower legs and the engine. And there isn't this big thing down there
plowing air. Yeah, that was the same conclusion that the Caltech guys, when Harley did the midget,
Don MD put that story together for us, but they reduced the frontal area. And that was
what they said principally was the advantage was reducing. That was the obsession in the tunnel,
was to reduce frontal area as the first big step. And that was the Harley Davidson Midget,
which you can read on magazine.cycleworld.com. But they just made the tiny wheels. They lowered
the bike just to make it smaller. So we should switch to consideration of the
devices being used in MotoGP at this point. Would you agree? I agree. Okay.
What we see is, first of all, downforce wings or winglets
attached to or near the fairing nose. And the purpose of these is not to exert downforce
to increase tire grip in corners, because when the motorcycle is at 60 degrees, 63 degrees,
65 degrees, any downforce is more pushing the motorcycle off the turn, making it go wide
than it is pressing it down against the pavement. So the real purpose of those wings and winglets
is to keep the motorcycle from wheeling in fifth gear and having to close the throttle to keep
the front wheel steering. Just a little helping hand that presses the front of the motorcycle down
enough to overcome the tendency of the motorcycle to blow over backwards.
And Mike Baldwin and other riders have spoken to me about wheeling over a hill crest at high
speed and having to go for the rear brake because the front wheel wasn't coming down.
I like that one. Real stuff happening. Yeah. Anyway, that takes care of that whole nose business.
That's what it's for. It isn't for in-corner downforce is to allow the use of more power
in higher gears without having the front end go light and lose stability. So
the next gizmo is fairing side panels that are so angled that when the motorcycle is at full lean,
that these panels are parallel to the surface of the earth and form a venturi that can generate
downforce. Now this is going to tend to increase the motorcycle's angle of lean so the rider's
going to have to cope with this. Oh, it's doing something unusual. Oh, that didn't work. Maybe
they say it takes some getting used to. And why not? The air is moving. It has math.
You can generate forces with it. Let's give it a try. And small scoops located on either side of
the fairing, front edge of the fairing at about axle level, which then become ducts that go down
underneath. When the motorcycle is operating on the fairing, on the fairing, on the straightaway,
the ride height is at low. And that means that a flat bottom on the fairing is another prospective
venturi. If only we could get air to it. We can't because the front tire is in the way. Oh,
let's put intakes to some little ducts and run the air down there and see if it helps. They keep
doing it so either I like the way it looks or to some extent it works. And all power to them
for trying something because this is not a contest to see who can design a motorcycle that looks
most like something Agostini wrote in 1966. This is not vintage. It's supposed to be racing. So
the those so-called downwash ducts are trying to use. And of course, when the motorcycle is
photographed, you usually don't see it at minimum height except when they're doing practice starts,
which is how the whole thing started in the first place. So item
number four, a spoon or small airfoil array located just ahead of the rear tire
where it looks like if it moved aft a little bit, it would run itself over.
I don't have any idea what that does. Some people say, oh, it blows cool air on the tire. But
a big problem with the rear tire has always been lack of grip, not too much. So usually,
lack of grip results from cooling off on the straightaway. And Dunlop published and I can't
find my copy, a diagram showing tires temperatureing up as they enter corners.
Because tire temperature is a strong determinant of tire grip. There is a thing that rubber and
other elastomers are subject to which is called the glass transition temperature, T sub G. More
science. And the glass transition temperature is a temperature at which the rubber becomes hard
and inflexible. It turns out that if you can raise the T sub G to something close to the operating
temperature of the tire, you can be in a not quite stiff range of rubber flexibility that
generates a lot of internal friction, hysteresis, which creates grip. This is the wet grip that
all the manufacturers talk about, which is just secret talk for good tire traction under all
conditions. So cooling off the rear tire, I can't, I don't get that. So I just, it's a cold case.
I'm, I'll think about that later, like Scarlett O'Hara said. Various forms of streamlining applied
to fork tubes, calipers, brake discs, what have you. This is to get rid of the appalling load
of excrescences that the 1958 rules burdened our sport with. But if you've got the tunnel
paid for until five and you've been through the program, get the modeling clay and let's start
slapping it on there and seeing what happens if we fill in this and we fill in that. Tape
cardboard around the fork tubes to make a an airfoil section out of them.
And that's what you see happening now is that complicated shapes, no doubt made by
additive manufacturing techniques, aka 3D printing, are covering up the ugly excrescences and
maybe having an effect. Well, various forms of shrubbery affixed to the rider's seatback.
And we have the stegosaurus plates, arrays of jutting airfoils. And I suspect that this
is another area where a little extra downforce when the motorcycle is at lean and the rider is
feeling for the grip to get off the corner, a little helping hand, even a few pounds,
like five, could make such a difference. And for at least five years now, everyone,
not just Yamaha, has been complaining about, well, we'd really like to have more rear grip.
Now, the coming of variable ride height has utterly changed motorcycle,
GP motorcycle, MotoGP braking, because it used to be that Marquez rush up to the corner,
brake like a madman with the rear wheel just hovering in the air, and then started to lean
the motorcycle over and let the rear tire drop on the ground already sliding on the pavement.
Today, people are having to use the rear brake. Well, there's no point in that. I mean,
if you can get the front brake to lift the rear wheel, then that's all the braking there is,
trying to use the rear wheel for a brake, that's not going to help. It is going to help,
because there's such a thing as initial braking. When you first begin to brake,
the front tire is not up to temperature. So if you want maximum braking, you're going to have to
feed in some rear brake, and coordinate the whole thing so that it works out,
looking like you have a mystical ability to get off the corner. There is some rear grip.
How are you going to get it? And all of that shrubbery on the seat back appears to be
intended to give that little helping hand. Now, when you see the rider tucked in,
you know that all of those little airfoils and so forth are probably in separated airflow and
have very little effect. But when they're supposed to help you is when the rider has moved the entire
torso off the motorcycle to the inside, and the airflow comes over the screen,
and there's the seat back array fully exposed. So, good one.
And now the mysterious rubber-lipped oval armrest holes on the Aprilius.
I was waiting for this, Kevin. I was waiting for this, because it's so interesting.
It is interesting, because clearly what happens here is that when the rider is
cornering, he's not tucked in. And so those holes, which appear to be three or four inches long,
and maybe a couple of inches wide, and have what looks like a rubber seal lip,
probably something that comes off of an alpha door in the junkyard. Here's a piece. Give me
those scissors. It just happens to fit. All kinds of the most marvelous analogies are being drawn,
and by which that I mean stretched, to accommodate the view that these are control holes, like those
used in Formula One for some kind of device that could stall the rear wing array to increase
top speed on the straightaway when you don't need downforce, because your tires are 40 inches wide,
or whatever it is now. Rollers, not tires. So, where is the duct leading from these holes?
Where does it go? It goes forward, where it gathers fresh air from the stagnation zone behind
the front tire, and just above the radiator, I think, on either side. Other ducts? Are there
other ducts that plugging those holes up when you're tucked in, and your forearms are sealing
against those rubber lips? We can't see, so we don't know. So then I thought, what special
problem does Aprilia have that its riders complain about constantly cooking the rider?
And then I thought, what if those holes deliver fresh air from the stagnation zone
at .7q, and there is an open-weave section sewn into the rider's leathers that fits up against
that lip, and it blows cooler air into the leathers, and much in the way that the leather's drying
systems that some teams had a few years ago operate. A blower is going, and here's this
thing looking like a rider filled with helium. Very popular at Suzuki 8-hour when I was there.
All the factory guys, you'd see all the castrol suits laying inflated on the floor.
Big fans blowing them up. Good stuff. So, I don't insist that this is the true
purpose of these devices, but it makes sense to me. You think about it and see if it makes
sense to you. And of course, perhaps they'll reveal something that none of us has thought of,
and that'll be even more entertaining. More interesting. Yeah, it is such a fascinating
thing, just that oval. And as you're tucked in, you're putting your arms down on the fairing and
yeah. Well, another thing that has been done in Formula One, there's a lot of energy in the exhaust,
and Formula One cars used to use the exhaust energy to blow the Venturi tunnel.
And when I was, when I had my seventh birthday, my dad took me to New York and we flew down there on
a Convair twin, a pair of 18 cylinder Pratt & Whitney 2800s. And extending back from each engine to
these big tubes. And my dad told me the exhaust pipes from the engine terminate right at the entrance
to those tubes and the rush of exhaust gas at high speed pumps air through those tubes to cool the
engine, greatly reducing the cooling drag in flight and increasing the top speed. So,
a motorcycle doesn't have a Venturi unless it's leaned over, or unless it's upright, and it's a
minimum ride height that, that sort of skateboard underneath the, that forms the bottom of the
fairing. So, where's the Venturi that can be stalled, or where's the, I'm not sure. So, this
there are a lot of people thinking about this now. Ducati kind of started the ball rolling,
but if you look back in history, you could see that downforce wing, winglets were tried by Suzuki
on their 500. There was a fellow who put a wing, it looked like a big dust pan,
up on struts behind the rider, and I don't know what its purpose was, but it had variable incidents
now. Variable incidents is not permitted in MotoGP, but Formula One, which is sort of the
big brother in this business, is now permitting some variable incidents. So, who knows what will
happen next? Because of course, if you have little stubby winglets that have an L over D,
lift over drag of three, it means that for every pound of, of downforce you generated,
you're generating one third of a pound of drag. And at 220 miles an hour, that's
a fair amount. Okay, so you make those, those moustachio wings that the Yamaha and the Aprilia
have, an array of three of them usually. Kind of like what you see on the front of Formula One.
Maybe they have a much better lift over drag, six, seven, I don't know.
My rule of thumb isn't working, but it means that you could get potentially more downforce
for a given amount of drag with longer narrower wings, aspect ratio, because then the tip region
where the losses are becomes less important in relation to the whole wing.
So, it would be very nice to be able to, to vary the incidence of these wings so that they didn't
produce, they produce hardly any drag at high speed. It was at Cheprel 2G, I think was one of those
the K&M car with the strut on it that could change the angle of the wing pretty neat.
There's a great photo of Formula One grid at the height of the, of the wings on stilts movement,
and it's just so silly looking. All these spindly little stilts sticking up with, with these boards,
arrow section planks being carried on high. Why put them way up there? Because the airflow
is cleaner, it is less affected by the car head. So, this whole thing with the aerodynamics
is tantalizing because of the high speed involved, but the advertising people who have to sell these
sport bikes think that their sport bikes would look great with stuff attached to them that really
doesn't have much effect until you're going 150. The rest of the time you're just lugging it around.
It's messaging, Kevin. Yes, it sure is. It's messaging. It sure is. I'm up to the minute here,
folks. I am listening. Well, the supersonic, the whole supersonic look that has overtaken, you know,
hard edges and all these, you know. Yes. It's supersonic. You know, our world is dramatically
subsonic. Yes, it is. Well, Tony Stefinelli, he worked at Buell, and he had an entire career
in Indy as a wing person, and his source document was like a NACA book from the 30s,
because it was all subsonic wing profiles. All those subsonic airfoils, yes. Abbott and Donoff.
And so, he was like, yeah, it was a great book, and we'd try different wing, you know,
airfoils, and, you know, we're turning them upside down because it's downforce.
They were thinking of flight, but that's what Tony did. And so, we have those nice soft curves,
and that's really what our bikes ought to look like is those, you know, bird-like or
fish-like curves. You don't see fishes looking like F-22s. Yes, with those angled forward intakes
on either side of the fuselage, so that work at rearing up angles of attack.
But that looks hot and new. And the Hawker Hunter, which is all Jaguar XKE sinuous curves looks old
and drab. So, the MotoGP guys have to make it work, otherwise it's just a drag.
Well, I liked your Convair discussion because it's one of my favorite planes. There's one,
there's Convair down at the airport where I go on the weekend sometimes, that you know.
And what I like about the cowlings is they open like the petals of a flower.
Oh, yes. You're not unscrewing things and taking off these huge cumbersome things,
they're on hinges, and it just opens like a flower, like the bottom one comes out, and then the top
two kind of go up like this. And there's struts that hold them there so they don't close on your
fingers when the wind goes. So, you just pop the hood, get in there to your thing, close her up,
hit it. Yes. But those ducts you're talking about are plain. And of course, that was the ejector
cooling. A steam ejector was used to drive feed water into boilers against the steam pressure.
Great stuff. But the people who think about this all the time, the aerodynamics people,
here's a whole new field for them, and they're having a ball.
And I don't mind it at all. I've got plenty of pictures of Hailwood on a 1960s Honda. That was
then, it was a tremendous advance in power generation through extreme RPM. The motorcycles
didn't handle very well, but they were fast. And now we have a different, we've paid attention,
and I mean close attention to engine design, to suspension design. The suspension revolution
started in the mid-70s with the revelation that compression valves were becoming rigid
obstructions at high damper rod speeds, which was why people had to make the upshift when they
came out, turned five onto the banking at Daytona. Because if you had the power on,
you were going to have an upsetting impact. And great developments have taken place in tires.
In 84 came the radial revolution. In 74 came the slick tire revolution. In 92 came the silica
reinforcement revolution. Tires began to be,
they automated the production of radial tires around 2000. And it's been a wonderful progress,
and enormous gains have been made. But all this while, aerodynamics has sort of been sitting there
because that 1958 rule said, hands off all these things. Here's a big long list of things you
can't do, whereas Roger Edmondson liked to put it. Modifications not specifically mentioned here
are strictly forbidden. Everything is forbidden, if I didn't mention it. Well, I liked the early
superbike rules, again, going to my recent time with Steve McLaughlin and John Ulrich.
They left a lot open because they knew a lot needed to be done, because we were racing like
motorcycles unfit for purpose. So the rules were broad. Repositioning of the shocks, which
Udo Guido interpreted as, I'll reposition one of them on the BMW to the shelf. So you could
reposition your twin shocks, but would they just stretch the interpretation? And when it got rid
of two shocks and put one of them in the middle, just as it was on a TZ750 in the later models?
So the Japanese took note of all the tremendous work that had to be done to win those
first-era sit-up superbike races. And they re-engineered the second-era bikes to benefit
from the experience in GP racing that they all had by that time, from 83 onward. And
it was a very important step forward. These were motorcycles that were raceable out of the box.
You might want to change the front fork dampers and the tires and the brake pads,
but otherwise that was it. So those motorcycles didn't need all that welding and gusseting and
throwing away the suspension and buying others. They were usable right out of the crate.
And that was a giant step forward. Well, gosh, those are 90Ss. Udo Guido moved the
entire powertrain forward. There's a spacer on the output for the driveshaft. It's about that long
that keeps the driveshaft in the right orientation, you know, distance-wise. So they moved the motor
forward and then you just put a cookie in there that connected the output to the driveshaft
because the engines slid far enough forward that the cylinder is hitting the front down tube.
Yeah. We've run out of room. Well, I went up into the engineering library, which is in that dome
that MIT has. I was working there as a technician, a lowly technician. And it described in the Japan
Society of Mechanical Engineers, it described motorcycle stability testing on a moving belt.
And they discovered that as they moved weight forward, stability was increased.
And at one point they talked about a less successful experiment that they made. And under
result, it said the doll is overthrown. The doll being a human-like dummy placed on the motorcycle to
have similar weight and arrow characteristics. The doll is overthrown.
Yes, the doll is overthrown. Same data out of Buell many, many decades later.
You know, the Buells were going very short trail and very steep rake. They were sort of 21-22
with trails that were quite short to something three-ish, you know, very, very short.
And it was talking to Steve Anderson, who was a longtime contributor for us, an engineer himself,
and also worked at Buell EBR. And he said, yeah, the more weight we put on the front,
the more aggressive we could be with our steering geometries. And they were stable,
I have to say. They were light steering and stable. The Buells.
And if you look at this the other way, turn the telescope around, you see the bevel drive Ducati
with its engine necessarily far back because the front cylinder was at a 15-degree angle
from horizontal. So it acted as a spacer pushing a crankcase back against the rear tire.
So what geometry did they end up with? 31 degrees and four and a half inches.
So sort of touring on the way to chopper hood. Yeah, I think if I'm starting with a frame
for my, you know, notional homemade sport bike, I'm going to stick with 24
and something around four inches. It's pretty pleasant. That's about where it is now.
Pretty pleasant geometry. It's real workable. It does all the things you want. I might go a little
bit longer than your 55.5 or your 54.9 as you do on your sporty bikes. I go to 57 just because
I'm that kind of person, you know. But I'm also a big believer in flywheel mass. We keep taking
all this flywheel mass off and I actually, I find flywheel mass quite workable. I'll go ahead and
say Vellisette. I have the, I have the old flywheels, which are the full circle flywheels,
but I have the hot cam. And so what I, I think I have an advantage the way that bike runs. I think
it is an advantage. Yeah, because there's less crankshaft speed variation. Yeah, and the later
to later cranks with more pork choppy. And one of, you know, our friend Gary Baran over there
at Millennium is building cranks for flat trackers. And he's just piling on. He's making the 450
single cranks full circles, big welds of chunks, all machined and beautifully balanced as he does.
Fascinating. Well, that's not aerodynamics at all, is it?
No, but while you were speaking of it, I was thinking of the aerodynamic experiences that we
all had as children, namely creating winglets with our hands out the car window. And you
discovered that the effect was increased with speed. Oh yeah. How close to the window and then
banking it in, giving yourself a nice face full. Yes. How I missed the wind wing. You know, I have,
I have cars with wind wings. I have my truck, my 8940 has wind wings, my,
my Jag, which I'm driving today, a little, a Corlo quarter. Yes. They were so effective.
Yes, especially in Kansas, if you don't have air conditioning.
Especially in Kansas. Well, I, I have not the fondest memories of crossing canvass,
Kansas in mid, mid summer, while one of my fellow van occupants insisted upon smoking.
I thought I was going to have to stop at one point, but I
manned up. Yeah, I think the, I recall flying on airliners as a kid having a, having a smoking
section inside an aircraft. That was pretty, that was pretty hilarious.
Well, that's not aerodynamics either, but
people write in and they say that digressions are welcome. Yep. So we believe you. Yeah,
we do. We listen as stresses is or not. Well, that's it folks. That's aerodynamics.
Thanks for listening. Share it with your friends. You know, if you like it, share it with your
friends. We appreciate the comments a lot. Likes all that stuff. It helps the whole program,
which we'd like to continue doing. So, and again, check us, check us out on Patreon. Thanks to all
the people who have already done that. We have a good chunk of folks over there on the subscriber
team. And we, like I said, we record short pieces and long, long form podcasts that are Patreon
or subscriber exclusives. So join us over there if you like. And that's it for now. We'll catch you next time.
About this episode
Mark Hoyer and technical editor Kevin Cameron break down why motorcycle aerodynamics are so unforgiving, from drag-producing vortices to the “plywood” reality check that fairings often can’t beat. They connect the physics to MotoGP design choices—nose wings for stability, venturi-like side panels, cooling ducts, and rider-position effects—while debating how much downforce and cooling actually matter. Along the way, they share vivid racing memories, explain why motorcycles lack a true “tail,” and argue that rules and protrusions shape what’s possible.
Find us on Patreon! https://www.patreon.com/cw/CycleWorldPodcastMotorcycles are just not good when it comes to aerodynamics. They punch a great big dirty hole in the air and do almost nothing to close it behind them. Kevin and Mark talk about moto aero, some historic solutions, and later in the podcast transition to MotoGP aero and related performance enhancing solutions. Tuck in and let's ride!
