Just like Harley-Davidson, I was born in Milwaukee, Wisconsin. That's not enough for me to cheer for them, though. It has a lot more to do with my wanting to see the "underdog" pull out a victory !!! 

I believe the basic ingredients are there... and with just a little tweaking: 

Harley - Davidson Will Win.

One of the problems with dyno testing is that it fails to take into account what actually happens on the racetrack. This kind of thinking usually makes power & speed seem mysterious. 

These first 2 pix were taken last summer at the Brainerd AMA national, and I posted them under the Brainerd racing coverage. The point of the story was to show that the pipes on the Harley weren't the same color, because the fuel / air ratio was different from the left pipe to the right pipe...

Then, I asked the question:
Can anyone see an even bigger problem ??

Well, it's been almost a year, and no one's guessed it. As you scroll down I'll explain the problem and reveal the answer.

See if you can figure out what it is. 
All you have to do is:  


Think Outside of The Box !!

Now For The Bigger Problem ... 
(Actually there are 2. )

Aerodynamics Aerodynamics have just as much to do with the front of the bike as the rear.  This toy model is from the original Harley VR1000 superbike. Although the 2000 VR1000 has 2 exhaust silencers, the problem is still the same.

3 Aerodynamic Forms
Imagine the wind is flowing from left to right:

The Plate. A plate in the wind. There is no worse shape.

The Bowl. This shape appears to work much better.  Yet it's actually almost as bad as the plate !! The wind comes around the back of the bowl and creates a tremendous amount of turbulence.

The Raindrop. Water falling forms this shape naturally.  This is the most aerodynamic form.

This Principle is Important to Understand:
 The cone that forms behind the raindrop is 
the most significant part of the aerodynamic form !!

This side view of the original HD superbike will help to illustrate the problem.

Enter The Secret Mototune USA Wind Tunnel !!

( Note: I realize there isn't a rider in the "wind tunnel." For this demonstration it's unnecessary. )

The air is flowing over the bodywork and rider in approximately the same ideal teardrop shape. 


The tail section and the rider help to form the cone.
Unfortunately, this doesn't even come close to simulating what happens on the racetrack.

Why ???

Because the bike isn't running !!!

So...

Let's Turn Off The "Wind" & Fire Up The Bike !!

Ooops..... 
At 11,000 RPM there's a big problem ! Look at the angle of the exhaust flow ...
The huge 500cc pulses of exhaust gasses are putting a new force into the aerodynamic equation.



O.K...

Now let's Turn the "wind" back on again to see 
what's really happening on the racetrack...

The exhaust gasses are pushing upward...
So the cone can't form properly. 
Notice that it "tries" to form, but now it's much further back. 

The aerodynamics are disrupted by the direction of the exhaust gasses. That's one reason the Harleys aren't as fast. The bike is fighting itself. 

PLUS: The wake it produces is larger and further back than most bikes. 
That gives the bikes behind it a huge advantage !!
So not only is it fighting itself, it effectively gives the other bikes 
More Power...

By making it:
"Super - Draftable"

It doesn't matter how much power the VR 1000 makes on the dyno...
The faster it goes, and the higher the RPM's are... the more it's design slows itself down
and
...the easier it is for Honda, Ducati, Suzuki, Yamaha, and Kawasaki riders to draft past.

The downslope of the tailsection is correct.  The upslope of the exhaust gasses cancel out the ideal teardrop aerodynamic form. Without the directional outlets of the competition's exhaust design, the gasses exit upwards, rather than backwards.

Now it's easy to understand why the Harley VR1000 should use this pipe design.  The silencers' outlets are simply pointing in the direction of the bike's aerodynamic wake.

There's another, closely related problem ...

Think About The Answer !!

Have a Cool Day Everyone !!
~ MotoMan

Next Article: Dynamic Aerodynamics !

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