The quest for 300 mph: Streamlining the sidecar

After our 270 mph (434 km/h) run last year, everybody is expecting us to make an attempt on 300 mph  (483 km/h). With essentially no more horsepower to tap into, we have to improve the aerodynamics of the bike to go faster. The 3D computer model showed that the primitive sidecar covering was the big item we had to address. My beloved diamond plate had to go. 🙁


Bill with the new sidecar cover. You can see just how thin it is in this picture.

After months of work (mostly by Bill), the new streamlined covering for the sidecar and sidecar wheel is finally complete. The old sidecar was basically the frame and ballast hurriedly wrapped in sheet metal at the last minute. The new covering is a carefully designed NACA airfoil that we fabricated entirely from sheetmetal. (Just like an airplane wing or tail.) The shape was generated in DesignFOIL and tested in CFD in Autodesk Inventor to verify the amount of downforce.

We had  to build the sidecar with a removable top panel for the ballast, since the tech inspectors have to take it out to weight it each time. We also put on aluminum wheel disks on the wheel itself to cut down on the likely “pumping” of the air by the wheel spokes, and fashioned a cover (made from a third wheel disk) for the exposed suspension components.


The old sidecar cover in the background. I used to call it a “X-mas gift”, because the red sheet metal was just wrapped around the sidecar in the same way you would wrap a gift in paper.

All of these modifications should cut the total vehicle air drag by perhaps 25%, maybe more. We will only know just how much when we take it out to the salt. We were very careful to build in ~ 150 lbs of down-force when we designed the new sidecar cover. Of course, I cleaned, scraped, sanded, and repainted all the sidecar components including the ballast trays, frame, and suspension components. The salt just gets in everywhere!


The Computation Fluid Dynamics (CFD) revealed that the sidecar caused a large portion of the aerodynamic drag.

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Just like an airplane wing, the sidecar cover has ribs on the inside.

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Because this is not a weight-critical application, a steel rod was added on the inside to make the leading edge a bit more rugged.


Bill built the new cover just like an airplane wing – but an upside-down airplane wing so we get downforce for stability and improved traction.


The required ballast of 132 lbs (60 kg) consists of lead plate stacked in steel trays. The new cover was built to fit perfectly around the frame tubes and ballast trays.


Bill got to use all his aircraft tools in this project.


Riveting the final pieces on the underside was a challenge.


A disk on each side of the sidecar wheel prevents the spokes to “pump” air, which reduces the aerodynamic drag.


Wheel disks and new cover in place. My beloved diamond plate had to go.


A third wheel disk was the perfect solution for covering up the suspension and improving the aerodynamics further.


The only drawback with using pneumatic aircraft tools is the noisy compressor. Ear protection is strongly recommended… (OK, the screwdriver in the picture is not air powered, but the compressor was running in the background because Bill had just riveted something else).

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The old sidecar cover.

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The old sidecar cover was really a last minute fix.




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