There’s been some increased interest in streamlining motorcycles lately, what with Terry Hershner’s bike and now Arthur Kowitz’s fully faired dustbin-streamliner Brammo Empulse, shown below. In spite of the fact that Kowitz claims this is “innovation” it’s not by any definition, but it’s still interesting. The first streamlining I’ve been able to find is via Craig Vetter’s site, the 1937 Joe Petrali Harley Davidson, above.
Honestly, I feel like from a safety standpoint on the racetrack, this is a case of ignoring history at your own peril. Though this is being represented as embracing a neglected technology, the plain truth is that because electric motorcycles are in the dubious position of scrapping for every inch of efficiency, it seems the bargain-with-the-devil solution of a fully enclosed fairing, though not necessarily the outlawed “dustbin”, is worth the risk. Is it? I hope we don’t find out the answer to that with people’s lives. In a recent interview, Hershner said that because his bike is heavy – over 1000lbs – it doesn’t get “tossed around by the wind”. Kowitz, on a test ride approaching 100mph said:
“As we approach(ed) 100mph, the bike gave me a bit of a vague feeling as if it would not be stable as I went even faster… this proved to be untrue, as it never got worse, and I gained confidence in its feel. There were some winds, prevailing and some gustiness, throughout the day. These winds were coming from the northeast, requiring some real muscle to make it turn into the wind. Turn 3 is a high speed left hand sweeper that bends into Sunday’s wind…it took noticeable effort to properly race through turn 3. Another, slower turn gave the same challenge, although to a lesser extent. I felt as thought there were no crosswind challenges..to my pleasant surprise.”
Anecdotal at best, especially in this age of measurable data and wind tunnels. This all leads me to ask exactly what kind of benefit can we expect from these types of fairings, and thus, is it worth some potentially serious, though pretty much unknown risks. So for that, I turn to probably the most authoritative site on streamlining, coincidentally focusing on electric vehicles, Shultz Engineering’s page, here: Kraig Schultz’s Opinions on Aerodynamics and Electric Motorcycles. The site really is just about the last word.
Here’s what I was looking for – a comparison of drag coefficients for various types of fairings over a range of speeds.
The two curves I’m most interested in are the “Modern Racing Motorcycle” and the “Dustbin Fairing”. And they’re not that far apart.
The issue here is that it’s the typical trade-off of Physics. To get the increased efficiency of a fully enclosed fairing you increase your exposed side area – ironically, to a cross-wind, just about the worst shape you could ask for, aerodynamically speaking. Look at it this way – as you increase your efficiency from one direction (the front), you’re sacrificing efficiency from other directions (the sides). So the issue becomes, what are the risks, and are they worth it compared to the savings over a typical, benign-handling sport bike?
For another reference from a legendary source, let’s look at Tony Foale’s site – again, pretty much the last word, but this time on motorcycle handling and frame design:
Aerodynamic design of motorcycles is more than just a matter of producing a low drag, low lift body with a C of P (center of pressure) behind the C of G (center of gravity). Stability is harder to achieve with well streamlined low drag bodies, this is due both to the greater side area present with such fairings and to more efficient production of “sideways lift” due to the angle between the airflow direction and the direction of travel.
So ideally we want a combination of sometimes conflicting requirements:—— Minimal drag for performance and fuel economy. Low frontal C of P. to reduce drag induced weight transfer. Low and rearward side C of P. to reduce the unbalancing moments, and give directional stability. A shape and value of side area that minimizes the side force produced. A high and forward C of G. combined with a large weight to minimize the effect of whatever side forces are generated.
Unfortunately, since the FIM ban on racing with a dustbin in 1957 the technology has been pretty much ignored, so we can’t benefit from any research or development in the face of current (or even ’60s through the ’80s) data-gathering technology. For the record, the ban was largely because of the IOMTT race in 1957. Surtees and MV removed the dustbin due to concerns about crosswinds on the mountain, and subsequently got beaten by a dustbin-faired Gilera ridden by Bob McIntyreon, raising concerns which led to the ban.
However, I have to assume a few things. First, there was a good reason for the ban. At a time when dustbins were at least not uncommon, there was enough concern to take an action like this. There’s no conspiracy theory explanation that holds water, period. So the relative danger of a dustbin, at least under race conditions, is just that – a relative danger. Second, I’ve got to assume that current sportbike technology can balance aerodynamic forward efficiency with safety under a wide range of wind conditions. Of course, they’re also balancing appearance as well, so who knows where the tradeoffs are made – but the numbers I’m seeing above? Hardly worth the risk for the meager payoff of what may be a big risk.
We simply don’t know. But I’m not going to be the one to be on the road with a handful of bike going 100mph who’s going to find out my dustbin doesn’t like a 40mph crosswind.
The bottom line is that I find this discussion disturbing. I have no issue with addressing this honestly, but to simply pass subjective conclusions off as fact, without any discussion of the actual facts of the science involved, seems to me to be particularly irresponsible. …and unfortunately, I feel like we won’t really appreciate the risks until, once again, we see the consequences of ignoring them.