Wind Tunnel Methodology

Ground Control to Major Tom.The Rail prototype did extremely well in the wind tunnel.  Our hope going in was that it would be aerodynamically close enough to the 404FC that with the wider inner brake track width, lower profile, and lighter weight, the Rail could be able to make a compelling case for itself - economics aside - as one of the best all around wheels on the market.  I'm in a bit of a state of shock after learning that that's exactly what the test results show. 

We put a fair amount of pressure on ourselves by making a big deal about our trip to the wind tunnel before we went.  Hypotheses precede testing, claims follow it.  As I recently told Mike, "until you know, you don't know, and if you don't know, you can't claim anything."  While we hadn't made any claims before the trip, it might have been a bit smarter to go there in stealth mode in case the results stunk, but where's the fun in that anyway?  Failing's no fun unless you get to look like an idiot in public while doing it.

The real risk we had in front of us was what we've come to regard as "supplier risk."  Supplier risk means simply the risks to which we were exposed in the event that the test went badly.  Yes, we'd look a little stupid, and perhaps our credibility would have taken a knock.  More importantly, we have a significant amount of time and money into this project, which would more or less go down the drain with a bad result.  I didn't have any "better design" or alternate take up my sleeve; what we sent down there was my final answer.  A bad test would at the very least have meant a big delay in bringing this thing to the market, and losing time on the market in a performance driven segment is never a good thing. 

Of course we could have sidestepped that element of "supplier risk" by not testing, assuming but not confirming that our hypotheses would be borne out in the tunnel, and gone ahead on that basis.  That would have introduced what we have come to think of as "consumer risk": that you would buy a product based on assumptions that haven't been objectively proven, with the risk of it not performing up to claims borne by the people who bought it.  Prototyping and wind tunnel testing are expensive and time consuming, but in this day and age they are accessable enough that you must do them.  Until you know, you don't know, and if you don't know, you can't claim anything.  You must know. There is still development and testing going on, we've got to ensure (and test, and therefore prove) that braking and heat management are good, and that the wheels are stiff.  Those all still reside firmly in the venue of "supplier risk" and we will not transfer them to "consumer risk."

But you're all here now because we were in the wind tunnel yesterday, so let me go through that a bit. The reason why we sent a 404FC to be tested among this batch is simply that transferability between tests is problematic at best.  We had planned to send each wheel with a tire already installed, and then we were advised that even different tires of the same exact make and model can skew results - the same exact tire should be used on each wheel.  The benchmark needed to be as exact as possible. We now know how the Rail compares aerodynamically to the 404, and each of our other wheels, under conditions that could not be replicated more closely. 

If the difference between two of the exact same tires could skew the results, you can imagine how introducing different variables like different types and widths of tires could throw things out of whack.  We knew we were sending a worst case down there on behalf of the Rail, as what we sent was an unfinished prototype with extra spokes compared to what the production version would have.  While more spokes is never aerodynamically better than fewer, the magnitude of the effect is unknown.  On one wheel, taking out four or six spokes might have a huge impact while on another it might have none.  We sent two 58s down there, one with 20 spokes and one with 24, to act as something of a learning point on what going from 20 to 24 spokes might do, but we had no plan to rely on the over-spoked 58 as a proxy for the over-spoked Rail.  While it might be tempting to do so, we aren't going to imply that the increased drag from the extra spokes on the 58s is directly transferable to the Rail.  That would constitute consumer risk.  Instead, we will re-test the Rail with the production spoke count (and we will re-test the 404FC at the same time to maintain that control baseline as accurately as possible) and then and only then will we make any claims about how the final Rail compares to the 24 hole prototype.

At this point, I've looked at so many aero graphs that I can somewhat reliably pick a 404FC out of a lineup based on the shape of its curve. Sometimes it is higher up on the y-axis, sometimes it's lower, but the shape is generally very recognizable.  The 404FC is the lingua franca aero baseline wheel, which is why we chose to send it with our test.  If the shape it produced in our test was markedly different than how it usually looks, even though we used a 23mm tire that we think more accurately represents what people actually want to use instead of the 21mm for which it's optimized, that would have caused us some doubt about our baseline's validity.  As we plotted out yesterday's results, I was very happy to see that familiar pattern start to appear.  The absolute values along the y-axis may or may not be exactly what they are in other comparisons, but we know that the shape is good and therefore we have a good, if necessarily imperfect, idea about how we stack up among other wheels.  As I said at the outset, we're just shy of over the moon with where that is.  

We learned a lot from this wind tunnel experience, and we owe a big thanks to Dave Salazar at A2 for his help.  I know a lot of people are chewing on the bit for us to post results and pretty graphs, which we will do soon enough (days not weeks, and well before we offer it for sale), but before we do that we need to make it as clear as we can what, and how much, the results of this round mean.