scca_ita wrote:
why Lotus shape vs Beam bike.... want understand the fundamentals.
The principal design goal with Omni's shape - what we call the Monofoil - was to guide clean air from the front of the head tube (or really, the front brake cover) back cleanly to the rear wheel, without interruption. The entire frame is basically just one continuous leading edge, which fairs the rear wheel. You can draw an aero chord from the front tip of the front brake cover to the back edge of a disc wheel's tire, with zero additional leading edges. (For what it's worth, the ratio of that chord is something like 30-to-1). We validated the concept in CFD with many rounds of testing, as well as real-world wind tunnel testing BEFORE we locked our 3D data and went to production. You can read all about it at
http://www.tririg.com/...ge=windtunnel_report It's worth noting that our transition from aerobar to frame is exceptionally clean - we found this to be very important on our first trip to the wind tunnel. Keeping all the shapes smooth and blended into one other proved very important to keeping a cohesive Monofoil that actually worked aerodynamically.
Interactions with the front wheel are quite a bit simpler than they are when a down tube is in play. Most down tubes try to hug the trailing edge of the rear wheel as much as possible, but always part ways with it somewhere, and you wind up with aero inefficiencies there, with air going in multiple directions simultaneously, causing drag. The Omni frame deliberately moves upward right behind the head tube, creating a little more free space to make way for the air coming off the front wheel, which is traveling in a nearly vertical direction right there. Additionally, the fork blades are very wide-set, and very deep aero chords themselves, so they don't disturb the air much, or interact with the air coming off the wheels, much. The result is that you can pick any front wheel/tire combo you like, and you won't ruin the aerodynamics of the frame. Omni is pretty insensitive to front wheel choice.
Regarding side/cross winds, you can already read about Omni's raw aero performance in the link above. But one thing we don't go into in depth in that report is stability, and notably perceived stability, in cross winds. But if you look at pictures of a rider on Omni, you can see that the bike adds very little surface area for the wind to see from a crosswind perspective, since the rider's legs shield much of the actual side-area of the frame. What we expected was that this would provide additional perceived stability, and we are happy to report that our riders have corroborated this. We frequently hear unsolicited feedback that Omni feels extremely stable in high crosswinds, much more so than other designs which add side area with deep down tubes, or other frame area directly behind the front wheel.
Is that helpful? Let me know if you have any further questions.
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