Thanks for coming to see the talk at the 2026 Sustainable Trails Conference in Boise, Idaho. I’m sorry it was not hands on or more conversational, 60 minutes was a big ask for all this…best of luck. Hopefully next year I can do a training on the ins and outs of how to use the application and the many settings and functions of BASE-Bf.
The PDF I promised(and see a little note not in the slides down below on this page):
Don’t hesitate to reach out
BUT WAIT, THERE’S MORE…
really dude, enough already….
But seriously, think of this…
Wind
- Do you design for calm conditions and accept that headwind riders land harder?
- Do you design for headwind and accept that calm/tailwind riders land on an over-built surface?
The answer is almost always: design for the headwind case. Over-built is safe. Under-built is a harder landing.
- Headwind compresses range AND steepens descent → rider lands shorter and harder → this is the dangerous case…because the TD is closer to perpendicular than parallel
- Tailwind extends range AND shallows descent → rider lands longer and softer → this is the “over-built” case (safe, just more dirt)
BUT, damn, designing for headwind produces a shorter, steeper surface. A tailwind rider on that surface could overshoot the designed landing zone entirely. You’ve traded one danger (headwind rider hitting hard) for another (tailwind rider flying past the end).
A single EFH surface cannot satisfy both headwind and tailwind simultaneously. They’re geometrically incompatible — headwind wants a steep short surface, tailwind wants a shallow long one. Nature win(d)s.
BUT what are the chance this is the case? I can’t say, the wind does what it does, but you should know your site. Chances are there is a prevailing wind, but some “prevailing” winds are seasonal, and may shift by a large margin. I mean, who’s going to be out riding in a tornado or hurricane (don’t answer that).
Wind analysis is more useful as a diagnostic than a direct design driver because the two constraints are fighting each other geometrically. A surface that’s steep enough to keep EFH low at the far end wants to be shallow near the lip to catch the short case softly, but “shallow near lip” means a flatter initial slope which tends to push the near landing point further out, not closer in. So you’re stuck between a windstorm and a soft place, like a couch or movie theater seat. Put up a wind sock, but if someone does not realize its better to fly a kite than bike, then…
BASE-Bf’s Variable and Constant EFH surfaces are NOT useful for BOTH tail and headwind at once, but maybe one direction or the other. BASE-B has a headwind and tailwind trajectory band that shows you the problem, you make the judgment call. The wind envelope is a “how bad is wind at this site” visualizer, not a “fix it” button. If you have a strong prevailing wind you can lean into one of them and decide what is best yourself.
The wind issue is really relative to how fast the takeoff speed is. On low and slow trajectories and short distances, it’s not that “big” of a deal or difference. Even in a pretty stiff wind on short jump ranges the differences are not massive, and perhaps you know this already. As the run-in distances increase and the speed and the flight above the lip increases it is more impactful. The best bet is to test the impacts yourself, no software, and/or use the simulator to see for yourself. As you may know too, jump one on a line after a starting gate might be OK, its jump 2, 3, 4… that often start to get progressively harder to compensate for depending on the site grade and amount of wind.
Equivalent Fall Heights (EFH)
The best I could do was to use ASTM F1292 and compare it to some of the ski research:
Dirt is not groomed snow and the safe bet is to consider it as hard pack always. And what if people land without their bike vs landing as expected on tires? They may aim to land on their feet if they are lucky and run it out, or take few steps before sliding. They may are more likely than not going to put their arms out to catch themselves, and slide if they are lucky. On something like concrete or asphalt the results may be worse than dirt:
 |  |
The info above is worth some contemplation. I can’t recommend what you do, and to bring all surfaces to around 2-3 feet will result in some shapes we see and some we don’t. BASE-Bf can get you there, whether you want to pursue that is up to you. For short range low angle jumps you might be fine doing what you have always done, I don’t know. I assume if multiple people are breaking bones on a particular jump you may hear about it. For the most part I think those cases are low if the stakes are low. How far you push the stakes is a conversation for you and your clients.
I just spent the day at the Rhodes skate park in Boise. It has really slick/smooth surfaces, more than I anticipated, but that can be a good thing as the sliding can help lower the negative mechanics of an impact on a rough surface. I know I prefer concrete over asphalt myself for this very reason.
…And one more thing
The 0 G off a lip on slide 37… Gravity is still on the rider when they leave the surface, but the normal force drops to 0 because the ground is gone.
- “0 G” meant 0 felt G (normal force through wheels/body)
- Gravity is 1 G always — but you can’t feel it in free fall, which is flight, though while jumping the free fall is sideways if that makes sense…