There are a lot of rules-of-thumb out there for building jumps that don’t actually work. Here’s the way to do it with SCIENCE.
I’m an engineer, jumps are physics, and physics is my baby. In a practical world, we can do this with a graph and a tape measure and have a way better jump versus doing it “how we always do it.”
First off: Here’s a link to the work I’ll paraphrase. Read it and weep.
Second: Don’t use rules of thumb like “matching the angles of the jump and the landing” because they only apply to one specific size and shape.
Jumps are entirely about “Equivalent Fall Height” (EFH) which just means impact. If you fall from higher, the impact is higher. 90% of what we need to do is limit the impact. (The other 10% is film)
Let’s all get on the same page
So we’re talking about the same things, these are the three jump shapes according to me:
- Step-Ups, where the sweet spot is above the takeoff.
- Step-Overs, where the sweet spot is roughly even with the takeoff.
- Step-Downs, where the sweet spot is below the takeoff.
The major difference is how long the sweet spot is. Step up/down both have a short ‘soft landing’ spot. If you land short or long it’s going to hurt. Step overs have a long soft landing.
The safest jump has a “constant equivalent fall height” – the impact feels the same if you land 4 feet past the lip, or 40 feet past.
We can judge a small impact visually by looking for a small angle (think like 10°) between the trajectory and the landing, like below.
Any trajectory on this jump has a pretty low impact.That was quick and easy, and we have a giant 25 meter booter from lip to sweet spot, and you’re going to have to go 37mph (16.5 m/s) to make it. Yow.
A hard landing would be something more like this, which might look pretty familiar..
These graphs have a few paths that I generated by changing the speed of the rider and the angle of the lip. Here’s the link to this exact plotting tool, (using metric measurements). Follow that link and plug in some numbers for what you think riders will reach at your hill, how high you can build your jump, etc.
Whatever your space allows, whip out that giant tape measure. In summary, try to build a step-over.
With a little bit of planning like this before we head out and push snow, we could have some crazy fun jump lines this year. Then hit me up and let’s take some laps.