Bike Jump Design

jump to bike jump calculator below

I’m not a (big) jumper, or hucker for that matter. Regardless, I’ve hit some good ones that seem to be dead on, take-off to landing that is. I’ve also gone too slow and too fast on jumps and suffered the consequences.

I think a lot of builders go with trial and error: ride it, reshape it, ride it… In other words, experimentation or science, and it’s the consistency or repetition of outcome, and even prediction, that riders seek— science meets mathematics. The math starts relatively simple for jumps and ladder drops, but a lot depends on the rider, the bike, and how they behave, but a little math will get riders in the ball park faster, so there is more science and success, and less trial-and-error witchcraft. Experienced builders are good at witchcraft, or perhaps its craftsmanship/art; they can see the parabolic line of flight when they build because chances are they have enough flight-time to render themselves Pilots in Command. The likelihood of a rough landing is lowered, however, if a little math is done first unless you want to move earth multiple times rather than ride. A little math may lower the amount of “experimentation” and tweaking, and get you closer to the desired outcome. And lower risks, may lower insurance premiums! In spite of geology and rider behaviors throwing the best intentions a curve-ball, break out rulers and protractors with your shovels…jump to bike jump calculator below

Parabolic Jump/Projectile TrajectoriesIdeal_projectile_motion_for_different_angles.svg

^Lines of jump (and huck) flight are parabolic. NOTICE how 30o and 60o (and other angles in light gray) yield the same distance or range, R, with the same initial velocity, but yield significantly different heights. 45o will give the farthest range– it’s not magic, it’s the Law. Try 30o and 60o degrees using the calculator below to see for yourself, or build two ramps side-by-side the same height and sharing the same landing area (the 60o landing side should be a little steeper though, or go between 30o and 60o for both, perhaps 45o).

Bike Jump Calculator
Standard Metric
enter speed or velocity and ramp/jump angle**, and see notes*
Jump velocity @ launch lip, v= mi/hr
Jump velocity at launch lip, v= m/s
Jump angle, θ= degrees Jump angle, θ= degrees
Horizontal range, R= feet Horizontal range, R= m
Air time, t= seconds Air time, t = seconds
Height, h=feet Height, h= m

*Notes:

  1. Read #5 and 6 first. THIS CALCULATOR ASSUMES same launch and landing height! (see black and red diagram). **”Jump angle” or θ = the angle of the bike the instant the back tire leaves the ramp, which should be very close to the last foot of the ramp under the lip.
  2. IMPORTANT: the bike jump calculator is for a “point” of mass. In turn, R will have to be shortened by: (wheelbase in feet or meters) x sin(jump angle) = distance to shorten R. For example, perhaps err for extra large 29er wheelbases that are somewhere around 46 inches: 46in/12in/ft= 3.83 ft, meaning 3.83 feet x sin(jump angle) = distance to shorten R for XL 29ers with 46 inch wheelbases.
  3. Launch and landing speeds will be the same (or negligibly different) if the launch and landing heights are the same (also see 6).
  4. For a slower/softer landing, landing ramps can be elevated, but this will change the range, R, to a shorter distance. If landing at a lower height than takeoff then R, or the the landing lip, can be pushed farther from the takeoff lip. Please see the “safer jump” pdf documents linked below for details about the best landing ramp design.
  5. Jumping is dangerous, and may cause serious injury or death (see this)
  6. Build and jump at your own risk, no guarantees are promised by the numbers output by the ramp calculator, but this calculator should get you in the ball park (if you know what average launch speeds will be– don’t forget speeds will slow as you climb up ramp, and drag friction will reduce R, sometimes significantly)
  7. WIND and rider behaviors like pumping, lifting, braking, spinning, flipping etc. could change any of the variables (h, R, t, and the angle of launch)– in other words the parabolic line of flight as as depicted in the red and black image will be altered, altering R
  8. Wind and drag may become a factor if strong enough or H and/or R is great enough
  9. ALSO: The above is for RIGID forks AND RIGID tails, i.e. hard-tails (see 10)
  10. Suspension can change the angle of launch, thus H and R. Recoil may also affect the outcome.

*props to Greg from dirtycentury for helping with the script

31072008_Capes_B

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