# Share your diagrams of trail features



## Bermzilla (Mar 12, 2015)

Are there any diagrams with universally accepted dimension of trail features. We are installing some doubles and triples into the tread and I want to get the shape and spacing correct. The trail is 7% grade average, fairly fast and somewhat flowy. Can any of you help?

thanks


----------



## Coldfriction (Oct 31, 2009)

You'll need to provide a little more info. Primarily we'll need to know the speed of the rider and how much you want the jump to throw the rider up. Where the landing needs to be depends on those two things. Lookup the "range equation." Nevermind, I'll just post it here.

R=(V^2*sin(2*<))/g

Where
R = distance between jump and landing
V = speed in feet/sec or meter/sec
< = angle of departure of jump
g = 32.2 ft/(sec^2) or 9.8 m/(sec^2)

This is simplified a little as it assumes the jump and landing are level with each other. Chances are the landing is lower than the jump. To be more precise you should look up the "kinematic equations for projectile motion". Using those the landing can be determined anywhere whether it is a step up, step down, etc.

I would probably start my first jump at around 30 degrees and see how that feels. You'll have to use a bike computer or something to determine your speed where you want the jump. So if you are doing 15 mph, that translates to 22 fps. R = (22^2* sin(2*30))/32.2 = 13 ft gap. You'll lose a tiny bit of speed hitting the jump; it's the speed you leave the jump at it's lip that matters. You'll also have a touch of air drag slowing you down. There might be riders that hit it faster than 15 mph as well. I'd probably start the landing at eight to ten feet and give it a slightly shallower slope out to 15 ft for the faster riders to have something to land on. Overshooting jumps hurts. If you are building a dirt jump park or a really nice pump track, you can be more precise with less margin for error.

Using the equation and example above, you should be able to get a good idea of what you need for your jumps. Someone else can probably offer better advice as to the dimensions commonly used.


----------



## Coldfriction (Oct 31, 2009)

That table gives you the idea of the gaps you should shoot for. It doesn't include energy losses due to drag, so cut a few feet off the ranges provided. The maximum range is at a 45 degree lip, which is a 1:1 ramp. So I'd probably try to build to that. Higher angles than that will throw the rider up more if you're looking for big air. Ideally the entrance to the ramp would be parabolic, but a circular style transition would be fine as well. Just don't put an angled grade brake at the bottom of the ramp or you'll go all Napoleon Dynamite.

The landing would ideally be a mirror image of the departure ramp, but hitting it precisely enough for that to work is hard, so maybe it's best to use a longer landing ramp with more give in it. It won't feel as smooth as a parabolic landing hit exactly right, but it'll be safer and accommodate different rider speeds.

If anyone wants that table in metric, let me know, or you can go find one using Google.

Also, always remember that in theory, theory and practice are the same, but in practice, they aren't.


----------



## slapheadmofo (Jun 9, 2006)

Dig around in here - cmc posts some great info on laying out jumps and pumps.

http://forums.mtbr.com/urban-dj-park/dj-pump-track-plans-402237.html


----------



## Bermzilla (Mar 12, 2015)

slapheadmofo said:


> Dig around in here - cmc posts some great info on laying out jumps and pumps.
> 
> http://forums.mtbr.com/urban-dj-park/dj-pump-track-plans-402237.html


That link was very helpful.


----------



## Coldfriction (Oct 31, 2009)

That link is pretty good. CMC goes into some of the theory behind the designs as well, which I appreciated.


----------



## slapheadmofo (Jun 9, 2006)

Bermzilla said:


> That link was very helpful.


Yeah, that thread has helped me out a ton.


----------



## cmc4130 (Jan 30, 2008)

Coldfriction said:


> View attachment 984578
> 
> 
> That table gives you the idea of the gaps you should shoot for. It doesn't include energy losses due to drag, so cut a few feet off the ranges provided. The maximum range is at a 45 degree lip, which is a 1:1 ramp. So I'd probably try to build to that. Higher angles than that will throw the rider up more if you're looking for big air. Ideally the entrance to the ramp would be parabolic, but a circular style transition would be fine as well. Just don't put an angled grade brake at the bottom of the ramp or you'll go all Napoleon Dynamite.
> ...


That's rad!!

Although I'm interested in the geometry, I have to admit I'm not as good at the math side of the physics, although I'd like to be.

The main diagram I point out to a lot of people is this one. 30 and 60 degree paths send you to the same spot, and 45 sends you a little farther. 









I also agree with you that circular-radius landings are not what people normally build with dirt, even if they do it with wood at bike parks.










A lot of wood bike parks do either large circular-radius landings or they do flat bank to tranny landings. In theory though, a parabolic landing might actually work too. Hard to say without riding one. I think some dirt jump builders build landings that closer to being parabolic.




























You can imagine one half of this being the side-view profile of a typical Dirt Jump landing.... 









Hmmm!


----------

