Dirt Jump VS Wooden Jump

[Dh2]

Just would like to get some peoples opinions, what is better all round for a large Dh Jump and landing;
Need to get the right idea to then design my jumps
~Completely made of wood
~Wood base then topped with dirt
~Made of 99% dirt (A lot of Dirt)
~Or using like a fallen over tree to build a big jump

Talking around a 3 - 6 Metre jump

 

[Dozer]

Dirt. No question. You can only tailor the shape of timber so much to suit a jump but with dirt............actually, in my opinion, timber has no place on a trail unless you need to clear a body of water.

 

[pink poodle]

The more important question here is how lazy are you? Can you be fucked digging up a box trailer of dirt/clay to make a good sized kicker? then repeat it for the lander? while wood is grossly inferior to pure dirt, it cuts out a lot of time. of course the wood will eventually rot and your jump will need some maintenance. other wood advantages include being able to prefabricate most of the ramp in the comfort of your own garage/yard...tunes blaring, bbq sizzling, food and drinks on hand, less/no mozzies, work in the rain no worries....

but it will never be as nice as a dirt jump.

 

[Flint]

Wood ramp, dirt landing. That way you can move the take off ramp to suit your skills. If you don't think you will need to do that then dirt. Using any logs to help build up the base is fine.

 

[Wiffle]

If you want to build it properly, you need to avoid organic material (ie wood) which breaks down over time. You can use large rocks to form the basic shape and save a lot of digging, but definitely a good thick layer of dirt on top for the final tread surface. Build it quickly/poorly and you'll be forever doing maintenance; build it right the first time, and ride it for life (thanks Crofty!)

 

[Quintin]

Dirt. No question. You can only tailor the shape of timber so much to suit a jump but with dirt............actually, in my opinion, timber has no place on a trail unless you need to clear a body of water.

like


10chars....

 

[bikesarefun]

Either dirt or wood can be great, or a complete disaster. The key is to do it properly.



If you're going to use wood, you only get one chance at picking the radius. So get it right. For a big DH jump, I'd suggest a radius between 2.8m and 3.2m (I'm assuming it's going to be at least shoulder high). If you don't have the construction skills to achieve that with precision, don't use wood.

For a dirt jump, you can modify the radius if needed over time.



Note the basic rules of lip radius :

- If the radius isn't constant, you're gonna get bucked (or at least it'll feel funky and people will have a shit time).

- As radius gets bigger, the jump becomes less technical to hit at higher speeds.

- The release angle (angle at the launch end of the lip) is a factor of radius and jump height.

- For maximum distance, you want a release angle of about 50-60 degrees (yeah, high school physics says 45 degrees, but that doesn't account for horizontal inertia).

- Any competent rider should be able to hit a lip of radius around 3m fast, regardless of how steep the release angle is, and be fine.



If going to have random crap buried in a dirt jump, make sure there's at least 60-80cm of good quality dirt over it, and make extra effort to pack down the good dirt so it's rock hard and stable.

 

[Klips]

The more important question here is how lazy are you? Can you be fucked digging up a box trailer of dirt/clay to make a good sized kicker? then repeat it for the lander?

Speaking from a friend's experience, best bet is to build the lander first, then the kicker. Finding out like he did that the kicker has no lander after take-off sucks a lot more than looking at a lander wondering when it'll have the kicker it deserves.

And yes, he is fucking dumb for boosting something without looking at the other side, but, you know.

 

[buffthatout]

build it using local resources, rock, fallen trees & dirt. but you need to make sure you're not building a dam! water flow is key to a good track with or without jumps.

 

[pink poodle]

get creative and think ahead...you know those tall thin gums that you would love to 'parrachute' on? well tie them down and in a few years they will be ready for having ramps up onto them...

 

[Ridenparadise]

Don't make anything you can't maintain. That's it

All this love for dirt suggests no-one rides it before completion and fucks it, it never erodes and it never shrinks. Fantasy.

If you use dirt, factor in a 15-25% shrinkage in the first 12 months. If you add stone to the dirt, then factor exposed rocks on the take-off in as well, because they are inevitable over time.

 

[Dh2]

get creative and think ahead...you know those tall thin gums that you would love to 'parrachute' on? well tie them down and in a few years they will be ready for having ramps up onto them...

I'm in extremely dense bushland