[Boxxer]

A few friends and I are building some steel(think moto X style) launch ramps. Wed like to build a few of them to suit novice and skilled dj'ers. Well be using steep dirt landers but want steel launches to beat the constant rains we get.

Heres the question. I need to lay out some rough sketches for the welders.... but what radius' would work? Should it be constant or progressively steeper(from larger to smaller radius on the way up). Does anyone have dimensions or plans I could copy? Id like to build 1 or 2 for distance and then 4 or so as classic steep faced DJs. Made of steel....

thanks in advance

 

[Bicyclist]

Make it steeper as you go up the ramp. You don't want a slab.

 

[pnj]

I would copy a known good transition. if you've ever ridden a box jump that you liked, and know the tranny then use that.

how tall did you want to make the lip?

 

[Boxxer]

between 4-8 feet. I might end up using a box jump i like as a template.

 

[spacemanspiff06]

give it a very slight decresing radius.

 

[don]

check out this thread on hcor.net from a while back. There is some info I quoted from a guy from the Austin area that seems to have building dirt jumps down to a science.

http://www.hcor.net/postlite25881-wheelie+nelson.html

 

[Boxxer]

Thanks, I came across that cad before. Its a good read though. I might scale some down using cardboard models cause once theyre welding, changing anything is gonna be dough.

The slight decreasing radius is something i suspected but havent ever put a tape to. Im going to look close at a few I like....

Telling a tube bender "a slight decreasing radius" should be fun....

 

[pnj]

why not just make it like a quarter/box lip?

if you want a four foot lip, use an eight foot radius. it will give enough kick to give some height but not be too scary..

if you want to go super big, just increase the size of the lip. say a six foot lip, use an eleven foot tranny....

I think you may be over complicating things. do you have any experience making quarter pipes?

check this thread on this other site...
http://www.bikeguide.org/forums/showthread.php?t=78095&highlight=ramp+building+101

 

[urbaindk]

why not just make it like a quarter/box lip?

if you want a four foot lip, use an eight foot radius. it will give enough kick to give some height but not be too scary..

That's a good number. When I used to make skate ramps that or something really close to it was what I used. If I remember correctly, the decking you need a 4 foot lip with an 8 foot radius will turn out to be almost exactly 8'. That turns out to be a really handy number since plywood comes in 4' x 8' sections. It was a very comfy tranny for skate and bmx. I imagine it would definitely give you a good kick for a DJ. I haven't done it though.

I have a plywood ramp with 3' lip with cut from a 7' radius in my back yard. It works very well for my MTB. I haven't gone bigger though, so I really couldn't say what ratios of lip height to radius work above 4x8. I could probably do a quick excel calculation to tell you which ratios would give you the same angle of take off or something like that...

Making a ramp with a constant radius will probably be much easier for your welder to make. What would the benefit would you gain for a decreasing / increasing radiused jump?

 

[pnj]

i've ridden many four foot tall box jumps w/ eight foot trannys. they work great for jumping. if you use the same tranny (eight foot) but make the ramp five feet tall, you get more kick off the lip, more hang time...