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I had a bit of a read about building dirt jumps but couldn't find a good answer anywhere.
Seems a few folk recommend building up the base of dirt jumps using logs etc, before chucking dirt on top.
My mate is lucky enough to have a narrow, yet 50m long garden with about 7m vertical drop. We were thinking about putting some fun jumps/drops down it. He also has loads of old bricks/rubble. Neither of us have built berms/jumps before.
Do people think using brick piles to structure dirt jumps is a good idea? Or a terrible one? (been on a couple of pump tracks where it seems something like this has been done). Any other top tips before we have at it?! Ta in advance for your wisdom.
We did this on a pals farm years ago. Had no issues layering over brick piles, just make sure to pack the dirt around it well
Bricks and rocks are fine as underlying structure, but make sure there is plenty of dirt on top - you don't really want any brick poking through.
Logs are rubbish to build over the top of - they slowly rot away and collapse the berm/jump.
The only reason I can think not to, is that moving and reshaping dirt is easier without bricks and rubble poking through if you need to change the spacing between them for example.
We built and maintain a set of jumps with permission in a local park and there is definitely an art to it.
The basic rules we worked to were for a metre high jump, the start of the take of was a metre away to give a 45 degree slope. For the landing 1.5m away to make it more mellow. I have it in my head that we left 3m between each but I would have to measure it to be sure. Ours are all tabletops to keep the place beginner friendly.
Our jumps are on a slope so grow in length as they go because your speed increases.
Across the top we start at 2.8m, 2.9m, 3m around a fast big berm then 3.2m and finally 3.5m. The last two jumps are lower and faster, the first two a bit steeper and a bit more dirt jumpy.
They didn't start life these sizes, they ended up like this after lots of riding and reshaping but thats the beauty of dirt. Good luck and enjoy the process.
Logs are a bad idea as they rot and collapse. The FC specifically hate this.
Building a base seems fine as long as the dirt is maintained. You don't want someone effectively riding into a brick wall at speed 😉
Dirt jump are constant work. If logs gets you up and running quicker nothing wrong with that but may need more work after a year or two. You probably would be wanting to change and do maintenance anyway
Build the lip out of pure dirt, put all that junk in the landing. Landings have significantly more volume to fill and you'll be less likely to want / need to shape it.
It can sink/compress differently over time (not as much as logs, but still a thing). But that's not a disaster and if it makes your build much easier then the only question is if it's a good trade off.
It does make rebuilding a little trickier and it's so annoying when you just want to take a wee bit of material out of something and you stick a mattock in it and find rocks or bricks instead of dirt. But again, that's just traded off against the ease of the build in the first place.