# Pump tracks: Building a tight 180

Hey Lee,

I’m in the early stages of building a backyard track with thanks to inspiration from your site and the awesome e-book. Over the weekend I started the process with building a 180 berm that is confined in a tight corner of our yard. The space between a fence and shed measures only about 10′ across so I’m actually building a wall with some landscaping wood and rebar to support the backside of the berm and save room for the berm itself. …

Even with this I’m probably looking at a 4′ radius 180 at best. Any helpful hints to making a tight turn like that as railable as possible? I know the e-book mentions 180s with as small as a 3′ radius (I know the one at The Fix is listed at 38″ on the site) so I’m pretty sure it’s doable, any key thinks I need to know? I’m thinking the taller the berm the better for something this tight?

Thanks for you time and all the riding stoke provided by you site, keep up the good work!

Brian Mulligan

 Some guy named Lopes pulls an honest 3 Gs at The Fix’s original pump track.

Hey Brian,

It sounds like you have a nice little project there. With a 4-foot-radius berm:

– Make it as tall as possible. Your retaining wall will help, as will good dirt.

– Make it as steep as possible. Build the slope gradually from flat to steep. Try for a constant radius, like a well-built wooden ramp.

Ideally, your tires will press directly into your berm, perpendicular to the ground. For this to happen, your berm angle must match your lean angle.

Here are some G-forces and lean angles for a 4-foot-radius turn:

 Speed Cornering accelleration Lean angle 5 mph 0.4 G 23 degrees 10 mph 1.7 G 59 degrees 13.5 mph 3.0 G 72 degrees 15 mph 3.8 G 75 degrees

As you can see:

– When you increase your speed, the G-forces and lean angle increase significantly.

– 3 Gs is a very aggressive turn, and about the most I’ve seen on a dirt pump track. If you can build your berm up to 70 degrees, you should be able to rip it as hard as you want.

Braaap!

— Lee