I dont want to hijack the other thread but we will be marking out a new spur trail soon and was wondering if anyone has figured out the equation for size of radius = to speed of travel. There is a just the right size of corner for different speeds to keep the flow going with out having to break and being able to pump the corner. Not to tight and not to wide. Im really getting into this trail building aspect of mountain biking.
If you have slope where water can drain it's not a problem to build berms using the cut/fill method. I do it regularly since it saves time and effort moving dirt. Useful when adding berms to existing trails where spoils from benching/construction aren't available.
Berms are a maintenance item. With low cohesive soils they will slump pretty quickly (2-4 yrs) from water erosion in areas with rain or be pulverized to dust in areas without rain (< 1 yr). To get the most lifespan, build the face of the berm less than the soil's angle of repose. Face armoring isn't a bad idea for dry areas with heavy use.
Ah, there's a name for that I learn so much on this site.
[/QUOTE]Berms are a maintenance item. [/QUOTE]
Its a bit of an adjustment, but I'm getting on board with that idea. Having the trail at my place of work makes that a doable proposition; that along with a bunch of kids to help keep it up.
Face armoring isn't a bad idea for dry areas with heavy use.
Something I've been trying to work into the plan is to have grass growing on the non-tread side. Seems like the areas that have grass hold the moisture more. Might be a bit backward thinking though because the areas with grass MUST be getting water, so maybe it's just the water that makes the difference.
Here is one of the chip seal trails in Bentonville. You can see how the shape is not a simple circular radius. The angle starts tilting maybe 20 feet back from the actual turn, ribbon style (like I was talking about ten years ago), and does the same on the exit.
This is a large-radius rock faced one on Barn Burner/Red Barn in Bentonville.
160-ish degree switchback berm, Rock faced, in Bentonville.
I am very new to trail building and have learned a few things from my efforts to rehab and improve existing trails in the park I manage. What I was taught as a general rule of thumb is a 16-17ft radius is ideal on a moderately fast section of trail if possible. We put a much larger radius berm on an existing trail that previously had no berm, and you really have to have a ton of speed going into it for it to feel right.
What I have struggled with is building the last 1/3 or so of the berm tall enough to keep riders up high and to feel comfortable maintaining speed. But our trails are traditional tight and twisty, so big berms don't really fit the overall feel of our trails if that makes sense. The other thing I need to work on is getting riders to get onto the berm at the very entrance of the berm, as I have seen a lot of people approaching at a terrible angle, and their path almost looks like a lower case ( r ) instead of a D shape if that makes any sense. I need to add natural looking obstacles at the inside radius of the berms to pursued the riders to move the f#ck over.
What I like about smaller berms that we are building is they still required a lot of thought and talent to ride fast. They aren't massively tall, so you don't have a lot of trail tread to work with if you are going fast.
12' to 15' radius if terrain will allow it. Not always the case that terrain will allow this. Inslope the turn so that the tread remains relatively dry and water drains off the tread in wet conditions. This is to minimize erosion in the turn. Grade reversal with nicks/drains at both the entrance and exit of the turn. In steep terrain climbing turns often require carrying material from the top of the turn down to the lower side of the turn. Raise the tread at the bottom. Lower tread at the top to decrease the gradient of the turn.
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