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a lil' observation of different berm styles, plus jumps can act as turns too (in bmx and skateboarding an off-set landing is called a "hip"), and curved wallrides are basically berms too...

First note that in a berm, the riding line is not always the same. You can have berms where you enter low, then go high in the apex, then exit low. Or you can have berms which are the reverse--where you enter high, go low in the apex, then exit high again. One of the reasons that pump track builders say to put a roller at the entrance and exit of a berm is not just for speed--it's also to basically push the rider down into the low part of the berm then exit upwards. For example, in this video, where the rider is going through the "M" section, notice how he drops down into the berm, gets sideways, whips around, then comes back up. I would call that a high-low-high 180. Pump Track "M" bermwww.youtube.com/watch?v=JhM022wo0PA

Here's a low --> high --> low. (Pay attention to the packed riding line!)


different style of low --> high --> low. (Note the shape of the packed riding line--the groove as it's called in bmx trails).


cool ribbon/wave style....



Note that when you build a berm that is looks like a skatepark bowl, the rider gets to pick their line. They can go high-low-high or low-high-low, whichever.

So, like this skater... is at the high position (at 6 o'clock in this view of the bowl). He could have skated it differently coming down from a high carve at 3 o'clock, then low, then exiting high again at 9 o'clock.) The same can be true of dirt berms on a lesser scale.



Jumping into a berm can be done different ways. The landing can blend directly into the berm, or than can be space before you get to the berm...
landing down "into" berm . . . riding line is low... thus the berm does not need to be tall.


landing, then some space, then berm. you can go high in the apex.


good example of entering high, going low around the apex, then exiting high




chiller version of this:




rad combo of the landing blending into a wave-ish berm with blended waterfall out....


g-force!!


super-tight 180 (leelikesbikes.com)






classic curve wallride berm.



tilted launch to tilted landing


no separate landing at all. jumping directly to berm wall.


short & steep


steep wall 180


massive speed berm:


bermed launch to straight landing


another launch-berm to straight landing (at cattywoods)


the opposite: straight launch to berm landing




launch up to 180 wallride (at Ray's indoor mtb park)


tilted (not vertical) wallride


another way to do 180 degrees. dirt berm with slanted curve wall - (Winter Park, CO)



if you need to turn around 180, a quarter pipe to vert wall (or just a way over-vert quarter) will generate a lot more speed than a 180 berm will. because you air up... you can leave a vert wall going faster than when you came into it. (Highland MTB Park)




a lot of these photos are from the What Is Trails? thread on ridemonkey:


help with jump line into berm" https://www.ridemonkey.com/forums/showthread.php?t=241208
 

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in this example, we had a huge-turnout work day and built a berm on the existing trail radius... I went for a curve at the right, then a flat extension to drop-down/waterfall roller...
(your truly on the right)


some more berm work at Walnut. we did the short steep-face berm mainly because we were doing this by hand with only 3-4 guys in one day.
As long as the steepness is there in the face of the berm, a good rider can use it with speed....

Winter Park Colorado. A crew of us Austin guys will be heading up there again in July. Great stuff up there.
 

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Unpredictable
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:thumbsup:
in this example, we had a huge-turnout work day and built a berm on the existing trail radius... I went for a curve at the right, then a flat extension to drop-down/waterfall roller...
(your truly on the right)


some more berm work at Walnut. we did the short steep-face berm mainly because we were doing this by hand with only 3-4 guys in one day.
As long as the steepness is there in the face of the berm, a good rider can use it with speed....

Winter Park Colorado. A crew of us Austin guys will be heading up there again in July. Great stuff up there.
I'll take a guess your berms will not get braking ruts like the one in the last pic.
 

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Unpredictable
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Funny; I didn't really think too much about this thread when I replied to cmc's last post. Then I looked back through the unbelievable beauty in pics of berms crafted with artisan skills and found one of my posts from nearly 2 years ago. It asked for advice about a berm we intended to build. One that crossed the falline in its entry and before the exit. Here is that berm and how it changed over time.

We decided to build the impossible and drain water through the berm. It was bound to fail eventually, but we had an exit plan. Somewhere in the following pics you will see radius sizing - otherwise this is just bermvelution.

In its infancy and during the end of a dry spell

P1020198.jpg

The low point is below the pile of soil

P1020194.jpg

The low point was dug really deep and wide and filled with large to massive stones leading to an exit drain of > 1m x 1m.

P1020305.jpg

P1020306.jpg

1800mm+ of rain fell on the berm in 2012 with several 200mm deluges, most of it in the first 8 months. It was also popular as the entire trail only opened after this berm was sound and it is a fun trail.

Over time the drain failed as expected. At first it drained a 100mm in 1 hour rainfall like a bathtub. Then slower. Then we had to be there to unplug the surface paving stones (we had a number of flat 50cm plates with gaps over the ballast) if it rained really heavily, or it would flow over the berm. In the end we could not lift enough stones to drain the pond and it was time for phase 2.

The plan was to lower the exit by removing all the ballast and digging the last part of the berm and the first part of the exit deeper. This moved the drainage point a little farther along to meet the exit point of the berm, but the radius of the turn and the line were almost unchanged (we believe your eyes change your chosen line as much as the trail does, so the last bit is only our opinion!!!). A better draining and deeper exit was the aim.

We made the changes immediately before another 200mm (in 24 hours) rain event hit. It had been pretty dry for months and we knew it could disable the trail for months if the berm blew out. Here's how it looked after we finished work and after maybe 50mm of lead-up "drizzle"

P1100413.jpg

P1100414.jpg

As you can see from some tracks in the last pics, some were anxious to bugger the turn before it was ready for re-opening, but it survived the deluge with loss of only topsoil

P1100486.jpg

P1100491.jpg

and in the end the balance of pleasure was restored:):):)

P1020725 1 1.jpg
 

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The Voice of Reason
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where i live in florida it's pretty sandy and we get lots of monsoon rain events. if i was to get a truckload of dirt to build some berms should it get straight red clay or sand/clay or something else? what do you use to compact the soil? i've got one of those 8"x8" steel tampers but i could rent a power compactor. i don't want to build something and then have it be all rutted and sloppy.
 

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Some pics from my recent trip to Steamboat CO.

Apparently they've been spending a lot of time and money on DH flow trails. One trail I checked out had really consistent 180 descending roller-coaster style turns. They were clearly purpose-built and not jsut adding a berm to an existing v-shaped switchback trail.

view from top down...


view from bottom back up the trail....




Looked like they used pavers on some of the higher-altitude stuff.. Probably due to the dirt being more exposed (and maybe the dirt quality itself as well).


Cool wall-ride berm:
 

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Some pics from my recent trip to Steamboat CO.

Apparently they've been spending a lot of time and money on DH flow trails. One trail I checked out had really consistent 180 descending roller-coaster style turns. They were clearly purpose-built and not jsut adding a berm to an existing v-shaped switchback trail.

view from top down...


view from bottom back up the trail....




Looked like they used pavers on some of the higher-altitude stuff.. Probably due to the dirt being more exposed (and maybe the dirt quality itself as well).


Cool wall-ride berm:
Where does the water go when it rains
 

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Where does the water go when it rains
quite a few of the berms have pipe drains under them. you can see in the second pic above the little pile of white rocks. pretty sure that was covering one of the drains. i took a different pic of one of the drains but i didn't upload it yet...
 

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Also, here was one of the rad S-berm sections at Granby Ranch CO (formerly known as Sol Vista). i was there for opening day (May 30, 2013):

 

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30° Czech
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heh, thanks.

here's another stoke:

The Physics of a Curved Wallride
By Ryan Fudger
Wed, Dec 17 2008

https://bmx.transworld.net/1000074334/features/the-physics-of-a-curved-wallride/



This method of finding Ryan’s speed shows that he must be going 9.04 miles per hour or he will fall over. This number is slightly less than the previous calculation when only the points of contact were considered. This also seems to be a reasonable outcome. It may be even more reasonable than the first outcome because it places Ryan’s weight at a more realistic position. The angle in the second method has a big factor in the speed needed to travel around the wall. Although many other combinations of riding angles or centers of gravity could be used to find different outcomes, it is reasonable to say that between the two methods used here, Ryan was riding around the wall at a rate of around 10 miles per hour.[/I]
Nerd alert:
the last set of equations has a calculating error, v^2 should be 26.something, and not 16.something, hence the speed is 5.xx m/s :p
 

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That previous diagram shows an example where there is plenty of inclination and no angulation whatsoever. As with skiing, it is the angulation that gives you stability and traction in the corner.
 

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K&K
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BEFORE:


AFTER:


All of my previous trailbuilding has been singletrack, with the goal of making the trail sustainable. I am now working on a training track for my middle school bike team and I am doing more of this kind of trail, berms and rollers. When I look at this, two questions that come to mind. Keep in mind I have no experience, so I'm just ask'n, not suggesting. Why not dig half the height of the berm down, into the ground? Related, won't a berm that high erode away pretty quickly?

As I re-read this I realize there is another issue that probably explains this; we get very little rain, so digging down makes sense, but in an area where rain is more frequent, that would probably make a mud-hole.
 

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Dirt Monkey
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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.
 

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K&K
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If you have slope where water can drain it's not a problem to build berms using the cut/fill method.
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.
 
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