# Decreasing Radius turns that steepen? good or bad trail design?



## BushwackerinPA (Aug 10, 2006)

so I am just curious. We have a local trail(s) that have a bunch of decreasing radius turn going downhill that also steepen as you get into the turn. They have erode very fast since they were built. Some have double apexes.....

should the trail have been built with a turn that opened up more as the rider is traveling downhill? or should they have been built to close off and tighten at the bottom.


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## rideit (Jan 22, 2004)

Depends. Sometimes that design can be an effective 'speed check' in order to reduce brake use and consequent stutter bumps. 
Sometimes that can be beneficial in creating a drain. 
Other times its just poor design, whether on purpose or not. 
Every turn is different...like snowflakes!


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## aero901 (Apr 11, 2012)

Typically, a turn radius should stay the same or slightly increase after the apex if riders are gaining speed through the turn. If the erosion is from riders grabbing a hand full of brake and skidding or front tires washing out because they loose traction, it is a problem that should be addressed. It could also be that the trail is too steep to begin with. Images would be helpful if you have them.

If rerouting is not an option, a small berm or slightly insloping the tread through the corner may be able to correct for the lack of flow.


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## epic (Apr 16, 2005)

rideit said:


> Depends. Sometimes that design can be an effective 'speed check' in order to reduce brake use and consequent stutter bumps.


I think it actually causes more braking because you enter the turn thinking it's open and then it closes down mid-turn. You can always grab a handful of rear-brake to help redirect mid-turn...


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## rideit (Jan 22, 2004)

epic said:


> I think it actually causes more braking because you enter the turn thinking it's open and then it closes down mid-turn. You can always grab a handful of rear-brake to help redirect mid-turn...


I am more thinking of after the turn, basically as a chicane like feature. Not how I would build it, but would achieve this function. Sometimes negotiating decreasing radii turns just boils down to rider skill...those with less confidence tend to brake more, basically.
They can actually be quite fun, IMO.


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## BushwackerinPA (Aug 10, 2006)

rideit said:


> I am more thinking of after the turn, basically as a chicane like feature. Not how I would build it, but would achieve this function. Sometimes negotiating decreasing radii turns just boils down to rider skill...those with less confidence tend to brake more, basically.
> They can actually be quite fun, IMO.


so lets say these trail are major though fairs that see a high number of riders of skill level and the trails all tend to have steeper second part of the turn while it decreases in radius.


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## Brandon_oma#692 (Mar 3, 2010)

Is this a one way trail?


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## aero901 (Apr 11, 2012)

If those kind of turns are on a high traffic trail with riders of all skill levels it is just asking for problems. This is not the proper way, or even a good one for that matter, to reduce riders' speeds. They need to be speed checked before entering the corner and not mid way through it (especially if there are poor sight lines). Choke points and/or chicane turns with good sight lines before the turn are the best way to check speed.

Was this a trail built specifically for mountain bikes? It almost sounds like it was a hiking path that got adopted by bikes which would explain why the trail is routed like it is.


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## radair (Dec 19, 2002)

In general I think decreasing radius turns are not a good idea, nor are steepening turns. Terrain, topography and obstacles like trees and rocks often dictate where the line is built.


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## rideit (Jan 22, 2004)

I agree, but occasionally terrain (and building permissions) transpire to make that 'the line', regardless of desire for it to be different. 
As to it being a speed check, I never suggested that a DRT should be designed or built to be one, just that they can serve as one, whether intended or not. That combined with terrain options before and after a turn can slow an entire section down, not just the turn in question. 
In other words, 'in the real world' not just theoretically.


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## Ridnparadise (Dec 14, 2007)

They sound like they were built as climbing turns, which would be a bummer on a descending trail.


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## LeeL (Jan 12, 2004)

Even as climbing turns they sounds a bit off. Steepens as you start and tight as you apply power? Does not compute


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## Ridnparadise (Dec 14, 2007)

LeeL said:


> Even as climbing turns they sounds a bit off. Steepens as you start and tight as you apply power? Does not compute


I tend to agree in some ways, but I have seen it on old trails and also on some pro trails with steep grades and it can be a reasonable technique on some climbing berms. It can work where the trail allows you to come in fast and ease out, thereby saving energy rather than wasting. It has a chance to work on tight corners.

Although it is wrong, I have often dreamed of making the ultimate tightening, descending berm. I suspect it is one for a Red Bull event though - a sickter off the richter J turn :yesnod:


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## DaveVt (Jun 13, 2005)

So full disclosure....The trails in question were hand built bench in steep and wet terrain. The route was not straight forward to begin with. The turns are bermed and surfaced wit 3/4 minus. Sight lines are excellent. BushWacker is a very active trail user. He is fairly obsessed with his strava times and attempts to race these trails everytime he rides. Rideit is correct in assuming these turns and other features were desgned to control speed. Whackers real problem is that he is not looking through his turn so he is entering to hot and exiting off the tread and having poblems with stones placed off the tread after the turn exit placed in an attempt to keep the bottom of the corner from getting blown out and to keep people on the prepared, hardened surface. He constantly interjects his complaints about all the trail work happening around Stowe Vt and does ABSOLUTLY NO volunteer work on any of the many projects the local club funds every season. He takes it very personally that I tell him he just needs to get better at cornering, slow down more before leaning it over, and look farther ahead. He has been ranting all over FB and the Vt forum. The trails in question, if you brake properly, and exit the turn on tread and accellerating, flow wonderfully, for me at least, with long sections of pumping and jumping that follow each thru-fall-line, bermed switchback. Whacker just can't get it through his head that sometimes to go faster, you have to get better at braking. Once he blew past some women I know who had just crashed...instead of stopping to make sure they were OK, he blew past them blathering something about Strava. He, on SO MANY LEVELS just does not get it. He came on here looking for support for his rants against all the people in his town that actually do trail work. Then went back to facebook to tell the world how the MTBR trailbuilding crew supports his views. Bizarre really. Enjoy!
I'm Faster Than You - YouTube


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## Ridnparadise (Dec 14, 2007)

DaveVt said:


> So full disclosure....The trails in question were hand built bench in steep and wet terrain. The route was not straight forward to begin with. The turns are bermed and surfaced wit 3/4 minus. Sight lines are excellent. BushWacker is a very active trail user. He is fairly obsessed with his strava times and attempts to race these trails everytime he rides. Rideit is correct in assuming these turns and other features were desgned to control speed. Whackers real problem is that he is not looking through his turn so he is entering to hot and exiting off the tread and having poblems with stones placed off the tread after the turn exit placed in an attempt to keep the bottom of the corner from getting blown out and to keep people on the prepared, hardened surface. He constantly interjects his complaints about all the trail work happening around Stowe Vt and does ABSOLUTLY NO volunteer work on any of the many projects the local club funds every season. He takes it very personally that I tell him he just needs to get better at cornering, slow down more before leaning it over, and look farther ahead. He has been ranting all over FB and the Vt forum. The trails in question, if you brake properly, and exit the turn on tread and accellerating, flow wonderfully, for me at least, with long sections of pumping and jumping that follow each thru-fall-line, bermed switchback. Whacker just can't get it through his head that sometimes to go faster, you have to get better at braking. Once he blew past some women I know who had just crashed...instead of stopping to make sure they were OK, he blew past them blathering something about Strava. He, on SO MANY LEVELS just does not get it. He came on here looking for support for his rants against all the people in his town that actually do trail work. Then went back to facebook to tell the world how the MTBR trailbuilding crew supports his views. Bizarre really. Enjoy!
> I'm Faster Than You - YouTube


Ouch! I did a rally driving course back in the day and remember whining about slow corners and how they prevented more aggressive driving. The instructor looked at me said - "Some corners are slow." I got it after that.


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## cmc4130 (Jan 30, 2008)

Although, this is slightly off topic, I'd like to commend Winter Park Trestle Bike Park on the trail Cruel & Unusual, because they use what I think is a superior design, which is using upgradient turns to shave off speed, in order to prevent braking. Rather than all DH trails being down or flat (cross-gradient), use some up-gradient sections to shave off speed ! It truly creates a better pump and flow design.

I know this isn't the greatest pic to illustrate . . . but after this drop on Cruel and Unusual, the trail turns left, upgradient, before turning right again (downgradient) and over another wood feature. definitely has the rollercoaster style of speed acceleration and conservation....


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## epic (Apr 16, 2005)

DaveVt said:


> Once he blew past some women I know who had just crashed...instead of stopping to make sure they were OK, he blew past them blathering something about Strava.I'm Faster Than You - YouTube


Most of what you are saying is true, but this is not. Both of the women there said this is not what happened. You don't need to make **** up to make your case.


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## epic (Apr 16, 2005)

DaveVt said:


> The turns are bermed and surfaced wit 3/4 minus.
> I'm Faster Than You - YouTube


What's this mean? Is 3/4 minus a typo or a trail building term that I've never heard?


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## DaveVt (Jun 13, 2005)

epic said:


> Most of what you are saying is true, but this is not. Both of the women there said this is not what happened. You don't need to make **** up to make your case.


This is what one of the women (the one who crashed) told me happened that day after it happened. Maybe his percption of what was going on was different being he was focused on becoming King of the Mtn. Hardly making anything up. You don't have to clean up after his messes bro.


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## epic (Apr 16, 2005)

I'm hardly cleaning up after his mess. I spoke to both of the women at last year's Leafblower and they said that's not what happened. Bro.


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## Ridnparadise (Dec 14, 2007)

cmc4130 said:


> Although, this is slightly off topic, I'd like to commend Winter Park Trestle Bike Park on the trail Cruel & Unusual, because they use what I think is a superior design, which is using upgradient turns to shave off speed, in order to prevent braking. Rather than all DH trails being down or flat (cross-gradient), use some up-gradient sections to shave off speed ! It truly creates a better pump and flow design.
> 
> I know this isn't the greatest pic to illustrate . . . but after this drop on Cruel and Unusual, the trail turns left, upgradient, before turning right again (downgradient) and over another wood feature. definitely has the rollercoaster style of speed acceleration and conservation....


So glad to have you back in this and the roller threads cmc. You are the Galileo of dirt. Sorry for the thread hijack!

Here's the type of turn you are talking about. The falline is the shadows across the exposed stones in the foreground









When we built it we got very cocky and decided that about 2 tonnes of rock built into the berm and under it at the low point would allow us to drain water through a low point that was inside the berm, rather than after it. In the first 12 months 1800mm of rain fell on it. In the first 6 months it drained really well. In the next 6 it started to fill and we had to dislodge surface stone slabs after huge rainfalls, allowing it to drain like a bath tub. It was really impressive with huge suction vortices.

However, with a major weather event coming, we knew the time had come to make a change we predicted from the beginning. What could not change was the uphill exit into the next corner, so we dug deeper in the last third or so, removed a lot of the rock fill and re-contoured the exit over a new, open drain. We also used harvested clay to resurface the whole berm. The rain started before we finished. Some local weather stations recorded 160-200mm, but the closest recorded >700mm in the next 4 days

















It is now faster through the berm, but slows more going up the increased exit slope. There have never been braking ruts in this turn. The G-out is long and you seem to have to twist your head up to see through the exit - it's a gas. Again, not the best pic, but you can see how the turn exits uphill and then goes over the seasonal creek and back on the contour. It also starts uphill off a jump with optional line, making it about 220 degrees in total









Using an uphill exit to slow speed is awesome, but hard to get right. We did we not use drainage pipes at the beginning - the land manager does not allow imported materials! You build with what you have. It works though, especially if you have an exit plan for failure (not commenting on the OP here)


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## epic (Apr 16, 2005)

Rip - where is your trail? Is it machine built, or did you move all that rock by hand/shovel/bucket/whatever?


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## BushwackerinPA (Aug 10, 2006)

yeah those turn are pretty ^^^^ nothing like what I am talking about. those turn looks FUN!!!


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## Ridnparadise (Dec 14, 2007)

It's in Nerang National Park, Qld Australia. It's all done by hand. We used rock stretchers made by one of our volunteers to carry larger rocks across country and sorted rock from soil, from clay in the diggings and then put it all together. That turn took 3 months for 2 of us to complete - we had to wait for rain to supply water multiple times. It is part of a short section of trail (about 500m) built to re-route an old, eroded, fall line trail. This turn is where the fun starts.


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## epic (Apr 16, 2005)

Ridnparadise said:


> This turn is where the fun starts.


I'm sure it does.


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## DaveVt (Jun 13, 2005)

epic said:


> I'm hardly cleaning up after his mess. I spoke to both of the women at last year's Leafblower and they said that's not what happened. Bro.


Well then that is a bit wierd. I don't think whats her name would fabricate some random story, and why would I even give a crap to make up some random story like that when all I want in your homie to drop the who guidestone/trail builder "war" (hi words not mine) eveytime there is conversation about trail building going on. The guy does no work. Rides all the time. And Whines contantly. End of Story.

My recolection is that I actually posted a hypothetical "strava vs manners" type question where I recounted the story as I heard it without any names. You knew instantly who I was talking about, named him then trid to clean up his mess over ther too. Very loyal. bro.


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## epic (Apr 16, 2005)

I'm not disagreeing with you here. The site won't let me give you any more rep btw - bro.


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## Ridnparadise (Dec 14, 2007)

I thought about this issue and a couple of other turns we have worked on came to mind. While I don't think of a decreasing radius, descending turn as ideal, they actually do come along. If you think about it, some consistent radius turns are ridden as though they have decreasing or increasing radii because the visual or physical clues lead riders to that arc of turn. There are also turns with increasing radius exits that feel like they tighten because speed increases.

Both these examples are on two-way trail. Here's one that interrupted the trail rhythm with a cupped, stony and nasty flow-killer





















Sorry about these almost night time pics showing what we changed. The downhill entry line was widened and we bermed the corner. The exit was also more open, but not like the entrance, so it is decreasing in radius. The reason was drainage. Water now crosses the trail rather than running along it. We transplanted all the grasses harvested from the new line. They all took, so now no-one knows were the original turn was





















The next corner was re-aligned to resolve erosion and drainage issues. There were 2 old lines acting as drains, plus the one to be closed. It is pretty steep here. Use the 2 trunks in the next pic as a reference









We shaped a new turn that included the chance to bounce from wall to wall and enter the turn high as you descend: tight but fun. There's no doubt speed increases as you turn downhill through the turn, but the radius of the turn also tightens through the second third















In this place it was really not possible to make the "perfect" radius turn. Significant effort went into looking after the environment and rider needs









There's an optional drop a bit over 60cm or 2 ft past the exit, so you want to get as much speed as possible (to prove $#!t to your mates). It's a corner that is really hard to get just right, but you can and it's fun keeping on trying. I imagine the climbing enthusiasts see it similarly


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