switchback advice?- Mtbr.com
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  1. #1
    outdoor miner
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    switchback advice?

    Hi guys,

    I'm building a bit of trail myself, using the excellent IMBA book as a guide.

    This isn't a heavy use trail, but all the same it might as well be as close to the guidelines as I can manage.

    The terrain I have to work with is pretty steep in places, and in one place there is really nowhere to go but up.

    My question: How can I make a switchback on a very steep sideslope without turning it into a major excavation?

    Should I make the worst of it stepped instead so that a bit of bike portage is called for?
    Experience is like a comb that life gives you when you are bald

  2. #2
    beer thief
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    Quote Originally Posted by leximog
    My question: How can I make a switchback on a very steep sideslope without turning it into a major excavation?
    I would take a really long look around to see if you can find a spot where there's a little break in grade or a bit of a flat area. Extend the traverse line in either direction and find some natural feature to help out? If there really is no other option, you're looking at cut & fill. If you can find a rocky area where you can move a few stones to help build a crib wall that may help reduce labor.

    That said, climbing turns in lieu of switchbacks can work, particularly on low traffic trails as you describe. Grade reversals on the approaches are important for the long term.

    Quote Originally Posted by leximog
    Should I make the worst of it stepped instead so that a bit of bike portage is called for?
    Personally, I hate to get off my bike. I'd rather do a few days more work and make it rideable (even if barely so) than have a mandatory hike-a-bike.

  3. #3
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    Tradeoff

    As I see it, the fundamental tradeoff in designing a switchback is the turn radius.

    In order to make a turn with a radius that is easy to negotiate on a bike, it has to be pretty wide, at a guess about a 10' radius. Check the IMBA book for more a more accurate number.

    The problem is that when you have a turn spanning, say, 20 feet of steep slope, the bottom leg of the turn is going to be *way* lower than the upper. That means the retaining wall on the bottom leg has to be tall, and you have to haul lots of dirt to fill it in. There will be lots of dirt available from the bench cut for the trail in the vicinity of the turn. Having a wheel barrow is a necessity IMO.

    The only ways I know how to make it less work are:

    Make a tight turn. It's not a problem, it's a technical feature!

    Situate the turn on top of a lump or other kind of flattened spot on the slope. Some folks call this a "turning platform".

    The problem with steps is that they are not going to get you away from having a fall-line section at the apex of the turn. The switchback will tend to erode badly at the apex unless you reduce the slope by building a ramp in the lower leg.

    Switchbacks are the biggest chunk of work in making a trail. Any chance you could get help?

    Walt

  4. #4
    mtbr member
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    Insloped turns

    I've attended a few trail crew visits now and they all have said that you should think it over very carefully before you commit to doing a switch back. As alluded to they are a lot of work both in the rock needed for the retaining wall, and the dirt need to fill it in.

    I've now done three builds on steepish terrain and we have yet to build a switch back. We do however build a lot of insloped turns, aka berms. They have held up well, and don't need nearly as much rock. Plus they are more fun to ride.

    This technique is in the IMBA book. Don't overlook it, as it is a useful approach.
    Jason Murray
    Rep for Ontario, IMBA Canada
    Visit the IMBA Canada site to keep current on all things IMBA in Canada.

  5. #5
    outdoor miner
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    plenty of food for thought

    thanks guys for some great info, I'm still digesting somewhat, but what you have said does make a couple of things clear.

    I'm going to have a longer look around the area in question armed with your ideas. The solution is going to have to cope with the rainfall as much as anything, I can see that is always going to be a big constraint on the design. There is also a fence I could cross to find a better turning place.

    The use of armoring could open up other places I wrote off as too steep. I'm for a gnarly turn if it doesn't scour in the rains.

    When you talk about a turn radius that is easy to ride being 10', how tight can a non-easy turn get?
    Experience is like a comb that life gives you when you are bald

  6. #6
    featherweight clydesdale
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    Quote Originally Posted by leximog

    When you talk about a turn radius that is easy to ride being 10', how tight can a non-easy turn get?
    Ride you bike in a tight circle in a yard or parking lot. Measure the diameter. May be 5-6 feet??

  7. #7
    Builder of Trails
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    The IMBA TCC of Mark Schmidt and Lora Woolner designed and helped build a switchback on a trail I steward at an ACoE property. It was on just over a 30% slope, so our cribwall was just over three feet high. The general rule of thumb is one foot of wall for every 10% of slope. It took 140 man hours to complete it, 20 volunteers working an eight hour day.

    I second (or third or fourth) the advice to avoid switchbacks if you can. Depending on soil type and other qualities, you can design a climbing (or descending) turn on maybe up to 15% slope. Allow for a wider radius than on flat ground b/c of body movement, etc.

    Dewayne
    www.talontrails.com

  8. #8
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    Thoughts concerning switchback planning

    I am replying to an old post but I thought I would add some suggestions that might help someone using this forum for research or to get some new ideas.

    It takes a huge amount of effort to build switchback turning platforms in steep terrain. For the amount of effort to build a single turning platform in steep terrain, you can build a lot of bench trail (1 turning platform = 1/4 mile bench trail). So the goal should be to gain the same elevation without the extra construction of switchback turns.

    As previously suggested, try to find places where nature has build the flat spot for you. Look on a topo map for places where the steepness of the slope eases. Side valleys, the top of rock outcrops, old mine dumps. In the end, even building signficant extra trail mileage to connect together these nature-made flat spots may result in less total effort.

    Also see if you can reduce the number of switchbacks or replace them entirely with longer straight trails. One trick is to consider using very long switchbacks. Longer switchbacks mean fewer turning platforms and also reduce the problems with hikers cutting switchbacks and water draining off of one switchback down on to another. Long enough sections of straight trail may entirely eliminate the need for switchbacks. For example, instead of switchbacking directly up from the valley bottom to the top of a ride consider extending the valley trail further up valley, the ridge trail further down the ridge and connect both with one long switchback. This allows turning to be done on the valley bottom and ridge top, entirely eliminating the need for platforms.

    Also consider using the back side of the ridge to extend the run of the straight trail to allow it to climb without turning platforms. Sometimes running the trail down one side of the ridge, around the nose of the ridge and continuing down the opposite side of the ridge can gain the same elevation without a single turn.

    Using these three planning tricks when designing switchbacks (look for natural flat spots, visualize longer switchbacks, don't forget the backside of the ridge) can signficantly reduce the amount of work to gain the same trail elevation.

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