# Average grade for optimal downhill "flow"?



## Markhpnc (May 5, 2011)

Let's assume a one way section of trail and by flow I mean minimal braking and pedaling to maintain a fast fun speed. 

Obviously lots of variables can factor into this and I think the design and construction of the turns is super critical for flow. But anyone have any general rules of thumb? 

~6% maybe?


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## Joules (Oct 12, 2005)

I don't think there is a rule of thumb; that is to say, I think average grade is so far down the list of factors that influence flow that the correct thing to do is completely ignore it.

The whole point of a pump track is flow - if it doesn't flow, it isn't really a pump track. They are, by definition, 0% average grade. The flowiest trail I've ever built, I don't have an average grade number, but it's negligible (1-2% I'd guess). OTOH, I've done some pretty flowy trails at DH parks that were well over 20%.


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## evasive (Feb 18, 2005)

As pointed out above, you can manipulate that experience somehow. I would disagree that grade plays no role, however, at least when assuming you're designing for a broad range of riders. The best trails flow for riders with a wide range of skill (I've never had the chance to ride Half Nelson, but I've read that about it many times) and less skilled riders are likely to be intimidated by steeper grades and ride the brakes. 

Considering grade purely on its own, 5-6% seems to be be sweet spot. That kind of grade keeps you on the gas and off the brakes. As you get to 10% and upwards, bikes start to roll pretty well on their own, and beginner/intermediates often find that intimidating. 

This is less relevant when designing a new trail, but based on a lot of trails around here (old USFS trails that were not laid out with bikes in mind), existing lower grade trails often provide a better ride. There are a few trails here around 10-12% that flow really well with few switchbacks, but those are relatively rare and occupy specific landscapes: running down long drainages, for example. Most of the other trails with grades in that range tend to be mostly switchbacks.

Edit - just noticed you also mentioned minimal pedaling. 6% would be too shallow for that, I'd think.


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## Bent Wheel (Oct 6, 2007)

Around here we have some new trails that were built not to exceed 8%, but as far as DH goes they are flowy but kind of slow, so I would say twice that to be a real "flow" trail. Just my opinion.


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## Wildfire (Feb 4, 2004)

To create a functional and durable trail, coming up with a design grade should be primarily based on factors like site climate, hydrology, terrain, durability characteristics of the soil and impact levels of users who will be sharing the trail but, in general, a preliminary layout grade of 7.5% maximum will allow the addition of flowy grade reversals while still keeping actual grades below a "sustainable" 10%.


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## Markhpnc (May 5, 2011)

Thanks for the input so far guys. Maybe in addition to the quote below I should have mentioned that I'm already familiar with standard "sustainable" trail building practices.


Markhpnc said:


> Let's assume a one way section of trail and by flow I mean minimal braking and pedaling to maintain a fast fun speed.


I'm not looking for the "maximum sustainable grade" which is indeed based on things like soil composition. Of course flow can mean a lot of different things so yes you can "flow" on 0% pumptrack and there is an element of "flow" (good or bad) on any trail.

I'm talking specifically about a fun downhill section for minimal braking and pedaling (though pedaling would be preferred to causing brake bumps). Probably similar characteristics of an actual "flow trail" but maybe closer to a narrower singletrack in the woods than a super wide run at a resort.

For simplicity let's say the average grade will factor in the "legs" of the run and any turns/berms all together.


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## Wildfire (Feb 4, 2004)

Markhpnc said:


> Thanks for the input so far guys. Maybe in addition to the quote below I should have mentioned that I'm already familiar with standard "sustainable" trail building practices.
> 
> I'm not looking for the "maximum sustainable grade" which is indeed based on things like soil composition. Of course flow can mean a lot of different things so yes you can "flow" on 0% pumptrack and there is an element of "flow" (good or bad) on any trail.
> 
> ...


Whoa, tough room. The answer is (you guessed it)... it depends. How packed/smoothed is the tread surface? How wide are the turn raddii? How tall are your berms? Theoretically you could make the thing as steep and fast as a luge run if you wanted to engineer in all the massive banked turns. And I hate the term "average grade" but, assuming a basic hand built trail, no pedaling, no braking, 4 - 6 percent sounds about right.


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## zrm (Oct 11, 2006)

Bent Wheel said:


> Around here we have some new trails that were built not to exceed 8%, but as far as DH goes they are flowy but kind of slow, so I would say twice that to be a real "flow" trail. Just my opinion.


16% is really steep, especially if you're talking average grade. The vast majority of people would be on their brakes most of the time, otherwise you'd be going 30+mph in no time.


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## aero901 (Apr 11, 2012)

4-6% is a good target for narrow (<2') singletrack trail. A few local trails built at this spec. easily allow riders to hit 20-25 mph which is plenty fast for most. An important feature of flow trails is a variety of both vertical and lateral position changes. The ideal is free from straight and flat sections similar to a pump track.

Another benefit of low average grades is longer trails.

Anything over 8% requires too much braking without having a wider trail surface and large berms.


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## Wildfire (Feb 4, 2004)

aero901 said:


> 4-6% is a good target for narrow (<2') singletrack trail. A few local trails built at this spec. easily allow riders to hit 20-25 mph which is plenty fast for most. An important feature of flow trails is a variety of both vertical and lateral position changes. The ideal is free from straight and flat sections similar to a pump track.
> 
> Another benefit of low average grades is longer trails.
> 
> Anything over 8% requires too much braking without having a wider trail surface and large berms.


It's your lucky day, I nerded out on just this subject awhile back and came up with some sort of surprising figures so thought I'd put this out there:

Since IMO the defining feature of a "classic" flow trail is the curving, undulating grades featuring dips followed by short mounded uphill sections - I'll call them crests but also known as grade reversals, jumps or rollers, whatever you prefer- and those crests take up linear space in the alignment, the actual prevailing tread grades between the crests and dips are going to be quite a bit steeper than the average grade of the trail segment.

If your average grade is 5% and the crest spacing is a nominal 100 feet, the actual grades go up to almost 7%. If the a.g. is 7% with 90 foot nominal spacing, you're looking at 9.4% actual grades. If a.g. is 8%, 90 foot spacing, actual tread grades will be 10.6%. At 10% average grades with the recommended "sustainable trail" 75 foot spacing go up to almost 14%. It gets worse on steeper average grades because the crest spacing needs to be tighter to keep water from gaining speed down the trail and with a 15% average grade and 60 foot nominal spacing the actual tread grades will be almost 22%.

And I'm talking crests just big enough to reliably shed water (5% grade reversals for 15 feet or so) so if you make your crests bigger/more "flowy" and or/ make the spacing tighter the actual grades are going to go up even more. Also, the dip/crest spacing may need to be tighter to get around trees or in response to terrain features like swales and microridges.

So my point is: it's really easy to exceed the design or "sustainable maximum grade" on flow trails if you lay the trails out based on average grade. That's why I kind of cringe when I hear that term related to trails. The average grade of the Grand Canyon from rim to rim is around 0% but the actual grades...well. Steeper prevailing grades may not be a big deal on decent soils with a one-way downhill trail designed for minimal braking, but if you get uphill traffic and/or hikers, moose, horses, etc. this can become a huge problem. So be careful is all I'm sayin'.


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## HypNoTic (Jan 30, 2007)

I was told, a long time ago, that A-Line in Whistler had an average grade of 8% and the builders found it to be too steep, requiring too much maintenance.


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## pinkrobe (Jan 30, 2004)

Yeah, A-Line is 7-8% average grade. That said, there are flat sections on the trail, but it can be completed without putting in a single pedal stroke. It should be possible to build a flow trail with 5% average grade, and even some uphill sections to reduce speed when needed.


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## drew p (Jan 20, 2012)

I'll speak of our recent experiences on our "flow" trail we have been building here in Santa Cruz. It is machine constructed w/ big berms etc., but not a 5-6' wide bike park swath, mostly 3-4'.

Grade is important.

First segment we built (#5) is 6% (150'/2465' - distance measured with wheel so flagged grade was probably a little steeper), the last few hundred feet are pretty flat. There are sections that are pretty steep but then there is a uphill or flattish area where you use the speed up and you can ride the whole thing without pedaling or braking much. Steep sideslopes and natural undulations in this segment let us get pretty aggressive with the ups and downs. Only a few spots had any significant braking wear after a long hard dry summer with lots of traffic, however we put LOTS of effort into good compaction and we have good soils with some clay which makes a big difference. A lot of the braking wear is also from lack of long line of sight more than excessive speed.






Strava Segment | Demo Flow Trail - Segment 5

Second segment (#3)is 4.9% (154'/3100') but has a few hundred feet of almost flat/slight climb at the end. The terrain is flatter so it was harder to roller coaster the trail as much. Take out the flat bit and grade is still only 5.5%. Even then you have to be on the gas a lot which is fun if you have the fitness and skills to ride it fast. Advantage to this is very little braking wear because the people who would be doing the braking on a steeper trail aren't pedaling hard enough to go fast enough to need to brake much...

Strava Segment | Flow 3

Not that these strava speeds are real on a trail like this in thick forest, but fastest average speeds are 18-19mph. Speed of 150th fastest rider (out of ~1500 who have ridden it on strava) is around 16mph. Speeds are similar for top riders on both segments.

Other trails in this forest are mostly fall line or on old logging infrastructure. Long sections have average grades up to 12-17%, with lots of 30-40% bits. LOTS of breaking wear, especially as geometry, suspension and brake technology have improved so much allowing the average rider to go much faster in straight lines, but they still have to slow for the turns. Lots of maintenance work, hard to drain. But fun. The new trail has very little maintenance, just clean the drains of the accumulation of needles and dust and a few small patches and tweaks, it is a nice change.

A lot depends on how tight things are, how long the site lines are, how wide the trail is, how much exposure there is, and how much exposure it gets. But a general rule of thumb is 5% if you want it to be mellow and have to pedal to go fast, but you can still coast down it. I think 7-7.5% is about as steep as you can get without getting lots of wear unless you make it consistently tight so you never can build up a ton of speed or wide and real big berms. But even then the novices go faster than they want to and skid anytime there is something a bit threatening. I'll guess I'll add these are grades I'm talking about are over long stretches, at least several hundred to several thousand feet. Within that I almost ignore grade and just use the terrain and natural features best as I can

Our uppermost segment will be more wide open with long sideslope traverses with good site lines and average grade top to bottom will be about 6.5% over 5800', it should be a blast. Segment we are building right now is a bit over 7% for 2200' but with tighter taller berms, it will be interesting to see how the wear differs.

So I wrote way more than I thought I would, but 5-7%.


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## Markhpnc (May 5, 2011)

Holy sh*t that trail looks like an absolute blast Drew! Do you guys contract with pro builders for these trails or is it all club/volunteer work?

Thanks everyone for all the detailed info and examples, it's very helpful and exactly what I was hoping for. :thumbsup:


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## Moe Ped (Aug 24, 2009)

Markhpnc said:


> Holy sh*t that trail looks like an absolute blast Drew! Do you guys contract with pro builders for these trails or is it all club/volunteer work?
> 
> Thanks everyone for all the detailed info and examples, it's very helpful and exactly what I was hoping for. :thumbsup:


Drew is da pro!

There's a bunch of project photos here http://forums.mtbr.com/california-norcal/demo-flow-scrapbook-897980.html

The bike club (MBoSC) has a couple of paid staff (Drew!) and a huge pool of disciplined volunteers to draw from.

Google "Emma McCrary Trail" for another area trail that has some "flow" features but isn't a flow trail per se. Same deal; some pro staff and lots of volunteers.


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## cmc4130 (Jan 30, 2008)

pinkrobe said:


> . . . , and even some uphill sections to reduce speed when needed.


Exactly. This is very important. If you want a true rollercoaster feel where people don't have to hit the brakes, then there should be sections that carve back upgradient to shave off speed.

Winter Park did this on the "Cruel and Unusual" trail (and probably others too) and it feels great.










This was one section that turned back up gradient and then back down again (off the feature):









Drain pipe under berm:


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## Moe Ped (Aug 24, 2009)

*Yes on 5%*

A couple of fun facts to consider on flow trail layout is that "just" a 5% trail grade will yield a MTB terminal velocity of around 27 mph; so that if the alignment is perfect and braking is never needed and no scuffing occurs at under-banked turns a rider will be "hauling ass" (27 mph is hauling ass for me) in short order.

Another fun number (given all the recent discussion about e-bikes) is that 5% is giving me (250# rider+bike+gear) the equivalent "gravity motor" of about 700 watts.

There's all sorts of physics calculators online for those who wish to play with numbers; in a way designing a flow trail would be a bit like designing a roller coaster.


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## cmc4130 (Jan 30, 2008)




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## Mark E (Feb 7, 2006)

Lots of good knowledge here from experienced builders! Many of the comments I've read and heard from people who are not as savvy reveal that many mountain bikers are way off base when they attempt to guesstimate gradients -- many people assume grades are quite steep (10 or 20 percent) because a trail feels fast. I once asked on of IMBA's most experienced trail designer/builders if he's comfortable eyeballing grades in the field after two decades of professional building. Nope! He told me he uses an inclinometer every time and is constantly surprised how off-base his initial guess was. Measure twice, dig once!


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## cmc4130 (Jan 30, 2008)

I know from my background in BMX and MTB DJ/slopestyle and DH-park riding that you really don't need that much decline for a run to still be very fast.

It seems like most bike parks or other amateur builders make the initial mistake of choosing lines directly down hills.

If you look at something like a dual slalom track, the original entrance part is downgradient, but most of the track does switchbacks across the gradient. The declining berms add to the speed, but the often the cross-gradient part is not very steep.

2010 Sea Otter dual slalom track. Photo from Leelikesbikes.com :








2014 Sea Otter:









Similarly, I took this photo of the Angel Fire 4-cross track. Switchbacks galore. 









If you run a section straight down the gradient, the jumps have to be super long.








2008 | KHS Factory Racing | Page 4

This is the most gross-gradient pump track line I've ever seen. But, if you want to maximize a short-run hillside, DEFINITELY consider stuff like this....









I stopped to take a pic of the slant walls on Whistler's Crank It Up. A flow trail with some wood slants like this feels great to ride....


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## evasive (Feb 18, 2005)

Mark E said:


> Lots of good knowledge here from experienced builders! Many of the comments I've read and heard from people who are not as savvy reveal that many mountain bikers are way off base when they attempt to guesstimate gradients -- many people assume grades are quite steep (10 or 20 percent) because a trail feels fast. I once asked on of IMBA's most experienced trail designer/builders if he's comfortable eyeballing grades in the field after two decades of professional building. Nope! He told me he uses an inclinometer every time and is constantly surprised how off-base his initial guess was. Measure twice, dig once!


I know some experienced trail builders who have probably never used a clinometer, and it shows in the trail. I guesstimate slopes all the time. I do a lot of stream surveys in my job, and my co-workers and I always predict the gradient of a stream reach before we measure it with a clinometer. We've gotten pretty good at it. You're right - people commonly overestimate slope.

I've never bothered to shoot the slopes on specific pitches, but I could tell you the average gradient of pretty much all the extended climbs/descents around here. Even something as coarse as the average gradient (roughly calculated on a feet/mile basis) gives you a decent prediction of how a trail will ride. I'm speaking mostly of legacy USFS and similar trails, not trails with bike-optimized features.


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## aero901 (Apr 11, 2012)

Mark E said:


> I once asked on of IMBA's most experienced trail designer/builders if he's comfortable eyeballing grades in the field after two decades of professional building. Nope! He told me he uses an inclinometer every time and is constantly surprised how off-base his initial guess was. Measure twice, dig once!


As far as I'm concerned, this can't be said enough!


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## mtbty (Jun 15, 2012)

If your arent shooting grades you are looking at twice the grade you think you are. 

I love to add in short 15-20%+ shots (15-30') that are followed by very mellow grades (3-5%) with an avg long grade of 6-10% with lots of good corners, never straight cuz turns are fun.


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## twd953 (Aug 21, 2008)

cmc4130 said:


> It seems like most bike parks or other amateur builders make the initial mistake of choosing lines directly down hills.


+1. The vast majority of our local terrain is very steep. Up until the last 2 years maybe, pretty much all of the unauthorized trails in the area were complete arse-dragging on the rear tire steep fall line trails, and a lot of the legit trails are built at much steeper than sustainable grades.

Most of those trails require that you almost always have to be dragging the brakes to keep speeds in check, especially during the 9 months of the year when the trails are wet. I get really sick of that type of riding. I grew up riding in much less steep terrain, so riding the brakes all the time seems like a fail to me. Many of the locals guys that have only ridden in this terrain don't seem to mind, or know the difference until you get them somewhere that has better trails.

With the adoption of disc brakes, slacker geometry and better suspension have made those trails somewhat more enjoyable than they were when riding them with 60mm of travel, canti brakes, and and a 71 degree head angle, there I still much prefer trails with a more reasonable and sustainable grade.

The new legit trails we are building have much more sustainable grades, and are way more fun IMHO, and are opening some eyes. But, I think there are a lot of hold-outs that just want more of the same steep fall line rake and ride trails. And I would classify a majority of those guys as XC types, I'm not talking about just DH/FR guys.

So, yeah, a trail doesn't have to be steep to be fun, or technical, or have flow.


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## Kronk (Jan 4, 2004)

The one on the right spits me out every time I try it.



cmc4130 said:


> I stopped to take a pic of the slant walls on Whistler's Crank It Up. A flow trail with some wood slants like this feels great to ride....


I like the short steeps, but it is more fun to have longer descents at the 8% grade.


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## Coldfriction (Oct 31, 2009)

*Energy Explained*

I'm not sure if I can add to this discussion without making it too complicated, but I figured I could help enlighten some things here.









The figure above is a somewhat idealized way to explain how you would have to design a trail from a physics perspective as if you were designing a roller coaster. I didn't include numbers or units because I only want to explain the concept. If it's too complicated, please let me know and I'll try to clarify.

Executive Summary: When designing a bike trail and thinking about the grades you're using, you should be thinking about the total energy grade line more than the actual physical grade of the trail.

The initial total energy of the rider at the beginning of the trail is a function of their elevation and mass, but mass may be ignored in design. A feather falls at the same speed as a bowling ball in a vacuum, and riders of different masses will more or less accelerate to the same speeds on a trail (this is somewhat idealized, frictional forces are affected by mass and surface area that comes with mass).

For now, assume the biker doesn't pedal. As the biker rolls down the hill, they gain some speed (kinetic energy) but lose some elevation (potential energy). The rider's total energy is their kinetic energy + potential energy. In a world without energy loss and entropy, the Rider Energy Grade Line(REGL) would be horizontal and you could build a trail where a rider could roll up and down hills forever (heaven anyone?).

The energy losses affecting the rider determine the slope of the REGL. These losses include drag from the air, rolling resistances, energy lost in the suspension components, etc. The roughness of the trail surface is a big factor in these energy losses. The most techy rock garden you can imagine will slow you down bigtime for example, whereas riding down a paved road will induce much less loss of energy.

So as the rider continues down the trail they are constantly exchanging potential energy for kinetic energy and vice versa if there are grade reversals of any kind. Because the rider isn't pedaling, where the elevation profile of the trail crosses the REGL the rider comes to a full stop and either has to point the bike downhill or pedal to move.

In the figure above the rider has too much kinetic energy near the end of the trail and must use their brakes to stop. Energy used in the brakes is completely lost to heat and brings the the REGL down as they are applied.

The reality is that the REGL isn't a smooth constant grade as shown above. Drag losses increase with speed, and I'm fairly certain other losses change with speed as well. Also the true REGL should include the rider's chemical energy and how much power they can put out cranking the pedals or pumping features. You could ignore a bunch of these things if you wanted a simple design model. Many design models are simplified to make the usable.

All in all, what is the answer to the question of the average grade for optimal downhill flow? The current methodology everyone seems to use is to simply feel it in the field with some average grade in mind using a clinometer, but a clinometer can't tell you the REGL. That gives credence to the guys who say they can eyeball a trail well enough.

If a few people wanted to, they could develop an equation with roughness coefficents for rolling resistant losses, drag coefficients for air resistance (more or less already done), and whatever other losses you'd like to include in the model and obtain the REGL to design to. It really wouldn't be that difficult to do. Someone would need a fairly constant graded slope with a good bike computer to measure the speed of a wide range of bike setups at specific locations as they roll down the slope. Doing this over surfaces of different roughness would allow you to determine their coefficients in the model and the slope of the REGL in the figure. Then you could lay out the elevation profile with the anticipated trail roughness so that it always stayed below that line to make sure your trail always has flow. There would probably be additional energy losses in cornering and other features on a trail to account for, but they could be determined experimentally.

Believe it or not, the above isn't too far off from the general concept of how water networks are designed to get water to your house and it's very close to how roller coasters are designed. Go to school in engineering or physics if you would like to do the above and get paid for it.

TLDR: You shouldn't design to surface grades, you should design to energy grade lines if you want to technically design a trail. Obtaining this energy grade line is much more difficult and really can't be determined in the field with normal trail building instrumentation. For the vast majority of trail builders, using conventional knowledge and experience is probably the way to go. Personally, I believe that using the average grade as the REGL is good enough for long single track design. I like 6-7% average downhill grades, and 4-6% uphill grades. I like the trail to take the energy out of my riding with hills, jumps, etc. and not my brakes. These grades are in truth more of an opinion than a realistic design standard, as are the grades anyone else gives. If a builder has nothing else, they should probably just look at other trails and see what has been done before and how it worked; trial and error and all that.

If you bothered to read all of this I hope it clarified somewhat the situation with designing to a grade.

Edit: I used an absolute that really shouldn't have been there.


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## BonkedAgain (Aug 23, 2005)

Coldfriction said:


> I like the trail to take the energy out of my riding with hills, jumps, etc. and not my brakes.


Yes please! :thumbsup:


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## Markhpnc (May 5, 2011)

BonkedAgain said:


> Coldfriction said:
> 
> 
> > I like the trail to take the energy out of my riding with hills, jumps, etc. and not my brakes.
> ...


+1 :thumbsup:


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## Coldfriction (Oct 31, 2009)

I just thought of an easy way to find the energy grade line (REGL in my figure above) for a given bike, roughness, etc. I believe this is similar to how most people actually do it in the field by feel.

The only instruments needed are a way to measure speed at different locations (bike computer with recording ability) and a clinometer that's accurate. 

To avoid wasting time with trial and error, first ride some similar trails near the new trail to be built and find a stretch of somewhat constant graded section that can be entered at the approximate design speed of the new trail. Find a stretch where it feels like speed is neither gained or lost (terminal velocity) and measure the grade with a clinometer. This grade should be close to the energy grade line (on the graph I drew above it would be below and parallel to the actual energy grade line). Record this grade for this design speed. If possible do this at different design speeds to get different energy grade line slopes; depending on the rider a trail designed for one speed might not be that fun.

If possible, test the design energy grade line on the new trail by building a constant graded section. Find a way to ride into the trail at the design speed and see if that speed is maintained over the grade. If speed is gained over the test, the energy grade line is a shallower grade. If speed is lost, it is a steeper grade. Repeat this process as desired for accuracy to obtain the design energy grade line.

Doing this a builder could set a bunch of flags or tape of a different color on the trail to mark the energy grade line, then they would know they should be building below those markings at all times to maintain pedaless flow. If a faster section is built, increase the grade and drop farther away from the marked energy grade line, but decrease the grade to return closer to the energy grade line afterwards. This places grade reversals in the trail which will accommodate drainage while also providing the feeling of accelerating and decelerating for that roller-coaster feel. Additional energy will be lost going down the faster dips (drag is a non-constant function of velocity) and the energy grade line will need to be adjusted downward mentally or physically for these features, so maybe just make the energy grade line slightly steeper than it was discovered to be.

This is all still a lot of work just to figure out the slope to build a trail to, but it's something that can be done without coming up with an equation and doing a bunch of modelling on a computer. Changing the design speed mid-trail makes things more complicated still, but can be done if the different energy grade lines were determined prior to building the different design speed sections.

I don't really expect anyone to go through the effort to do things this way, but I would love to hear about it if someone actually ever attempts it. I also would love to measure some really great dirt jump courses and see how close they are to a sinusoidal wave with an average grade parallel to the energy grade line. I'm also confident the best jumps are all parabolic, both on take off and landing, but I haven't measured any to find out. If anyone knows the answers to these questions, please let me know. Thanks.


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## slapheadmofo (Jun 9, 2006)

http://forums.mtbr.com/urban-dj-park/dj-pump-track-plans-402237.html


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## Coldfriction (Oct 31, 2009)

Another long post from me as another idea entered my head for determining energy grade line slopes. This method is for determining the energy grade line of a trail that's already built. I have a handheld gps unit that records elevations and location, as well as records speeds. Something similar would be needed for this method to work.

Get as accurate of an elevation profile of the trail as possible. It might be necessary to walk the trail, or someone might already have a gps file online with elevations in it. If possible, get the data into a table in a spreadsheet and graphed with distance on the horizontal and elevation on the vertical.

Record the speed of the rider and bike on as much of the trail as possible without using brakes. Knowing where braking can't be avoided will help clean up the true energy grade line of the trail later. The speed needs to be recorded at known locations and added to the table next to elevation for the corresponding distance location.

Now add another column that converts the speed to potential energy using the energy equations

kinetic energy: k = (1/2)*mass*velocity^2
potential energy: p = mass * gravity * height
gravity = 32.2 ft/(second^2) for imperial and 9.8 m/(second^2) for metric.

Setting these equations equal to each other, the only unknown is the height, solve the equation for height:
(1/2)*mass*velocity^2 = mass * gravity * height->
height = ((1/2)*mass*velocity^2)/(mass*gravity)->
height = ((1/2)*velocity^2)/gravity

Since masses cancel out (like I said in the other post here), and gravity is known, and velocity has been recorded at specific locations, we can add another column for this height to the table. Now add another column to the table that sums the newly found height with the original elevation. This summed column represents the energy grade line of the trail.

There should be dips in the energy grade line where braking occurred. These can be removed and the energy grade line segments shifted up to give a more realistic energy grade line for the trail. Pedaling will also affect the energy grade line and those sections removed in like manner.

I actually might do this on a few trails because it is so much less effort than the other stuff I've mentioned, but the majority of what I ride I am braking half the way down, bleh.

The better grade lines obtained this way could be used for designing new trails.


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## Coldfriction (Oct 31, 2009)

I wouldn't expect pump tracks to be measurably sinusoidal. I'm thinking about a line of dirt jumps where the rider is airborne a great portion of the time and the jumps are fairly large. In the air, every rider follows a parabola whether they want to or not.


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## slapheadmofo (Jun 9, 2006)

There are a number of sketches in that thread that illustrate what you're thinking, as well as some good great info on now to build jumps and pumps.


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## Coldfriction (Oct 31, 2009)

I saw a few sketches in there, but haven't had time to read the entire thread in detail. I'll do that later today. Pump tracks are a special breed of bike trail; enough so that they call them tracks instead of trails. To me the naming alone of "track" seems to imply more precision than "trail." The difference with a pump track vs this thread is that nearly all of the energy comes from a rider pumping and not gravity. There are so many different styles of trails and design philosophies out there. It should be possible to reverse engineer a pump track or dirt jump course to find the energy profile of a rider on it, but I imagine that it'd require more precise instrumentation than any normal person has access to. Everything I've said here was written thinking more along the lines of a large scale downhill flow trail with the intent of not pedaling.

I'm 6'3" and ride xl size bikes with full suspension. I've found the pump tracks I've ridden seem to be designed for a younger audience with shorter wheel bases. I have been where I could pump an entire track without pedaling and maintain momentum, but it wasn't all that fun as I couldn't get much speed and had to work hard for the little I had. If the local cities build some good pump tracks, I might have to get a bike and get into it; there are two planned but not yet constructed nearby. I've volunteered to help on one, but the city hasn't gotten back to me.


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## Mark E (Feb 7, 2006)

Watch a few videos of Jeff Lenosky riding pumptracks -- he's 6' 4" and well over 200 pounds but can style out even the tightest tracks. 

If your full suspension bike has lockout settings try using them in the pumptrack. Suspension soaks up the energy you're trying to create by pumping the bike. Drop the saddle to get low and fast in the turns. 

I'm nobody's idea of a good park rider -- 48 years old and raced XC for many years -- but learning to ride park stuff has definitely improved my bike handling.


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## Coldfriction (Oct 31, 2009)

Unfortunately my bike doesn't have a full lock out and the climbing mode on it is fairly soft (ccdba w/cs). What I really need is a local track to ride. I'm going to have to bug the city here some more. There are plans for a pretty nice park near my work, but I think the pump track is probably over a year out.


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## slapheadmofo (Jun 9, 2006)

Coldfriction said:


> Unfortunately my bike doesn't have a full lock out and the climbing mode on it is fairly soft (ccdba w/cs). What I really need is a local track to ride. I'm going to have to bug the city here some more. There are plans for a pretty nice park near my work, but I think the pump track is probably over a year out.


When I wanted a pumptrack for our town, I didn't bug anyone to make it for me, I put in a few hundred hours building one myself. No graphs, no f'ing virtual biometric study BS...that's not how **** gets done. It gets done by getting really really dirty, sweaty, bug-bitten, and tired on a very regular basis.

I'm 48 and love riding pumptracks and park stuff (and I'm trying to learn how to dirt jump). My main riding buddy is 6'-5", also late 40's, and kills it all. It's got nothing to with age or size, everything to do skill set. Though I personally strongly prefer 20" wheels for that sort of stuff, I can still get around on pretty much any hardtail. FS bikes are tough. Also, most mtbers I see having trouble trying to ride pumps/jumps don't give themselves enough room to move around the bike, and aren't comfortable laying it into berms.

I've done a handful of chainless DH days - that's a great way to find out how well a trail can be flowed (and to find out how crappy you are at creating and maintaining said 'flow').


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## Coldfriction (Oct 31, 2009)

Without permission I won't touch anything, not established trails or new ones. If I were to get in trouble with any government agency over building illegally, I'd could easily lose my job and license. Let the kids who's records get wiped when they hit eighteen build the illegal stuff, but I think it's better to work with the system than against it. I'm guessing the local city wants an insured contractor to finish the larger infrastructure before they get to the phase where building the pump track with volunteer labor will be allowed. Anything built there now likely gets dozed over soon. I'm not native to the area; I don't know people nearby with land. The "just do it" attitude works for some, but not for me.


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## slapheadmofo (Jun 9, 2006)

Who said anything about building illegally?


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## Coldfriction (Oct 31, 2009)

Quit being so damn antagonistic. I said something about building illegally, I never said anything about you building illegally. Quit being poison.


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## slapheadmofo (Jun 9, 2006)

Just a total non sequitur huh? 

So why not take all this info you've been playing around with and use it to make your vision of a great trail happen? Legally, of course.


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## Coldfriction (Oct 31, 2009)

Not everyone is building a pumptrack. You haven't contributed to thus thread or the OP, but you sure have made it an unfriendly thread for no reason.


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## Markhpnc (May 5, 2011)

Damn, everything was fine until the conversation turned to pumptracks (which I'm all for btw)  :skep: :madman:

Ok moving right along then...


So the project I was starting when I started this thread is moving right along. Still in the early stages though and building from the top down so I can test and get a feel for it as I go before continuing with the planned alignment. 

Basically it's 5 to 10% at the top through the first 3 back to back berms. This is only due to space constraints with the layout before it opens up and then it's down to 5% through the first long leg to the next berm. Hoping this will work just to get up to speed quickly at the beginning without having to get on the brakes right out of the gate.

Funny thing is this is actually a kiddie flow trail in my sister's backyard and no doubt the different weights, wheel sizes, and skill sets with kids probably affects some things to a degree.


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## Coldfriction (Oct 31, 2009)

The kids must love you.

Edit: 
The wheel size would be inversely proportional to the roughness of the trail. So, smaller wheels would lose more energy than larger wheels on the same trail up to some point where a trail is so smooth that it doesn't matter what the wheel size is concerning roughness. It would make a difference in rotational energy in the wheel and the ability to spin up, where smaller wheels are better. Theoretically, weight shouldn't make a difference for flow, but I don't actually believe that. Friction between the tire and the ground depends on weight, and a lack of confidence in traction changes rider behavior. Skill can make everything anyone designs and builds completely moot. Without riding skill, there is no flow unless you're on a roller coaster buckled in.

Any chance for some pics?


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## Ridnparadise (Dec 14, 2007)

It is a fascinating concept - just how do you get a trail to flow and not be "dumb"? Unfortunately clinometers and physics equations cannot account for natural trail features and the need to avoid certain trees or other sensitive areas. What that means is that sensible and educated compromise becomes essential. Checking and re-checking trail lines before commencing work is vital. In addition, you have to be prepared to change how you do things on the trot depending on unexpected, local challenges like hidden rock bands or large roots. You also have to use the bike as a tool to test bit by bit as you work. Clearly this is not how a pro on a machine would work.

I am lucky enough to be able to estimate trail grade very accurately. I don't rely on it and we use a clinometer, but it gives one of my digging buddies a laugh testing me. It is an advantage though, because being able to visualise grades after building and how to make corners and other features work is very often something that comes from the gut. Being prepared to accept opinions and advice from trusted helpers is another thing that cannot come from a clinometer or the use of physics (as much as I really like the practical use of maths and physics). Trail grade is not something you can set in stone.


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## cmc4130 (Jan 30, 2008)

I don't know the average grade of the sideslope at Tamarancho Flow trail, but when I rode it a while back, I noticed that they do a great job with berm shape. These are not "V" shaped old school hiking switchbacks (like this: Vail, Keystone and Winter Park 
They're engineered to be ridden. 

Tamarancho Flow Trail, NorCal

























Flow Check! Tamarancho Flow Trail Update: 1/20/13









https://forums.mtbr.com/california-norcal/tamarancho-flow-trail-party-if-you-live-bay-area-you-should-show-up-831235-2.html


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