You call that a road?

Tl;Dr: is Tour Divide a gravel race? Not exactly, photos here. A model of route surfaces follows….

People riding and racing the GDMBR/Tour Divide have a lot of time to think, and a lot of incentive to think about the route surfaces. As an observer it’s a little hard to understand – are you riding roads? (Yes, but mostly not what you would think of as a road). Is this a Gravel thing? (Yes, but pretty different than the groomed railroad trials many people ride). What’s this about mud?

Honestly, words just don’t do it justice, here are wayyyyy too many photos of the roads, trails, and downright disasters of route surfaces I’ve been over on this trip.

Note: I don’t really touch on the other big Tour Divide obstacle – Snow. Very little of that down south, and I didn’t see much in 2016.

I’ve been thinking about a model for describing route surfaces, maybe as a way of providing more surface data to riders, but mostly because I’m nerdy. By chance I ran into Rocky who works at Garmin, and we were talking about how their cycle computers represent surfaces… Got me thinking.

Generally people think of surfaces as:

• Paved – flat, solid smooth(ish) surface that a car can drive fast on
• Un-paved – dirt, bumpy, roughish surface that a car could drive slow on
• Trail – dirt, maybe some obstacles that a person or animal could walk or run on without having to watch every step

These are pretty good categories, but miss the nuances of route surfaces.

I like to imagine a route surfaces as a geometric plane – like a very long rectangle. It has length (direction of travel usually), and width (so your car, or shoe, will fit on to it). An arterial in any town is a good example. And if you get right down to it, most roads have some curvature over the width – your city arterial is higher in the center, so water and trash flow to the margins (gutters).

The nuances of paved roads mostly have to do with the style of paving, the inclination of the surface across with width, and what’s happening at the margins (Gutters? Shoulder? Guard rail? Terrifying drop off?).

Paving styles I’m aware of are:

• Concrete – used on freeways, usually the smoothest
• Tarmac/pavement – gravel mixed with oil and tar, usually very black and super smooth, close second to cement
• Chipseal – Gravel embedded in a tar under base – looks more like a gravel road that’s frozen in place. Rougher than Pavement

Cyclists often complain about the chipseal cabal – we’d prefer more fresh tarmac TBH. I’m sure there are more styles of pavement – help me out in the comments!

Curvature – is the road straight or curvy? Curvey roads are probably better for cyclists, as people often drive more cautiously (not always), and they can be more fun downhill. Easier to digest a 1,000 foot climb as a collection of short straight sections between curves. (I’d like a better term for this, curvature isn’t quite right. Linearity?)

Then there’s grade (or steepness). No explanation needed.

Inclination – most roads are pretty flat across their width, but occasionally they are banked in curves, especially on freeways. Usually the inclination is opposed to the direction of the curve aka ‘on camber’, to help prevent vehicles from sliding off the road due to (centripetal? Centrifugal? I dunno!) some force. Occasionally they are off-camber like the curve at the bottom of Golden Gardens road in Seattle. This makes it much harder to corner quickly.

Margins are what’s at the edge of the plane. On roads it’s usually a shoulder (or not), a gutter, or a ditch for trash and rain water. Cyclists like wider shoulders, since it gives the impression of more safety from cars. Gutters are just traps for everything that’s gonna fuck up your tires – generally to be avoided. Ditches are gutters on steroids – better than getting hit by a truck, but often worse than a fist fight. Guard rails are kind of hit or miss – a low guard rail can work for a car, but cyclists with a higher center of gravity will go right over those in a flight of summersaults. Higher guard rails can help in case of a ‘No Brakes’ emergency. And of course, there’s always the nihilistic option of ‘absolutely nothing off the edge of the road for hundreds and hundreds of feet’s. Eeek.

When roads go south (figuratively), the surfaces start to degrade and you can get depressions: pot holes, dips, gaps, washouts. These make it worse for cycling because of the sudden drops and impacts you experience as you traverse them.

When roads get dirty they can become decorated with stuff like trash, lose gravel, sand. All of these make the roads worse for cyclists because they make the predictable pavement suddenly hard to trust. A sharp turn on lose gravel on a paved road is a great way to visit your local emergency dentist.

And, roads live in the environment like you and me. They get wet from rain, or flooded from storms. Iced in the cold or bakingly hot in the sun. Our model should account for the environmental effects of the day as well.

So there’s a pretty good model for a paved roadway:

• Paving style
• Curvature & Grade
• Inclination across the road surface
• Margins/edges
• Depressions & embedded obstacles
• Decorations (gravel, trash, other b.s.)
• Environment – black ice etc

You can take that model and apply it to unpaved roads and trails too, but things become exaggerated pretty quickly.

For example: the best unpaved roads are like a kind of clay – very smooth, little decoration floating on the surface and few depressions. Roads like this seem to last about 15 minutes until something starts to degrade them.

For example: with frequent use unpaved roads get washboarded (it’s a mystery to me how this happens, but it is definitely a fact). Heavy rain or flooding can change the inclination of a road, as material flows downstream across the road. A flood can decorate the surface with rocks or gravel from upstream, or worse – Wash away the surface exposing embedded obstacles (roots, rocks) or carving out huge depressions. And if there was water, you can bet the depressions are filled with water hiding more obstacles and mud.

For trails thing get even weirder. Some trails are quite wide, even as wide as a single lane road. Many are quite narrow – ‘singletrack’ is a common name. A lot of single track trails are actually pretty nice surfaces from thousands of footprints forming them into a nice clean Trail. Things get tricky at the margins on narrow trails. If the trail is depressed compared to the surface that you’re traveling through, it’s very easy to hook a pedal on the margin of a smooth, simple single track Trail and end up in the weeds.

I imagine that the amount of engineering that goes into trails is somewhat less than goes into a unpaved or paved road. It’s easy to imagine that the kinds of forces that degrade roads work even better on trails. Water exposes embedded rocks and Roots more easily, depressions form more quickly. And because The travelers on trails move more slowly and nibbly than cars, the directionality of trails can change very very quickly. All of this makes writing single track walking trails (like the CDT) on a bicycle very challenging.

And hikers can behave very differently than wheeled vehicles. Many single track trails have sections that a hiker can scramble up with relative ease compared to a bicycle. In the terms of our model the curvature and grade are much higher than you would expect to unpaved road. The amount of decoration and embedded obstacles can be much higher because hikers can simply step over a log on the path.

Another interesting margin effect on trails is that things on the margin can shade the trail, making it very difficult to see what you might be getting yourself into.

It’s getting to be dinner time so perhaps in another post I will talk more about highly degraded roads. Like the ones that I saw in New Mexico. We haven’t even scratched the surface.