Wednesday, July 06, 2011

Road Surfaces, Chip Seal & Rolling Resistance


John Howard noted that the bicycle is a curious vehicle in that its passenger is its engine. Because of this fact, the bicycle rider is immediately and intimately aware of the resistance or ease offered up by various road surfaces. While the motorist or cartographer may find road surface to be a minor detail, one to be noted with a bit more pressure on the gas pedal or slightly different line on the map, those of us who turn the pedals to roll our wheels grade our roads on a much finer scale. Roads are not merely paved or unpaved, smooth or rough, they are complex characters revealing their true natures when the rubber meets the road.

It is not surprising that the driving force behind the early movement to create smoother roads were the bicycle riders. Beginning in the late 1870s and continuing for the next half a century, The Good Roads Movement preached the Gospel of Good Roads. If we were to whisk one of our cycling forefathers and his highwheeler forward in time to show him the world we've built upon that vision, he would no doubt be amazed but might just as likely to gaze upon eight lanes of cars stuck in freeway traffic and inadvertently quote David Byrne, "My God... What have I done?"

While some may argue that we have in fact paved paradise and put up a parking lot, we nonetheless seek to smooth our way in the world. While I can and do love a rough road or a trail too tough for any wheel, I also must admit that I'm a sucker for a smooth stretch of highway. I guess that makes me human.

While smooth asphalt is good for going fast, smooth concrete is better. I'd love to see somebody with a Watt-meter put some numbers down to back up my assertion, but my legs tell me it's true. It's not just your tires, it's the road your tires are on.

My friend Jan over at Bicycle Quarterly has done some great studies relating tire pressure, construction and road surfaces and anybody remotely interested in the subject would do well to read his magazine. To overly simplify a complex subject, it's complicated and high pressure tires are not always your best, fastest or most comfortable choice.

Somewhere between gravel and pavement is a creature feared by bicyclists, the chip seal road. Chip seal is a base of soft asphalt overlaid with crushed stone aggregate. Cyclists dislike chip seal because it is a rough ride and it tends to be slow going. Somewhere years ago I found a reference to trucking companies actually factoring chip seal roads into their fuel calculations because it's higher rolling resistance affects mileage. Cyclists tend to feel the roughness via their hands and butts while the resistance is felt in their legs.

Chip seal is often used on roads with low traffic volumes, the ones cyclists often tend to favor. In a conversation with a DOT traffic engineer I learned that a road can often be maintained with chip seal at a cost about 1/8 that of a full re-pave and while the lifespan of chip seal is less than full asphalt repaving (about half) the cost savings are what is driving it's continued usage. In today's tight economic times, the traffic volume guidelines for which roads get asphalt paving and which get chip seal have been revised upwards. While a few years ago only roads having traffic counts below 2500 cars per day might get chip seal, now roads having as many as 10,000 cars per day may be chip sealed. (I'm recounting this from memory and my exact numbers may be wrong, but the basic message is this: many more roads are getting chip sealed these days.)

I also learned that there are grades of chip seal and while the finer aggregate costs more per ton, it is often the case that in the field the engineers have to use less aggregate with the finer grade stone. This results in a smoother road for drivers and cyclists with a final cost that is the same or less than if the locality had opted for the cheaper, coarser aggregate. So if you are a cyclist and you hear of chip seal projects upcoming in your area, try to make sure the project uses the finer grade of aggregate. Also, often the road repair doesn't need to extend the full width of the road. Chip sealing the main traffic lane but preserving a strip along the road shoulder both saves material and gives cyclists a smoother defacto lane. The photo below shows a portion of US Highway 20 (the North Cascades Highway in Washington state) where the chip seal has been applied in this manner. While the state DOTs tend to be aware of these considerations, that is not always the case in local municipalities so it's important for local cyclists to do what they can to express their concerns in the planning stages of local repaving projects.


Roadie or Mountain bike, triathlete or tourist, we all ride on roads or trails. And the routes we travel don't just happen, we make them happen. On my best days, I remember to do my bit to keep things rolling.

Kent "Mountain Turtle" Peterson
Issaquah WA USA

10 comments:

Jim Laudolff said...

I toodled around Fremont and Ballard on Monday and think that concrete does not age well. The slabs shift and joints widen. While the surface may be smooth for a few feet, the maze of cracks and slots are unnerving to my spoiled suburban psyche. I prefer chip seal to concrete for that reason and do sense that in an emergency when the ground is wet, I am less likely to skid in a hard stop on asphalt (my opinion only).

In the rain, I think chip seal wins out over regular asphalt because the water runs down between the aggregate instead of sitting on top. All that water your wheel picks up on an asphalt road has resistance too.

In some ways, chip seal lets you know that you are trending a bit off the beaten path.

Interesting topic, Kent.

PM said...

"John Howard noted that the bicycle is a curious vehicle in that its passenger is its engine. "

I've just been re-reading Monkey Wrench Gang and of course came across the quote, "Wearing his legs out to give his ass a ride."

Anonymous said...

I rode across Texas a few years ago on the "Southern Tier" route. Many secondary roads in the state are called Farm Roads and use a very large aggregate. This made for a bone jarring surface.

I nicknamed this surface "Texas Cobblestones" and swore that never ride on them again.

The best bet for riding on chip seal after it has worn a bit, is to go right done the middle. On these typically narrower county roads in Indiana the left hand tires of cars going in either direction wear the surface down and make for a smother ride. Of course keep an eye on the traffic when doing this.

DOug said...

SR-106 is a road that leads from Seattle to some sweet, excellent, and amazing places on the Olympic Peninsula. I am totally and utterly sick of riding it, though, because it is 20 miles of relentless and rough chipseal. UGH.

Bob said...

Yea; I'm not a fan of chip seal. At a recent MS150 event Day2 had a number of miles on "fresh" chip seal. I hit a patch of gravel 4-6" deep. Fortunately I was not going fast (12-14mph) and was on a hybrid with rather wide tires(1.6"). I didn't crash but the thought of crashing on chip seal really didn't sound like something I want to check off my been-there-done-that list.

Johann Rissik said...

The road in the first pic looks interesting? Looks like it goes on and on and on...and ends up somewhere intersting! Chipseal? No thanks.
Interesting topic.

Garth said...

What I've found the most disconcerting and uncomfortable while riding on chip seal is just what you point out as often the most comfortable area to ride in, right on the shoulder where they don't use any aggregate. I've found in areas where the chip seal starts to flake, creating a jarring ride going over the disintegrated chipseal. That's my least favorite part of that material.

Anonymous said...

Bob in Texas:
I live north of Fort Worth, and I am forced to ride on chip seal while riding my bicycle to work. I say 'forced' because while there are other non chip - sealed routes that I can use, my most direct route has wide shoulders which lend a great deal to safety. Unfortunately, my direct route is paved with chip seal, and it makes for a very uncomfortable commute.

Anonymous said...

Texas cyclist here where course chip seal is pervasive. Cuts my speed by about 2 mph, increases tire wear, and jars the body. Ugly stuff.

Texas motorist are being taken to the cleaners with the decreased gas mileage and increased tire wear this stuff causes.

I ridden in a lot of states. Texas is by far the worse for chip seal. Others that use it, lay down a much less damaging version.

iowegian3 said...

Texas highways are the worst! They do keep up with maintenance, but that agressively big aggregate is loud. And that's just in a car. By the way, it's loud enough that it's hard to carry on a conversation, or listen to the radio without sending it to ear-splitting levels.

I've had many good days in the sun, riding the Iowa trails and highways before partial paralysis in my legs and arms ended my riding days. But I can vouch for newer concrete and a tail wind as being a couple of the best things to hope for on a good ride. Next to that though, is good chip seal. Generally those country chip seal roads aren't graded to the same standard as regular paved roads, so cars and trucks simply can't go as fast.