Nearly all races in Belgium feature an attraction that is foreign to American riders, especially those from the left coast: cobblestones. And while a majority think that cobbles are a remnant of the middle ages, most cobblestone stretches in Belgium were laid down very recently indeed. Even the cobbles of legend, such as those covering the infamous Koppenberg were re-installed as recently as four-five years ago.
Cobblestone roads were popularized by the Roman Empire and some of the old Roman roads are still in existence today. The Via Appia or Appian Way was one of the earliest and most important roads of the ancient republic. It connected Rome to Bridisi and parts of it have been preserved to this day. None of the cobblestone stretches in Flanders or along the Paris-Roubaix course (which is in French Flanders) have that kind of history.
In recent years cobblestones have become a very popular material for paving town centers and pedestrian-only streets. The stones form natural rumble strips and cause drivers to instinctively slow down. The increased noise also alerts pedestrians to oncoming traffic. Most of the newer cobblestone roads are in fact paved with setts or Belgian blocks instead of real cobbles. A sett is a rectangular quarried or shaped stone and it has a more regular shape and form than naturally occurring cobbles. Setts also present a smoother surface than real cobbles.
In California, cobblestone roads are often equated with bad pavement, and quite a few races that feature stretches of bad pavement try to make a connection to Paris-Roubaix, the temple of cobbles. Such is the case for the Copperopolis Road Race and the Leesville Gap race in Northern California. But while Paris Roubaix, and the Ronde van Vlaanderen are famous for bad sections, there is a rather significant difference between a cobblestone road and an gravelly-asphalt road in poor condition.
First of all, even newer cobblestone roads without potholes present an obstacle that test both a rider's skill and their fitness. The surface is uneven and has a higher rolling resistance than an asphalt road. The vibration is constant and takes its toll, especially on inexperienced riders. Cobbles can get very slippery when wet or very dry and dusty. That effect is often accentuated by a rounded cross section with a distinctly elevated center or crown.
Riding cobblestone roads is easier when using a bike with a longer wheelbase and a more relaxed geometry. It also works better with relatively lower air pressure.
Both automatically favor bigger riders. The increased rolling resistance also favors more muscular types over light and skinny climbers. Riding cobbles works best in a big gear, something that is counter-intuitive to beginners. Also counter-intuitive is the fact that you need to relax your upper body when riding cobblestones. Mountain bike riders often do quite well riding on cobbles because the optimal riding style is very similar to that of cross country racers.
If you do what most people naturally do, i.e. ride a smaller gear and hold on for dear life, the cobbles will punish you in no small measure. Your wrists will hurt, your arms will go numb, and your teeth will feel like they are falling out. You won't be able to concentrate on the road because the shaking will make it hard to focus your eyes, while your helmet and glasses may dance all over your head. When excessive these are symptoms indicative of bad technique, although perfect technique will not completely abolish the punishment you invariably take.
Cobbled climbs add another challenge. The key here is to watch your weight distribution and make sure you keep traction on your back wheel. Once again this is similar to mountain biking and it is something road bikers are not familiar with.
When faced with wretched cobblestone roads, such as those in Paris-Roubaix or some of the worst sections along the Ronde, you have two options. The first is to ride beside the road, in the gutter. It often looks the most attractive and beginners naturally choose this option. Be aware though that it is the path of trouble. In many spots, the gutter won't be free as spectators or barriers will block access. You will then be forced onto the cobbles at the worst possible places. Either way, riding off to the side is a sure recipe for flat tires.
The best way to ride bad roads is to ride on the crown. It is more punishing than riding the gutter but it is far safer and it is the best way to avoid flats or other mishaps. Unfortunately it is only available to those willing to ride in the front. But the trade-off is more than worth it and if you watch Paris-Roubaix you will see that that is where the winners ride.
If you plan to do a race with cobbles -nearly all races have some- be sure to check them out beforehand, lest you'll be in for a big surprise. Remember that even the nicest looking cobbles are a serious obstacle and plan accordingly. Be especially aware of the transitions to and from cobbles and the cobblestone turns. That is where most of the mayhem takes place. Also remember that the local kids won't slow down and if you do, you are likely to get into a crash right then and there.