Road Biking pt. 2 - Draag

When I first bought my road bike, I never understood the reasoning behind why they go so fast. Granted, I bought it because I knew they somehow go significantly faster than my old moutain bike, but there are a couple of factors that contribute to the speed advantage.

I just finished my first long ride on the road (about 15 mi) and noted a couple things.

1. There are in actuality 2 important gradients. The first being uphill and downhill variations on the terrain where the biker will have to work against gravity or will be boosted by its effects. The second gradient is wind. At near zero velocity, wind pressure does little to hinder your progress, but on the road you might be pedalling at 20-25 mph. If the wind is gusting at significant speeds, riding in the opposite direction is going to be very hard on the biker.

Force of Wind = -1/2 * density * biker velocity ^2 * drag coefficient * unit vector of wind

So this means the force is a square relationship to velocity making this a very formidable force at higher speeds. Now there are three factors in this equation in the control of the biker: biker veloctiy, unit vector of wind, and drag coefficient. Reducing biker velocity to decrease the force of wind (or drag) is out of the question because we want to be going faster. Changing the unit vector is not entirely in the biker's control, and thus a factor that isn't desirable to necessarily change. The reason road bikes are so much faster is that you can reduce the drag coefficient. The person on the bike can use the drop down handles to their advantage and cut their surface area down to half - thereby potentially halving the drag coefficent and the force of wind. I can attest to the force of wind as while I was pedalling against it, I could only ride in the 1st wheel, 5th cog on a flat surface. Going down the gradient, however, allowed me to shift up to the 2nd wheel 9th cog, thereby allowing me to go near car-like speeds.

2. The second factor that contributes to the speed of the bike is that the tires are much thinner. Thinner tires means less friction on the road that potentially slows down the biker. The tires of road bikes also lack treads making the surface much smoother. This allows the biker to go much faster with a drawback, however - the tires are more suceptible to punctures.

3. Road bikes are much lighter, perhaps shaving 3-4 lbs. While this weight might not seem like much compared to the average weight of a human 140-160 lbs, 3-4 lbs on the frame accounted for large distances will wear the biker down more. Try riding a 30lbs frame over long distances (ie like those heavey cruisers) and then ride a 20 lbs road bike - you will feel the difference.