On a recent bike trip, a downpour sent me running for cover. But when the rain eased up to a maneuverable amount, I had to get back on the road to make it to my destination before dark. Would I get there in time? And does cycling in the rain make slow you down?
Cycling in the rain will actually make your bike faster due to several factors, including decreased air density, increased humidity, and the tires’ reduced traction and rolling resistance. However, due to more dangerous conditions and extra layers of clothing, you will probably want to ride more slowly in the rain.
If that overview caught your attention, then you’ll probably be interested in the deeper details I’m going to get into below.
In particular, check out the next section where I dig into how rain affects (positively and negatively) the speed of a bike.
How Cycling in the Rain Affects Speed
Cycling in the rain is a mix of several components that affect your speed. For example, air density, rolling resistance and road traction, and aerodynamics all play a significant part in how fast you go when it is raining.
First, let’s take a look at air pressure and its effect on how you ride.
The number one force slowing down bicyclists is air drag. Air drag makes up about 80 or 90 percent of the aerodynamic forces that slow a rider down. The faster you ride, the more aerodynamic drag affects you. The denser the air, the slower you go because denser air slows you down.
On the other hand, lower air pressure will slow a rider down much less. In addition, cyclists are able to ride faster at higher elevations because the air is less dense.
Temperature and Humidity
However, higher temperature, higher humidity, and a lower barometric pressure also create less aerodynamic drag on the cyclist. Therefore, for every 10% drop in air pressure, speed actually increases by about 3%. (You can read about the scientific data and specific calculations here.)
Essentially, these conditions happen right before, after, and during a storm. So technically speaking, riding in the rain could actually make you faster. If you are trying to beat a personal record, bad weather might be the right time to do it. But there are other factors, involved, too, such as rolling resistance and tire traction.
Rolling Resistance and Tire Traction
According to Schwalbe, “Rolling resistance is the energy that is lost when the tire is rolling. The main reason for the loss of energy is the constant deformation of the tire.” In other words, as you ride your bike, your tire is constantly coming in contact with the road surface.
At this contact point, the tire flattens slightly as it grips the road and then returns to its shape as that portion of the tire leaves the road. The wider, knobbier the tire, the more contact, and the more the tire deforms, the greater the rolling resistance, making you go slower.
The amount of grip that the tire has on the road is known as traction. The more traction the tire has on the road, the slower you go. Conversely, the less traction your tire has on the road, the faster you go.
For example, a track cyclist rides on a surface that is even smoother than the road. For this reason, they ride on very skinny tires pumped up to a very high PSI. This lessens the traction and the rolling resistance of the tire so they can ride faster. In addition, since they aren’t making sharp turns, they don’t need as much traction to stay upright.
When it is raining and the road is wet, the tire has less grip on the road, or less traction, just like a track cyclist’s tires. As a result, the tires will slip over the surface of the road more easily, essentially making you faster.
But air density and traction aren’t the only forces at play when riding in the rain. Aerodynamics and weight also make a difference.
Aerodynamics and Weight
The more aerodynamic you are, the faster you can go on your bike. And when climbing, the lighter you are, the faster you go on your bike. Conversely, anything on you or your bike that creates more wind drag will slow you down. And anything that adds weight will also slow you down.
What does this have to do with cycling in the rain? Well, to be honest, when it’s raining, you’ll probably suit up a bit more to stay warm and dry. This is important because a cold, wet ride can lead to dangerous hypothermia and other issues, so it is critical to dress for the weather. But the extra layers might slow you down. For example…
- A bulky rain jacket that flaps in the wind will slow you down.
- Thick heavy gloves will slow you down.
- Bulky or heavy rain covers on your feet might slow you down.
- Restrictive clothing that helps you keep warm could also prevent you from moving freely, which will slow you down.
So although dressing for the weather is critical, you should still be aware that it could make your ride happen at a slower pace. Riding in the rain is one thing, but what about wet roads?
Is Cycling on Wet Roads Slower?
Cycling on wet roads can technically make you faster, but due to road hazards, you’ll probably want to ride slower. Here’s how.
Traction and Rolling Resistance
As we discussed above, reduced traction and rolling resistance of wet roads will help you ride a little bit faster on your bike. In addition, the damp road keeps the tires from gripping and sticking as tightly to the road surface, so your tires will spin more smoothly and quickly. And although this aspect of cycling on wet roads makes you faster, there are other aspects that are sure to slow you down.
Because you have less traction on the road, you need to take turns more slowly. So although the bike may seem to want to go faster, you need to brake carefully before turning. You are much more likely to skid in a turn on wet roads than on dry ones.
And although slightly wet roads are faster, deeper water is much, much slower. Riding through more than a coating water will definitely slow you down, as water has much more resistance than air pressure.
Is Biking in the Rain Harder?
Biking in the rain is challenging for several reasons. Bike handling skills are critical for safe riding in the rain, although many people who avoid riding in less-than-ideal conditions never learn the skills. You’ll want to watch out for a few hazards.
Road paint is very slippery when wet. If you try to ride on the painted surface of the road when it is raining, you could go down just as if you are riding on a sheet of ice. Some other hazards when riding in the rain include wet leaves, which are just as slippery.
And if the rain has only lightly coated the roads, the oil could come to the surface of the road, causing it to be slick where you might not expect it.
You’ll need to adjust your technique when cornering in the rain. You want to go slower than usual around a turn and try to keep your turns as straight as you can. Since the bike has less grip, you could skid out more easily, so try to avoid leaning the bike heavily in a turn since you can fall more easily.
Braking in the rain is a little more complicated, too. Rim brakes are not as effective in bad weather, and even disc brakes can get a little squeaky.
Braking too hard will cause you to skid or go over your bars. Brake gently, and if the back wheel begins to skid, ease up a little bit until the tires can catch again.
One of the hardest aspects of riding in the rain is being able to see clearly. You don’t want rain hitting your eyes, but it can also fog up or blur your cycling glasses. You may have to ride more slowly just to be able to see the road clearly.
So, even though riding in the rain can technically make your bike travel faster. There are a number of risks associated with riding in raining or wet conditions, which will probably make it safer for you to ride more slowly and cautiously.