Question : Is it Easier/Difficult to Ride in The Rain?

After cycling close to 50 miles yesterday in pouring rain, some people in the group were throwing an interesting question around at the coffee table.

Is it easier or more difficult to ride in the rain? The question was more in terms of rolling resistance but what might make riding in the rain a more easier or difficult experience?

There's all kinds of directions you can go with this. I've got some thoughts so bear with me.

1) I have noticed that in short term rain, with a very fine layer of moisture on the road, it makes it somewhat easier to go fast. This is not just because of the fact that its raining, but because of what is happening at the road surface itself. Water mixes with dirt and other crap and creates a fine emulsion that acts like a lubricant. You can take some sand, add water and just feel it between your fingers yourself. [Read Lennard Zinn's take on a film of water reducing rolling resistance]

2) A lot of relentless rainfall cleans the road of all this dirt and increases the friction component once again. So the friction component is time dependant on rain. [See Road Surface Properties]

3) The lesser friction you have, the lower your skidding resistance. A decent amount of friction is good!

Picture Courtesy : Graham Watson

4) Think about road condition. Suppose there are potholes everywhere and they are filled with water, that's not going to be fun to ride in. There is an interruption of friction coefficient. I guess surface tension might also play a tiny role there.



5) Okay, what about surface tension? I don't know about surface tension, but I've heard a few things or two that it makes all the gravel and other grit on the road 'stick' to your tires making the chances of a puncture higher. [See Surface Tension]

6) Regarding rolling resistance again, a nice thin film may be nice to cut friction by so many units, but if you have too much water and cross a threshold, you're literally trying to ride in water. After a point, all the buoyant forces kick in and you've essentially made a sail bike, with you as the sail...and the clown.

7) A cool, wet day is constantly spraying moisture on the skin so it decreases the body temperature during exertion and could perhaps increase performance (like being able to ride harder for a longer time interval for instance).

8) But a rainy day also makes jerseys and shorts soggy so there you are with some more added weight to pull with you. So if you're a fatter person wearing more area of clothing, you suck in more water.

Well, that sucks!

9) Racing bicycle tires are so thin and high pressured (100-120 psi) anyway so it doesn't take a lot to keep water away from the point of contact. What I'm saying is that there's not much chance that bicycle tires can hydroplane [See Hydroplaning]. The contact shape in very thin and almost single plane (isn't it) as compared to a car tyre that's almost square or rectangular in shape.

Leaving rolling resistance aside, what about drag?

10) Some might say that moist air is less denser than dry air which is true isn't it? So lesser density of air allows you to go through it easier than the same quantity of dry air, huh?

11) But wait, there are pellets of raindrops falling from the sky so the bicyclist is literally trying to shove his way across this confusion. The interaction of wind, and rain is complex that I'm wondering how they affect bicycling performance. My idea was that someone should use computers to CFD simulate such conditions so we can see through the model what is actually happening. [See CFD Analysis]

12) Finally, this might be a trivial point but in an industry that talks so much about light weight wheels and lesser moment of inertia, think about your wheels running on water. Rain water is being picked up by the tire and thrown off a tangent (which is why if you're directly behind another rider who's riding in the rain, its not such a good experience)..

Plus, if you have a tall rim depth, more water and grit can stick onto that surface essentially increasing the weight on the rims by so much amount.

Moreover, if you have carbon aero wheels with drain holes in them, the water collects in the wheels through these holes and there's some addition to weight there as well. Water can also seep through frame tubing and collect in the bike itself, increasing weight.

So what is it finally? From a rolling resistance standpoint, can we purely state that it makes bicycling easier? There's a lot of other factors to consider that can take away from this little gain, if gained at all, in bad visibility, poor traction, and the feeling of being wet and dirty which robs from the general pleasure of cycling CLEAN.

In the world of post EPO, if someone asks you if you're riding clean, they generally mean - "ARE YOU DRY?" Or are you dry clean. Or dry cleaned... whatever...

Whats your theory? Maybe we can round up all theories and arrive at an average. I guess the average would be "Man are you crazy, could you stay at home when it rains??!!!"