Best weather for KOMs

So I love Strava.

I love Strava as in I started using it when I lived in Tucson in 2011 and owned EVERY KOM in the city (this is obviously and sadly no longer the case). Strava nay-sayers be damned, it’s a great thing for cycling for a whole bunch of reasons. Really the only complaint is that Strava turns leisurely group rides into smash fests….which has been happening to generations of cyclist long before clincher tires were even invented, much less the internet.

Since it’s settled that Strava is sweet and everyone who hates it just had their favorite KOM just stolen, we can move onto important questions: How to maximize your KOM winning potential?

One of the easiest and most overlooked things you can do is look at your local weather forecast. Most would think weather shouldn’t matter whether or not you get a KOM, but hopefully a rash of new KOM’s precipitated by this post are a bellwether for how to go after KOMs. Weather is important to cycling because it doesn’t just indicate rain or sunshine, but air properties, and the primary thing you spend fighting while on the bike is….air!

Now, I know what you’re thinking: Weather? Who cares?

Well….Eddy Merckx, that’s who (and I guess Tom Zirbel)!

When Eddy Merckx went for the Hour Record (which is really the ultimate KOM), he did so in 1972 in Mexico City.

The Mexico city velodrome is an outdoor that looks downright primitive compared to the climate controlled environment at the velodrome where Wiggins set the new hour record. However there’s a VERY important reason why he went for the record in Mexico City: the city resides at 7,500 feet above sea level. The very obvious benefit is the reduced air density due to altitude, which reduced air resistance by a full 25%. There were other weather considerations as well: temperature and humidity. While the temperature was a relatively normal 75F, it had rained several days prior to his attempt as well which likely increased the humidity during his attempt which also helped (this is counter-intuitive and I’ll explain in a sec).

In order of importance, things that affect air density:



3.Weather Systems


Since your KOM is in a fixed location, altitude is set, you cannot change that. But these last three you DO have control over when you’re attempting your KOM, also they’re all related and affect each other.


This might be a somewhat obvious one, recalling high school physics, hot air rises since it’s less dense than colder air. So warmer air temps equate to generally lower densities. For instance from 32F to 50F is a 4.5% difference in dry air density (not counting moisture, which also increases with heat). Raise temperatures further to 90F and your density reduction is nearing 10% over a freezing day.

So, don’t go for KOM’s during winter

Weather Systems

Want a KOM? Look for storms!

Seriously, storms and low pressure are peas in a pod, and low pressure means low density, which means MORE KOMS! Storms form around low pressure areas because the low pressure draws up warm moist air to higher altitudes which then condense the moisture in the air to create clouds, rain, hail, etc.

So, Summer Thunderstorm on its way? KOM time!


Finally Humidity, intuitively I know that I would think a bone dry desert would have a lower density than a tropical rain forest. Water is heavy after all, however water is only ‘heavy’ in it’s liquid form. Molecularity speaking it’s pretty lightweight, just one Oxygen atom and two Hydrogen atoms puts water in the anorexic category of atmospheric gases with a molecular weight of 18, meanwhile most of the atmosphere’s Nitrogen gas weights in at 28, and fatty McGee Oxygen has a molecular weight of 32. So at a some fixed pressure, there are a set number of gas molecules smacking into your face while riding. If there are more skinny water molecules hitting your face (i.e. it’s humid out), then those skinny molecules hit you with less force than heavier Nitrogen and Oxygen and drag is reduced. (Note: I realize molecules in the wind don’t ACTUALLY hit your face, their much nicer than that and just exchange momentum with other molecules in your facial boundary layer).

Additionally temperature plays a factor in your humidity calculations. For instance 50% humidity at 70F has less water in the air than 50% humidity at 90F. This is because warmer air can ‘hold’ more moisture than colder air and relative humidity that you hear quoted in the weather is a measure of how much of this capacity is used.

Because of this the amount of water is relatively small with regards to drag calculations until you begin to reach higher temperatures of +85F, see graph below for good visualization of this:

So if it’s oppressively hot, you’re drenched in your own sweat, and it’s about to thunderstorm, SUIT UP, it’s time to poach some KOMS.


All this being said…truly the best way to get KOMs is with a group of your buds doing a TTT and/or a good tailwind to get the segment.




One Comment

  1. However, if it is 100% humidity at 113*F, that means the dew point would also be 113*F meaning water would condensate on anything less then 113F like lung tissue, thus you would quickly drown. The big question is, how long would it take, and how long is the segment?

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