Most North American Transportation Bikers who commute by bike show up sweaty. Common solutions are bringing a change of clothes, taking a shower after you arrive at work, or giving up after a few tries.
But it turns out it's not that difficult to prevent sweating while you're on your bike. I spent the last few days combing through Bicycling Science and derived these helpful tips.
1. Don't Wear a Backpack
Did you know that your backpack doesn't just trap heat against your body? it also eliminates some of the most valuable surface area where moving air would carry away heat.
The above graph explains heat transfer from a cylinder (your body) to the air based on the air's position around the cylinder. 0 on the X axis is directly in front of the cylinder and 180 is directly behind the cylinder. Higher values on the Y axis indicate more heat transferred from the cylinder to the air.
For both low and high speed scenarios significant heat transfer occurs not just at the front of your body, but also directly behind you. This is especially true for high speeds where laminar flow changes to turbulent flow (22-33mph). At this speed optimum heat transfer occurs at approximately 110 degrees from the front of the rider. Right in backpack territory.
This means wearing a backpack doesn't just trap sweat to your body, it has a significant impact on your body's ability to transfer heat to the air!
If you want to stay cool and dry, add some cargo capacity to your bike.
2. Ride Slower
Riding a bike gets harder the faster you ride. Duh. But understanding why it gets harder can allow us to optimize how we spend our energy.
The purple area in the graph above shows us the sum of all resistive forces that are not air resistance. This includes friction in the drivetrain, rolling resistance of the tires, friction in bearings, etc. The important takeaway is that all of these types of resistance increase linearly as the bike travels faster.
The gold area is air resistance. Air resistance increases at an exponential rate with speed. This means the amount of energy the rider has to expend, and therefor the amount of heat they produce, also increases exponentially with speed. Riding at 13mph instead of 15mph could have a negligible effect on commute times while also keeping your body below the temperature where you begin to sweat.
Want to get to work less sweaty? Spend less energy fighting the air.
3. Select a Flat Route
As with so many things transportation biking related, route selection is key. It turns out that, even though wind resistance is the ultimate foe of any biker, slope of the road can provide even greater challenges than wind resistance.
Each line on the above chart represents a road with a given grade, from 2% up to 14%. What's important to notice here is that the power required to travel at a given speed on a low grade is non-linear while the power required at steeper grades becomes more linear.
This indicates that, at low grades, our good friend air resistance is the dominant source of friction. However, at steeper grades this is no longer the case. Overcoming the force of gravity becomes the prevailing challenge.
Take time to refine your route. Avoid steeper grades when possible.
I encourage you to come up with some solutions for your own commute based on these data. It might turn out that riding a longer route at a slower speed while your bike carries your cargo still gets you to work on time, but without the swamp ass.