An interesting topic has come up lately in a number of conversations with a lot of different people in the sport of cycling: the impact of aerodynamics in road races. Over the past few years of being involved in cycling and triathlon I’ve seen and heard a massive range of opinions on where the biggest gains are to be had in equipment, position, training etc. My approach has always been to trust the physics and maths, as Neil deGrasse Tyson famously said “The good thing about science is it’s true whether or not you believe in it.”. My engineering bachelor’s and master’s projects have both been on applying physics to the real world of cycling to generate some highly accurate predictive models, so I’ve luckily had the ability to assess the sensitivities and impacts of each critical determinant of cycling performance. I’m still refining these models as I learn what others are doing in the field, so it definitely pays to work with leading sports scientists, engineers and athletes!

I’ve always been a proponent of taking aerodynamics seriously, and have been mocked for it many times, but at the end of the day the science doesn’t lie. I decided to put together an Excel tool for people to play with so they can assess first-hand what impact variables such as CdA, weight, rolling resistance and drivetrain efficiency have over the course of a time trial or road race. It uses linear equations so ignores accelerations (the effect of which is actually quite minimal) and assumes constant gradient on climbs (a reasonable assumption, as long as the total elevation is correct).

The Excel tool is available here: https://drive.google.com/file/d/0B8wvrvMee88XY240Q080elJJY2M/view?usp=sharing

Feel free to download it and have a play yourself. The sheet is locked with the unlocked yellow cells the ones you can edit. Scenario 1 is the baseline set of variables, scenario 2 is the comparison variable set. At the top is the savings you’ll make going from scenario 1 to scenario 2. I’ll do a quick run through of what each variable is so you know what to edit and why.

  • CdA – Coefficient of drag x frontal area. The metric that defines your aerodynamic efficiency. Typical non-aero road bike ~0.3, typical TT bike ~0.23. Smaller riders will have a lower CdA, bigger riders a bigger CdA. This is the variable a wind tunnel measures.
  • CdA reduction in the pack – Percentage reduction in aero drag when behind another rider. Current empirical studies suggest 30-50% saving dependant on position and distance of separation.
  • Percentage time on the front - Self-explanatory, percentage of time spent riding on the front of the pack.
  • Percentage of time in the pack – Percentage of time sitting in.
  • Total Elevation Gain – Total amount of metres climbed over the whole race distance.
  • Total Distance – The whole race distance in km.
  • Distance Climbing – The amount of race distance spent climbing, normally around 10-20% of the total race distance.
  • Distance Descending - The amount of race distance spent descending, normally around 10-20% of the total race distance.
  • Crr – The coefficient of rolling resistance. Check this link for more precise values for your particular tyre: http://www.biketechreview.com/tires_old/images/AFM_tire_testing_rev9.pdf
  • Bike Weight – Total mass of the bicycle (including water bottles, garmin etc).
  • Body Weight – Total mass of the rider (including clothing, helmet, shoes etc).
  • Air Density – At 15degC at sea level air has a density of around 1.225kg/m^3. It varies with temperature, pressure, humidity, dew point and elevation. You can estimate the air density here: http://www.gribble.org/cycling/air_density.html
  • Drivetrain Efficiency – The percentage efficiency of the drivetrain system, normally around 97.5%. Can be as bad as 90% in poorly maintained drivetrains.

The savings section shows how many watts you save when on the flat, climbing, descending and on average. It also shows how many calories you save, how many gels that is and how many grams of carbs. It also shows the average speed increase and therefore time you would save if you were to ride at the power required for scenario 1 but with the scenario 2 variables over the length of the race. Obviously if you were sitting in then this would require the guys in front to ride harder, but you get the point.

Hopefully you enjoy having a play with the tool and can see first-hand how dominant aerodynamics is in the importance of road race performance. Here are a few comparisons comparing a typical circular tubed road bike (CdA of 0.300) to an aerodynamic road bike (CdA of 0.275) in a number of different race scenarios over a typical 130km rolling road race course  at 40kph: solo break, 2 man break equal turns, 4 man break equal turns, taking a turn every 20th man and sitting in. The bottom is the effect of reducing the bicycle mass by 1kg, which is the same for all scenarios.

Solo

  • 26.8w Power Flat
  • 5.3w Power Climbing
  • 56.0w Power Descending
  • 25.0w Average Power
  • 334.9kcal Energy
  • 3.9 Number of Gels
  • 83.7 Grams of Carbs
  • 1.2km/h Average Speed
  • 294.7 Time Gained (seconds)

2 man break

  • 22.7w Power Flat
  • 4,5w Power Climbing
  • 47.6w Power Descending
  • 21.2w Average Power
  • 284.7kcal Energy
  • 3.3 Number of Gels
  • 71.2 Grams of Carbs
  • 1.2km/h Average Speed
  • 307.3 Time Gained (seconds)

4 man break

  • 20.7w Power Flat
  • 4.1w Power Climbing
  • 43.4w Power Descending
  • 19.4w Average Power
  • 259.6kcal Energy
  • 3.0 Number of Gels
  • 64.9 Grams of Carbs
  • 1.1km/h Average Speed
  • 314.4 Time Gained (seconds)

Turn every 20th man

  • 19.1w Power Flat
  • 3.8w Power Climbing
  • 40.0w Power Descending
  • 17.9w Average Power
  • 239.5kcal Energy
  • 2.8 Number of Gels
  • 59.9 Grams of Carbs
  • 1.1km/h Average Speed
  • 320.7 Time Gained (seconds)

Sitting in

  • 18.7w Power Flat
  • 3.7w Power Climbing
  • 39.2w Power Descending
  • 17.5w Average Power
  • 234.5kcal Energy
  • 2.7 Number of Gels
  • 58.6 Grams of Carbs
  • 1.1km/h Average Speed
  • 322.3 Time Gained (seconds)

1kg Mass Reduction

  • 0.5w Power Flat
  • 4.8w Power Climbing
  • -3.9w Power Descending
  • 1.0w Average Power
  • 13.1kcal Energy
  • 0.2 Number of Gels
  • 3.3 Grams of Carbs
  • 0.0km/h Average Speed
  • 6.8 Time Gained (seconds)

It’s clear to see how much of an impact aerodynamics has, even when you’re sitting in! Who doesn’t want to have 20w+ saved by the end of the race? Or 3-4 less gels eaten? If you’re a bit of a nutter and go for a solo break from the off during a 130km road race, you will be 5 minutes up the road by the end if you rode an aero bike instead of a round tube bike. I’ll say that again, 5 minutes. 5 whole minutes! That’s over 3km further up the road. Breakaways are often decided on a matter of a handful of seconds.

Notice how little power was saved by reducing the bicycle weight by 1kg? Just 1w over the whole 130km race. The power saved when climbing was about equal to the power saved from aero during climbing. So at 25km/h up a 5% climb the aero gains from a round tube to aero road bike is equal to saving a kilogram off your bike. And who said aero doesn’t mean anything on climbs?

I could sit here firing out scenario after scenario, but at the end of the day it’s your choice what equipment you use, hopefully I’m just providing you with some tools to make an informed decision. I’ll share a quote a very wise sports scientist said to me when I was working at Team GB: “In the age of information, ignorance is a choice.”