Watt Matters is a blog about training and racing with power and other related musings.

Aside from writing items here on occasions, I also provide cycling performance improvement services via coaching, aerodynamics testing and host a cycling tour.

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Aero for slower riders

Aero for slower riders

A quick chart today for future reference whenever that classic online nonsense argument about aero benefits only being for faster riders, or that aero only matters above a certain speed....

Let's set people straight now: Aerodynamic improvements benefit riders of all speeds and power outputs. But who gains the most benefit?

Whether a slower rider should be putting time/energy/effort/resources into gaining or buying an aero improvement when they might perhaps be better focussed on losing weight and training more (or harder or smarter) is a moot point. Really, though, such an argument is a false dichotomy. Why not do both?

The other consideration of course is if you are going to chase an aero improvement, then there are two main ways to achieve that:

  • improved aerodynamic positioning, or
  • improved aerodynamic equipment

But again, this is not a case of one or the other. It's quite OK to do both and train better. You know, one could train to improve fitness, work on gaining a better aerodynamic position, and treat themselves to some nice aero wheels, or move from using a road bike with clip on bars extensions to a time trial bike. This is not an either/or scenario.

If you are a back/middle of pack rider, then some bling wheels are not going to make you the next world champion, so some perspective here is warranted but the rationale for why you are looking to improve your performance is a matter of personal choice. If you want to be faster, then you do all the things you can given the constraints you have (time, money, knowledge, rest of life factors etc). And we are talking about people riding in competition-like events, not your cruiser to pick up some milk at the local shops (let's be sensible here).

If you are just happy with participating rather than competing, then sure, what does it matter? If you just like having nice equipment and have the money to spend, heck, go for it. Enjoy yourself.

But let's get the physics out of the way with a chart to quickly summarise the situation with an example.

The chart below plots the time taken to complete 10km on a flat road with no wind at various power outputs, from a modest 150 watts, through to a solid 350 watts. Other assumptions are shown on the chart, but changing the parameters really doesn't change the basic principles here. Click on the chart to see a larger version (right click to view in a new tab/window).

Aero Benefits - fast or slow.JPG

There are two lines, showing the reduction in time to complete the 10km as a rider's power output increases. No surprises there, more power with all else the same, you go faster.

The two lines also show the difference between a rider with a coefficient of drag-area (CdA) of 0.30m^2 and 0.27m^2 (a 10% reduction). That's roughly the sort of reduction in CdA you might expect going from standard low profile spoked road bike wheels to specialist aerodynamic wheelset, or riding on the tops to riding on the drops.

Under that are the blue columns, which represent the time saving over that 10km by reducing CdA from 0.30m^2 to 0.27m^2. As you can see, the slower less powerful rider saves more time in absolute terms than the faster more power rider. However, when expressed as a percentage of time saved, they are nearly equivalent savings, with the faster more powerful rider making very slightly better gains in percentage terms.

Now of course some parameters do change under some conditions, e.g. cross winds can affect the apparent CdA to differing degrees at different speeds, so in those situations, a faster rider may benefit a little more in percentage terms, but in general, there really is no physical reality to the old myth that aero only benefits the faster rider, or that óne needs to ride at X km/h to see benefit.

Pithy Power Proverb:

The largest absolute time savings from a given aerodynamic improvement are made by the least powerful/slowest riders.
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