Aero field testing is available to all Premium members with power meter data by simply viewing their Strava Activity Weather or uploading a TCX file. Learn more about Premium.

When you head out to do an aero test using myWindsock, there’s always a question of how much you can trust your results. We understand this and have a tool for this in our aero test mode – confidence!

In the above image you can see that the rider (Ben) alternated between two positions. The first two runs went reasonably well and the Orange Test Range around the Test Average is very narrow. I had enough good consistent loops and the bad loops were detected well by the filter. This is a test with ‘High Confidence’. The narrower the confidence bar, the lower the variance between calculated cda values. The aim, when doing an aero test, is to make this range as narrow as possible.

Top 5 reasons you have a high test range

1. Traffic at turns – Leaving your position or using the brakes on a large number of your loops will cause a high Test Range. Choose quieter times of day or ensure a greater quantity of good loops vs bad. Ensure when you do use your brakes you use them sufficiently enough to greatly impact the loop CdA otherwise it may not be filtered and make its way into the test range, take the opportunity to sit up and relax before the next loop.
   
2. Traffic passing – Your CdA is affected by traffic in both directions. Oncoming traffic will increase your CdA whilst traffic passing you in the same direction will decrease your CdA. Choose times of day that have the lowest or most consistent level of traffic. If you suspect a bad loop due to traffic brake to a stop to demonstrate to the loop filter that it is a bad loop.
   
3. Gear changes – Changing gear will change your drive train efficiency. If you do have to change gear (ideally don’t) make sure you always change at the same location. Do not change loop to loop and test to test. Pick a gear, make a note of it, check that you’re in it and leave it.
   
4. Insufficient test loops – If you have a really good test loop, a velodrome for example, you can get away with a handful of loops per test. If however you aren’t that lucky more loops are required. Remember using a short loop will isolate problems and speed up your test. 
   
5. Position discipline – Make sure you are paying attention to your position. Doing some loops relaxed and some loops focused will lead to a wide range. Small changes to position are too subtle to be weeded out by the loop filtering process and will therefore produce a large Test Range.
   
   Aero field testing is available to all Premium members with power meter data by simply viewing their Strava Activity Weather or uploading a TCX file. Learn more about Premium.

This blog post was written by Ben back in 2017 but has been adapted and reposted in November 2022!

Any reader of this blog will likely understand the virtues of myWindsock for athletes looking to improve their performance. We know the detailed forecasts can allow us to pace races optimally, target Strava segments and figure out where to attack. The performance aspect of myWindsock is used by world class athletes to break records and win olympic medals. 

Most of us have no chance of making the Olympics, most of us will not be breaking the North Coast 500 record and most of us aren’t even trying to break personal bests over ten miles most of the time. Primarily we just enjoy riding our bikes. Racing is a huge part of what inspired myWindsock, but we aren’t only a tool for racers. The one thing all cyclists have in common is that they enjoy riding their bike. 

That enjoyment varies by ride, let’s not pretend we enjoy getting soaked in British lanes as much as we enjoy railing alpine descents in the sun. We don’t. However, it’s easy to enjoy cycling without rain and wind. The real challenge is learning to enjoy riding on the roads of the UK throughout the miserable months. I’m writing this on the 14th of November and the next time I plan to get back on my bike is the 16th and I plan to avoid the rain! 

Planning what to wear 

I live in a relatively small flat with a small washing machine – as a result, I have to plan my kit a little in advance. One thing that helps, is deciding what to wash with the assistance of an accurate weather forecast. I live in Southampton and tend to ride in the New Forest, of course the weather can vary quite a lot over the course of a 100km ride, so rather than checking the weather in every town that I’m planning to ride through I shall use a windsock forecast.

As we can see, I shall possibly be getting wet but the temperatures aren’t particularly cold. As a result, I’ll locate a breathable, packable raincoat to avoid the ‘boil in the bag’ effect of my sturdier ones! On top of this, I’ll probably get my legs out and wear my waterproof bib-shorts.

The interesting thing is, despite being extremely interested in performance, I use myWindsock for this purpose more often than I use it as a means of predicting performance. Let’s face it, we all train a lot more than we race – even if we don’t train much at all.

Planning where to go

Ok, two weather related factors of rain and temperature have been taken care of and we know what to wear. But there’s still one open question – where should we go? I never used to bother with wind direction on rides but, thanks to my mate Harry, I’ve become addicted to the “tailwind home”. Obviously, you feel much worse at the end of a ride than you do at the start – you’re tired, ready for a shower and a snack and the last thing you need is a headwind for the final 10 miles. Luckily, myWindsock has us covered. Let’s take a look at the route map… 

Blue means tailwind, red means headwind. The arrows show us where the wind is pointing in any direction. Generally speaking, the New Forest is pretty flat and the wind is the main thing that provides riders with resistance. We can see from this that, broadly speaking, I’ll have a headwind at the start and tailwind on the way home.

With it being a loop, we have mostly an even split in wind direction. The distribution of wind directions can be seen on the “Apparent Wind Direction” plot and the proportion of Tailwind to Headwind can be seen below this.

Using myWindsock is not the preserve of elite athletes. Sure, it’s a great tool for them – probably the best! It’s a great tool for anyone heading out on their bike too. I know that on the Wednesday ride, I’ll be doing my turn on the front in the last half of the ride with the tailwind. We can help you pick the right kit, pull the easiest turns and time your segment hunting to perfection. If you’re interested in signing up, many of the best features of myWindsock are available on our free version. Take a look here to sign up! 

This weekend, it will be unseasonably warm for many of Britain’s cyclists meaning the summer kit might just get one more run out – plus a waterproof layer or two. One thing you might notice though, is that you tend to go a little faster in the heat. Why is this? 

The first reason is quite an obvious one, you’re wearing less clothes. A jersey and shorts is much tighter fitting than a winter jacket. That flapping in the wind costs energy – as the jacket presents a larger surface area and increases the amount of turbulent air. But, cold air itself is actually slower too!

Why is cold air slower?

If we have a think about the aerodynamic equation which governs how the force on something changes as it moves through the air under various conditions we notice that the power re quired to move our bicycle is proportional to the density of the air. Air density is not static, some air is more dense than other air. Remembering our GCSE science, we know that density is directly proportional to pressure – and pressure is proportional to temperature! This means, on a hot day, the air is less dense.

Why is less dense air faster?

Density is a quantity which describes how much of something takes up a given space. The density of air describes how many air particles are in any given square metre of space. If the air is less dense, there is less air to ride through. This is the reason many record attempts take place at altitude. With less air to ride through, it’s much easier to go faster!

If you’re out on your bike this weekend, you might see a notable uptick on your average speed. If you’re interested in how the weather can impact your riding or want detailed, up to date forecasts – sign up to Mywindsock for free here.