As you ride, both wind speed and wind direction shift relative to you, meaning one of the key factors in aerodynamics—the yaw angle—rarely stays consistent for long. Despite this, manufacturers often claim they have optimised their designs for particular yaw angle ranges. Some even argue that certain tube and rim shapes can behave like sails, helping to push the bike forward when the wind strikes from the right angle. Data from myWindsock shows us that over most rides, races or training, that yaw angle changes constantly. We thought we’d write a blog that tells you what Yaw angle is and how it can impact your aerodynamics.

What is Yaw Angle?

In cycling aerodynamics, yaw angle is the angle between the rider’s direction of travel and the apparent wind (the vector sum of the rider’s forward speed and the true wind). A yaw angle of 0° means the wind hits the rider directly head-on, while higher positive or negative yaw angles occur when crosswinds shift the apparent wind sideways relative to the bike’s path. That is to say “what direction does it feel like the wind is coming from relative to my direction of motion?”.

In this blog we wrote a little about the idea of “yaw dependent” cda, that is to say that your aerodynamic properties are dependent on the angle the wind comes from.

How does all this impact my forecasts?

It’s early TT season as we write this and while this is a difficult time to get new PBs, it’s a great time of year for data gathering. One useful piece of information you can gain from this time of year is how the wind can impact your cda and while obtaining granular yaw dependent cda is tricky, but not impossible, with myWindsock you can very easily get an idea of whether you’re particularly “un-aerodynamic” on windy days.

This will help improve the accuracy of your forecasts which will allow you to preserve your biggest performances for days when a PB is more likely.

Sign up to myWindsock here.

It’s no secret that here at myWindsock we love a TT and with 5 time trials on the first Sunday of March this year it’s fair to say we are well and truly back. Early season Time Trials aren’t all about PB times though, as there’s a lot of factors that can make them a bit trickier – even if you have great legs from a perfect winter of training. It can be cold, the air feels thick and the wind can blow! This blog will discuss how these conditions can impact your ride.

The Temperature

It’s no secret that it can be cold in March. In a TT, being very cold can blunt your ability to sustain high power as the cold shifts you away from the “sweet spot” of muscle and core temperature. Peripheral vasoconstriction reduces skin blood flow to preserve core heat, while muscle temperature drops, slowing contractile speed and nerve conduction. This makes each pedal stroke feel heavier so the same perceived effort can yield less power, especially during surges or on rises.

Cold can also increase breathing discomfort and stiffness, and if you start the TT even slightly chilled, you often spend the opening minutes “paying back” heat debt rather than settling into an efficient rhythm. In real-world pro cycling, a pilot study reported that cold conditions (with wind-chill–adjusted temperature around ~8°C) were associated with meaningful changes in power, speed, cadence, heart rate, and core temperature, suggesting performance can be limited when conditions and airflow overcool riders.

It is possible to mitigate the cold and this is mostly about starting warm and staying warm without overheating. Do a longer, more progressive warm-up where logistics allow it and minimise the gap between your warm-up and the start. Getting your layers right is important too, a breathable base layer can add a little warmth and keeping your hands and feet warm can reduce the impact of the cold significantly.

The Wind

In my experience, the early season TTs are often the ones most likely to get cancelled for wind and 4 out of my 5 worst all time wImpacts on rides have been in the UK in March.

We all know that riding with a headwind makes you slower, and a tailwind makes you faster but something that goes under-appreciated is how important bike handling can be in the wind. Getting comfortable handling your TT bike can save you valuable seconds during short TTs.

The Air Pressure

Cold air is more dense. When air cools down, its molecules lose energy and move more slowly. As they slow down, they don’t spread out as much and instead pack closer together. Imagine a room full of people: if everyone is moving around quickly, they spread out and bump into each other less; if they’re moving slowly, they tend to cluster more tightly. In the atmosphere, this means that at lower temperatures the same volume of air contains more molecules, making it heavier and more dense than warm air.

Early season time trials are rarely straightforward. Between colder temperatures, denser air and gusty winds, March can test more than just your FTP. While you can’t control the weather on race day, you can control how you prepare for it. Turning up properly warmed up, dressing smartly, pacing with the conditions in mind and being confident handling your bike in the wind can make a meaningful difference. The riders who perform well in these events aren’t always the ones chasing PBs, they’re the ones who manage the conditions best.

Stay prepared for any race day conditions with a myWindsock subscription.

Last week, we published a blog all about how myWindsock calculates your cda from the data that you collect while you’re out on your bike. If you’re a consumer of cycling media, like us, or find yourself having a chat to your mate who has been in the wind tunnel recently, you might have noticed people saying “my cda is [insert number]”. This can be a little confusing, because although you get “average cda” when you look at a ride in myWindsock, you see that your cda graph looks something like this…

During the blog on how myWindsock calculates your cda, we looked a little into the origins of where this formula comes from…

All of these variables in this equation, are themselves functions of something else. Power is a function of time (unless you do an exactly evenly paced ride of course, then it’s constant). Air density is a function of altitude and weather and speed is a function of many things but changes during the course of the ride too. All of these variables are known at each point on the ride and cause cda to be different at each point in time.

It’s currently the case that you can use the myWindsock advanced settings when making a forecast to enter a speed or gradient dependent cda – something that may reflect you sitting up out of the TT bars over climbs and getting back into position on the flatter segments. This will change soon, but more on that in the future.

The key thing to remember is that your cda is not a fixed number, but a parameter which constantly changes and has many dependencies feeding into it. The best time trialists and triathlon cyclists have a sixth sense for minimising it at all times. Narrowing their shoulders, shrugging their heads and staying in the TT bars even during slower parts of the course.

If you want to know your cda while you ride, sign up to myWindsock here.

Physics was not everyone’s cup of tea from their school days, however we thought the myWindsock website needed a place which did explain some of the basics of cycling aerodynamics to give our curious users a place to begin to look under the hood. This blog will give you enough of an idea to understand how myWindsock makes predictions but without overwhelming detail (or giving away too much of the magic).

As such, we need to skip some steps to communicate the basic point without losing people with unnecessary formalities. This will possibly irritate readers with advanced degrees in Aero Engineering and I suggest they stop reading immediately.

Imagine you’re riding a bike at constant speed through the air. 

We’ll start with the drag equation, skipping on the details of how we get from physics first principles to it. We can calculate the drag force (the number of Newtons a cyclist is pulled back by) with this formula, which will look very simple or very confusing, depending on when you last did maths and how much you enjoyed it at the time.

In English, this says that Drag (D) is equal to air density (the Greek letter rho) multiplied by velocity squared (v, multiplied by itself) multiplied by the product of drag coefficient (Cd) and frontal area (A). In even simpler terms, you calculate the drag on a cyclist by multiplying a bunch of numbers together – some of which are to do with the cyclist and others to do with the environment.

We can also calculate the power needed to ride at this constant speed using the following equation. This is useful to us because we are able to measure power much more easily than we are able to measure drag while we’re out on the road. 

Using some algebra (sorry) which you’re welcome to try at home, we can combine these two equations and obtain the following result… 

This tells us how we can calculate the aerodynamic drag required to ride at the constant speed we mentioned earlier. As a cyclist, you may know what power you’re riding at because you’ve got a powermeter on your bike. You are unlikely to know your CdA. As such, we can re-write the equation with stuff we “know” (reasonably estimate or measure to sufficient accuracy) on one side of the equals and the stuff we don’t know (or that’s much harder to estimate) on the other side of it.

Time for a quick disclaimer, the power on our powermeter here displays all the power we are using to overcome all resistive forces, but we’re only talking about aero power here so we are going to have to make some slightly wild, but fine for illustrative purposes, assumptions. Let’s try and plug in some numbers. 

Right now, where I am, the air density is 1.19 kilograms per metre cubed (which means, if you were to somehow weigh a cube of air that’s one metre by one metre by one metre it would weigh 1.19kg) and we’ll imagine I’m doing 30kph on my bike with my power meter reading 220W on a road and we’ll assume forces that aren’t related to air resistance make up 20% of our power output. As such, the amount of power we are using against the air is 176W. If we plug all of those numbers into the expression above it gives us an estimate for our CdA of 0.517. 

This isn’t a complete description of how myWindsock calculates CdA, nor is it a rigorous explanation of the equation of motion of a cyclist but it gives you a fairly solid introduction into the mathematics of cycling…at least at a constant speed on a flat road. 

Two minutes doesn’t sound like much—until you’re halfway up the climb at National Champs and every pedal stroke fills your legs with that burning feeling. Mastering your pacing for a two-minute effort can be the difference between flying over the top or blowing up halfway.

Recent research on 800-metre runners, the ultimate two-minute specialists (ish), offers surprisingly direct lessons for hill climbers. Studies reveal exactly how elite athletes distribute effort, manage energy, and stay fast when the body is screaming to slow down.

This weekend, riders head to the National Hill Climb Championships, where the race will be won in approximately (just over) 2 minutes. Here’s how you train for and pace it…

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 Build a Bigger Engine (VO₂ Peak Still Rules)

Watanabe’s team found that even in a race lasting only around two minutes, athletes with higher VO₂ peak ran faster. In other words, you can’t fake endurance, even in short, explosive events. The aerobic system kicks in within seconds, not minutes, and it supports sustained output once the initial surge fades. It’s not really a revelation that having a higher VO2 max helps during a short endurance event – but the extent to which it matters does surprise a lot of people. It’s NOT a sprinter’s race!

Hill-climb takeaway:
To prepare, include workouts that stress your aerobic ceiling:

• 3–5 × 2 min uphill at 90–95% max heart rate, with full recoveries.
  
• Longer tempo climbs (4–6 min) at controlled effort to raise aerobic power.
  

A strong VO₂ peak means you’ll hit the climb harder and last longer before the legs “flood with” lactate.

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Train to “clear lactate”

The same study identified lactate removal ability (γ₂) as a crucial determinant of performance. Those who could clear or reuse lactate faster maintained speed better through the second half of the effort. On a climb, that’s the rider or runner who keeps pushing while everyone else fades.

Hill-climb takeaway:
Train your body to tolerate and clear lactate:

• Do repeated short hill sprints (30–45 s) with 30–60 s easy recoveries.
  
• Add “float” intervals—alternate hard 45 s pushes and moderate 45 s efforts without full rest.

These sessions teach your muscles to recycle lactate as fuel instead of letting it shut you down.

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Fast Start, Smooth Fade

Hanley’s analysis of world-class 800 m races shows that almost every top performance follows a fast-start, controlled-fade pattern: an aggressive opening to hit top power early, followed by a gradual deceleration. The secret isn’t a final sprint—it’s slowing down less than everyone else. 

Hill-climb takeaway:

• Launch confidently to get up to race power quickly.
  
• Settle into a sustainable rhythm within 20–30 s.
  
• Focus on holding form as fatigue builds—shoulders relaxed, breathing deep, cadence steady.
  

A small fade is inevitable; the goal is to make it gradual, not catastrophic.

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The Art of the Final 30 Seconds

In the last stretch, you’re no longer chasing speed—you’re fighting to keep it. This is where aerobic strength and lactate clearance combine with mental control. Keep your upper body calm, eyes fixed just ahead, and drive through the burn.

Remember: perfect pacing isn’t even pacing. It’s knowing exactly how much burn you can handle and stretching that line to the summit.

Take a look at the course here and sign up to myWindsock today!

It’s the night before the big dance – and athletes in Kona are currently having their penultimate night’s sleep before the women’s Ironman World Championships in Kona and we’re of the opinion that course records will probably fall. Historical precedent tells us that it’s the first year where it’s within the realms of possibility that the winner of the women’s race in Kona this year will be faster than the male winner from 2014!

A lot has been made of the weather forecast in the triathlon media this year at Kona, it’s going to be pretty windy with the average wind speed picking up to around 30kph in the back half of the bike course and the famous crosswinds on the Hawi descents are looking like they’ll make an appearance.

Even though the wind on course is pretty high, the wImpact on the day is between 0 and 1.5% – this is pretty low and means athletes will only be a maximum of 1.5% slower when compared to a completely neutral day. In 2018 conditions were similar when the bike course record was broken by Daniella Ryf.

Using a system mass of 72kg (that’s bike and rider) and reported rolling resistance and drivetrain losses values that represent the best of the best – a rider with a cda of around 0.19 will need between 210W and 215W to break the course record. This will be a power to weight of around 3.5W/kg.

If you want to play around with the forecast for the Ironman World Championships bike course, click here.

It’s become less fashionable a term recently, on account of its horrific overuse, but marginal gains is the idea that if you make incremental improvements to your setup or training that it will add up to something significant. It was popularised in the early 2010s by Team Sky (now INEOS) back when they used to win stuff. 

Recently, I’ve been on a bit of a buying spree for my TT bike and have been thoughtfully shopping – aiming to prioritise by Watts saved per pound spent, but while doing this I realised that the thing that matters really is time saved per pound spent.

The marginal gains we will test in today’s simulation will be…

• Switching from GP5000 to GP5000 TT, both with latex inner tubes
  
  Independent tests of this set up have shown an improvement of around 1-4W per tyre.
  
• Removing the front derailleur and switching to one chainring
  
  This could save, again, between 1 and 4W in aerodynamic savings.
  
• Adding an aero OSPW system
  
  This has a claimed saving of 2.4W relative to a dura ace set up.
  
• Using a super slippery waxed chain
  
  Wattshop claim their ‘Cratus’ waxed chain can save 3-5W compared to a standard clean chain.
  
• Very moderate weight savings

Using a combination of factors, I’ve also managed to shave 650g off my set up and body weight. 

Before we get started here, it’s worth noting that all of these claims are probably wrong in the context of this specific simulation with this specific setup. However, that’s not really the point of this blog. It’s actually to answer the question of “We know you can accumulate meaningful savings but how much of a difference does it actually make?”

The first step we’ll do is run each saving individually and then finally, we’ll put them all together and see the time difference between the standard set up plus all the marginal gains. 

It’s worth noting that aerodynamic savings scale with speed whereas rolling and drive train resistance savings remain more stable (they’re not actually constant, but for the simplicity of our model approximating them as constant yields acceptable results). 

We will assume that, for the sake of simplicity, saving 1W is the equivalent of riding 1W harder – this is not actually true (as 1W saved at 30kph might be 3W or something at 50kph) so, if anything, this is likely to underestimate the time savings from our marginal gains – especially the aero ones. That said, it makes the simulation much simpler to carry out – so we will make the assumption none the less. 

The final assumption we’ll make here is that our rider is riding at a constant power of 300W – this is not realistic, or optimal, but makes it easier to isolate changes so we’ll do this for illustrative purposes. At the end, we’ll have a perfectly paced simulation – centred around 300W. 

Standard Set Up

After each run, we’ll reset the simulation to the original conditions so when you see a time saving, it’s with respect to our baseline set up.

Weight Savings

As we’ve saved 650g – that’s about 0.7% of our total system mass, we might see a gain in speed as a result of this, considering it’s a pretty punchy circuit. Let’s run the simulation taking 650g off our set up and see what happens. 

Waxing our chain

Let’s see if the Wattshop waxed chain, with a saving of 3-5W (we will use 4W) can save us a decent amount of time… 

Oversize Pulley Wheel

Going “one-by”

Typically, the 1X chainring’s aero savings are dependent on yaw angle but savings between 1 and 4W are common. As such, we’ll see a saving of around 35s here.

Fresh Tyres

This is actually one of the most interesting examples of non-obvious speed improvements. Independent testing has shown the difference to be about 3W per tyre – so a total saving of 6W. Running a simulation with a 6W boost in power we see this… 

All together

In total, these savings add up to 15W (plus our 650g) saving.

Marginal gains AND perfect pacing…

That’s not the end of it though, we all know that riding a course (especially one that’s hilly) with a flat power is not the fastest way to do it. 

As much as it pains us to say (not at all, we love it), marginal gains really do add up, without getting any fitter at all we’ve just saved ourselves almost 4.5 minutes simply by throwing money at the issue and pacing properly. 

Save yourself time and money with a myWindsock subscription today. 

IRONMAN 70.3 World Championships 2025 course preview

This year, the IRONMAN 70.3 World Championships take place in the Spanish seaside town of Marbella. 2025 is the year of “Carbs before Marbs” and you’re going to need it in order to get round this monstrosity of a bike course – with 20m of climbing per kilometre it’s got to be the hardest 70.3 World’s course in history. The course map really doesn’t look that bad but it has 1.5 times the amount of elevation per mile than the “mountainous” IRONMAN World Championships course in Nice – it’s way harder. Of course, myWindsock is the only acceptable tool to quantify exactly how hard this course is.

The hardest thing about this course is the fact there’s long climbs with vicious pinches in gradient that peak over 20%. We can look at the gradient plot and distribution of gradients here.

How to think of the course?

This might be the hardest 70.3 World’s there will ever be – in order to get prepared properly myWindsock is the only place to nail your pacing, planning and post race analysis all in one subscription.

Here at myWindsock we care about two things – predicting how the weather will impact your speed on the bike and riding fast time trials. That’s it. Today we have three tips for you that will help you, backed with some myWindsock science, ride a faster TT without simply pedalling harder. 

Hold your position 

Staying in the aero bars during a time trial sounds like a trivial piece of advice but it’s something that was recently demonstrated by Red Bull Bora riders at the 2025 Tour de France – riding uphill in the aero bars during the mountain time trial to some pretty good success. Being more aerodynamic is typically faster even when speeds are pretty low. 

How much difference does it make?

For this we’ll take the sort of segment you might find in a TT in the UK, a 3.3km drag of around 3%. For a 70kg rider on an 8kg bike with a typical “sat up” cda of 0.35 doing 300W this gives us a ground speed of 26.4km/h and time on the segment of 7:31. 

What happens if we put that same rider in the TT bars and drop their cda to 0.23? Good position discipline comes down to one thing, training. Ride your TT bike a lot, on hard days and easy days – if your time trialing is your primary goal then it shouldn’t even matter if you can do less power, as you’re training the muscles you’re going to use on race day. One of our favourite sessions is to go and ride up the longest climb you can find in the TT bars at a low cadence to really practice recruiting all of those TT muscles. Let’s take a look at what happens on that climb if the rider stayed in the bars…

Pacing 

The old adage of riding fast is about minimising the amount of time you’re riding slowly for is as true now as it ever was. Efficient pacing is a game of energy investment – put more energy in when the resistive forces are lower and you’ll get more seconds back for your power investment. 

How much difference does it make?

For this example we’ll use the world famous (well, moderately well known in Hampshire) P164 time trial course. It’s a rolling 10 in the New Forest with 130m of climbing over 16.1km.

This course doesn’t suit a smooth power output as we used in the example above, as you can see by the elevation profile…

Let’s input a series of pacing rules, that yields the same normalised power but distributing our power slightly differently. myWindsock settings allow us to do this and we’ll impose a series of pacing rules (like “if speed > 60kph, power goes to 0W”).

How to do it?

Make use of the “Where Power Matters Most” graph on your event myWindsock forecast and avoid just doing a flat, smooth power.

Tyres, chains and gears

A clean bike is a fast bike, and a bike with a waxed chain and ceramic bearings is a slightly faster bike on top of that. This final tip is often marginal, but time trials often come down to small margins and that’s half the fun. Let’s delve into the myWindsock advanced settings and see how it impacts our TT on the P164 remembering our well paced effort yielded a time of 22:44, what happens if we fully optimise our tyres and chain?

That’s it then, riding a fast TT is simple – good pacing, good position discipline and spend money. The most efficient pound per second save expenditure you can make is a myWindsock subscription. With this, you can test your pacing and equipment strategy on a given course to help you plan race day down to the second.

This Sunday riders will take on the RTTC National 25 mile TT championships on the N1/25C course in Cambridgeshire. The National 25 Mile Time Trial Championship is part of a long-standing tradition in British cycling that dates back to the early 20th century. In 1922, a group of cycling clubs formed the Road Racing Council (RRC) to bring uniformity to road time trials, which were growing in popularity. Initially limited to founder clubs and those hosting open events, the RRC set out basic rules and recommendations to ensure consistent race conduct across the country. As the sport expanded and modern traffic conditions posed new challenges, the RRC evolved into the Road Time Trials Council (RTTC) in 1937, opening its membership to all cycling clubs and introducing a national framework for managing the sport.

Since then, the RTTC—now operating under the name Cycling Time Trials (CTT)—has continued to oversee and support the sport at all levels, from grassroots club events to national championships. The aim has remained unchanged: to ensure fair, safe, and standardised time trials across the UK, preserving a discipline that has thrived for over a century. The great history of this event amplifies the prestige.

Course Profile

Weather Forecast

The wind direction should play a role in rider’s pacing though, with Sunday forecast to be a cross tailwind on the way out and a cross headwind on the return. The course is an out-back-out-back with a roundabout on the return and the finish line sits at the bottom of the starting hill. 

If you want to play about with the forecast and see how you’d stack up at the National 25 mile championships the forecast is here.