Why are winter time trials so much slower?

It’s January which means one thing only – TT season is round the corner (ok maybe it also means other things). Races are popping up from mid February which means some early season form testing is on the cards. You might find that, as a result of a really consistent winter, your power numbers are really good this time of year yet you churn out a couple of slow time trials before it warms up. New kit, new bike fit, more watts and still going slower, but why? Winter time trials are slow!

Rest assured, it’s probably nothing to do with how powerful or inherently aero you actually are yourself and is more to do with the conditions. Of course, by subscribing to myWindsock you will have confidence in knowing this as the conditions are taken into account and you’ll know it was a slow day with high Weather Impact.

Cold is slow!

The speed you ride at for a given power on a given day with some given cda is proportional to one over the square root of the density of the air that you’re riding through. This basically means that as air density goes up, our speed will go down. Air density is impacted primarily by temperature. Hot molecules move faster and spread out more. This means more air occupies some given space when it’s cold compared to when it’s hot. In a time trial, the amount of space we need to pass through is fixed at the distance of the race, but the amount of air occupying this space varies quite a lot from one day to the next. 

If you have left your house at any point since October, you might have noticed it’s become rather chilly. As time trialists, we think “gosh, the air is rather dense today” and people look at us like we have just started speaking Spanish. Cold days are slow days. It’s just the laws of physics. 

If it’s slow, what’s the point of racing in February? 

Time trialing is part art, part science. The ratio of art to science will vary depending on who you ask but everyone agrees, to get good at time trials you have to do them. As with anything though, blind practice only gets you so far. Practising with purpose is the key. 

What would be handy is some kind of service which analyses your winter time trials and tells you how much impact the weather would have and how aero you are. Of course, you can see all of that information here. 

Use myWindsock to dial in your pacing and kit choices so that by the time summer comes around you’re dropping massive PB performances with confidence. 

FTP RACING – U7B – 9th April

We’re excited for the FTP Racing U7B time trial on Saturday 9th April. This is a quick look at some course dynamics. All charts are correct to the current forecast. We recommend viewing your own forecast, to see the most up to date course forecast and data. View the course and the forecast for Saturday here.

How the course will feel

‘Feels Like Elevation’, helps us to visualise the wind in the same way as we would the elevation profile of a hill. We are equating the wind to the hills. Helping us to see how the wind would feel, by viewing it’s equivalent gradient. This helps us formulate our mental strategy for race day.

Below is the graph for Saturday’s race. The Westerly 10mph wind, is now combined with the elevation profile. The grey area is simply the standard elevation profile. However, the coloured line shows the wind and elevation together to give you a clearer idea of how the course will feel.

The red areas are showing that the wind has created harder feel than the original elevation profile would suggest.

Feels like elevation, when we factor the feel of the wind combined with gradient

Where should we put more power out

We next turn to where the course will give us the most return, for a little extra power. The green areas of the line chart below shows were on the course we get the greatest return for each additional Watt. Pay attention to 3.5-6km, 9-9.3km and 10.75-11.25km, those locations will give you a good return on a slightly increased power output.

On the flip slide, the red section, will give you an idea as to where it would be less advantageus to increase your power. Looking at 11.25km to 14km, it wouldn’t be as efficient to increase power here. Better to increase the power in the preceeding 0.5km.

Where power has the greatest affect on time. Green shows where you get the most return for each Watt.

Where aero is most important

Next, where on the course does an increase in our focus on aero pay off the most. This is depicted in Green below. In red aerodynamics are having less affect on the overall speed. This is not to say aero is unimportant in these areas. This graph simply shows that if we were to increase our aerodynamic efficiency where along the course would that increase in efficiency give us the greatest return.

Where aero has the greatest affect on time

You can make your own experiments using myWindsock for all your time trials. We have all the UK time trials already preloaded for you. Simply visit our CTT Time Trial Forecasts.

Time Trial Prep: Part 1, the wind

The 2022 time trial season is just around the corner. In this series, I’m going to show you how I would use a myWindsock forecast, to prepare for the first Cycling Time Trial event, the Ely & District 25 mile SPOCO on BS19.

PLEASE NOTE: Weather forecasts are updated hourly, this forecast may have changed from the time this article is published. View the forecast for yourself here.

In this first part we look at how understanding the challenges of the course weather so we can prepare a mental strategy. This is what we refer to as the Descriptive side of myWindsock. We are describing race day, so you have all the information required for optimal mental preformance.

In our second part we will look at the Prescriptive tools. We will show you how to formulate the optimal power plan.

First thing, we need a Virtual Athlete to Ride the Course

We want to ensure everything we are looking at reflects our performance on the day. To do this, we need a Virtual Athlete (VA). Your Virtual Athlete will ride the course as many time as you like, with infinite setup choices. The beauty of your VA, they never get tired!

In the next part of this blog series, we will look at how to use your Virtual Athlete to formulate the best race plan. For now, we just need to have a good estimate of race day performance.

Clicking on the Bike icon for cycling events will reveal the Virtual Athlete menu and settings. Ensure this reflects your own performance.

You may want to create a new Virtual Athlete for this race distance, I have one simply called “25 mile”. I will use this as the basis to begin all 25 analysis and then, as we will learn in the next post create a race specific VA for the event when I come to plan power.

Pay specific attention to Power, weight and aerodynamics.

Often I am asked about what to enter for aerodynamics. You can use this post to find your CdA from a previous race activity. You can also use the icons to guide you. For time trials if in doubt use 0.200.

What to expect

We start in the Metrics tab. My attention is initially drawn to the Moving Time and average ground speed. Notice that we refer to ‘Ground’ speed rather than simply ‘Speed’. This is because we also have metrics for ‘Air’ speed.

Power and Aerodynamics are as we have set for out VA.

Weather Impact is quite high at 8.1%. This tells us, for me to achieve the same time as on a weather free day, I’d require an additional 8.1% power. Find out more about Weather Impact.

General Summary

Moving down the metrics panel we have our Feels Like data. Feels Like gives us an alternative way to view the wind. We equate the wind to it’s equivalent gradient. Why? Well, I find it is easier to imagine a how difficult a gradient will feel. Whereas, the combination of prevailing wind direction, wind speed etc. is more difficult to imagine.

Our Feels Like Elevation panel

Next, we move down to the Aerodynamics panel. There are two pieces of information we should be aware of. First is Yaw Angle. This is the average Yaw, we have a chart showing the Yaw distribution, to help make informed equipment choices. I have a couple of wheelsets and some technical data on them that gives me the best operating Yaw angles.

Also in Aerodynamics we have the Air Resistance. This is the percent of your power absorbed by air resistance.

Weather Overview

Our Virtual Athlete has now collected data at the correct speed. So now the data will reflect the correct time and locations for our weather data. Let’s take a look under the Weather Overview.

The above numbers are an overview of the data collected from around the course. It is forecast to be a chilly ride with strong 19.5mph average wind speed, gusting up to 29.5mph. Some rain may be present.

The headline from the forecast has to be the 20mph plus wind, so our next stop is to see where that wind will be on the course. We head to the Course Navigator.

Finding the Headwinds

First thing we note is that there are no significant climbs listed. However there are Headwinds.

Two headwinds are brought to our attention, each around 9-10 minutes in length. The first starts 5 minutes into the ride, then the second almost 38 minutes in. We also note the additional 8km/h air speed, this is quite significant. Why 8km/h. We calculate this additional air speed from the prevailing wind angle, wind speed and wind shear, which is the slowing of the wind close to the ground.

To see each headwind we simply click the headwind we are interest in. This highlights the headwind on the course so we can visualise where to expect the wind to start and finish. This also creates metric summaries for the selected portion of the ride.

First Headwind 5 minutes from the start, lasting just under 9 minutes.

How to use this data

Why do we need this information? By understanding how the headwinds will affect our performance, we can create an effective mental strategy.

What usually comes into your mind when racing through a headwind?

I’ll tell you what comes into mine.

Sometimes, I can be defiant, “I’m not going fast enough”, “I need to push harder”.

Then there is, “this sucks”, “I’m having a bad race” and “today’s not my day, I don’t have the legs”.

Non of these thoughts keep us in a calm high performance mindset and are likely to sabotage a race performance. To combat these thoughts we need facts as our weapons. This is where our analysis goes next.

By being mindful during a race we can discover what information we need to have. This is personal to you. However, I will outline from my experience what helps me.

  • When and where to expect the headwind to start.
    Use the map and the Course Navigator to ensure we know the start position.
  • Know what the affects of the headwind will be
    • Check the Average Speed Graph. How much does the speed rise all fall during the headwind. This helps with any thoughts around not going fast enough.
    • View the Feels Like Elevation chart to visualise how the headwind relates to gradient. You may find it helpful to imagine this theoretical hill you are climbing. Imagine the summit to be where you know the headwind finishes.
  • Know where and when the headwind will finish
Rolling Average Speed. The Black line indicates the overal ride’s average speed evolution. The orange is the rolling average for the highlighted section.
Feels Like Elevation Profile. The grey section is the actual gradient. The red section and coloured line depicts the Feels Like elevation gain due to the wind.
The Feels Like Summary for this headwind. It will have an average gradient feel of almost 1%.

We repeat the above for each of the significant headwinds. The crucial part of this planning phase, what we call the descriptive phase, is to minimise the unknowns. I think of it this way, if we were tennis players we would expect to know what court surface we would be playing on. The weather poses as much of the race day challenge as the distance and terrain.

In our next post we plan the optimum power strategy.

Discover the truth, was it a fast day or not? Revealing post race analysis.

Discovering how your weather compared to others in the top 10 of a Segment, reveals the truth about your effort.

It was my first time out on the JC19 course held by Weaver Valley. It’s a challenging course, mostly due to the Cheshire pot holes putting the word ‘trial’ in ‘time trial’. The result landed me a top 5 on the course’s Strava Segment. That was a suprise! I didn’t feel it had gone paticularly well. So my question this evening is, were my conditions this evening better than the rest of the top 10? Were my efforts flattered by the time trial course’s weather conditions?

Screenshot 2021-06-16 224029
The Weaver Valley 10

One of the first features of myWindsock was to compare segment weather. The technology has come along way from simply stating wind speed and direction. wImpact% now shows the percentage of energy required to match the conditions of a windless day. So a wImpact% of 5% simply states that you would require an additional 5% more power to achieve the same time on a weather neutral day. [Learn more about Weather Impact]

So how about tonight’s effort that landed me a top 5 on the Leaderboard. Did I have a lower wImpact% than the rest? meaning my conditions were better. Time to checkout the Leaderboard Weather [Find out here how to do this Leaderboard Weather].

Screenshot 2021-06-16 215506

Well a weather impact of wImpact% of 0.8% is very good and as we can see it’s the best conditons of any in the top 5. So I think I can say I chose a pretty good day to go along to Weaver Valley Club 10 to try out the course. Next time out I think I’ll be a little more settled on the bike. My CdA measured 0.010 greater than my most recent events [Find your Ride’s CdA] and my power was a bit low. So it’ll be good to go back and have another trip around the Weaver Valley 10 mile.

Am I getting back my aero? : Post race analysis

In tonight’s race I was hoping to move another step forward with my aerodynamics. In my race plan, Crosswindy JC/27, I was predicted a 21:14. However a complete stop a mile into the race and I still finished with a 21:12, let’s find out why!


At least my stop was early in the time trial, so I can cut this out and get some decent aero data. I did this by creating a new Interval [learn how to create intervals]. This allows me to isolate that part of the ride and ensure my CdA analysis is not including any of the braking or the strained and overgeared return to race speed.

Screenshot 2021-06-08 234707

Am I getting back my aero…

From the start of this season I’ve been struggling with getting my head comfortably low. So I’ve been making some methodical alterations to my setup. Changing just one thing at a time. First of all I swapped my Aerohead to a pointy Giro Advantage helmet. I did this as I felt the helmet’s tail may be the best band aid while I figure out why I can’t get my head below my shoulders. There was a small aero improvement with the Advantage helmet.

I then looked at why I couldn’t tuck my head like I have been able to in previous years. At first I put this down to decreased flexibiity during the off season. I eventually decided this could be due to repositioning the saddle a little more reawards. I did this as I was having issues leveling the saddle. In training I didn’t feel much difference from the change. In racing however I think it could have been a tipping point.

I’ve been using myWindsock CdA analysis of my time trials to track all my changes and the results are measurable. Having raced with my saddle forward by 1.5cm in the Giro Advantage pointy helmet I thought it best to see if it is still the correct choice. [Learn how to measure your CdA]


Success! The more forward position is further improved by returning to my Aerohead helmet.

Sprint finish

In my race planning I wanted to know whether it was better to be out of the saddle at the finish. I decided, from my analysis, the extra power cancelled out the aero penalty. So I jumped on the pedals over the small hill to the finish. It just felt right at the time.

Was it a quick night?

Overall the wImpact% was 1.3% which is very good. In past events on this course the wImpact% has been as high as 7.2% [learn more about wImpact%]. The crosswind added an additional 4 metres of ‘Feels Like’ elevation gain which again isn’t too bad when compared to the additional 18 metres last time at this course [learn more about Feels Like Elevation].

You can analyse all of your time trials or training ride with myWindsock, find out how to get started.

Crosswindy JC/27 : Club Time Trial Prep

Before our Tuesday evening club 10 I always look up our time trial’s forecast. WIth some experimentation there may be some extra speed available. At the very least knowing what to expect when out on the road is always useful. It’s super easy to do, you can find yours on the UK Time Trials Club Events page. This is where we have listed all the UK’s evening club time trials ready with forecasts.

This week’s forecast

The feature for this week’s club 10, on our JC/27 course is a moderate crosswind. To get the best data for the course I need to update my Virtual Rider with my latest performance data. To do this, I will use the Suggest Power Settings button and Select Best Effort [Learn more about Suggest Power Settings].

From my last time trial (Post race analysis: M&DLCA J2/3) I discovered my CdA has improved to 0.202 so I’ve entered that in the Aerodynamics of my Virtual Rider [Learn more about Virtual Rider Settings].

This gives my Virtual Athlete a time of 21:14. Whilst the time is interesting to have as a goal for the race, it is more about simulating the race for better data insight.

How will the ride feel?

The first graph too look at is the ‘Feels Like’ Elevation Profile chart. This is how the Wind + Gradient combined will feel. [Learn more about Feels Like Elevation].

Screenshot 2021-06-07 173336
A crosswind will often cause Feels Like Elevation to increase across the route, as in it’ll feel harder than a windless day. This is because air moving across you, even if it is not directly head on, still increases the air flow over you and resistance. So this is the case tomorrow, the day will Feel a little headwindy each way. The good thing is that the angle and speed of the wind for the time trial creates just a small increase in Feels Like Elevation across the ride.

Splitting Out from Back

I want to see how a 10 Watt difference between the Out and Back will change the Virtual Athlete’s time. To do this I create an Interval for both the Out and Back portions of the ride [see how to Create Intervals].

Screenshot 2021-06-07 195153

Next I customise the Out interval with a 5 Watt increase and reduce the Back interval by 5 Watts. Now let’s see how the reversing the power output to higher Back than Out, changes the time prediction. There is just 3 seconds difference between the two stratgies, not a significant change. However I will ensure I am well warmed up so that I have my top end power ready from the start.

One last experiment…

I’m always tempted to sprint out the saddle in the final minute of this course. It’s up hill and begs me each time to leap out of the saddle. But the speeds are high, still averaging over 25mph. There is however a 50 watt difference between my out of saddle finish and my seated sprint for the line.

So let’s do a little bit of modelling. I’ve entered my aero finish params as  below.

Screenshot 2021-06-07 222557
But now I need to modify this Interval for an out of the saddle effort. But was is my out of saddle CdA. Luckily I did succomb to the urge to leave my aero position in a previous TT. So I have a Live CdA line to give me some guidance. This puts me at around 0.280. Not too bad but I am still leaned forward and attempting to maintain some aeroness.

Screenshot 2021-06-07 223121
Highlighted finish Live CdA

So let’s put those numbers in 480 Watts with a CdA of 0.280. The result…

Screenshot 2021-06-07 223818Interestingly the 50 extra Watts merely compensates for the loss of aero. So tomorrow I’ll just go with what feels natural, knowing there’s nothing to be gained or lost there on this occasion.

Out of curriosity let’s move the forecast forward to later in the week to see what a 10mph headwind rather than the crosswind would do to the same experiment. This time a slightly different result with a 1.2 second benefit to staying in the less powerful but more aerodynamic position.

Last change delta chart shows the time lost.
Last change delta chart shows the time lost.

How will my average speed develop during the ride?

The predicted time indicates an average speed of 46kmh. Now if I went straight from the start expecting to see that number on my bike computer I’d be burying myself pretty deep. This is why studying the Rolling Average Speed Graph is so useful. We want to know how we are doing against the plan. I usually check at the very least my expected average by the turn.  [Learn more about the Rolling Average Speed graph]

Screenshot 2021-06-07 180159
There isn’t a significant drop from the turn to the finish if all goes to plan, just 0.5kmh. So fingers crossed it’s a case of get to the turn an hold on.

To start analysing your club’s evening time trial, find it on the UK Time Trials Club Events page.

Post race analysis: M&DLCA J2/3

Today’s race was the M&DLCA Invitational. The weather can be summed up simply as HOT! This did mean however the air density would be at least a bit lower than the cooler evening club time trials I’ve been racing. The J2/3 is not known to be a quick course, with the finish 14 metres higher than the start. However, with a South Westerly wind and an Easterly finish, just as we had today, it can offset some of the positive elevation gain.

Screenshot 2021-06-05 184259


Aero Check, what was my CdA?

As usual post race, the first thing I look at is my CdA. I left my Garmin running from the start of my warm up, which was actually mostly trying to keep cool, so I need to select the race from the Activity Navigator [Learn how to use the Activity Navigator].

Screenshot 2021-06-05 180207

Once I’ve selected my race lap or segment, my summary stats including CdA are recalculated. But the average CdA number can sometimes not give the full picture so it’s always worth viewing the CdA graph. [Learn more about finding a race CdA]

Screenshot 2021-06-05 181544

As you can see, highlited line has a small step down. This is usual with an out and back course as the loop that controls the CdA line starts reading opposite on the road to where the ride finishes to complete the loop. So we ignore that first bit of the line. The line reveals I had an average CdA of 0.202.

Since starting back racing my CdA has been much higher hovering around 0.215-0.220. So I am happy to see it going in the right direction with a small saddle tweak and a helmet change.

‘Feels Like’ Elevation for Time Trialists

‘Feels like’ Elevation allows you to mentally prepare for the event you have coming up. A huge part of racing is being prepared and knowing the course you are going to be riding.

With this graph and metric you will get a perspective on the effect the wind will have. This will give you a better and clearer image on how to pace yourself during a race so you don’t burn yourself out. Our graph allows you to visualise the wind, like you would the summit of a hill. Have a look at this event The S6/10 Tri-Logic Event time trial.


This course is up hill on the way out to the turn and downhill on the return. However with the added tailwind on the up hill and headwind on the downhill, on this particular day, the course would feel flipped. The uphill with the assisted tailwind would require less effort and power and would actually feel like you were going downhill.

The headwind is very harsh and strong on this particular day and would make the downhill would ‘Feel Like’ an uphill effort. Find out more about ‘Feels Like’ Elevation graph and metrics.

We have all the UK Time Trials ready for forecasting each week. Discover the ‘Feels Like’ elevation for your next race in our Time Trial Events section.

Extracting CdA from a Time Trial

Discover your CdA, how aerodynamic you are, from past races. myWindsock can analyse all of your Strava Activities, Segment Efforts or uploaded TCX file from your power meter data. To use the features described you will require Premium membership and power meter, learn more about Premium.

IMPORTANT: Please ensure you disable Auto Pause on your GPS device when field testing.

What your CdA is and why it’s important

Knowing your CdA is useful to help you improve and squeeze out as much speed from your power. In most cases the most important determinant of performance in time trials is not Watts/Kg it is Watts/CdA. Here are a few ways you can use this number to improve your future time trial performances.

  • Improve your position – small changes to your position can make large changes to your CdA. Make purposeful changes and record how your CdA changes for better or worse.
  • A measurement of position discipline – when the adrenaline is pumping and you’re cranking the pedals as hard as possible it is easy to loose focus on position. Post race you can discover how disciplined you were at maintaining your position during the race. It is another performance measurement very much like your wattage.
  • A more accurate time prediction  – Entering a measured CdA into the Performance profile for your next race will dramatically improve the time prediction myWindsock generates. This means charts such as Rolling Average Speed will be of greater accuracy for your next race.

Short video tutorial

This video shows how to extract the CdA of a the time trial from the ride file or Strava Activity and how to ensure your CdA is comparable to other time trial CdA measurements. Most of this is covered in the video however below the video I have included some further explanation and tips.

Loading up your time trial

To analyse your time trial there are two methods of upload to myWindsock.

  • Through your connected Strava account, simply click on the Activity from the Strava Connect menu.
  • Or from the course Strava Segment myWindsock forecast go to > Leaderboard Weather > My Efforts and select the effort.  This requires power data to be included in your Strava upload.
  • If you prefer to keep your ride data private you can upload directly to myWindsock from the homepage using the ‘ GPX/TCX’ button.

Creating an Aero Test profile [Optional]

This is a recommendation and not required, but will ensure your CdA is not affected by changes to your Profile settings. It is easy to forget the settings previously used for Weight, Rolling Resistance and Drivetrain Loss when calculating previous race CdAs. To keep it simple it is recommended to keep a profile for just CdA calculations.

This assumes that race to race you haven’t changed these actual values and they remain static in the real world. If you have altered tyres, gained/lost weight, changed the location of your power meter or the course has a significantly different road surfice, you may need to factor these changes in the CdA calculation.

Viewing the CdA of the Time Trial

The average CdA for your ride may include your warm up and cool down CdA. To extract the the time trial CdA you will need to access the ‘CdA Profile’ chart. Locate the line in the chart that represents your time trial. If your activity includes wam up and cool down your time trial is likely to look like the below. The point to point CdA of an out and back course is usually easy to spot.

The CdA for your time trial
The CdA for your time trial

“I used my brakes, is that a problem?”

Braking will affect CdA calculations, however myWindsock can detect when you brake and remove these moments of braking from your CdA calculation. View the chart ‘Detected Braking Points’, this chart shows where on you ride you braked. Using this information we can remove the brake elements from your CdA calculation. This dramatically improves the accuracy of your CdA calculation.

Detected Braking Points in an Out and Back time trial.
Detected Braking Points in an Out and Back time trial.

My CdA line has a step at the turn

The best CdA is calculated from a route in which you pass the same point of road twice. This can either be in the same direction ‘A loop’ or in opposite direction ‘out and back’. If your time trial course is slightly longer in one direction, so the start is up the road from the finish, this bit will not be as accurate and is probably shown on a different line. This uses elevation information rather than the more accurate loop. Look to the line that covers most of the time trial from two identical points on the course.

If at ‘the turn’ you have a different CdA experiment with increasing the Minimum Loop Distance. This will ensure a loop detection for more of your time trial.

Increasing minimum detectable loop will remove step for better CdA calculation
Increasing minimum detectable loop will remove step for better CdA calculation

Go to > Settings > Aero Firstly increase the Minimum Loop Distance to a bigger distance but less than the distance of the two points on the course that you cover twice in the time trial. If this doesn’t resolve a better CdA line reduce the Loop Tolerance by a point.

A quick note on Yaw angles

A difference in wind direction and wind speed can produce a different CdA calculation. The greater the wind speed difference the larger the difference  of CdA will be for the same position. Your position’s CdA will be better or worse for various Yaw ranges.

Bike speed, wind speed and it's direction relative to the bike alters the yaw angles and affectiveness of your aerodynamics.
Bike speed, wind speed and it’s direction relative to the bike alters the yaw angles and effectiveness of your aerodynamics.

Yaw is determined by your speed and the wind speed and direction. The best description I’ve heard for explaining yaw is to think of the angle that a balloon held on a string would make to the bike if you were to hold it whilst moving. In a crosswind as you increase your speed the angle of the string to the bike reduces.

So in extraordinary weather you may expect to see a very different calculation of CdA. It is therefore best to discount these days.

To use the features described you will require Premium membership and a power meter, learn more about Premium.