18th August 2021. We don’t think it’s hyperbole to say that day will go down in pursuiting history. Just 3 years ago the world record stood at 4:10.534. Set by Jack Bobridge on a stormy day in Australia riding against Rohan Dennis, where Bobridge achieved a near perfectly timed catch. Many thought the record would stand for many years to come, but those people didn’t predict the pursuit battle that has ensued since Lambie took a big chunk off Bobridge’s record in August 2018.
The individual pursuit has seen a huge resurgence in popularity as the best riders in the world see it as a pure measure of their athletic prowess, without the pain and hardcore preparation demanded by the Hour. When pulling the individual pursuit apart, it becomes clear how it is a delicate balance of many aspects: aerobic & anaerobic power, aerodynamics; pacing; execution and much more. There are many combinations of attributes that can achieve the same performance, and Ashton has used this fact to great effect. He isn’t a World Tour road pro. He isn’t even an Olympic track cyclist. He’s an ambitious individual with a single goal in mind. Never underestimate the power of a steely focus and the will to hunt down every single watt of improvement.
Without an Olympic team pursuit to focus on and Paris 2024 sometime away, Ashton signaled to the world that he wanted to be the first man to break 4 minutes for a 4km individual pursuit. Aside of the performance challenge, it takes confidence and belief to say you are faster than anyone who has gone before you. You pick the day, the equipment, the strategy. There’s nowhere to hide. You carry the weight of your convictions to the startline. Don’t underestimate how much motivation can provide when your legs are screaming and the splits start to slip tenth by tenth.
On 18th August 2021 Ashton achieved the monumental goal of breaking the 4 minute barrier. It wasn’t without mishaps or mistakes. The day before Ashton felt that was the day. Taking to the boards early he missed the 4 minute mark by 2.4 seconds. The start gate had failed three times, holding him in the gate, wasting previous physical and mental energy. That was hard to take. How do you find 2.5 seconds in 24 hours!? Willed on by those close to him he dug deep to return the following day, and the rest is history.
Unsurprisingly, everyone is interested in the details. How did he achieve it? What was his pacing strategy? His gearing? How did altitude impact his performance? And what about riding against another competitor? Don’t you worry, WattShop has you covered.
Firstly, let’s take a look at his pacing strategy. To ride 4:00.0, Ashton targeted an opening lap of 21.2 seconds, meaning he had to average 14.587 seconds (61.699km/h) for the remaining 15 laps. Riding a 64x15 gear, this would require a cadence of 114.4revs/min once up to speed. Ashton will be the first to say his pacing in previous competitions hasn’t been optimal, but he pulled his A game out of the bag for this ride. Excluding the first and last two laps, he averaged 14.534 seconds per lap (61.924km/h), with his fastest lap being 14.457 (62.253km/h) and slowest 14.608 (61.610km/h). This is genuinely one of the best paced rides we’ve ever seen, not just from Ashton but from anyone.
To see how his pacing varied in comparison to his target lap splits, we’ve presented two graphs below. The first showing how much time he gained or lost each half lap, and the second showing how far behind or ahead of schedule he was as the ride progressed. Effectively Lambie was quickly on to pace and was taking around 0.02-0.05 seconds out of the schedule each lap until 500m to go. At this point the effort started to catch up and the times slipped, slowing Ashton from 61.8kph to just above 60kph for his final half lap. This is actually an effective way to pace an effort as you reduce the kinetic energy stored within your mass at the finish line, utilising that stored energy to overcome parasitic losses such as aerodynamic drag and rolling resistance. In power terms, this means as Ashton’s input power reduced, his stored kinetic energy gave 18w of “assistance”.
There are many numbers being flung around about the power numbers Ashton sustained for his record breaking effort. In true terms we will never actually know! Ashton did not ride with a powermeter, however we do have many power files from training and other competitions so can make some calculations as to how he broke the 4 minute barrier.
At sea level, Ashton’s personal best was 4:03.640 at the 2020 World Championships in Berlin. He also didn’t ride to power there, but based on the atmospherics at this competition we can calculate a Watts/CdA ratio required to achieve this performance and then utilise training power data to estimate his CdA for that race. This value comes out at 3200W/m^2, so for a 510w power input, his CdA for that competition will be 0.159m^2. We’ll call this his sea level competition CdA.
When you go to altitude a number of things happen that both positively and negatively impact upon performance. The first thing that most cyclists know is that altitude reduces air density. This happens because the barometric pressure reduces as altitude increases. Air density linearly impacts on aerodynamic drag power, so a 10% lower air density means 10% less aerodynamic drag power. This is great for a cyclist as aerodynamic drag power is the biggest power loss of the entire system, around 90% of total drag for Ashton's IP. At the 2020 World Championships the air density was 1.155kg/m^3. At Aguascalientes during Ashton’s ride the air density was 0.932kg/m^3. A very welcome drag reduction at 62kph of around 70 Watts.
However, this isn’t the entire story. The reduction in barometric pressure also reduces the partial pressure of oxygen, meaning aerobic power reduces significantly. Ashton is fairly well acclimatised from his time spent at the USAC altitude training facility in Colorado Springs but power losses at altitude vary significantly between athletes. Based upon Basset et al 1999 study in to aerobic power drop off at altitude, we can expect to see a 7.5% reduction in aerobic power at Aguascaliantes for acclimitised athletes, and 11.5% for non-acclimtised. Based on our experiences with elite athletes, these aerobic power drop offs can vary from 2 to 20% in practice. If we take the 7.5% drop off, this equates to around a 27 Watt loss of power.
The next effect isn’t too well documented but is very meaningful. CdA is not a stable constant across altitude. It's something we investigated heavily alongside HUUB & Vorteq in our involvement with the HUUB Wattbike altitude project. Without going in to the deep science, riders get draggier at altitude through no fault of their own. The effect is very rider specific, however we can make some good calculations based on tests we’ve previously conducted. Going from sea level to Aguascalinates would have increased his CdA from 0.159m^2 to around 0.1655m^2, a 4% increase or around 15 Watts more aerodynamic drag.
We need to also account for the impact riding solo on a track has when compared to a ride in competition where a well-timed catch can save significant time due to the reduction in aerodynamic drag. This effect is variable depending on the size of the rider you are catching, the speed difference and how long you spend in the draft, however from our own studies on the velodrome a typical catch is worth around 0.003m^2 CdA reduction over a 4km individual pursuit, or 7 Watts in power terms.
When all of this is accounted for and factored in to our inhouse performance model, the outcome is that Ashton will have needed a Watts/CdA ratio of 2760W/m^2. With his altitude and solo rider adjusted CdA of 0.1685m^2, he will have averaged 465w over the entire 3:59.930. This would be a lap one average of 821w and then a “cruising” power of 431w for laps 2 to 16. There are probably plenty of you out there thinking “that’s not that much, I could do that!”. There are many compounding factors at play here: position, altitude and track riding to name but a few. If it was so easy, everyone would do it, right? But only one person has shown it to be possible and their name will forever be written in the history books; Ashton Lambie.
Hi shopforwatts.co.uk webmaster, Your posts are always well-supported by facts and figures.
what a great evolution of the material of the bike
aesthetics and aerodynamics …. I love this cockpit
Concerning the impact of altitude and solo riding, does it really impact CdA or are all this effects just asigned to CdA for convenience?
Great breakdown. Can you elaborate on how riders get draggier at altitude?
Hey, I was at Aguascalientes velodrome! amazzing performance from Ashton and this is a fantastic article. Do u have Ashton’s lap partials?