Meet our speakers: Tim Carew
How do you design a performance bicycle that can adapt to the shape of its rider? Tim Carew (Jesus 2020) is in pursuit of the answer. From Formula 1 to elite track cycling, Tim explains why embracing uncertainty is a key part of the design process.
Tim's Festival talk on the aerodynamic performance of the HB.T Olympic Track Bicycle, will explore his research which helped to develop the Team GB track bike for the Paris 2024 Olympic Games.
Tim is a part-time PhD student at the Engineering Design Centre in Cambridge. A former Formula 1 aerodynamicist, he's turned his attention to applied aerodynamics in track cycling. We spoke to him about his research...
How would you describe your work?
My work focuses on aerodynamic development for sports engineering applications. This means reducing resistance to motion and controlling aerodynamic forces to provide predictable and reliable performance. The aim is to characterise, control and optimise these forces against specific design requirements. While an aircraft designer might prioritise lift generation on take-off and drag reduction in cruise, a Formula 1 car designer will care less about reducing drag and maximise cornering performance through downforce generation. For a human-powered object, like a track bike, where the available power is lower and limited, it's different again. Despite sharing the same underlying physics, the operational requirements of aircraft, racing cars and bicycles dictate profoundly different aerodynamic design solutions, which I find fascinating.
What initially attracted you to this research?
I'm inspired by my industry experience. I can clearly recall sitting on night and weekend shifts in the Ferrari wind tunnel, waiting to see if the expectations from our aerodynamic simulations would be confirmed by scale model experiment. We would often get good agreement whenever the experiment precisely replicated the simulation conditions, however in ‘off design’ conditions (such as an unsimulated steering angle) the agreement was poor. It got me thinking that while the simulation tools were fit-for-purpose, our use of them really wasn’t. Huge amounts of time, money and effort were being spent on a design process that couldn’t deliver reliable aerodynamic performance across all of the car’s operating conditions. This shaped my research to investigate new methods of using aerodynamic simulation data, so that off-design performance could be characterised before any experimental testing takes place.
What have you taken from Formula 1 into the world of cycling?
Suprisingly little! Design requirements in Formula 1 are so different to track cycling that there isn’t a lot that's directly transferable, which is an interesting finding in itself. I did use my knowledge from motorsport to design, manufacture and mount a wake measurement system to the Olympic bike, which we successfully tested at the Manchester velodrome and was a first for British Cycling.
In many ways, motorsport has more directly influenced my approach to the PhD rather than the work itself. In Formula 1, the deadline for everything is ‘yesterday’, so after spending time in the sport it becomes second-nature to simply get things done. This has been especially useful for me as part-time student, helping to ensure that I deliver good progress in my PhD alongside a full-time academic post at The University of Manchester.
Testing on an Olympic bike at the Manchester velodrome.
What’s different about working on elite sport compared to motorsport?
In elite sport, the athlete is at the centre of the design process. While the driver is clearly a key element in motorsport design, enclosing them within the fixed geometry of a racing car gives motorsport designers much more engineering freedom than in track cycling. The personalisation of equipment is a key factor in sports engineering and an increasingly important factor in bicycle design. An elite cyclist is continually changing shape, not just as they pedal but also as they go through different training programmes in preparation for competition, meaning that the parameters of the design problem are also continually changing. A one-size-fits-all approach clearly won’t work in this scenario. My research asks: what if we design the bike not to be the most aerodynamic it can be, but the most robust it can be to changes in rider, rider shape and rider posture? My hope is this will ultimately help increase performance across the entire squad and not simply for a single rider or type of rider.
What are the biggest challenges in designing a track bicycle?
One of the main challenges is ensuring that the bike accommodates the rider, rather than asking the rider to compromise their position to fit the bike. From an engineering perspective, the bike must be lightweight to maximise acceleration, be stiff to ensure efficient power transfer and have a shape that provides aerodynamic efficiency. However, all of these factors must also simultaneously optimise the rider’s biomechanics and their ability to actually ride the bike. Lowering the handlebar, for example, will tilt the athlete forwards and reduce drag, but will also close the angle between the athlete’s back and thigh, reducing their power output. Designing a bike that optimises these trade-offs and still leaves room for setup changes is hugely challenging, especially when considering that the timeframe to design and produce an Olympic bicycle is much less than the four years between Games.
"My research asks what if we design the bike not to be the most aerodynamic it can be, but the most robust it can be to changes in rider, rider shape and rider posture?"
Left: Tim with the Tokyo 2020 Olympic bike at the Whittle Laboratory. Right: Presenting his work at Jesus College.
What did your research reveal that changed how Team GB approached bike design for Paris 2024?
My early research focused on how the flow field around the bike changes through the pedal cycle, which revealed interesting findings about flow direction in the region behind the rider’s legs. Given that highly turbulent flow is expected in this region, I looked at how flow direction varied as a function of pedal position and used this information to realign the bike geometry, leading to a more nuanced design and reducing overall drag. Though only a minor contribution, it was great to see the final components on track and being ridden to medal success.
What’s a small change that you’ve made that’s made the biggest difference?
My research sustains a conversation about the design conditions a track bicycle actually faces, given an increased understanding of the unsteady flow conditions around the rider and in the velodrome. While some of these uncertainties were already known, through scientific investigation we are increasingly able to quantify them so that uncertainty can be managed as part of the design process. I have seen a fundamental shift in the design approach taken by British Cycling since the start of my PhD, which has all resulted from our continued conversation.
How has Cambridge influenced how you think about solutions compared to your time in industry?
My work at Cambridge has fundamentally changed my mindset towards engineering design. By having the space to think deeply and originally on the nature of design, Cambridge has encouraged me to take a holistic view of design problems and elevated my thinking away from traditional methods or procedures.
If there’s one ‘takeaway’ you want to leave people with from your talk at the Alumni Festival, what would it be?
To understand that embracing uncertainty is a key and acceptable part of good design practice. By permitting a degree of tolerance within our definition of ‘acceptable’ performance, it is more likely that we'll deliver consistently good performance than if we aim for the ideal scenario.