Cold comfort re-defined for high-intensity winter riding

High-intensity winter efforts present a unique thermoregulatory challenge for competitive cyclists; I cannot think of another sport, aside from Biathlon, where athletes face such extreme thermal fluctuations. Riders produce significant metabolic heat during sprints and climbs, only to lose a great deal of warmth through convection on descents, where high speed greatly increases the impact of wind chill. Additionally, sweat unable to evaporate due to poor clothing choices will cool the body further, exacerbating the issue.

It's a familiar problem for any performance rider, that horrible ‘out of the oven - into the freezer, out of the freezer - into the oven’ cycle that drains both energy and mental resilience. The traditional solution has been to ‘layer up’ with multiple items of clothing, which has its advantages but isn’t as effective for cycling as it is for some other winter sports. Wearing numerous layers adds bulk, increases aerodynamic drag, and – crucially for competitive cyclists – riding at high speeds makes it difficult to quickly remove, stow, and put garments back on as conditions change.

Fortunately, recent fabric innovation and advanced garment engineering might hold the answer. Assos has been refining its cutting-edge Johdah winter jacket for seven years, transforming the traditional layering system into a highly contemporary solution that’s more versatile, more discreet, and significantly more performance driven. The result is the Assos Equipe RS Johdah Ultraz Winter Jacket S11, a low-volume softshell with a second-skin fit that can regulate body temperature during high-intensity rides in the worst conditions.

Constructed for competition

The Johdah S11 jacket delivers its unique cold-weather performance through a zoned, multi-textile design, where different proprietary fabrics are strategically positioned to balance wind protection, insulation, and breathability across the rider’s body. This system eliminates the need for excessive layering by regulating the microclimate directly at the skin.

Fit is fundamental to the Johdah S11; ideally, the jacket should contour to the body in an aerodynamic second-skin profile that reduces drag while ensuring its intricate pattern of technical panels is positioned accurately where needed. To achieve a race-ready fit, Assos’ R&D team employed the brand’s Advanced Ergonomic Pattern Design (AEPD11), which provides 360° compression and stability in a WorldTour-proven silhouette.

At the core of the jacket’s effective thermoregulation is Assos’ new Diamond Medium fabric, which combines a softshell membrane with a velvety backing. This proprietary material, which is deployed across the front panels and upper sleeves – the areas most exposed to high-speed wind chill – is engineered to be elastic, comfortable, protective, and breathable. Diamond Medium acts as a self-contained insulator and stormproof barrier, preventing convective heat loss that causes immediate chilling on descents. Complementing this is ZigZaggy, a highly elastic, three-layer softshell material used in the sleeves for stormproof protection and a snug, zero-pressure fit. Its plush lining is comfortable against the skin, while its elasticity ensures a full range of arm movement without compromising weather resistance.

Internally, Assos has incorporated an integrated core vest, or gilet, made from its new Lithium Medium insulating fabric, which boasts a grid construction that promotes high levels of breathability. The dual-layer design enables the rider to fully unzip the Diamond outer shell for instant ventilation during intense efforts, while maintaining essential warmth over the chest courtesy of the Lithium vest. Essentially, the vest, or intraBooster in Assos parlance, regulates temperature accurately without exposing the torso directly to cold air.

To prevent overheating during high-effort climbs and sprints, the Assos has taken a multifaceted approach. The jacket’s back panel, an area less exposed to wind but prone to sweat buildup, features Osmos Heavy, Assos' most insulating thermal fabric, which keeps warmth in while maximising breathability and moisture transfer. This is complemented by Assos’ signature feature – its unique valveTec Diffusor system, which places vents at the shoulders to direct cool air between the outer softshell and inner vest, preventing internal humidity from building up and avoiding the dreaded sweat-and-chill cycle.

A jacket invested in winter riding

The Johdah S11 is designed to be worn next to the skin, significantly reducing bulk, increasing mobility, and decreasing the rider’s frontal area. The race fit also eliminates that annoying sound of excess fabric flapping in the wind. Lighter than traditional layering systems, because the jacket comprises fewer separate items of clothing, it potentially offers good value despite its premium price tag.

Even so, it’s impossible to overlook the cost of this jacket; it’s such an investment that I suspect some competitive riders will prefer to tolerate a little discomfort. However, if performance truly matters to you, this could be a false economy – thermoregulation matters.

When you become too hot during a ride, your body will pump a significant volume of blood to the skin’s surface to promote cooling through convection and sweating – a process called vasodilation. Sadly, blood that should be solely dedicated to delivering oxygen and removing lactate from the working muscles is instead redirected to the skin. This decreases muscle efficiency and capacity, resulting in a noticeable decline in power output for the same perceived effort.

During the chilling phase, usually on descents, your body responds by doing the opposite – aggressively restricting blood flow to the skin and extremities, a process known as vasoconstriction. The problem here is that the muscles can cool down too quickly, losing not only power but also flexibility, which increases the risk of injury. If shivering occurs, it will burn through your glycogen stores, and the cold will also impair your fine motor skills, making it much harder to maintain optimal road handling.

Then there’s the mental and cognitive toll. Thermoregulatory stress impairs the mind, diverting mental energy away from maintaining focus and strategic thinking. Being either overheated or deeply chilled significantly increases the perception of effort for the same power output.

Everyone is different, and each winter riding situation varies, so it’s impossible to specify exactly how much poor thermoregulation might impair your performance. However, when considering the potential performance gains – whether marginal or significant – and the jacket's craftsmanship (supported by a two-year warranty), the cost of the Assos Johdah S11 begins to seem less like an indulgence and more like a purchase worth considering.

For a complete performance-focused winter clothing system, Assos has developed the Johdah Ultraz Winter Jacket S11 to work optimally with its Equipe RS Johdah Ultraz Winter Bib Tights S11 and Ultraz Winter Gloves P1. In particularly harsh, wet conditions, Assos recommends layering the jacket beneath a Schlosshund or Alleycat shell for total protection.