Riders of the Wind

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A headwind need not sabotage your ride if you know how to handle it By Rob Kemp. Riding into a headwind can be a demoralising experience — it can feel like riding uphill when blustery conditions strike — but there are ways to minimise the effects of cycling in the wind or, indeed, make the most of it. Check the forecast before you ride and plan accordingly. If the wind is due to drop and you have the option to delay your ride, brew another coffee and head out later in the day.

Choose a route that accounts for the wind. The weather can change quickly in windy conditions, when squally showers can seemingly appear out of nowhere. Dress appropriately and take a jacket if rain is a possibility. Otherwise, lightweight layers are key, especially because blustery conditions are common in the changeable seasons of spring and autumn.

Riding against the wind: a review of competition cycling aerodynamics

A gilet will help keep the wind off your chest without overheating and provide some rain protection if you unexpectedly get caught out. As your route twists and turns or the wind changes direction, you need to keep your wits about you. Maintain your focus on the road and be aware of crosswinds as you change direction or the protection afforded by your surroundings disappears, especially on winding routes.

Taking shelter within your group can counter this. While it may seem counter-intuitive to ditch your aero wheels, deep-section rims are particularly susceptible to crosswinds and strong gusts. While following our tips can help you get the better of blowy conditions, sometimes cycling in the wind is an unavoidably dispiriting experience — or just plain dangerous. Home Features How to ride into a headwind 10 tips to battle blustery conditions.

Various commercially available wheel designs tested for aerodynamic properties by Tew and Sayers [ 73 ], including a traditional spoke, b spoke, c spoke, d quad-blade-spoke, e tri-blade-spoke, and f disc wheel designs. Over the last 15 years, a number of studies have looked at cycling wheels under yawed flow conditions. These studies have looked at spoked wheels with various rim profiles, as well as unconventional spoked wheels and disc wheels.

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A substantial body of work on the specifics of wheels, however, remains either proprietary or has been published as unreviewed white papers or articles. Nonetheless, there have been a number of studies conducted both in wind tunnels and, more recently, using CFD. Tew and Sayers [ 73 ] performed a wind tunnel study, examining six different wheels: a conventional spoked wheel, a low-spoke count wheel, a bladed spoke wheel, two wheels with a small number three or four of structural bladed carbon spokes, and a disc wheel, which are depicted in Fig.

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With the exception of the conventional spoked wheel, all of the remaining spoked wheels featured deep rim profiles, nominally intended to reduce the wake behind the rim and, thus, the drag of the wheel. A critical characteristic of the deep section wheels that the authors observed was a nearly flat drag coefficient across the yaw angles and wind speeds.

The disc, however, showed a sudden increase in the drag coefficient at intermediate yaw angles, particularly at low speeds. The critical angle increases with speed, and the sudden nature of this rise suggests a boundary layer separation effect. In recent years, a significant amount of work has been done using CFD. Godo et al. These studies simulated the flow around the wheel in isolation of the bicycle—rider system.

Transient simulations were also performed that simulated the rotation of the wheels at an equivalent ground speed of 20 and 30 mph. Both of these studies by Godo et al. The authors noted the similar discrepancies to those that have been noted above, with the drag coefficient at zero yaw theoretically the cleanest and simplest case varying by a factor of two across many of the different experimental studies. This highlights the magnitude of uncertainty associated with aerodynamic forces and moments acting on wheels as a result of variability in test fixtures, measurement apparatuses, and wind tunnel conditions.

As such, while the results by Godo et al. For the disc wheel, the drag dropped over the entire range of yaw angles; however, the study was unable to replicate a proprietary result by Zipp, which showed that the drag coefficient dropped below zero over a small range, supposedly producing a net propulsive force. A time-resolved analysis of the wheels showed the formation of several recirculation zones at the upper and lower sections of the wheel.

These recirculation zones were seen to be the largest on the disc and trispoke compared to the conventionally spoked wheels. Mechanistically, it seems clear that the formation of these flow structures and their periodic disruption by the spokes play a critical role in the production of drag; however, the analyses have not yet gone into sufficient depth to understand their role. The studies did explore other aerodynamic forces and moments experienced by the wheels, including side force, vertical force, and turning moments, were also examined; however, those are omitted here, as their role in performance is less clear.

As the effects of aerodynamic drag on performance have become more widely acknowledged, helmets initially designed to meet the safety standards set forth in various jurisdictions while providing substantial ventilation for thermal comfort have given rise to specially designed time-trial helmets. Modern time-trial helmets are designed for speed over comfort and, more recently, has led to the development of hybrid helmets that attempt to reduce drag without compromising ventilation and mobility.

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  4. Blair and Sidelko [ 63 ] conducted an experimental investigation of 14 time-trial helmets accounting for helmets that came with a detachable visor using a mannequin that represented the upper body of a cyclist at several different yaw angles [ 75 ]. In addition, the helmets were mounted in three positions, based on the inclination of the leading edge. Extremely high inclination angles resulted in high drag across the board; however, no mechanistic correlation between helmet design and performance was identified.

    System Requirements

    The study further showed that while a visor has a statistically significant effect, reducing the drag of the helmet, forward-facing vents do not tend to result in a drag penalty. Brownlie et al. Furthermore, this study showed that while, in general, a time-trial helmet has superior aerodynamics to a more conventional helmet, a time-trial helmet also produces less drag than a bare mannequin head. The study experimentally showed the time-averaged velocity deficit behind these three helmets all of which produced similar total drag ; however, in the absence of a comparison to other helmets with substantially different characteristics, the authors were not able to present a mechanistic story of the drag characteristics.

    1. The slower you are, the more important aero is.

    The particular geometry of any particular helmet, as well as the geometry of the riders head and upper back, limits the ability to make generalisations about helmet design. Careful placement of vents allows for some measure of cooling in time-trial helmets without significantly compromising their performance.

    The main flow regimes are labelled for the smoothest cylinder which is highlighted in red. Schematics demonstrate the relative difference in the wake width between a subcritical regime and the point at which drag crisis is said to have occurred. The actual flow topology of each regime is much richer than what has been depicted here. The arms and legs exhibit transitional type behaviour for Re relevant to cycling. The motion of the legs throughout the pedal stroke combined with turbulence generated from upstream components of the bicycle and body reduce the effectiveness of textured fabrics to induce drag crisis on any part of the legs.

    In areas of attached flow, smooth fabrics should be used to target reducing skin friction. In areas of completely separated flow, such as the lower back, surface texture has a negligible effect on aerodynamic drag and any appropriate fabric may be utilised. Reductions in aerodynamic resistance can be accomplished through tight fitting apparel with few wrinkles and aligning seams with the airflow. Critical to understanding the aerodynamic performance of skin suits is the process by which turbulence can be induced at lower Reynolds numbers.

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    As the human body has components that resemble cylindrical cross-sections, modern skin suit development has its foundations deeply rooted in early work into the laminar—turbulent transition process of flows around, and the aerodynamic drag acting on, circular cylinders. It is noted in Sect. As with cylindrical geometries, the aerodynamic drag acting on body components particularly the arms and legs also displays similar dependence on Re and surface texture.

    When optimising skin suit design, the choice of fabric will depend on the size of the athlete wearing the suit, cycling speed, air properties, and UCI regulations governing allowable fabrics. Modelling the body as a composite of simple geometries in isolation of one another in a pure cross flow has a number of limitations when attempting to minimise aerodynamic drag.

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    This simplification does not take into account flow interactions between limbs and body parts and the influence the motion of the legs has on the flow field around the body. In addition to this, the relative orientation of limbs, the wind angle, and freestream turbulence levels have all been shown to be the relevant factors when reducing aerodynamic drag [ 84 , 85 ].

    The influence of freestream turbulence intensity on the critical Re on two-dimensional cylinders is shown in Fig. Note: Intensity is only one characteristic of turbulence that is of importance to bluff body flows. The geometric characteristics and relevant length scales of turbulence are also important to transition and mixing processes.

    The defining characteristics of turbulence experienced on the road and track are currently not well understood. As skin suit aerodynamics is sensitive to the wind environment, the size, position, and shape of the rider, there is no one skin suit that will have texture optimised for all cycling conditions, athletes, and cycling positions.