The Grenchen weather gods shine on Ganna’s Hour Record

Live weather conditions from track centre and how they impact Ganna's Hour Record attempt.

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GRENCHEN, Switzerland (CT) – For all the marginal gains, new frames, and aero testing that go into each and every Hour Record attempt, ultimately, the weather can make or break even the best attempts. On the face of it, weather conditions may appear to have little impact on an indoor attempt, and while this is true of both wind and rain, air density is a critical factor in any speed-focused track event.

According to, air density is defined as the mass of air per unit volume. Increased density means decreased speed for the same rider power output. Lower air density means riders can travel faster for the same power. How much difference can this make? Well, experts have calculated Bradley Wiggins could have ridden as much as 500 m further had his attempt been scheduled for just four days earlier. Of course, Wiggins’ team had to nominate the date of his attempt weeks in advance, and with no idea how the weather conditions would be on their selected day.

The weather conditions in question are barometric pressure, temperature and humidity. Fast forward to today, Ganna’s team can somewhat influence air density by tweaking both temperature and humidity within the velodrome.

Temperature seems like the easy part of this equation. Warmer air means lower density, and the Tissot Velodrome in Grenchen has central heating, it is well-insulated and offers stable conditions. Furthermore, a large crowd could push up the temperature significantly and help drop the density. Humidity is also within their control up to a point, and again, more spectators mean more humans breathing, which in turn increases the humidity.

However, there is a tipping point, with high temperatures and humidity impairing the body’s natural thermal regulation. As we heard from the current record holder, Dan Bigham, on a recent episode of the Nerd Alert podcast, thermoregulation is one of the key factors in a successful Hour Record attempt. As temperature and humidity rise, the body’s natural evaporative cooling suffers and, in turn, drives up the athlete’s core temperature. Athlete performance significantly decreases if the core temperature increases too far.

With this in mind, the Ineos Grenadiers have limited access to the velodrome tonight. The team are even implementing a strict access plan, with doors closing an hour before the start and spectators asked to restrict their movements within the velodrome. This is to both let the air flow conditions within the velodrome settle (lock the doors) and control both temperature and humidity.

Barometric pressure is the one variable beyond the team’s control, and air density is directly linked to barometric pressure. Increased pressure equals increased density. While the performance teams are able to influence both temperature and humidity in an attempt to lower air density, the final distance of every Hour Record attempt, successful or otherwise, is at least in some part determined by the barometric pressure on the day.

So how is Ganna’s luck on the weather front? As we sit here with just an hour to go until the start, the conditions are looking good. Not great, but better than we were predicting even yesterday. We have measured the barometric pressure throughout today since arriving in Grenchen, and it’s lower than forecasted at 972.8 mb.

Right now, the conditions air density is 1.124kg/m³, and pressure is currently at 972.2mbar, with both temperature and humidity expected to rise from their current 26°C and 53% marks as the crowd makes its way in.

For comparison’s sake, the conditions for Dan Bigham’s record were more favourable at 27.2°C, 52% humidity, 967mb, for an air density of 1.115kg/m³. Bradley Wiggins on the other hand, managed 54.526 km despite soaring temperatures and humidity after the performance team was forced to ramp up the temperature and admit a capacity crowd, with air density said to be as high as 1.176kg/m3. The differences may seem small, and we can barely feel the difference ourselves, but the impact on performance is huge.

More details on what Ganna might achieve and how to watch the attempt can be found here.

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