Bespoke Blog

Bioracer Virtual Wind Tunnel - A Case Study

Chris recently came for a new bike fit with us here at Bespoke Cycling, and has been riding his new Trek Speed Concept over the last few months. Primarily racing 10 and 25-mile time trials, as well as the occasional 50 mile, we had already dialled in the fit with Chris. Nonetheless, he was really keen to take his performance further and really maximise his performance. Therefore we arranged a Virtual Wind Tunnel session for Chris, below is a summary of the session.

As we've explained before (read the article here) the Virtual Wind Tunnel from Bioracer allows us to measure frontal area, and the hypothetical wattage it takes to maintain this position at a given speed.

Firstly, in order to quantify the change we'll make, we need to create a baseline position. Here we'll ask the cyclist to setup normally on the aero bars in their current cycling position.

Once we have set the baseline, the next step is to identify key areas we want to focus on making improvements. We could be pretty aggressive with Chris' position as he is rarely on the bike for longer than an hour- while comfort is still extremely important, we are giving equal thought to aerodynamic efficiency.

The first step was a little 'tune-up' on Chris' fit. He collected his new bike 3 months ago, so I made a couple of little tweaks including increasing the aerobar reach around 8mm. The aim here was to facilitate a more 'stretched out' position, which will decrease back angle slightly.

The reference/baseline position is represented on the picture by the yellow outline. You can see here not too much change from the increased cockpit length - on average this saved about 3-4 W at 40 kp/h. Time to move onto head position.

Okay now we're seeing improvements. Once again the yellow outline references the baseline position. This is Chris riding with coaching from me on head position. With this advice, he's saving around 15 W at 40 km/h.

Chris reported this position was slightly harder to maintain, therefore I advised he work on this in training and especially indoors on the turbo trainer. Muscles that are being called upon to stabilise this posture are just like any other muscle, they can be strengthened. Therefore this position will become easier to maintain as muscle strength and stability increase.

Certainly this is easier than training a threshold increase by 15 W!

Chris does find times when he's riding in the basebar, either on the ramp of a dual carriageway approaching a turn, or on hillier TT courses. I wanted to identify the threshold at which the aerodynamic advantage of riding in the aerobars is outweighed by the easier climbing position:

At 40 km/h it would 'cost' Chris around 40 W to ride in the base bar. Of course at this speed he'd always be in the aerobars.

When we drop the speed down to 25 km/h, it only 'costs' Chris 10 W to ride the aerobars. Therefore, we decided that Chris would keep an eye on his speed when climbing during a TT. If he sees <25 km/h on his Garmin, he knows that while it will cost him 10 w in aerodynamic drag, the easier climbing position outweighs this increase in drag. When he goes over 25 km/h, he can settle back into the aerobars as he's likely to be saving at least 15 w and therefore the aerodynamic drag has a larger impact on Chris' speed.

In summary, we were able to show Chris how training a lower head position can improve his aerodynamic efficiency, particularly at speeds over 25 km/h. At speeds below 25 kp/h, Chris would be better suited to remain in the basebar for an easier climbing position with only a small aerodynamic disadvantage.

If you'd like to benefit from aerodynamic testing at Bespoke Cycling, get in touch via the contact page, or email Head Fitter dan at dan@bespokecycling.com.