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Test 3: tyre choice

The Parcours wheel range features an internal rim profile that is fully tubeless-ready.  With an internal width of 19-20mm (depending on model), it is also the perfect match for a wider tyre – this allows riders to choose to run a lower tyre pressure, giving a smoother, more comfortable ride whilst also reducing rolling resistance.

As part of our wind tunnel testing, we wanted to quantify the aerodynamic impact of choosing to run a wider tyre.  In our previous testing, the main hurdle was the point at which a wider tyre caused the airflow around the wheel to stall, massively increasing the overall drag.

We tested a number of the most popular tyre choices over two test sessions (one in 2018, the other in late 2019).

Drag chart - tyre selection

Learn more about how to interpret a drag chart here

The chart above shows a combination of our existing data from our 2018 test results with the results from the updated tyre selection in 2019.  Where a tyre has been updated by the manufacturer since our 2018 test, we have excluded the slower version (in all cases this was the 2018 model).

An interesting observation was that older model tyres (tested in 2018) would inflate to 10-12% wider than their stated width, when fitted to our Chrono front wheel (internal rim width 20mm). However, the newer 2019 tyres would only increase by < 5% versus stated width.  Given the reduction in frontal area, this likely had an impact on aerodynamic performance.

Prior testing also showed that, when a weighted average taken across the yaw angles tested, there is no material difference between a 23mm and 25mm tyre (both wheel depths tested were <2s/40km).  With maximum rim widths across the range varying from 27mm to 29mm, this would fit with the often-quoted Rule of 105%.  This states that the rim must be at least 105% the width of the tyre in order to recapture airflow from the tyre and control or smooth it. 

An additional point to note is that, across the entire wheel range, the yaw angle at which the airflow begins to stall shifted from the 7.5 to 10 degree range to greater than 12.5 degrees.  This indicates that the updated rim profile performs better in a stronger crosswind.  It was also interesting to note that the 25mm tyre delayed the stall point on both rim depths.

More analysis, including rolling resistance can be found on the blog.

All tyres were tested on the Chrono (77mm) front wheel.