Help: which tyres should I run?

This may be the #1 most-commonly asked question we receive.  And to be honest, it's one of the trickier questions to answer.  There are two major considerations when looking to determine the "fastest" tyre overall:

1. Rolling resistance
2. Aerodynamics

There are a number of excellent resources available that have a wide range of data on rolling resistance - we particularly like Bicycle Rolling Resistance.  Our research and testing has focused on 2. above - the aerodynamic comparison between a number of tyre options.

Full results are shown in the chart above.  Firstly, we chose to focus on 25mm tyre sizes given our previous testing had shown that there is no material difference between a 23mm & 25mm tyre on our rim profile.

We then grouped the tyres tested by construction as this appeared to show the greatest trend:

Textured tread:

• IRC Formula Pro RBCC (25mm)
• Vredestein Fortezza Senso (25mm)

Smooth tread:

• Schwalbe Pro One (25mm)
• Pirelli PZero Velo (25mm)

Open tubular (cotton casing/sidewalls):

• Vittoria Corsa Speed G+ (25mm)
• Specialized S-Works Turbo Cotton (24mm)

Overall, this showed the following difference in aerodynamics:

The results were really interesting, with a textured tread tyre testing the fastest.  In fact, the fastest overall tyre was the IRC Formula RBCC, closely followed by the Vredestein Fortezza Senso.

Tyres with a smooth tread were slightly slower (an average of 2.4W), whereas a fast-rolling (i.e. low rolling resistance) open tubular tyre is up to 5.0W slower aerodynamically than the fastest tyre construction tested.

We believe that the construction of an open tubular tyre, with a small “lip” at the point where the edge of the tyre tread joins onto the cotton casing, will trip the airflow running across the tyre in a higher yaw angle scenario (i.e. where airflow is passing across the tyre), causing an increase in drag.  Meanwhile, there is clearly a factor reducing drag for a textured tyre tread versus a smoother equivalent.  Again, a theory at this stage, but we believe this could be down to the textured tread acting as a vortex generator on a micro scale, similar to what we are seeing appear on various aero-focused clothing designs.

So what to take from this?  It may well be the case that when looking at the absolute fastest tyre option for a particular event, you should take wind conditions (and therefore likely yaw angles) into consideration, as well as the rolling resistance.

Note: all test protocols and additional data can be found here.