Aerodynamics of racing tyres
The goal of this test was to evaluate the aerodynamic performance of some of the lowest rolling resistance racing tyres, against the benchmark Continental GP 5000.
We selected four tyres for this test - which represent some of the best rolling resistance tyres on the market. All were mounted on an AEOX ZEPHYR front wheel (78mm deep).
Vittoria Corsa Speed 2.0
We have consistently found that both the first version and the 2.0 versions of the Vittoria Corsa Speed have the lowest rolling resistance we've tested for a road tyre. Corsa Speeds are tubeless compatible but can also be run with latex tubes for the same rolling resistance, but the better puncture protection afforded by running tubeless tyres make tubeless Corsa Speeds an excellent choice for racing.
Michelin Power Time Trial
Whilst the Corsa Speed wins in terms of rolling resistance, the clincher only Michelin Power Time Trial is a close second (when fitted with latex tubes). There is less than 1w difference in the rolling resistance between a pair of Michelin Power Time Trial tyres (25mm) and Vittoria Corsa Speed tyres (23mm) at 45kph. The Michelin tyre has a smooth tread with no tread lines.
Schwalbe Pro One TT
Another clincher/tubeless tyre, after Schwalbe released the original Pro One tubeless tyre the lightweight TT version in 25mm came on the market. Using a similar tread design to the Pro One, it has tan sidewalls. In our rolling resistance testing there was a ~3.5w penalty for a pair of tyres, compared with a pair of Corsa Speeds, and a ~2.5w penalty to the Michelin Power Time Trial.
Continental GP 5000
Continental have two different versions of the GP 5000 - one which is clincher only (23mm and larger) and the TL version which is tubeless compatible and slightly thicker (25mm and larger). They have roughly similar rolling resistance, and the tubeless/TL version in 25mm has just over a 7w rolling resistance penalty for a pair of wheels compared with a pair of Vittoria Corsa Speeds. For the purposes of this test we used the clincher version in 25mm with a latex inner tube.
WIND TUNNEL
When interpreting wind tunnel results it is important to understand yaw angle weighting.
Real world cycling is affected by changes in wind speed and direction.
The angle of attack of the wind on the cyclist is referred to as “yaw angle”, and this is affected by four components - rider speed/direction as well as the wind speed/direction.
While cycling on the road, you will experience a range of yaw angles. Very high yaw angles are much less common than lower yaw angles, and this can be expressed as a weighting function - for example at 45kph you spend ~80% of your time at 7.5deg yaw or less. At <40kph this extends out to 10deg, and at >50kph you will typically see 5deg or less.
We tested the aerodynamics of the tyres at our typical test speed of 45kph. This allows us to get good clean data (compared with testing at lower speeds, where the resolution isn't as good) which can then be applied to lower speed calculations later. As an example, a 10w aerodynamic drag saving at 45kph is equivalent to 4.7w at 35kph.
VELODROME TESTING
We also validated the wind tunnel results by performing track testing, changing tyres on the same wheel to establish a combination of aerodynamic and rolling resistance performance.
We use the Garmin Track Aero System to measure performance on an indoor velodrome, which allows us to either calculate CdA (aerodynamic drag), or also Crr (rolling resistance). Rolling resistance around an indoor velodrome will be lower than outdoors, but the relative differences still hold true when riding on tarmac or concrete outdoors.
The combined results are shown below. Aero data is included in the calculations for the front wheel only, as aerodynamics of rear tyres on the wheel used in testing (AEOX Disc) is negligible.
Given the aero performance of the Schwalbe Pro One TT and Michelin Power Time Trial, the small rolling resistance penalty that exists compared to the Corsa Speed is nearly overcome by their better aero performance. The Corsa Speed is extremely fast in the real world, but the difference to the other TT tyres is much less than just the rolling resistance data would indicate.
The Continental GP 5000 has excellent aerodynamic performance in this test, but because of the Crr penalty is slower by 5-6w for a pair of tyres in the real world (depending on the model of GP 5000). We have previously found similar aero performance between the tubeless and clincher GP 5000 tyres.
The Vittoria Corsa Speed is still an excellent tyre, but the very small overall differences between the Corsa Speed and Michelin/Schwalbe tyres when aerodynamics are taken into account means that riders can realistically choose any of those three tyres based on other preferences such as grip, puncture protection and of course colour!
For a more puncture resistant tyre the penalty of 5-6w for a pair of GP 5000s is worth considering over the above lightweight tyres.
