Cyclists have long known about the importance of rolling resistance in selecting tyres for racing, group rides or even general training. A tyre with a high rolling resistance will require more power to travel at the same speed, whilst a low rolling resistance tyre requires less power.
Continental's Grand Prix (GP) 4000 is renowned for being both puncture resistant as well as having good rolling resistance, and is also regarded as an "aero tyre" given that the tread pattern often performs well in wind tunnel testing.
The goal of this test was to evaluate the rolling resistance performance as well as the aerodynamic drag of Continental's brand new tyre, the GP 5000.
We selected three tyres for this test - the GP 4000, GP 5000 and the super fast rolling GP TT. First up was a trip to the wind tunnel, so that we could see whether the new GP 5000 could match or even surpass the aerodynamics of the GP 4000. For all of the tests the tyres were inflated to 90psi.
All the tyres were mounted on a shallow section aluminium rim - this was to ensure a fair test between the three tyres, as many manufacturers use the GP 4000 to develop their rim shapes. As an example we used Vittoria's ultra fast Corsa Speed tubeless tyre in the development of our AEOX tubeless front wheels and AEOX tubeless disc. The rim external width was 24.7mm with an internal width of 19.6mm, and a Vittoria latex tube was used.
On this rim a "23mm" GP 4000 measured up at 25.66mm wide, and 23.09mm high.
The GP 5000 is newly released from Continental, and is fêted to give lower rolling resistance along with improved puncture protection. The moulded directional shapes on the tread of the GP 4000 have been replaced with lazer etched shapes of similar design, and extra "5000" text written above some of these shapes on the drive side of the tyre.
A 23mm GP 5000 measured up as quite a bit smaller than the GP 4000, as the width was 25.19mm (0.47mm narrower than the GP 4000) and height 22.18mm (0.91mm lower than the GP 4000).
We tested an extra tyre from Continental, the GP TT. This is a popular clincher tyre choice with time triallists as it has some puncture protection as well as being fast rolling. Unlike the GP 4000 and GP 5000 the tread is unidirectional, with a smooth raised central section along the centre of the contact patch of the tyre.
The GP TT in 23mm measured up the widest: 26.23mm, but its height was only a little more than the GP 5000 at 22.27mm.
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.
It was important that we had a very consistent test rider for this experiment as we knew we'd be looking at extremely small differences. We recruited our head engineer, Andy, who is extremely stable during wind tunnel testing to make sure we got repeatable numbers.Andy was riding a Cervélo P2 with the test wheel in front and an AEOX tubeless disc in the rear. We only changed the front wheel tyres for this test, and performed multiple runs to improve the accuracy of the testing.
WIND TUNNEL RESULTS
Results from the wind tunnel test between the three tyres are shown below.
When interpreting wind tunnel results it is important to understand yaw angle weighting.
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.
The picture to the right illustrates this process:
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 see 5deg or less.
At low yaws (0-2.5deg) all the tyres are very tightly packed together, with overlapping error bars - indicating that any differences between them are within the error measurement. As the yaw angle increases up to 5 degrees however, the GP TT becomes much less aerodynamic - whereas the GP 4000 and GP 5000 follow a similar yaw curve, increasing in drag past 10 deg.
ROLLING RESISTANCE RESULTS
Of course the most important characteristic for a tyre's performance is its rolling resistance, as aerodynamics are a small fraction of the overall result.
In order to test rolling resistance, we used the same tyres and swapped between them as a rider rode a bike on rollers, measuring power output and speed, as well as atmospheric conditions and bike/rider weight. This allows us to calculate what is known as the Coefficient of Rolling Resistance (or "Crr"), which can be used to model the power output required to travel on a normal road. A lower Crr is better - in that it requires less power to travel at the same speed.
The GP TT was the fastest tyre on test, requiring 7.1w less for a pair of wheels than the GP 4000 to travel at 45kph on a flat smooth road. The GP 5000 was 4w faster for a pair of wheels than the GP 4000.
So far we've found that the GP 5000 is a slightly more aero tyre than the GP 4000, and that the rolling resistance has also been improved. The GP TT was the fastest rolling tyre of the three, but had worse aerodynamic performance. What happens when we combine these savings? The graph below takes into account the rolling resistance performance of a pair of tyres as well as the aerodynamic performance for the front tyre only. The aero savings from the correctly shaped rear tyre will be much reduced compared with the front tyre, so we haven't included those in our calculations.
Even though the GP TT had worse aero performance than the other two tyres, in combination with rolling resistance it was the winner by 1.4w. The GP 5000 was excellent for both aerodynamics and rolling resistance, a large 4.3w improvement over the GP 4000 at 45kph.
The savings in the graphs above relate to 45kph speed - at slower speeds the power required is reduced.
At 35kph, the combined power of the GP TT is 21.5w, GP 5000 is 23.1w and GP 4000 26.4w. The gap is increased between the GP TT and the GP 5000 because the aero penalty of the GP TT is less at lower speeds, so the better rolling resistance of the GP TT begins to outweigh the aero drag differences.
The GP 5000 is the updated tyre to the GP 4000 and out performs it both for aerodynamics as well as rolling resistance. Given how close it got to the GP TT in combined performance it would make an excellent race tyre, especially on broken road surfaces where extra puncture protection is needed.