Traditionally, cyclists often assume that tubular tyres are the fastest, as they are still the choice of most professional riders. However, recently many teams such as Katusha, Quick-Step, Cannondale and Tinkoff have been spotted using clinchers or tubeless tyre set ups in time trials. Tony Martin even won the World Championship time trial on clinchers!
We wanted to try and find out which of the three tyre systems has the lowest rolling resistance and is consequently the fastest.
To do this our experiment has two parts. Firstly we are going to ride the tyres on rollers at a set cadence, in a set gear, and record the power output and wheel speed achieved. The second test involved riding around the velodrome in a bid to get an idea for the rolling resistance in some more real world conditions, on a more realistic road surface.
On the rollers, the tyres were ridden at around 250-300W for 5 mins, to allow them to warm up. Once stabilized they are ridden for 5 more minutes at 300W as test run. Around the track, the tyres were ridden at roughly 300W for around 15 minutes. This duration gave plenty of time for plenty of data, from which a snapshot could be obtained.
To minimise variables, we used the same profile wheel in both tests – DT Swiss RC65 Dicuts in both the tubeless clincher and tubular versions. We also used Vittoria tyres throughout the test. Power measurement was recorded using calibrated Power Tap P1 pedals.
The tubular Vittoria Corsa G+ has latex inner tubes, so for consistency, we used latex tubes with the clinchers too.
For all the runs, tyre pressure was 100psi and the complete system weight was recorded prior to each run. The fit. files from the rides were processed and correction factors were applied to calculate the coefficients of rolling resistance for each tyre on a flat surface. This was done for each power and speed value at 1 second intervals and then averaged over 5 minutes.
The tubulars’ coefficent of rolling resistance (Crr) was 0.0029.87, which equates to 30 watts of rolling resistance at 40kph for an 87kg system weight.
The clinchers’ coefficient of rolling was 0.002852. Interestingly this is slightly lower than the tubular and equates to 28 watts of rolling resistance at 40 kph.
The tubeless tyres’ coefficent was 0.00265. This equates to 25 watts of rolling resistance at 40 kph for an 87kg rider plus bike. A surprising result perhaps, but the tubeless tyres were by far the fastest and this was consistent in both the velodrome and roller tests.
Why is tubeless the fastest? Having spoken to engineers, the explanation is to do with friction.
In a tubular system there is friction in the glue layer and between the tyre tread and inner tube. In a clincher you don’t have the glue layer, but you still have the friction of the inner tube.
A tubeless system removes the tube and a large chunk of the friction in the process. Some tubeless tyres have a thicker carcass, which can be slower, however the Vittoria Corsa Speed has just 1.7mm thickness compared with 2.4mm for the Vittoria Corsa G+. This is less of a problem as the sealant can prevent flats.