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It is not exactly a new realisation that tyres play a part in the overall aerodynamics of a road bike. Mavic was the first manufacturer to experiment with tyre-and-wheel systems to optimise aerodynamic performance. However, the most successful collaboration to date has been between Swiss Side, Continental and DT Swiss: The Conti Aero 111 demonstrated remarkably good performance in the TOUR wind tunnel test. Its special tread pattern prevents the airflow from breaking away from the front wheel – and does so across a wide range of speeds, from leisure to racing pace. According to our wind tunnel tests, the benefit to the overall system can amount to several watts; furthermore, the tyre’s handling improves in gusty winds, with the front wheel wobbling less when the aero tyre is fitted.
Pirelli is changing the tyre shape
Pirelli has now achieved something similar with the new P Zero Race SL-R achieved. However, the Italians’ approach is slightly different. Pirelli does not rely on a special tread pattern like Continental, but instead manipulates the shape of the tyre to control the airflow. Specifically, Pirelli makes the tyre thicker just above the rim flange. The tyre transitions more steeply into the rim; the sidewalls are almost vertical and – when viewed in cross-section – do not take on a pear shape. Pirelli calls this patented feature ‘PAAS’, which stands for Pirelli Advanced Aero System. It was developed in a virtual wind tunnel and tested in four (!) physical wind tunnels. The airflow management is designed to work with various rim shapes and widths.
Our test model is the slimmest version of the tyre and has a nominal width of 28 millimetres; on a rim with an internal width of 23 millimetres, it bulges out to a width of 30 millimetres; and on a 25-millimetre rim – which is not compatible according to ETRTO regulations – it even reaches 31 millimetres. Above the rim flange, the tyre leaves a gap of 1.8 millimetres.
The lightweight tubeless-ready carcass can be fitted by hand; thanks to a high-flow spare Fillmore valve, the tyre pops straight into the rim flange. With the classic Presta/Sclaverand valve, we had to remove the valve core to pump enough air into the tyre quickly. In the centre of the tread, the tyre is noticeably flexible and thin thanks to just two layers of carcass.
On the bike, the 277-gramme tyre rolls very smoothly. It steers nimbly, holds its line well through bends and is very quiet. During rides in gusty winds, the front wheel runs smoothly, though this may also be down to the aerodynamically efficient Leeze rim. It is always difficult to assess a tyre’s grip whilst riding freely. However, the tyre performs flawlessly and feels safe at all times during the 1,000-kilometre test, even on wet roads.
Design from the wind tunnel
The aerodynamic test we carried out in the GST wind tunnel in Immenstaad reveals just how much of a role tyres play in the aerodynamics of a bike. We used our reference bike, the Canyon Ultimate, as well as a very fast, as yet unannounced aero road bike. We fitted the tyres to various wheelsets and compared their aerodynamic performance with the classic Conti 5000 STR in 28-millimetre width, as well as the Conti Aero 111 in 26- and 29-millimetre widths. For the set-up, we’re using our pedalling dummy to get as close to real-world conditions as possible.
Pirelli does not market the P Zero Race SL-R as a specific front tyre, but intends it for both the front and rear wheels; one reason for this is that rolling resistance has also been optimised. However, in our experience, measurable aerodynamic benefits from the tyre can only be expected on the front wheel. We have therefore limited our aerodynamic investigations to the front wheel in order to save valuable wind tunnel time.
We tested the tyre on wheels with internal widths of 19 to 25 millimetres and rims 40 to 60 millimetres high. The measurements show that Pirelli’s 28er, at a racing speed of 45 km/h, in a fast aero road bike and fitted to a fast wheel (DT Swiss ARC 1100 65), is almost on a par aerodynamically with Conti’s 29-millimetre-wide Aero 111. Only when the airflow is very oblique are Conti’s aero tyres a fraction faster, by a weighted average of 0.5 watts.
Pirelli and Conti are almost neck and neck
On the slightly less aerodynamic Canyon Ultimate frame and fitted to a 50-millimetre-high DT Swiss ARC 1100 wheel, the Pirelli tyre performs slightly less well; aerodynamically, it ranks between the Conti 5000 (28 mm) and the Conti Aero 111 (29 mm). However, the average differences are still small, at 1.5 watts each.
The measurements show that Pirelli’s 28er, at a racing speed of 45 km/h, on a fast aero road bike and fitted to a fast wheelset (DT Swiss ARC 1100 65), are almost on a par aerodynamically with Conti’s 29-millimetre-wide Aero 111. Only when the airflow is at a very oblique angle are Conti’s Aero tyres a fraction faster, by a weighted average of 0.5 watts.
On the slightly less aerodynamic Canyon Ultimate frame and fitted to a 50-millimetre-high DT Swiss ARC 1100 wheel, the Pirelli tyre performs slightly less well; aerodynamically, it ranks between the Conti 5000 (28 mm) and the Conti Aero 111 (29 mm). However, the average differences are still small, at 1.5 watts each.
Fitted to a wide Leeze wheel with 42-millimetre-high rims and an internal width of 25 millimetres, the Pirelli tyre integrates very well with the rim’s smooth airflow pattern. There is no disruption to the airflow up to a 20-degree oblique flow angle. In terms of handling, this means a safe ride even in gusty winds; the P Zero thus demonstrates its aerodynamic effectiveness.
Outstanding smooth running
Let’s move on to rolling resistance. As usual, we carry out our measurements using our manufacturer-independent method on two surfaces: a very fast concrete track and a rough track. According to these results, the P Zero Race SL-R ranks amongst the fastest tyres, on a par with specialist time trial tyres.
At 35 km/h, we measured a rolling resistance of just 13.2 watts at 5 bar for a system weight of 85 kilograms. Within the limits of measurement accuracy, this is on a par with the 28-millimetre-wide Conti TT time trial tyre and is an excellent figure. The new Pirelli tyre thus outperforms the Conti GP 5000 S all-rounder in terms of rolling resistance and lives up to its promise of being faster than the P Zero RS.
The tyre performs particularly well on rough surfaces. To put this into perspective: Pirelli’s racing tyre rolls more easily on the very rough test track than an average tyre does on perfectly smooth tarmac. Fascinating!
Despite its excellent rolling resistance, the tyre offers sufficient rubber for a normal mileage. In the centre, the tyre is only 1.9 millimetres thick, which is very little. Thanks to a very thin carcass – consisting of just two layers in the centre – around 1.5 millimetres of this is accounted for by the rubber layer.
Over the course of 1,000 kilometres of test driving, the rear tyre lost a quarter of its tread, suggesting a potential mileage of 4,000 kilometres. The rear tyre remained free of cuts. The tyre does not have any wear indicators that could provide a guide as to when it needs replacing.
A thin puncture-resistant layer is integrated, but its effectiveness is below average. We measured a puncture resistance of 330 newtons, which is at the lower end of the scale. Towards the end of the test rides, an unknown object cut right through the tread of the front tyre. The sealant allowed us to carry on riding, but it would be advisable to replace the tyre.
Conclusion
With the P Zero Race SL-R, Pirelli has produced an exceptionally fast road bike tyre that combines many features: it rolls with excellent ease, just like a time trial tyre; its aerodynamic performance at high speeds is very good; and the ride feel is superb. The tread compound and puncture protection are adequate for racing, but rather poor for everyday road cycling.
At launch, the tyre will be available in 28 and 30 mm widths, with a 32 mm version due to follow after the summer. The recommended retail price is 99.99 euros per tyre. The tyre is manufactured in Bollate, near Milan.
