Continental Aero 111: are aerodynamic tyres the next watt-saving frontier?

As bike brands continue to slim down their aero bikes, seemingly deciding that peak aero has been reached as far as deep frame tubes are concerned, we’ve seen attention focused on other areas of the rider and bike with new dodges designed to save watts without adding weight. Skinsuits for the road, narrow handlebars with turned-in hoods, pointy and visored helmets… these are all proven to make riders faster and not in a merely marginal way. But tyres? 

Focusing on tyre aerodynamics is nothing new: Mavic’s CX01 Blades were thin foam hoops that clipped onto its CXR 80 wheels to fill the gap between the tyre and the rim wall in order for the air to transition smoothly… and were banned by the UCI in 2012. Meanwhile, amateur time triallists, notorious for home-brewed aero, would use a thin coating of silicone sealant to do the same job – until Josh Poertner of Zipp (now with Silca) advised against it, saying it probably impacted the tyre’s hysteresis, increased rolling resistance and reversed any aero advantage. Next, the Continental Grand Prix 4000 was discovered to have an fortuitous aerodynamic benefit thanks to a tread pattern that turbulated the airflow as it transitioned to the rim.

There are currently other specifically ‘aero’ tyres on the market, but none with the claims of the new Continental Aero 111 tyre, spotted on the bikes of Decathlon AG2R-La Mondiale and officially launched today. A joint venture between the German tyre manufacturer, wheel brand DT Swiss and aero experts Swiss Side has produced a ‘wheel-tyre system’ (WTS) that is said to set a “new benchmark in aero performance”. It’s sold as a front tyre only, since that’s where the aero benefits take place.

How does it work? The 48 cavities of the tyre tread pattern – square-edged and also patented – “act as vortex generators that control the turbulence of the air as it hits the front wheel. This action promotes the adherence of airflow to the front wheel rim profile and delays flow separation, maximising the sailing effect.” And the greater the yaw angle, the more watts are saved, according to the three brands. Bigger yaw angles from crosswinds are typically seen at lower speeds, since a higher speed narrows the relative angle of a crosswind – which means that, unlike most aero equipment, this tyre can benefit the amateur rider as well as the pro. In fact, Continental says the rider who rides at 30kph will benefit most from the optimisation of the WTS (meaning the Aero 111 combined with the DT Swiss wheels with which it optimised it – though the tyre's benefits are available with all wheels). “We call this the democratisation of wheel aero performance.”

The three brands decline to give exact watt-saving figures, preferring instead to supply a series of graphs with lines that plot wind tunnel data with yaw sweeps and aero power against competitors and against its own Grand Prix 5000 as a ‘standard’ tyre. However, the graphs clearly show the sailing effect increasing as yaw angle increases, turning into negative drag or forward propulsion whereas a standard tyre stalls as the airflow breaks away. “The wheel with the Aero 111 does not stall in +/- 20 degrees of yaw, which is what you’ll typically experience,” says Swiss Side’s CEO and co-founder JP Ballard. “You’ll feel it pushing but not shaking, and you’ll also feel it pushing you forwards.” Ballard did later say that overall the Aero 111 can supply “about a 50% improvement on the front wheel drag at 30kph so it’s a pretty massive enhancement”

From the graphs it’s possible to see that the watt savings at the higher speed of 45kph and a high yaw angle of 20 degrees could be almost 20 watts – which is considerable. At lower angles the savings decrease and it’s only really when the yaw angle goes beyond seven degrees that the big savings with the Aero 111 start to be seen.

The competitor data, a graph which compares the Aero 111 against competitor aero tyres and racing tyres including the Schwalbe One Aero and the Cadex Aero Tubeless, looks very similar to the testing against the ‘standard’ Grand Prix 5000 and that’s because, according to Ballard, “the truth is there is no aero tyre on the market right now. There is not an aero tyre that actually works – but this one does. We’re not usually the type to do the comparative stuff against other brands, but this time we do. We tested all the aero and non-aero tyres out there and the Aero 111 is literally a gamechanger.” Perhaps one of the most fascinating snippets of information that came out of the media briefing – these can often be more revealing than the press release – was that the Aero 111 has the potential to give a budget aluminium wheel the performance of a deep-section carbon wheel. Ballard said: “This is one of the most exciting points – if we stick it on one of the new [DT Swiss] aluminium wheels it will outperform most aero wheels on the market with a standard tyre on. We put the Aero 111 tyre on the new [alu] 38mm rim and a standard tyre on the [carbon] 62mm rim and the 38mm with Aero 111 tyre wins. If you add the Aero tyre to the 62mm rim you’re in a completely new ballpark.”

But about the rest of the tyre? When I asked Xavier Disley of AeroCoach whether he’d independently tested the Continental Aero 111, he said he hadn’t yet, but he did say that historically tyres that were designed to be aerodynamic suffered from poor rolling resistance because a sharper leading edge negatively affects the contact patch. However, Continental’s product manager Hannah Fernle says the Aero 111 had the lowest rolling resistance of any of the benchmarked tyres it was tested against for the aero comparison, but that it’s not just a Grand Prix 5000 with a different tread pattern. “It is not a super lightweight tyre,” she says [it weighs 250g in the 26c size]. “We didn’t just take an S TR and put it in a fancy aero mould – that was not the case. We had to change a lot. Construction wise it is most similar to the S TR but has a lot of the features of the TT TR. It has a casing of 2 x 220 tpi and is more similar to the Grand Prix 5000 S TR than the TT TR."

The Aero 111 includes Conti’s Black Chili compound and Vectran puncture resistance – like the other Grand Prix 5000 tyres. Ballard points out that Decathlon AG2R-La Mondiale have been riding the Aero 111 since December to give feedback on grip, wear and puncture resistance areas and it “didn’t throw up surprises”.

DT Swiss will be offering the Continental Aero 111 pre-installed with its Aero and Endurance wheel ranges at a €100 supplement, or it can be bought separately in 26-622 or 29-622 sizes for €119.95 (no UK prices so far). It’s quite a lot more expensive than the Grand Prix 5000 S TR but, as Ballard points out, “there’s four years of development, which needs to be paid for.” And of course there’s only one required for the front wheel.”

If the tyre works as well in real-world conditions as it does in the wind tunnel it genuinely could be a gamechanger – and a relatively cheap one for those who want to use the tyre with their existing front wheel. Although the Aero 111 was designed to “create the world’s most aerodynamic WTS when used in combination with DT Swiss Aero or Endurance wheelsets,” the brands say it also also provides a competitive advantage for riders who install it on their preferred wheelsets from other brands.”

Can we expect more aerodynamic tyres or wheel-tyre systems? Before the launch of the Continental Aero 111, Swiss Side also published some of its findings relating to gravel tyres. Since aerodynamics in gravel is becoming increasingly important – Unbound was won this year at an average speed of 22mph – it’s inevitable that that elite gravel racers will be looking to optimise their tyres and wheels, and this is what Swiss Side found: “In general, the rougher the tyre and the size of the knobs, the higher the aero drag and hysteresis in particular, the sailing effect is reduced. However in our wind tunnel test, the Continental Terra Speed was a slight exception with a low aero drag level and relatively good sailing effect for its comparatively large sized knobs." We know that there’s work being done in this area by both Parcours and Zipp, so we fully expect to see gravel wheels and tyres designed around front-wheel aerodynamics.