We test the differences in rolling resistance and aerodynamic performance between the Continental GP5000 S TR and the Continental Aero 111
At the Grand Départ of the 2024 Tour de France, as I wandered about the Piazzale Michelangelo, which hosted the Teams Presentation ahead of stage 1 in Florence, I spotted an unusual tyre.
It was Continental-branded, but with what can only be described as 'divets' chipped out of it at regular intervals along each shoulder, instead of the usual Continental sipe design.
A few days later, Continental announced it to be the Aero 111, a front-only tyre designed in conjunction with DT Swiss and aero experts, Swiss Side, with claims of reduced aero drag compared to the brand's ever-popular - and excellent, I will add - GP5000 S TR, as well as a host of other competitors from Pirelli, Vittoria, Enve and more.
Those divets - or cavities, of which there are 48 in total - are described by the brand as 'vortex generators' and, in the words of the accompanying DT Swiss whitepaper, create "turbulent airflow on the surface that enables the air to stick to the rim shape of the front wheel. The result is a maximization of the sailing effect."
Here at Cyclingnews, we've spent the past 18 months testing bikes, tyres, wheels, and all manner of things in a lab setting, and when we tested the rolling resistance of two dozen tyres last year, we found that the Aero 111 was worse than its GP5000 S TR stablemate, and that immediately threw up a question.
Does the aero benefit outweigh the rolling resistance loss?
Therefore, during our recent trip to the Silverstone Sports Engineering Hub, with the wind tunnel at our disposal and some time to spare at the end of a day of bike testing, it was time to put the Aero 111 under the microscope and try to find out.
For the rolling resistance portion of our test, we used Silverstone Sports Engineering Hub's Pedalling Efficiency Rig.
This is a system that mounts a bike via the fork onto a large drum, which is printed with three road surfaces. For the purpose of this test, we used the 'smooth road' option, which is formed from a 3D scan of the road used in the Paris 2024 Olympic Games Time Trial.
It measures 'power in' at the pedals, and 'power out' at the drum. There's no aerodynamic component to measure, since the bike is fixed in position, and it is therefore able to measure total system loss - which generally comes from drivetrain friction, frame flex, and tyre rolling resistance - with incredible accuracy.
By then switching from one tyre to another, keeping all other variables (such as the bike, rider, tyre pressure and temperature) the same, and then measuring the total system loss again, it is able to calculate the difference between two tyres.
We tested at two speeds, nine and eleven metres per second (round numbers are easier to focus on as the rider), which equate to 32.4 and 39.6km/h.
We tested each tyre in a size 28mm, or the closest equivalent, which in the case of the Aero 111, was the 29mm.
For the aerodynamic portion of this test, we used the cycling-specific low-speed wind tunnel, also at Silverstone Sports Engineering Hub, which allows you to test the aerodynamic drag at various yaw angles (the direction of the wind in relation to the bike, where 0° is a perfect headwind) at a chosen wind speed.
We tested at 40km/h, replicating our usual aero bike comparison tests. Our understanding is that riders interested in the Aero 111 are likely competing in road races or time trials, where average speeds often hover around this point.
The earlier-mentioned DT Swiss whitepaper suggests that the tyres offer improved performance at slower speeds too, but with limited wind tunnel time available, we opted to just test at the one speed that we felt is most relevant to these race-focussed readers in the Cyclingnews audience. More testing can be done, though, so if you'd like to see it, let us know.
We tested at seven different yaw angles: -15, -10, -5, 0, 5, 10 and 15°, again replicating our aero bike tests, because this is reflective of the wind angles most road racers and time triallists will experience in the real world. According to the research paper we use for calculating our weighted yaw averages, the probability of experiencing +20° or -20° yaw at 40km/h is only around one per cent, hence we choose to stop at 15°.
We tested with the bike alone to ensure maximum accuracy, given the expected small differences between each setup.
In our rolling resistance test, we found a difference of 2.5 watts at 9m/s and 3.7 watts at 11m/s between the GP5000 S TR and Aero 111 tyres.
We don't have an exact number for the coefficient of rolling resistance, but we do know that Power = Mass x Gravity x Velocity (m/s) x CRR, so we can be confident that the growth will be linear as speed increases.
Therefore we can use the graph above to extrapolate the same setups at different speeds.
This shows us that the difference at 20km/h is approx 0.4 watts, and at 70km/h, it's just less than 9 watts.
Before we get into the aero data, we'll take a quick detour into the measured widths of each tyre tested in the wind tunnel, where interestingly, both of the Aero 111 tyres actually measured narrower than their nominally narrower GP5000 counterpart.
We measured each tyre three times at various points on the wheel and calculated the average.
Now for the aero data. Even though we only have a rolling resistance comparison for the 28mm GP5000 vs 29mm Aero 111, we chose to aero test the 25mm GP5000 and 26mm Aero 111 too. We'll focus more heavily on the 28 v 29 test, though.
If, at 40km/h, the Aero 111 is more than 3.7 watts faster than the respective GP5000 S TR, it's a no-brainer pick.
I'll start with the answer and work backwards, and hopefully the reasons for doing so become clearer below.
When we apply the same weightings used in our bike tests, we see that the 25mm GP5000 takes 66.29 watts to overcome the aerodynamic drag. The 26mm Aero 111 is marginally more aerodynamic. The 28mm GP5000 is slowest of all at 67.28, while interestingly, the 29mm Aero 111 is fastest of all.
This is likely because we used the Hunt 54_58 Aerodynamicist wheelset from Hunt, which are designed and optimised for use with wider tyres, featuring a front rim with a 31.7mm external width, 22mm internal, and hooked bead.
The differences, therefore, are as follows:
This tells us that, when using a protocol designed to reflect the real-world probability of seeing each yaw angle at 40km/h, the average wattage saving is just 1.23 watts for the wider tyre, and 0.29 watts for the narrower tyre.
With the 3.7w rolling resistance difference added back in, that's a net loss of 2.47 watts for the 29mm tyre. Therefore, based on this data alone, if you're looking to upgrade your GP5000 S TR to an Aero 111 for riding or racing around 40km/h, don't.
Next up, given the power (watts) required to overcome aerodynamic drag increases with the cube of speed, what if we take our aero drag and solve for higher speeds?
When we compare these savings with the extrapolated Rolling Resistance data above, we can see that even at 70km/h, the 6.62-watt aero saving isn't big enough to overcome the approximate almost-nine-watt loss.
There would be an inflection point, but at speeds well in excess of the averages that cyclists will be experiencing, and where the applied yaw angle weightings become less applicable.
It's worth noting that this isn't a scientifically perfect approach, and testing at each speed, rather than extrapolating, would have been the optimal way to get this data, but the aforementioned time constraints meant we were limited with our approach.
To try and understand what's happening here, let's take a step back and look at the raw data for each yaw angle.
It's interesting to see here that the drag of each wheel-tyre system is very similar at lower yaw (experienced more often at higher speeds), whereas at the higher 15° yaw angle, the two Aero 111 tyres both perform well, whereas the two GP5000 S TR tyres lag behind.
This shows that, at those higher yaw angles, the Aero 111 tyre helps the wheel to sail - essentially harnessing the wind to create 'lift' like an aeroplane's wing or the sail of a ship - as claimed by DT Swiss and Continental, effectively creating forward thrust and in turn reducing the aerodynamic drag.
It's impressive to see that a tyre is able to have this effect, but let's now quantify what that means in terms of watts saved for you in the real world.
Given the relative symmetry, I have averaged plus and minus 5°, 10°, and 15° to show that as the wind angle widens, the performance of the Aero 111 tyre improves.
It once again shows that the four tyres track reasonably close to each other until +/-10° yaw, and then at the 15° yaw, the two Aero 111 tyres come into their own.
Working out the differences between the Aero 111 and its similarly-sized GP5000 counterpart, we can see that the savings are essentially nonexistent at lower yaw, but grow to a saving of 8.68 watts at 15° for the 29mm.
Remember, this is still subject to the 3.7w rolling resistance penalty, equalling a net saving of 4.98w at this wind angle.
The problem here, though, is that the reason we - and aero experts - choose to apply yaw angle weightings at all, is because the likelihood of riding in 15° wind is incredibly low, and therefore, the likelihood of seeing the 4.98w benefit for any extended period of time is low too. The rest of your time riding will be spent at a deficit.
So once again, based on the data we have here, it's hard to recommend the Aero 111 as a worthwhile upgrade. In very niche circumstances it might work. For example, if your race is make-or-break in a strong crosswind, it might make sense to accept the penalty in favour of the high-yaw benefit. But more realistically, for all-round performance, the GP5000 S TR is the faster tyre.
As ever, testing breeds more questions, and if Continental and DT-Swiss' claims about the tyre's ability to help a wheel sail at slower speeds are true and (as shown in our testing), can help the wheel to sail at shallower yaw angles too, we might see bigger aero savings at those slower speeds compared to the extrapolated data we have here from our test at 40km/h.
Those slower speeds would also increase the probability of experiencing those higher-yaw wind angles, too, so a bit of a double-whammy benefit.
What's more, 'slower' in this sense refers to wind speed, rather than ground speed. A rider in the shelter of a peloton might be riding at 50km/h, but, as a result of the shelter they're getting from the riders around them, the headwind created from their own movement is significantly reduced, once again increasing the possibility of spending time at higher yaw.
One of the other claims from DT Swiss and Continental is a more linear steering moment, which can possibly equate to greater stability in windier conditions, instilling confidence and, in turn, meaning the rider can stay in a more aero position for longer. That's harder to quantify, but a consideration worth including nonetheless.
These are all new hypotheses to chew over, though... a mission for 2026, perhaps.