Aero record: Watt comparison of 4 aero racing bikes

The record was almost broken at customs. But only almost. Because Stromm Cycles, a three-man company from San Juan Bautista in California/USA, wanted to take part in the TOUR wind tunnel test at all costs. And so Ben Rothacker, one of the co-founders and chief developers, got on a plane to do himself what the parcel service had failed to do: fly the bike across the pond to Lake Constance for the final validation of the promising wind tunnel data from the USA. Stromm had already tested his bike against a Cervélo S5 in the San Diego low-speed wind tunnel and claimed clear advantages for himself.

The only problem is that measurements carried out by a small manufacturer on its own account do not have the same leverage as those carried out by an independent organisation. This is the only way to ensure credibility and comparability in order to be heard on the market.

The importance of aerodynamics

On a Friday morning in February, Ben Rothacker, who had just arrived from the USA, delivered his bike to the wind tunnel gate and added a completely different interpretation of the subject to our illustrious test bike crowd. Next to the Factor One with its massive flared fork blades and overall beefy appearance, the Stromm Raktt looks like a filleting knife. 'Epee vs. sabre' comes to mind, one thinks in the category "weapon against the wind". We've never seen such a sharply cut head tube before, and the fork hugs the front wheel as closely as possible.

Who will win the race? The beefy Taiwanese-British Factor machine with a professional background or the razor-sharp racer from the USA? Our field of new high-end racing bikes is completed by the new Merida Reacto, the fifth edition of which boasts significantly more striking lines and a slimmer silhouette, as well as the Ridley Noah Fast, a flat aero racer from Belgium with a very deep profile.

The bold look fuels expectations. For top-class bikes, we expect values below 200 watts on a weighted average. With the Pride 2, Simplon was the first manufacturer to undercut this mark with 199 watts, and Storck followed suit with the Aerfast. Tadej Pogačar's work tool, the Colnago Y1Rs, also landed at 199 watts with the TOUR tuning upgrade, a few watts better than the standard bike with less aerodynamic wheels and tyres.

Wind tunnel

When the first points in the measurement chart light up on the screen, it becomes clear that the Stromm is delivering. The wheel enters with very low values in a diagonal flow, so it sails very well in crosswinds. However, it becomes particularly spectacular around the centre position. The further the curve crawls across the screen, the clearer it becomes that new ground is being broken. When the wind blows from the front, Stromm undercuts everything we have seen so far. This is where the ultra-thin head tube has the greatest measurable effect.

The best conditions for shooting, because the faster the speed, the more the angle range around the zero position comes into focus, especially with little wind. The computer spits out the result: 196.4 watts - a new world record!

But it goes even faster: we put the DT Swiss ARC 1100 65 wheelset on the bike as a test, with Continental's Aero 11 tyres in 26 millimetre width. Result: 194.9 watts. This makes Stromm the first bike to undercut the 195-watt mark. However, as our test of all the other features of the bike from page 36 onwards shows, the price for this is very low frame stiffness.

Rapid development

When we started measuring the aerodynamics of racing bikes at GST in Immenstaad 13 years ago, values below 210 watts were rare. These are now commonplace - and at the top end, the best bikes require 7 watts less, despite disc brakes. The gap between this and a conventional racing bike without aero features, which consumes 235 to 240 watts, is striking.

This also proves that technology is playing its part in making the sport ever faster. However, it is also true that what we see and measure in the wind tunnel is only about half of the aerodynamic progress. Body posture and clothing, including helmets, are other major levers for reducing air resistance. The fabulous speed of the professionals is the result of numerous endeavours in all areas: The aerodynamics of man and machine are the most important factor, but other driving resistances have also been further reduced: The tyres roll better, the chains are lighter and the riders are much better nourished. The bottom line is that a much higher speed is possible, which can also be sustained for longer.

Merida's Reacto makes the leap forward

But back to the topic of aerodynamics: Merida has made an impressive leap with the Reacto. Development engineer Arne Burkhardt and his team have not only made the frame and cockpit faster, but also offer the bike ex works in a version that consistently exploits the aero potential: top wheels, aero front tyres, aero cranks and classic hub gears enable a total jump to 197.4 watts in the aero measurement. In absolute terms, this is the second best value ever measured for a production bike. Above all, however, the Reacto is a fully-fledged bike without any limitations. Compared to the outstanding result, the frame isn't all that exalted. It's a shame that the bike won't be represented in the 2026 World Tour after the sponsorship of the Bahrain Victorious team expired at the end of 2025. However, the return to the premier league of racing is planned for 2027.

The off-centre Factor One is almost a little disappointing in comparison. With 202.3 watts, the bike is also very good, but the extreme shape does not result in a corresponding advantage. The level corresponds to that of other good aero racers such as the Cervélos S5 or Canyon's Aeroad.

We want to find out whether the bike has even more potential and swap the standard wheels for the set-up we used to tune the Stromm. The Factor One breaks through the 200 watt threshold and ends up at 198.2 watts. We then removed the front derailleur to simulate a single drivetrain, similar to Merida. This pushes the bike up to 196.8 watts - a value that is more in line with the expectations of the extroverted design. Factors One demonstrates in an exemplary manner that it is not the extremely well-designed frame that makes the difference; it is the overall package that counts, just as with weight tuning. A bike only becomes really light if all parts are really put on a diet.

Fast and suitable for everyday use: Ridley Noah Fast

The fourth superbike in the test, the Ridley Noah Fast, achieves 202.3 watts in the factory set-up and thus also joins the ranks of good aero road bikes. However, the bike is already fitted with fast DT Swiss wheels with the Conti Aero 111, and a single crankset is also on board. The Ridley therefore has no further tuning potential.

Aerodynamically optimised racing bikes such as those presented here are the spearhead of a development that now goes back a long way. Back in the early 1990s, carbon pioneer Look introduced the KG 196, an aero bike that anticipated today's development with bayonet steering and flat frame sections. In 2002, Cervélo launched the Soloist model, initially as an aluminium model. It was used intensively by Team CSC in the following years, including by perennial breakaway rider Jens Voigt.

What else counts

Today, no rider breaks away from the peloton without a sophisticated aerodynamic set-up. When Voigt's revenant Ben Healy sets off on the breakaway, everything is aerodynamically optimised. The one-piece racing suit fits wrinkle-free, the bike is of course trimmed for aerodynamics and the Irishman wears an aero helmet on his head.

But it's not just the breakaway riders who wear aero. Even on mountain stages, classification riders wear aero outfits. This is because it is now accepted that aerodynamics are more important than low weight in the vast majority of race scenarios.

Racing engineers work in the teams and advise the drivers on which material strategy promises success. However, the 6.8-kilogramme rule of the world governing body, which stipulates the minimum weight of bikes, is also likely to play a major role in the aero trend. Modern aero racing bikes come close to this limit, while all-rounders such as a Tarmac SL 8 can even be slightly lighter.

Relationship between aerodynamics and weight

The once arbitrarily set weight limit creates scope for aerodynamic optimisation. That was not its original aim. The rule was intended more for the safety of the bikes, perhaps even to reduce development costs. This did not happen. Without a weight limit, 4.2-kilo bikes would also be possible - less aerodynamic, but so light that they could equalise the competitive advantage of aerodynamic all-rounders and aero racing bikes, at least in the mountains.

The 6.8-kilo rule is therefore one of the reasons why aerodynamic bikes have been able to establish themselves in racing. With their latest generation, the idea that one bike (such as a Specialized Tarmac) is best for all distances is once again coming under pressure. The latest bikes are significantly faster again, which gives them an advantage on flat to undulating terrain at least, which pros don't want to do without. However, the fastest bikes are heavier than 6.8 kilos if you don't pay meticulous attention to the weight of the add-on parts. This again creates room for manoeuvre to differentiate between light and aerodynamic bikes.

As an amateur athlete, you don't need to worry about this. If an aero racer suits you and its looks are inspiring, why not? But nobody has to ride a flounder when there's no clock ticking and no opponent is stretching and flattening out. We have the choice between very different, fantastic racing bikes that not only impress on the road, but also inspire as sculptures.

Wind tunnel standard from TOUR

TOUR has been measuring in the GST wind tunnel in Immenstaad since 2012. Since 2013, we have established a standard centred around a dummy without a torso with kicking legs. This set-up has become the globally accepted standard. Half the bicycle industry makes the pilgrimage to Lake Constance to develop bikes in the "TOUR wind tunnel", which belongs to GST.

Our wind tunnel test has a long history. TOUR testers carried out their first wind tunnel tests more than 30 years ago. But it was the standardisation and the unique test procedure, which was developed in collaboration with GST, that gave the test the orientation that helps the industry: reproducible, practical data that everyone can measure themselves against.

The problem with wind tunnels is that the absolute values vary from turbine to turbine. This is due to the fact that wind tunnels are only approximations of reality. Structural conditions and the measurement procedure itself influence the result. Therefore, weighing in a wind tunnel is not as comparable as with a kitchen scale that delivers the same values around the world. Manufacturer values determined using other methods are therefore not comparable on a one-to-one basis.

The special features of our test include the fine resolution of the inclined flow, the interaction between the frame and moving legs and the very good reproducibility. We have been measuring our reference bike for twelve years with a deviation of +/- one watt, within a measurement campaign we are significantly more accurate (+/- 0.25 watts). The fact that the dummy does not have a torso serves to improve measurement accuracy. We concentrate on the interaction between frame/wheels/legs and exclude the rider's posture, as we primarily want to measure material effects. A human generates significantly more resistance than the bike with dummy legs. We take this into account in our simulations and basic stories.

Top speed tips

Whether a bike is fast depends on a multitude of details. An aerodynamic frame is just one piece in a big puzzle. Accordingly, there are also tuning options for bikes with less aerodynamic shapes

Manufacturers put most of their efforts into aerodynamic optimisation into the frames, forks and cockpits. However, the wheels and tyres, especially the front tyre, also contribute to the overall aerodynamics, as do the other add-on parts.

The rule is: less is more - especially less frontal area in the wind brings speed.

This applies all the more to the rider, who causes at least three quarters of the total drag, with the bike accounting for only a quarter. So if you lean lower over your bike, keep your arms close (narrow handlebars), wear aerodynamically optimised clothing and ride fast wheels and tyres, you will already realise a lot of the possible speed potential. You can go for it.

To maximise the bike's acceleration, the silhouette of the frame should be clean and the frontal area minimal. Slim tubes are essential, especially at the front of the frame. The fork blades must also be thin and low. Aero handlebars, wheels and tyres also add up to 15-20 watts. Single drivetrains are the cherry on the cake and add another 2-3 watts.

The latest trick, implemented by Hope for the first time on a track bike: Flared, plate-like seat stays to stabilise the caster of the legs. No other bike in the test field has this feature in such a pronounced form. According to current regulations, up to 145 mm seat stay spacing would be permitted. There is therefore still some room for further development.

measured with alternative wheels and without derailleur

The 4 aero road bikes in the test