Visit any WorldTour race paddock, and you'll find it littered with radical-looking aero bikes. Tadej Pogaar (UAE Team Emirates XRG) has won prolifically using the Colnago Y1Rs, banishing the V5Rs lightweight bike to the team van. Perhaps most eye-catching is Factor's One bike, with its new take on geometry and wide forks that verged on UCI-illegal. While many brands Specialized with the Tarmac, Cannondale with the SuperSix Evo and Trek via the Madone have dropped dedicated lightweight and aero models in favour of a 'one bike to rule them all' approach, elsewhere, it seems that aero bikes are here to stay. And they look weirder and more wonderful than ever. Tadej Pogaar one-of-one Colnago Y1Rs (Image credit: Aaron Borrill)Pogaar's dominance is such that he could probably ride pretty much any bike in the WorldTour and still win, while the Factor One has seldom been used by either the NSN Cycling team or Human Powered Health, with most riders instead opting for the Ostro VAM 2. Are these latest aero bikes really offering the best solution for riders to be their fastest, or are they perhaps not quite there yet? If so, what refinements might come next?The radical Factor One isn't always used by pro riders on sponsored teams (Image credit: Richard Butcher)Rider and bike, together as oneThere is one annoying trend in the bike industry: vague, unclear testing or white papers. There are often quotes about the watts saved versus another bike, be that a previous generation one from the brand or, quite commonly, the leading competitor. Very often, details are limited: just the speed is given, maybe the yaw angle if were lucky. But it is often neglected which wheels were tested, tyres, handlebar width and geometry setup, or even if a rider was present on the frame for the test or not.Our sister publication Cyclingnews has been testing bikes in the wind tunnel over the last few years. A common trend has been that, just because a bike alone shows itself to be fast, or even slow, with no rider present, it does not necessarily mean that it will maintain that relative position when a rider is added.Some frames may perform badly without a rider, then be significantly faster with a rider present. Meanwhile, others test fast as a frame only, yet drop down the charts once a rider is onboard.Adding a rider makes a huge difference to the performance of a bike (Image credit: Future (Sam Gupta))The reason for this is that a cyclist's legs are two large moving pistons that disrupt airflow and create more frontal area than the entire bike frame and wheels combined. Add a great big torso on top of the bike, and total drag increases dramatically. This is why the performance differences between frames tend to get significantly closer with a rider present. Partly because the total drag percentage of the bike is so small when a rider is present, but also because some aerodynamic features of a bike can be rendered somewhat inept once you add legs on either side of it.Some aerodynamic features of a bike can be rendered somewhat inept once you add legs on either side of itThe industry has taken note of this, and some bikes are being designed and tested with a rider present. In developing the latest Specialized Tarmac SL9, for example, the engineers used a moving-legs mannequin as part of the design process. We may be reaching a point where aerodynamic gains in bike design are slowing down the low-hanging fruit has already been collected but designing bike frames with riders in mind is where we will most likely see the next set of gains.Shape shifting Wide tyres and shorter cranks make a difference (Image credit: Aaron Borrill)There are a few other interesting design features that have become commonplace in cycling, which need to be considered when taking aerodynamics into account. First and foremost, the acceptance of wider tyres.Previously, riders typically used 19-21mm tyres, whereas now 30mm tyres are commonplace, often measuring as wide as 32mm due to the wide rims they are fitted to. The wheel size, however, has remained consistent. These wide tyres marginally increase the height of the bike and the circumference of the wheel. The introduction of shorter cranks has an impact, too. Short cranks, which open a rider's hip angle, require a higher saddle to achieve the same leg extension at the base of the pedal stroke. This again raises the COM and the frontal profile by a small amount and does increase drag.Given that road frames have not changed significantly since tyres have gone from 19- to 32mm, and crank length from 175- to 165mm, there is clearly scope for aerodynamic frames to be designed with these factors in mind. For example, a lower bottom bracket drop would account for shorter cranks, and I think it is likely a design path that frame manufacturers will pursue.Track cycling leads the wayTrack cycling leads the way in aerodynamic innovation, in part because, in individual efforts as well as small-team events like the Team Pursuit, aerodynamics accounts for most of the forces riders must overcome.Factor, for example, takes several design cues from its track bike that won gold at Paris 2024 for Team Australia in the mens team pursuit, and applies those to the Factor One. The latest BMC time-trial bike, used by Stefan Kng and his Tudor Pro Cycling teammates and currently offered to the public in limited quantities, shares several design features with the Hope track bike used by Team GB.BMC's newest Timemachine (Image credit: Getty Images)This wide-fork, high-seatstay design is a perfect example of bikes being designed around riders. The new BMC Timemachine features high seatstays, directly contradicting the approach taken by most brands in their aero bikes. Seatstays dropped across the board when aero bikes first appeared on the scene; doing so reduces frontal area and frame-only drag. But when a rider is present, the difference is smaller. This is where it gets interesting. BMC has not only raised the seatstays, but also deepened them and extended the aerofoil profile forwards. This, in theory, should result in a smoothing of the airflow off the back of the riders legs and decrease turbulent pressure drag behind.The integrated cockpit of the S5 (Image credit: Andy Carr)We are also seeing more customized cockpits and handlebars solutions. This is not new in track or time trial events, but road setups are more tailored now. The latest Cervelo S5 uses a one-piece bar and stem, but what the pros are using features bespoke effective stem lengths, bar widths, and stem angles that are not readily available for the public to use, even if the overall design is the same.Bikes designed for purpose While track and time-trial bikes may influence road design, they're generally designed to travel at much higher, more consistent speeds. A design that is fast at 60-70km/h (track speeds) might not be relatively as fast at 40-50km/h (road race speeds), let alone at WorldTour climbing speeds. In the same way, riders use specific skinsuits for expected race-speed averages; frame designs suitable for track and time trial might not work as well for road racing, let alone for consumer frames.Mathieu van der Poel rides his Canyon Aeroad up the Kapelmuur (Image credit: Getty Images / Tim de Waele)How a bike actually rides also matters. Lets take the radical Colnago Y1Rs and the more traditional Cervelo S5. The Colnago is not quite as refined and direct in the front-end handling, while the rear compliance is not at the same level as the Cervelo S5. Weve tested the S5, and it is genuinely a superbly balanced race bike, with stiffness and comfort where required. The design principles of the bike have remained similar in all its iterations going back over 10 years, but each model has been refined and optimised based on rider feedback.The Cervelo S5 (Image credit: Andy Carr)Potentially, the reason the Factor One has not been used as much at the pro level is that, given its design choices, it lacks versatility. Tech editor Aaron Borrill, who tested the Factor One, found it was an absolute rocket at higher speeds. But, several design elements and feedback Ive heard suggest that it is not the most comfortable for long days in the saddle. The Factor One might be fast, but feedback over its long-ride comfort has been less positive (Image credit: Richard Butcher)Its also been suggested that it can be prone to variable wind directions experienced at lower speeds and when riding in a bunch. Its a great piece of specialist design, and I applaud Factor for it. But being a revolutionary bike, it will likely need some refinements to find that balance between out-and-out aero and a bike that offers all-day compliance, comfort, and confidence.The weight factorAero frame design can be held back by our obsessions around weight. Weve seen with the new Giant Propel, Merida Reacto, and Trek and Specialized converging on a do-it-all aero lightweight bike that some manufacturers are still chasing low weight over total aero efficiency. This does result in a somewhat compromised aero bike, but one that can hit the 6.8kg UCI weight limit, or even drop below it for consumers.Merida's latest Reacto aero bike (Image credit: Aaron Borrill)The aero bikes, even if heavier, are faster, with the caveat that speed remains consistent. Even over longer climbs with some accelerations, a 500g weight difference does not hinder the aero bike, especially at the WorldTour level. But there is a tangible difference between a bike that is 500g lighter vs a frame that is five watts less draggy. Psychologically, we can feel the weight difference, but not the watt difference. Personally, I can also attest that a lightweight bike is more fun to ride. It is lively, accelerates perceptively faster, and feels nimble and effortless. I used to train on my TT bike and do 40km/h endurance rides, but it felt sluggish to accelerate, climb, and descend, even though it was undoubtedly faster. I cant feel the difference between riding at 30- or 32km/h, but removing a bottle from my bike makes it feel better to ride, which in my mind has a psychological impact.The final wordEven though we are seeing some wild and wacky aero bike designs, in my opinion, they are not going far enough, given how technology and equipment choices have advanced. We are starting to see more technology from track cycling make its way into bike design, as are rider- and frame-engineered solutions. But larger tyres and shorter cranks accommodating new frame designs might be the most interesting direction that frame design will likely travel.Of course, this needs to be balanced with the other factors that contribute to a good bike. There is a good chance that the next lot of revolutionary aero bikes will be refinements of what we are seeing now, with features that improve ride quality, not just wind-tunnel performance numbers. But there will still be the ever-present limitation of weight, where riders are unwilling to sacrifice the tangible, perceptible difference of a lighter bike, versus the less perceptible to humans yet clearly genuine advantage of a less draggy bike.