In the aero bike arms race, it can be hard to stand out from the crowd. But Italian manufacturer Wilier has done just that with the Filante SLR ID2.
Announced in October 2025, the bike has some impressive credentials, shaving a claimed 13.1 per cent off the previous generation’s drag when ridden at 50km/h. But this isn’t the metric that matters most to Wilier.
Instead, the iconic heritage brand has redesigned its flagship aero bike around the full system – including rider and bottles – and not solely the bike’s performance in CFD simulations or the wind tunnel.
Impressively, Wilier says it still shaves 5.04 per cent off at 50km/h and a 15° yaw angle with a rider – a more accurate simulation of conditions in the peloton during a WorldTour race. This reduction translates to a 105-second saving on a 70km ride at 290 watts, according to the brand.
According to Wilier’s own testing, this was better in a direct comparison with five rival WorldTour aero bikes, and the Filante SLR ID2 had an average aerodynamic resistance coefficient that was 2.42 per cent better – the difference between first and second in a one-day Classic or over the course of a three-week Grand Tour.
Wilier says the Filante SLR ID2 manages all this without sacrificing its handling, compliance or looks, with the finished article an Italian masterpiece that Michelangelo and Raphael would be proud of. Here, technical product manager Giacomo Sartore explains how.
Rider-focused redevelopment
The starting point for the second generation was the Filante SLR ID1. A WorldTour-proven aero platform with some prestigious victories under its belt (including Sir Mark Cavendish’s record 35th Tour de France stage win in 2024), it was due an update after five years.
“The key goal was to improve the performance, not only of the bike, but the system,” says Sartore.
The ‘system’ he refers to includes the rider, componentry and riding essentials such as water bottles.
An approach first adopted during the development of its time-trialling platform – 2024’s Supersonica – it involved investigating the aerodynamic impact of the system as a whole, and seeing how things interacted with each other when it came to turbulence.
“We divided and split the bike and the components into many single parts – 83 for the bike, plus 10 for the rider. These 93 parts were developed in the CFD tool, and we are able to see in every single pixel how the air is interacting with the bike and with the component.”
Wind-cheating front end
After numerous rounds of testing and prototyping, Wilier settled on the Filante SLR ID2’s shape.
While it has a similar silhouette to the first generation, alterations have helped it shave a significant amount of drag from its predecessor.
The biggest contributor to the improved results is the introduction of the Aerokit. A complete redesign of the down tube, bottle cages and bottles, it acts as a spoiler, reducing air turbulence around the frame. Part of the system-focused approach, the Filante SLR ID2 is faster with the specially designed 550ml Elite aero bottles than without them.
But Wilier also understands that, in certain situations, riders might want the choice to use standard bottles and cages: “We didn't forget about usability and the everyday rider. On the seatstay tube, you can also put a 750ml bottle if you want to go for a longer ride.”
Staying at the front of the bike, a new NACA aerofoil-derived fork profile has reduced turbulence, while refined features such as an encased thru-axle clamping bushing and a countersunk thru-axle head minimise drag.
The F-Bar ID2 cockpit is also aerodynamically and ergonomically optimised.
The S-shaped flared design has a straight section where the hoods are clamped, ensuring they remain in line with the flared drops when turned inwards. “[Without this], your bike is aerodynamically inefficient because you have the airflow which attaches first to the brake lever and then the handlebar,” explains Sartore.
Going off-script
Sartore explains that the rear triangle is less clear-cut when it comes to aerodynamics: “You have the legs that are spinning. You have a wheel that is turning. You have a drive system, which is turning and running. So, airflow on this section of the bike is not as straight as from the front.”
But it was still an area that Wilier looked to improve, discovering an advantage through testing that goes against traditional rules.
“If you have [the ID1 and ID2] next to each other, the new generation has the same shape and design, but we have slightly inclined the angle of the seatstays by 2.5°," he says.
“If you go by the theory, the straighter it is, the more aerodynamic it is. But after testing and going back and forth, we found that by moving the angle of the seatstays slightly, the bike was more aerodynamic. It’s an example that shows that Wilier doesn’t just stand by the rules.”
Above the rear triangle, Wilier looked to its Supersonica platform for the seatpost, creating a much thinner, aerodynamically optimised profile that doesn’t compromise on stiffness or comfort.
Improved handling
While an aero bike has to be able to cut through the air with minimal drag, Wilier’s system-first focus meant the Filante SLR ID2’s rideability wasn’t forgotten in the pursuit of results in a wind tunnel.
Sartore explains that the reduction of turbulence around the front end has an added handling benefit – making the bike easier to control for all riders, with less air to push and pull it in crosswinds.
“We need a fast bike for the pros, but we also need a bike for everybody. If you are an amateur and you reach 50km/h on a descent, if you have less turbulence behind the frame, it's easier for you to handle the bike,” he says.
The thinner seatpost meant Wilier had to come up with an alternative solution for the placement of a Shimano Di2 battery, too, which was lowered to near the bottom bracket, aiding the bike’s planted feeling.
The frame’s stiffness and comfort, meanwhile, are taken care of by Wilier’s carbon fibre “recipe”. “Over 20 years, we have found the best compromise – to give the right stiffness to the pro riders and enough comfort for everyday riders.”
Pro-rider input
WorldTour professionals have been integral to the Filante SLR ID2’s development, with Wilier working closely with Groupama - FDJ during the prototyping and refinement stages of the process.
“They came in at 60-70 per cent of the development status when we already had something physical to touch, see and test,” says Sartore.
“We were out on the road with the very first riding prototypes in March ’25, and Roman Gregoire rode Il Lombardia with the final prototype – he had the bike at home for at least two/three months beforehand.”
The French team had input in all aspects of the finished article, too. “We did 37 iterations of design just for the handlebar,” he adds.
Finishing flourishes
The Filante SLR ID2 stands out from the aero bike crowd courtesy of its Italian flourishes.
A small recess has been made in the chainstay behind the chainring to house a Shimano power meter magnet, which is then covered by a smooth, silver cover.
Sartore says this has three advantages: “When your chain drops, your magnet doesn't get ripped out from the chain itself, which sometimes happens; aesthetics, because you have a surface which is flat; and a little bit of aerodynamics.”
While not as integral as the Aerokit that sits above it, “it’s that 0.01 per cent which adds to the project as a whole,” he says.
Other drag-minimising and image-boosting tweaks include fully integrating the cockpit’s bolts by hiding them under a cover.
“The main focus of the Filante SLR ID2 was on the aerodynamics,” concludes Sartore. “But this also led us to a clean design and a full integration, and ultimately a WorldTour sticker of approval.”
