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The Castelli Free Aero Race S Bibshorts are pro-level performers that undercut many of their rivals on price.
The bib shorts pack in Castelli’s flagship chamois pad, with a nod to aerodynamic performance that some may find appealing.
They also feel very well ventilated, although the lightweight design isn’t without a drawback or two.
Castelli Free Aero Race S Bibshorts details and specifications
The Castelli Free Aero Race S Bibshorts are said to be the most comfortable iteration of the brand's racing-focused shorts yet.
They employ a new fabric – called Forza2 Stretch – that's said to improve both comfort and aerodynamics.
A series of woven trip lines are positioned on the outside of the thigh and inner part of the groin, which are claimed to manipulate the airflow as it passes over your legs.
Castelli says this yields a 3 per cent reduction in rider CdA (drag coefficient), compared to a ‘normal’ woven fabric, although this was measured at “higher speeds” than most riders are likely to ride at.
Overall, the fabric feels slightly thinner than average for summer-season bib shorts, complementing the lightweight bib section.
The straps are notably thin too, with a slightly abrasive surface on the inside for retention on a baselayer.
Castelli claims the Free Aero Race S Bibshorts are best suited to riding in temperatures from 15-35°C (59-95°F). That’s on a par with most brands, albeit a little lower than Maap’s claim for the Team Bib Evo shorts I tested these alongside.
However, these bib shorts differ from the modern norm, in that the grippers take the form of silicone strips, rather than a textured approach.
These are low-profile, though, and oriented vertically to avoid pulling or chafing. The largely seamless design is also sleek and should help avoid this.
Castelli has utilised its top-level Progetto X2 Air Seamless chamois. This has a bobbled texture under the top layer, with zonal padding designed to offer support for a relatively aggressive position.
Despite the racy, lightweight design, the bib shorts are priced competitively. They're the cheapest among those I tested in spring 2025 (see ‘how we tested’), yet they don't have any shortcomings on paper.
The shorts are available in black, blue, brown and – for those who dare – white.
Castelli Free Aero Race S Bibshorts performance
The Castelli Free Aero Race S Bibshorts are very strong performers, especially given you can spend more for little gain.
Like all padded inserts, personal preference is hugely important, but I found the one used here equally supportive both in a more forward-leaning posture and sat up on the tops. It feels relatively well ventilated too.
The shorts’ main niggles lie in the bib straps – these are about as light as they come (which is great for warm summer rides), but while they distribute pressure well when arranged properly over the shoulders, getting them there is a slight challenge.
They roll up on themselves quite easily, and I found it took a fair amount of fiddling to get them to lie flat.
I noticed they had sometimes folded over slightly on their inside edges by the time I finished a ride, but most importantly I didn’t feel this happening on the bike.
The bib section felt slightly shorter than average for a size large, and I popped a stitch on a joining seam when donning them for the first time.
This hasn’t happened since, indicating that this is more down to the sizing than a notable quality issue, but it’s fair to say I’ve dressed more carefully in the Free Aero Race S Bibshorts since this happened, given my fairly long torso.
Castelli adopts a longer leg cut than average, with the raw hem reaching relatively close to the crook of the knee – this offers a good amount of coverage and the compressive fit (alongside the grippers) ensured they stayed in place.
I found it comfortable and just shy of causing any rubbing issues, but many may prefer a mid-length leg.
I didn’t notice a real-world aerodynamic benefit from the leg fabric’s trip lines, but the claimed improvement is small. If searching for every marginal gain is your thing, you might find their presence reassuring, at least.
The shorts breathed very well overall and felt low-profile – if I were selecting bib shorts for the sunniest, warmest weather, the Free Aero Race S would be among my top picks.
That said, you have to accept that the bib section can’t quite offer the same sturdy, locked-in sensation as many competitors.
How we tested | pro-level bib shorts
For this test, we focused on the latest generation of pro-level bib shorts.
I tested the shorts on shorter control loops, plus at least one longer ride. With chamois comfort so subjective, I focused on identifying more objective differences between the shorts, including sizing, feature positioning and quality.
I had brands submit medium and large samples for testing, enabling me to comment on relative fit and sizing. In the end, size large fitted my 188cm (6ft 2in) frame best across the board – although, of course, your mileage may vary.
Testing was carried out on a Fairlight Strael 3.0 road bike with a Pro Griffon saddle, and a Scott Addict RC fitted with a Syncros Belcarra R perch.
Each pair of shorts was put through 40℃ (104℉) wash cycles with standard non-biological detergent, rather than a sport-specific wash.
Shorts tested
- Rapha Pro Team Bib Shorts III
- Maap Team Bib Evo
- Castelli Free Aero Race S
- Q36.5 Dottore Pro
Castelli Free Aero Race S Bibshorts bottom line
The Castelli Free Aero Race S Bibshorts are great pro-level bib shorts for summer weather, as long as the sizing works for you. As a relatively tall person, I found the body a little short, but fit is subjective.
The lightweight construction doesn’t feel quite as resilient as some other premium-level bib shorts, but the upside is it’s certainly among the coolest-feeling on a warm day.
The fact that they're slightly cheaper is also a feather in their cap.
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Product
| Brand | Castelli |
| Price | A$330.00, €200.00, £199.00, $230.00 |
Features
| Gender | mens |
| Features | Sizes: XS-3XL Colours: Black, Belgian Blue, White, Deep Mocha |
