Castelli Free Aero RC bib short review

It might be an evolution of one of the best bib shorts available but is it an improvement?

Castelli Free Aero RC Pro bib short
(Image: © Josh Ross)

Cyclingnews Verdict

Castelli continues to make one of the best bib shorts on the market. It's aero optimised and race-focused and the chamois is better than the competition. When your ride lasts days, instead of hours, the Castelli Free Aero RC bib shorts are an option you can depend on


  • +

    Radio pocket becomes an actual useable feature for the rest of us

  • +

    Straps don't roll when worn or twist in the washer

  • +

    Progetto X2 Air chamois is the best on the market

  • +

    Aero optimisation

  • +

    Logos won't peel off


  • -

    Inner thigh seam still isn’t flat locked

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Take a look at our list of the best cycling shorts on the market and you'll notice that Castelli makes multiple appearances. Castelli knows how to make a top-quality bib short and it has options depending on what you are looking for. The variety it offers gives it opportunities to land on our best lists for different reasons. For those looking for a race-focused option, the previous option from Castelli was the Free Aero Race 4 bib short. It was a bib design that had been on the market for longer than most but continued to be one of our favourites. 

This year, Castelli has replaced those bibs with an evolution. The new option comes to market as the Castelli Free Aero RC bib short and brings with it a host of changes. We've spent time with the new option and now we are ready to talk about what's new, what's old, what's great, and what could use some work. If you are looking for a new pair of summer bib shorts then keep reading to see if you think this update from Castelli is going to be the best option for you. 

Castelli Free Aero RC Pro bib short rear view

The view from the rear shows the extensive simplification and revised strap design (Image credit: Josh Ross)

Design and aesthetics 

In the world of clothing, performance-focused or otherwise, three years since a major update is a fairly long time. That's the last time Castelli updated its race bib shorts. This year it's time for a new model, and it's almost an entirely new design. It still represents the same race-focused placement in the Castelli line-up but even that has undergone a small shift. 

In particular, Castelli is precise in the way that it refers to the Free Aero RC bib short. 

"Notice we don’t call it a race short or a comfort short. Maybe the closest we could say is that this is our WorldTour-level race short, which by very definition of the demands placed on it means that it must be exceedingly comfortable. And exceedingly fast."

That's a little bit different than the language used in the past and it sets the stage for what these bibs are. 

In an effort to make the Free Aero RC bib short an all-day option as well as a race-day option, one of the biggest things that's different in the new version is the level of simplification. The previous Castelli Free Aero Race 4 is a complicated bib short. There are a lot of panels and a lot of aero detailing. With the Free Aero RC the process has been simplified at every opportunity. 

While the previous generation had ten panels to make up the shorts, that has now dropped to half the number with a total of five. As part of that change is the loss of the 3D texturing that defined the aero detailing of the previous generation. However, the simplification of panels goes hand in hand with an updated aerodynamics understanding. Castelli has moved away from using texture to keep the air attached and instead smoothed and minimised seams. The end result seems to have worked with aero figures quoted as "very close to the outgoing short at 0-degrees yaw" but 0.7 per cent faster when yaw changes to 5 per cent or greater. 

Granted, 0.7 per cent isn't much, but what's important is that it's there as a bonus. A 300-watt effort becomes a 302-watt effort for bibs that have other advantages. In fact, some of those other advantages align perfectly. Some of the changes to the panelling, which benefits aerodynamics, is the loss of a bottom panel that includes silicone grip material. The new design has no silicone grip and instead uses a "brand-new 215 g/m² double-face circular-knit fabric" that's 32 per cent elastane. That's about double the elastane of other brands and it's enough to keep the Free Aero RC feeling snug and compressive without needing any silicone. 

As Castelli revised the design, one place that did not see any simplification was the design of the straps. The previous straps used a single piece of fabric for the complete system. The new design uses multiple pieces with different properties in different areas. At the front the straps tie into the structure slightly lower than the old version and they are thinner. The material has a texture to it with strips of elastic alternative with a very thin mesh. It does not stretch at all side to side while keeping plenty of vertical stretch. Gone is the part of the straps that used to cover the sides of the body and that's now part of the same panel as the thigh. 

Although the straps are thin, they don't fold much. When the straps hit the top of the pecs, they gain a backing material. The combination of the two fabrics makes it hard to bend and these will not roll up. They also don't run any risk of wrapping into a knot in the washer. On the upper back, the straps come together and there's a bit of the same material from the shorts in use as a gusset. Below that the straps change to a single strip of mesh through the central back before tying in below the top of the shorts. It's here that you'll find a radio pocket that's now just as useful for non-radio use. 

Castelli Free Aero RC Pro bib short detail of radio pocket

The radio pocket is now reasonably useable no matter who you are (Image credit: Josh Ross)


I've been vocal about my love of Castelli bibs in the past. The previous generation of this bib was my all-time favourite bib short design. I actually have a stash of them in case I didn't love these. For the most part, I'd say I don't need to worry. After spending time in the new design I can say that what's new is an improvement and what isn't new is just as good as it's always been. 

As far as what's not new, that's the Progetto X2 Air chamois. Unsurprisingly, Castelli has a whole section in the press release covering the merits of this pad. It's been around since 2009 but it's been continually developed. As it stands right now, there are three important pieces. At the top is a soft layer that's not attached to the lower layers. The top layer sits against your skin and moves separately. There's no opening but inside the pocket it forms is a "cushioning layer." 

Exploded view of the Castelli Progetto X2 Air chamois

The Castelli Progetto X2 Air chamois is one of the best available on the market (Image credit: Castelli)

As Castelli says, the cushioning layer is "in the shape of a saddle and provides progressive cushioning exactly where you need it. There is a soft foam for immediate comfort, with a medium-density foam for support." 

These pieces don't have any distinct steps like some pads do. It's a smooth transition from thin to thick at the places needed. None of the pieces so far are what make the Progetto X2 air really special though. The special pieces are 3mm gel pads under the sit bones and perineum. For the rider, it means that no matter how long you spend on your bike, you'll never feel bruised. Ride for long enough and some chamois systems will leave your sit bones tender and bruised but not the Castelli. 

In terms of what's new, it's the straps that are the highlight. Of all the great things that come together in the last version, the straps were a weak point. They were okay, but not exceptional, and the radio pocket was useless for most people. The new straps tie into the rest of the structure lower and do a better job at the shoulders. The new pocket design is unlikely to see much use but it's at least possible now. These are genuine improvements. 

I'd call the move to fewer panels and no gripper more of a lateral move. The grippers in particular were never something I would have called out as an issue. The new fabric is definitely softer but in both cases, I wouldn't say the updates are a big move forward. More accurately, it's a different experience and one isn't necessarily better than the other. 


The Castelli Free Aero Race 4.0 were the bibs I always grabbed when I knew I'd be riding from sunrise to sundown. I've ridden thousands of miles in them and multiple days wearing them after a sink wash, or without. The new Castelli Free Aero RC is an improvement. I haven't had the chance to spend as much time, or have as many adventures, in this version but in the few hundred miles I have enjoyed them. When I leave for my next longest ride, these will be the bib shorts I choose. 

The only defect I can point to is something that hasn't changed since the last generation. There is one seam along the inner thigh that's not flatlocked. It was there before and it's there again, still without a flatlock stitch. It's the only place I've ever noticed an irritation from Castelli bibs and it should have gotten some attention in the update. That said, the new fabric is softer and it may be enough to solve the problem. It takes a ten plus hour ride to see if it's an issue so for most people it won't be an issue and even for me, it has rarely come up. 

Castelli Free Aero RC bib shorts detail of seam without a flatlock stitch

This one seam along the inner thigh should use a flatlock stitch just in case it's an issue (Image credit: Josh Ross)

 Tech specs: Castelli Free Aero RC bib shorts  

  • Price: £175 / $219.99 / €179.95 / AU$279.99
  • Weight: 170 grams
  • Size availability: XS, S, M, L, XL, XXL, 3XL
  • Colour Options: Black, Dark Gray, Savile Blue

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Josh Ross

Josh hails from the Pacific Northwest of the United States but would prefer riding through the desert than the rain. He will happily talk for hours about the minutiae of cycling tech but also has an understanding that most people just want things to work. He is a road cyclist at heart and doesn't care much if those roads are paved, dirt, or digital. Although he rarely races, if you ask him to ride from sunrise to sunset the answer will be yes.
Height: 5'9"
Weight: 140 lb.
Rides: Cannondale Topstone Lefty, Cannondale CAAD9, Enve Melee, Look 795 Blade RS, Priority Continuum Onyx