The Free Aero RC Bibshort. The latest premium short offering from Castelli has been 15 years in the making.

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. Yet without any superfluous parts to slow it down. If you’re comfortable, aerodynamic, and not overheating then you’re going to have a great ride.
 
 
A LITTLE HISTORY
Let’s start with some history. Castelli’s Free bibshort has always been driven by the concept of its name: to make you feel freer by eliminating anything that’s unnecessary. This is the fifth major update to the Free heritage, with the original concept going back to 2007, when we launched a new and innovative race short for Castelli’s return to the ProTour, as the WorldTour was called back then.
 
The original Free Bibshort had a couple of innovations that would change the canons of shorts for at least the next few decades. First was the leg gripper. Shorts of the time had a stitched-on thin elastic leg gripper that could best be described as a tourniquet. The Castelli Free was the first to introduce a raw-edge fabric gripper that didn’t bind. Second was the bib straps, which back then typically covered half your upper body in hot, sweaty bibs, to the point that you’d sometimes see the pros taking scissors to their bibs in hot weather. The Free had the most minimal mesh bibs we could make.
 
 
WAIT! NO GRIPPER ELASTIC??
That’s probably the first thing you’ll notice about this short. There’s no grip whatsoever. No silicone applications, no stitched-in elastic, nothing to detract from the smooth, flat fit and comfort of this short.
 
But does it stay in place? Most of us have used shorts in the past that “ride up,” and it’s incredibly annoying. The gripper elastic has always been the solution, but any sort of elastic or silicone or grip brings some sort of discomfort. Maybe you never noticed it but you definitely won’t miss it.
 
A few years back, we came out with the Omloop thermal short after seeing some of the pro riders at the Omloop Het Nieuwsblad cutting off their knee warmers to just above the knee. We made that fleecy thermal short without gripper elastic and realized that the right combination of fabric, length, and circumference can make a short leg stay in place without grip.
 
As we looked at making a significant update to the Free bibshort, we knew we could do the same thing with a summer shorts fabric, but we underestimated how challenging it would be to find the right fabric — the smooth summer fabrics are more slippery on the inside than the fleecy Thermoflex of the Omloop mentioned above. But we started testing fabrics. We actually went through 28 different fabrics to find the one that gave the right support and was the right weight but didn’t move. Then we went through a dozen or so trials to find the right length and circumference so it wouldn’t move. Then we made 50 pairs each of two versions of test samples for an extended field trial with 50 Castelli ambassadors in every condition from spring cold in Norway to heat and humidity in Dubai and Texas.
 
Finally, the short went through testing by the riders of Quick-Step Alpha Vinyl, making sure it would work on everything from the skinny climbing legs of Pieter Serry to the powerful sprinting legs of Fabio Jakobsen. We’ve come full circle from the first attempt to improve leg endings 15 years ago, now with the best solution of all: nothing.

 WHAT’S UP WITH THE BIB STRAPS?
Revisiting the theme of using less to do more, we’ve reengineered the straps. Again.
 
The theory here is that the straps should do nothing but hold up your shorts. They shouldn’t provide insulation; they should just stay out of the way. To reduce material, we created the new monofilament strap on the front that’s super stretchy with just the right amount of modulus (that means it holds your shorts up) but yet doesn’t absorb much sweat. The back portion is soft mesh and very narrow, but over the shoulder we’ve reinforced the straps so they lie flat and distribute the load rather than bunch up. Even the attachment points have been engineered to distribute the force across the hemline. You feel freer than ever.

THE PROGETTO X2 AIR SEAMLESS SEAT PAD
If you think that name seems unwieldy, you’re probably right. We just kept adding words as we’ve evolved this pad since 2009. Originally developed with the Cervélo TestTeam, this pad has been in constant evolution. We think that’s vitally important. A wholesale redesign means you start completely over from the beginning. But with over a decade of continual improvement, Castelli’s top-of-the-line seat pad is more comfortable than ever.
 
The key aspect of the X2 is that it’s really two completely separate components, each designed for a completely separate function.
 
Next to your skin we place the appropriately named Skin Care Layer. It’s the softest and stretchiest layer we’ve ever made, to move with your skin and avoid abrasions.
 
Beneath that layer is a completely separate component that we call the Cushioning Layer. It’s 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 and 3 mm gel pads under the sit bones and perineum. Thanks to the 3D forming process, the pad thickness is infinitely variable and has no pronounced steps like many pads that are simply punched out with a die.
 
This iterative process of continuous improvement means that not a single material used today is the same as it was in the 2009 version. It just keeps getting more comfortable. Naturally, in men’s and women’s-specific designs.

WOMEN’S AND MEN’S
The design and performance goals for this short are the same for both the men’s and women’s versions, so the two versions are also quite similar. Same fabrics, same raw-cut leg endings, same materials in the bib straps. However, the patterning was completely different from the very first sample, so the fit is very specific for men’s and women’s, as are the different seat pads. Two different development routes to provide the same performance.
 
 
 
FREE AERO RC VIGNETTES
Every detail of this short has been obsessed over, so here are a few more details that you should know about:

FABRICS – The shorts portion is made up of a brand-new 215 g/m2 double-face circular-knit fabric with a 32% elastane (spandex in USA) content that gives it that snug, compressive feeling. The 68% nylon gives durability, and the central portion goes through an embossing process for further durability. The fine gauge of the yarns means it’s soft to the hand, and the multi-filament yarns mean it wicks moisture away better.
 
REAR POCKET – The narrow rear strap of the bibs continues to attach closer to the seat pad to better secure the short, which makes a convenient functional rear pocket. Great for race radios for the pros, while the rest of us can stuff in money or keys to keep them secure.
 
LOGO DURABILITY – We want this short to last, so all logos are either stitched, embossed, or sublimated. The embossing and sublimation are permanent, while the stitched logo would only come loose if the stitching breaks, but even then it can be easily repaired. No more cracking or detached logos with the new Free.

AERODYNAMICS – It’s not normal for aerodynamics to be buried in a minor point of a Castelli press release, but yes, we’ve also developed this short to be fast. It is very close to the outgoing short at 0° yaw (i.e., no crosswind), but the new version starts to make significant gains in even minor crosswinds (yaw angle 5%), saving up to 0.7% of the overall aerodynamic drag of the entire system. In other words, your 300-watt effort produces 302-watt speed, thanks to this short, in anything but completely still winds.
 
VERSIONS – This short is available in the dyed fabrics like the pair you’ve received for testing, as well as the team version, as seen on Quick-Step Alpha Vinyl, which will soon be available through Castelli Custom. There’s also a non-bib version for those who prefer not having bibs.
 
REFLECTIVITY – We’re firm believers that you should ride with lights on your bike rather than counting on a little bit of reflectivity on your clothes. But we’ve all been there — staying out a bit too late or riding through a tunnel on that one day we left home without a light. There are two reflective tabs sewn into the seam on the back of the legs. They’re generally out of the way, but when a car comes up behind you, the two tabs moving up and down will catch the driver’s eye.