Castelli Free Aero Race 4 bib shorts review: Top cycling shorts straight from the pro peloton

Castelli's Free Aero Race 4 bib shorts are an aero optimized, race fit pair of cycling shorts that can go the distance

Castelli Free Aero Race cycling bib shorts
(Image: © Josh Ross)

Cyclingnews Verdict

Almost the perfect bib shorts for every situation. The Castelli Free Aero Race 4 bibshort has a chamois that can handle century-plus rides without issue while also being aerodynamic and stylish. Don’t bother searching forever, these are the bib shorts you need.


  • +

    Aerodynamically optimised

  • +

    High-density chamois under the sit bones

  • +

    Excellent fit

  • +

    Flat front


  • -

    Not every seam uses flat-lock stitching

  • -

    Graphics come off

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There's no introduction needed for Castelli. It's a brand so deeply embedded in cycling that it's impossible to miss, and the Castelli Free Aero Race 4 bib shorts are just one product in a long line of extremely well-revered cycling garments, taking full advantage of Castelli's equally long list of technological innovations.

Castelli has been a stalwart in the cycling industry for decades. Both at the top level, in the most prestigious races that cycling has, as well as in nearly every cycling shop of every size. Whatever level of cyclist you consider yourself, Castelli has options. If you like the idea of wearing WorldTour level cycling gear, that's what you are getting with the Castelli Free Aero Race 4 bib shorts, but let's take a look at what that means, how they compare to the best cycling shorts on the market, and whether they make for a good choice for you. 

Castelli Free Aero Race 4

(Image credit: Josh Ross)

Design and aesthetics 

If you are looking at the Free Aero Race 4 bib shorts from the outside, the dominant visual detail is actually a performance detail. On the outside of each leg, from the hip, down to the gripper section, is a section of dimpled fabric. This is part of the aerodynamically optimised design and is said to work in the same way dimples on a golf ball work, in that the extra turbulence from the dimples helps keep the air attached across that section of the leg and reduce drag. 

CFD modelling and testing from Castelli says it works, and if aerodynamics are important to you, then every little bit in every location adds up. There is, of course, no practical way to measure and quantify these claims, but there's also no harm in it.

The importance of the dimples goes beyond performance though. Consider the dimples the promise of performance translated into a visual language. It doesn't matter how much they help, just the fact that they do in some way, allows them permission to make that promise visually. Said simply, they look fast and because they are fast it feels okay. Big black expanses of lycra on bib shorts aren't the best for style and the dimples get rid of that problem. The curves and placement of the dimpled panel push that design language even further. It has an organic shape that radiates movement even when static. 

Below the dimpled panel, there's a gripper panel. The fabric used isn't different from the rest of the legs and it's a single layer. On the inside of this panel there are strips of silicone running vertically about 3/4 of the way up. 

The dimples might be the most noticeable thing visually, but when it comes to fit, it's the inside of the legs and the front that stand out. There are a lot of different designs that tackle this area but Castelli goes with a rather complex option it calls Doppio V construction. It's a five-panel solution that ultimately keeps the front modest, as well as providing compression to the lower abdomen without making it hard to breathe. 

The last component of the design is the straps. Everything above the waist of the shorts uses a striped mesh for extra breathability. You can easily see through these thin sections, and you can physically feel the thick-then-thin construction.

On the lower back, you'll get another reminder that the Castelli Free Aero Race 4 bib shorts were designed with professional athletes in mind, with a radio pocket that, in all honesty, most people are unlikely to use. 

Castelli Free Aero Race 4

The leg grippers are constructed from striped silicon that provides a secure hold without over-compression (Image credit: Josh Ross)

Ride experience 

The Castelli Free Aero Race 4 bib shorts were introduced to the market in 2019. As we come up on three years of availability, these are the bibs I have worn more than any other out there. I am constantly testing new options from all kinds of companies and yet I come back to these over and over again. Recently I used them to cross the state of Washington with back-to-back 200+ mile days of 12- and 13 hours. Previously I used them to cross the state of Oregon while riding 160-ish miles a day and washing them in sinks along the route. Given the option, I've even bought extra pairs just in case they went off the market or weren't available. 

I feel comfortable saying I know these bibs as well as anyone out there. Knowing a product that well means I know all the flaws, and there are a few. Despite being a leader in dye sublimation, Castelli loves to bond its logos with glue, which means they invariably come off. The only good thing about this being that they generally come off without any sign that they were ever there. 

There is also one small flaw in the way that the panels come together. Most of the panels use flatlock stitching but not all of them. The complicated Doppio V design consists of mostly standard seams. There is a seam up the inside of the leg that then connects to the panels at the front and it's not a flatlock seam. After about 10 hours in the saddle, I have noticed chafing from the spot on the inner thigh before it heads under the chamois. 

That's two paragraphs about flaws in these bib shorts but consider the context. I always go back to these and one of the flaws is chafing after about 10 hours in the saddle. I ride a lot of long-distance and even for me, that's not a frequent event. 

On the other hand, there are a lot of great things about these. From a performance standpoint, the reason I choose these is because of the Progetto X2 Air Seamless seat pad, otherwise known as the chamois. After my recent 400-mile, two-day ride, I spent some time really looking through all the bibs I have on hand and evaluating the different solutions. Castelli just simply does it better than others. It's not bulky but it's dense. For really long rides these are one of the best options on the market but they also work for short, fast, rides. 

Leaving performance behind, I also really like the aesthetics of the Doppio V design I've mentioned a couple of times. It's not a perfect solution in terms of construction but visually it nails it. If you are standing around, off the bike, the front of the bibs are flat and featureless, which I consider a benefit. 


The best way to sum up the performance of the Castelli Free Aero Race 4 bib shorts is just to say that with a closet full of the best cycling clothes on the market, I go back to these over and over again. They aren't perfect, but even despite the few small flaws, they are some of the best out there.

If you like the idea of riding in top-of-the-line bib shorts with an excellent chamois then these are a great option. The design is well thought out and fashionable. They are fast and aero optimised but not at the expense of comfort. The chamois design is good enough to last through rides with double-digit time frames and three-digit distance numbers, and if at the end of those rides you need to run them under hot water in a hotel bathroom sink, they'll hold up for the next day's ride too. 

Castelli Free Aero Race 4

(Image credit: Josh Ross)

Tech Specifications:  Castelli Free Aero Race 4 bibshort  

  • Price: £160.00 / $199.00 / €160.00 / AU$269.00
  • Materials: [legs] Vortex dimpled fabric, [inner thighs] Forza fabric with 38% Lycra 
  • Colours: Black, Dark grey, Saville blue
  • Size availability: S-XXXL
  • Weight: 172 gr

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