The Sidi Aeron shoes are the latest high-end off-road race option in the Sidi lineup, featuring the new, updated Millennium fit system that widens the toe box and straightens the last for a better fit on most feet. It still keeps some of the modular look Sidi has used for the past few decades, but it's more refined with the new Nuun 001C dials and a sleeker silhouette.
Sidi’s famous heel adjustment system remains, but new materials such as the no-stretch Firmor X are designed to offer enhanced stiffness alongside the improved fit. Combine that with a carbon-fibre sole and high levels of breathability, and this is a shoe designed to excel in fast-paced, high-intensity off-road scenarios.
To find out how good a gravel shoe this is, I’ve racked up over 1,000km off-road from forest trails to canal towpaths, to really put them through their paces.
Design details
The Sidi Aeron shoes are a high-end gravel race shoe built upon a carbon-fibre sole with Sidi’s own Firmor X material, which is designed to provide support through its lack of stretch, similar to Dyneema.
The shoe features a conventional tongue design, but the retention cable runs through the upper section. The retention dials are the new Nuun 001C dials from Sidi, now used across the entire range of its higher-end shoes.
Three standard colours are available, with this white option, black, and an orange and black version. A lilac-and-fluoro-yellow special edition is also available for a slight price increase.
Size-wise, the Sidi Aeron has a fairly expansive 36-48 size range with half sizes all the way up to 46.5.
Design-wise, the shoe still features some of that more modular look Sidi used to have with the Ergo, Wire, and Shot range. However, fewer parts are now removable or replaceable, though the rear heel adjustment system is, and the stud treads on the sole can be, too.
Specifications
The biggest change to Sidi shoes over the last two years is the introduction of the Millennium fit. This replaces the old long, narrow last with a slightly curved last that previous Sidi shoes featured, widens the toe box, straightens the last, and moves the cleat mounting plate further back on the shoe. This follows the design trend of nearly every major cycling shoe manufacturer over the last few years, with Sidi among the last to adopt it.
With this shift in design methodology, the brand has also undergone a drastic design change. Previously, Sidi shoes featured many removable and replaceable parts, whereas now these have been trimmed down to reduce weight across the ranges. Customizable elements remain, with the upper retention fitment having three attachment points, while the ankle retention system remains but has been significantly slimmed down.
The dials have been completely overhauled to the same Nuun 001C used on the Sidi Shot 3 shoes, which are now lighter and also sturdy, hence their use by Nasa apparently. These dials tighten by turning clockwise, rather than towards the exterior of each shoe individually, while a push-to-release system loosens them. These shoes feature two dials for upper and lower foot adjustments.
Inside a fairly basic insole is provided which is lightweight but rather flat without any arch support.
Externally, the shoe features a mesh-like structure for greater breathability, but the Firmor X fabric running through it prevents the panels from stretching. Combined with the stiff carbon fibre sole, the shoes are designed to offer the highest level of stiffness in Sidi’s off-road range. The external tread and removable toe studs provide security when walking over muddy terrain.
Performance
Wearing the Sidi Aeron shoes, the Millennium last is a huge improvement over the previous one. I had this with the Sidi Shot 3 as well, but I personally prefer the Aeron's retention system, with the dials on the side of the foot rather than on the tongue. However, you need to adjust the tongue into the correct position; otherwise, the internal wire mounting point can put uncomfortable pressure on the inside of your foot. In terms of toe-box room, however, it was fantastic, better than Shimano Wide-Fit and on par with Nimbl, Quoc, and Q36.5.
The most impressive thing I have found about these shoes is their overall stiffness. The soles are incredibly stiff and transfer power well. I used these shoes with the WolfTooth DEL pedals, and the tread on the Aeron was the correct height to make use of the high contact patch on the pedals. When stamping down on them, the power transfer was direct, which I can attest to with various Strava KOMs gained across testing loops.
On top of that, the Firmor X upper strands do a great job supporting the upper structure, so there is limited material flex across the top of the shoe. This was a slight issue with the Shot 3, but still far better than the Shot 2S. The biggest improvement is the dials, which clamp down on the foot fantastically without needing to over-tighten them. The tabs are easy to operate, even off-road with jarring ride surfaces. I also appreciate being able to flick them up or down, and I hope they'll last longer than other dial options. One issue, however, is that turning clockwise to tighten the right shoe is fine; on the left shoe, it feels counterintuitive. Most dials, such as Boa, rotate externally to tighten. There is also no micro-adjustment for loosening, instead a push to release system. This is, however, great for getting your foot in and out of the shoe easily, as the opening is large.
I did, however, find the ankle adjustment somewhat superfluous for me. I have a narrow ankle/heel, and the Specialized S-Works 6, with its notoriously narrow heel, fit me perfectly. With the Sidi Aeron, I didn’t need the adjustment, which, to be fair, is a testament to the retention system.
I also thought the insole was a bit cheap. I’m in two minds here, as Nimbl also offers a very basic insole, and I think if you spend over £300 on a shoe, custom insoles will offer a bigger performance gain. But then Shimano and QUOC offer brilliant customisable insoles at the point of purchase with adjustable arch support. Specialized meanwhile offers different insoles, but no option to choose at the point of purchase, annoyingly.
I also have to say these shoes are heavier than I'd like for a high-end gravel race shoe. 407g for a size 45 is not bad, especially with the tread required on the outsole, but the Fizik Ferox 2 are 342g in the same size, while the Nimbl Urano are an insane 248g. When racing, accelerating, and riding at higher cadences, a 150g difference at the point of rotation is noticeable. For more casual riding, it isn’t, but then these are race shoes. However, the Sidi Aeron is more durable than the Urano shoes, which I would personally save only for race days.
Value
At £349, the Sidi Aeron is a premium gravel shoe. That’s to be expected with the carbon-fibre sole and other high-performance features. This is far cheaper than the Nimbl Urano (£550) and the Specialized S-Works Recon Evo (£399.99). However, the Fizik Ferox 2 are cheaper at £319.99, while the Specialized S-Works Recon SL are also £350 and claimed to be a fair bit lighter.
From testing, I can confirm the Fizik Ferox 2 are a bit more comfortable, although the total system stiffness might lean toward the Sidi Aeron. However, the S-Works Recon SL are similar at that level and a fair bit lighter. I personally prefer their fit too, but the varus wedge works well for my foot; it won’t for everyone.
Honestly, system weight is the main deterrent from a gravel-race perspective. Those races have a strong bunch-racing element, where accelerations count, and they also tend to have a lot of elevation gain for the distance in UK events such as Gralloch and Graean. Where the Sidi Aeron have really impressed me is the comfort over longer durations and when doing more ’Fastest Known Time’ style rides where the pace is more consistent.
Although stiff, they don't lack comfort, which can be difficult with gravel shoes, in my experience. I'd personally opt for something like the Sidi Dominator X, which has a carbon sole, a similar retention setup, the same last, and costs £226.
Tech spec
- Price: £349 / €399 / $569.99
- Sole: Carbon
- Sizes: 38-48 (half sizes 38.5-46.6)
- Weight: 407g per shoe (size 45)
- Retention: Dual dials
- Colours: Three (plus Coffee Grinder special edition)
- Cleat mounting: Two-bolt
Scoring notes
Design and aesthetics 9/10
I personally prefer the sleeker less modular design of these over previous Sidi shoes, while the colour palette is a good mix and impressively easy to clean mud off of.
Fit 9/10
The new Millennium fit is a huge improvement over previous Sidi fits. It’s accommodating but not so big as to leave excess wiggle room. The heel adjustment works well but wasn’t really needed for me personally. Insoles are a bit basic though.
Performance 10/10
When it comes to power transfer these shoes are excellent, perhaps not as locked in as the Nimbl Urano, but brilliant by comparison to most competitors. A more reward cleat fitting allows a better power generating fit personally as well.
Weight 6/10
This is where the shoes struggle a bit, as they are heavy compared to other similar specification gravel race shoes. It’s not just a small weight penalty either, it’s a significant one that is perceivable in race efforts.
Value 7/10
These are expensive shoes and unfortunately do not offer the greatest value with the higher weight. There are similar performing shoes for less, or slightly less stiff shoes for a significant reduction in price.
Total
42/50