Sidi Nix review: a performance winter boot that, with the brand's new fit, makes a lasting impression

Nike Poobahs are back! Well, not really, but the pastel colours and prominent ankle strap of the Sidi Nix reminded me of my first, slightly garish MTB SPD shoes. The Nix are part of Sidi’s comprehensive range of winter road, gravel and MTB footwear and are billed as "A performance road shoe primed for cold weather”, although they are clearly more of a boot.

The decision whether or not to take the plunge and buy a pair of dedicated winter cycling shoes is one that a lot of committed riders face at some point - extra warmth, protection and comfort paired with less faff than overshoes makes them an attractive proposition if you spend a lot of time riding in cold and wet conditions. Furthermore, you won’t be getting your shiny summer shoes grimy and you can size up the winter boots to allow for nice thick socks. Although there can be a significant cost involved, this is offset by the reduced wear on your summer shoes.

Typically, winter cycling footwear will have a higher-cut ankle, waterproof membrane and some form of insulation, along with a roomier fit and slightly less stiff sole than a summer race shoe. It’s hard work keeping feet warm on cold days; they are stuck out at the furthest extremity from the body and are largely immobile while riding. Warm winter tights and long socks help to keep the warm blood at a higher temperature on its long journey to your feet, but the more insulated your shoes, the better. The trade-off is weight, bulk and ride ‘feel’ - big, padded boots can feel clumsy and sloppy on the bike.

Construction

A passing resemblance to iconic 90s footwear aside, the Nix has a few other interesting things going on. The Gore-Tex membrane is part of the new wave of waterproof fabrics necessitated by the ban on PFAS and it features Sidi’s new ‘Millennium’ last, which seems to be about one full European size larger than previous Sidis.

The 3-bolt sole unit is made from nylon and glass fibre, with lots of markings to help get your cleats nicely aligned. The grips are pretty shallow though (the front one particularly) and are not replaceable, which is a big shame on a shoe at this price. Sidi gives it a stiffness rating of 9 (out of 12), so a few notches down from their full-on race shoes but still plenty stiff enough for winter miles.

Lovely, cosy fleece from Primaloft lines the boot, and even the insole has a warm, brushed feel to it. On the outside, potential wear areas get tougher TPU reinforcement, while the remainder of the upper is made from slightly lighter, perforated microfibre. Whether these perforations are for breathability or aesthetics on a shoe like this is debatable.

The BOA-style dial laces finish roughly where a normal shoe’s laces would end with the softer ankle cuff secured by a wraparound Velcro strap. This strap runs almost 360° around the cuff and is only secured by the ‘S’ of Sidi to provide better heel retention.

In addition to this blue option, the Nix is also available in a chic, if ridiculously unpractical, white colour and a rather more sensible black with full sizes from 36 to 50.

The ride

First off, as mentioned above, these are very different size-wise to Sidis of old. The size 44 fitted me fine and is the same as I’d wear in Quoc, Specialized and Giro summer shoes or Northwave winter boots. Previously I’d have needed a 45 in Sidi, although these are still on the narrow side with no wide fit option available. The thick pile fleece lining makes them feel snug too, particularly when new, but I know that this packs down a little after a few rides to leave a bit more wriggle room. The fleece has the added advantage of being quite grippy, so it helps to hold your foot securely in the boot which can be an issue with roomier, more comfort-orientated winter footwear.

When wearing summer shoes with thick overshoes, the extra bulk can sometimes cause rubbing on the crank arms and chainstays, rubbing off any anodising or paint and wearing through the overshoes. This is less of an issue with specific winter boots and even less of a problem with the slim and neat Sidis - there was a decent gap between my boot and any metalwork or carbon.

The level of sole stiffness was not discernable when pedalling, or at least not with the kind of steady winter miles I did in them, but they were definitely less wooden off the bike with the section in front of the cleat exhibiting visible flex when under pressure (such as when kneeling down). In a winter boot, this is a good thing as the small movement helps keep your toes warmer.

Sidi’s dial lace system is very similar to the ubiquitous BOA design, with a rotating knob spooling in a thin Dyneema cord. Releasing it involves pinching the sides of the dial to release tension fully, so there is no micro-adjust available, but again, on a relatively bulky winter boot this doesn’t really matter.

The cuff isn’t particularly high, and whilst the ankle strap does a reasonable job of securing the heel, it doesn’t entirely snug the opening of the boot up to the front of the ankle. Thus, in very cold or wet weather I was aware of a bit of a draughty gap at this point (but I do have quite skinny ankles). This was particularly noticeable when worn with the Castelli Sorpasso RoS Wind tights which could have done with a couple more inches at the bottom in my opinion.

The combination of slim fit, grippy fleece inner and decent retention system translated to a very secure feel when pedalling, whether in or out of the saddle. Heel lift was non-existent as was any foot movement, making the Nix feel much racier than they have any right to be. Given this, I can see them being of use in quite a wide range of conditions rather than just being reluctantly worn when the mercury dictates. Wearing them doesn’t feel like the performance compromise that some sloppier winter boots can.

It is hard to comment in any meaningful way about a boot's warmth as there are so many factors involved; fit, temperature, other clothing, effort levels, tiredness and metabolism, but I happily wore these for rides of three or four hours in low single digit temperatures and I would imagine that they would work for a couple of hours on below zero rides too - anyone sensible has stopped for a coffee by then anyway I’m sure!

Value and conclusion

There is plenty to like about the Sidi Nix; the new last is more in line with other brands, the Gore-Tex membrane promises reliable protection and the fit is very neat and secure. The warmth of the cosy fleece inner is slightly compromised by the low cuff though, so make sure that your bib tights are long enough to make up the shortfall. It is a shame that the sole lugs aren’t replaceable.

£300 is up there for a pair of cycling shoes, but you are getting branded Gore-Tex and Primaloft fabrics along with Sidi performance, and if the outlay encourages more winter miles then it sounds like a reasonable deal to me.