With an in-moulded lid packed with features, with four different sizes and a whopping nine colours, the Bell 4Forty Air MIPS mountain bike helmet isn’t lacking options

Product Overview

Overall rating:

Score 8

Bell 4Forty Air MIPS helmet


  • MIPS is seamlessly integrated, loads of features, plenty of colour options, aftermarket padding and bolt replacement


  • Heavier than competitors, ventilation and sweat management isn't great


Bell 4Forty Air MIPS helmet review


Price as reviewed:


This 4Forty Air MIPS is part of Bell’s latest helmet range, and thanks to considered design and features it’s one of the best mountain bike helmets we’ve tested.

It’s an in-moulded lid packed with features, and with four different sizes and a whopping nine colours, it isn’t lacking options. Weight is claimed at 360g, but my medium was almost 400g, which is at the heavier end of the spectrum for an all-mountain open face.

The all-new outer shell has a slightly more angular shape at the rear than more rounded Bell lids I’ve seen previously. Inside, however, it’s so smooth, you might not even notice the MIPS rotational impact reduction tech as it’s so neatly incorporated into the brand’s ‘Float fit’ system; itself offering a full wraparound cradle with four rear height positions and a rubberised tensioning wheel.

Internal padding is cushy and uses an anti-bacterial material, that’s designed to be quick-drying, and a unique ‘sweat guide’, which sees the padding extend round and curve under the brim in the centre of the forehead. The idea of this feature is that sweat generated when climbing is channelled away from the brow and eyewear to drip down further away from the face.

I was pleased to see that the padding (and visor bolts) are available as aftermarket replacements too, which should extend the lid’s lifespan.

Riders looking to store eyewear are covered by a rubber goggle strap gripper round the back and notches in the forehead vents to hold glasses arms. Goggles will also fit under the adjustable peak if it’s flipped all the way up.

The 4Forty Air has pretty big vents, but unlike some lids there are no ports directly feeding air onto the front of the forehead or brow. As a rider that really sweats, ventilation in this zone is key to cooling and keeping dry, so the 4Forty Air didn’t score well in this regard.

I also didn’t get on that well with the ‘sweat guide’ feature as it actually seemed to achieve the opposite of Bell’s claims and drip more sweat onto my Smith glasses than usual (maybe this was a consequence of lacking brow vents that help dry sweat too?).

If you’re not a serious sweater like me, Bell’s lid has a lot going for it though. Fit, stability and comfort are dialled, and all the fixtures, fastenings (including a magnetic Fidlock chinstrap) and finish are high quality, and the fully wrapped shell won’t get dented or damaged too easily either.


For me though, I’ve got other lighter and ‘lighter-feeling’ extended coverage lids where the outer shell (and weight) seems to sit in closer to the skull to minimise any centrifugal force effect as your head swings around when riding dynamically. And, as mentioned, the ventilation here doesn’t work as well as personal favourites like the Sweet Protection Trailblazer.


Weight:394g (medium)
Colours:Nine colours
Sizes:S, M, L, XL