Milkit Booster head with bottle

The milKit Booster is a lightweight, multi-purpose way to reinflate tubeless tyres when travelling or riding. Just be sure to practise beforehand and confirm that it will work with your tyre-rim-valve-pump combo before heading out. And be aware you may need a different bottle cage.

milKit is a Swiss firm best known for its unique tubeless valves, which feature one-way rubber 'flaps' that let you insert and retain air or sealant with the valve core removed, greatly aiding air inrush or ease of checking and topping up sealant without unseating the tyre bead. I've been a fan since testing the Tubeless Valve and Refill Kit back in 2016, and have used milKit valves and sealant injector on countless tubeless setups.

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Important note: milKit recalled the first generation of Boosters in 2018, easily-identifiable as they were made from blue plastic. These could fail under high pressure, so if you see a blue Booster in the wild, after throwing your body over it to protect nearby children from plastic shrapnel, let the owner know they can get it replaced for free via milKit's website or reseller.

milKit bottle

When not in duty as a tubeless airtank the Booster doubles as a metal water bottle, with the standard 'adventure' threaded plastic cap found on SIGG and other alloy bottles.

The Booster measures 73.4mm in diameter compared to the recognised standard of 73mm – therefore, given it's solid metal with no give, it didn't sit all the way down in any of my metal bottle cages. Also, the curve in the top of the bottle doesn't fit the industry standard bottle cage retaining 'tab' height of 127mm either. The curve starts at 150mm up the Booster bottle, kicking in much higher than that on a normal bottle. So the Booster bottle doesn't sit in the bottom of the cage and is pushed out by the cage bottle tab, only held in place by metal-on-metal friction as opposed to the springiness of the cage holding the bottle down below the tab. This means the bottle is hard to remove for a drink if securely stowed, even passing a finger through the lid and pulling, while pushing up from below. Certainly not doable on the move, should you attempt it.

milKit does a larger bottle size of 1L for £3 more, which also doesn't have an indentation in it at the standard cage tab height. Of course you could opt for a tabless bottle cage like the Zefal Pulse Aluminium, which doesn't have a retaining tab and holds the Booster just fine. This larger bottle size should do a better job of seating difficult tyres requiring more volume of air (see below) and also may be more practical for bikepackers wanting to carry water in it.

Pressure points

The Booster is rated for a maximum of 160psi, but in reality no mini-pump you're likely to have out on a ride is capable of more than 120psi. Indeed, it took 300 strokes of the Birzman Mini Apogee pump to get to 120psi, and you really want to be wearing gloves while doing so. So when you're testing your setup, remember to use what is a realistic achievable pressure for your use case.

When you're seating tubeless tyres two things are your friend: volume and airflow. You need lots of air to flow quickly, and keep flowing until the tyre is in the right shape to pop the beads over the rim ridges and prevent further air loss. Pumped to 160psi, the Booster didn't seat a particular rim/tyre combo with the valve core installed, while the Birzman 2L tank did succeed, charged to the same 160psi pressure. Arguably, the Birzman tank should rate worse, as there's more airhose/valve gubbins in the path. There's a lot to be said for more air that keeps on coming.

milKit suggests removing the valve core to obtain maximum airflow, but the Booster kit doesn't include a valve core removal tool (missed opportunity in the plastic valve cap there) so you'll either need to carry one, or only install them finger-tight. At 120psi the Booster inflated a supple 38mm Compass tyre without valve core no problem – but with the valve core in, no dice – the air pressure just wasn't strong enough. This is where you should be considering running the milKit valves (around £25, or £40 with the whole milKit system), as they have a one-way rubber flange inside that lets air go in, but not come out with the valve core removed.

> How to choose your correct tyre pressure

Going off a realistic trailside maximum pressure of 120psi the Booster did seat a 38mm tyre, but as above, only with the valve core removed. At a workshop-friendly 160psi, it was able to seat the same tyre with the core installed.

I see this difference – 120psi max road/trailside vs 160psi if you're near a floorpump – as the main factor to bear in mind with the Booster. In both cases you'll definitely benefit from using milKit's one-way valves. I certainly could have used the Booster during my ill-fated Dirty Reiver tubeless fiasco where the ability to get a fast shot of air in to reseat the tyre would have meant I could run tubeless instead of resorting to a higher-pressure and more risky inner tube.

Need a Booster

'Burping' tubeless tyres (where all the air falls out as the bead pulls away from the rim under heavy cornering) is becoming a rare occurrence – and even then I've only ever heard of it happening on low-pressure mountain bike tyres. So the most likely cause of need for the Booster in a road or gravel context is when you've suffered a puncture so bad that your sealant couldn't work (or had dried up) and pressure had reduced to the point where the tyre bead slipped back into the centre of the rim – an impossible situation to recover from with just a handpump. In that case the Booster is a near-guaranteed way to get rolling again tubelessly – assuming it works for your combo.

One thing the Booster most likely won't do is give you that 'snap of confidence' as the tyre beads pop over the centre channel ridges and seat fully home all around the rim wall. For that you generally need pressures in excess of 30psi in the tyre, and I never managed more than 20psi even in a super-tight-fitting tyre using the milKit, such was the loss of air during the reseating process.

A 35mm 700C tyre has an inflated volume of around 2 litres – so a 600ml Booster bottle is at best only going to get you to 27.7psi – or quarter of its 120psi starting pressure – and that's before accounting for leakage. So you need to keep your pump handy and be quick about getting more air into what will be a quickly-leaking, yet-to-fully-reseal tyre. As above, if you've had to remove the valve core to get sufficient inrush, you may be unable to get the core reinstalled before all the air falls out again. Hence the recommendation to use milKit valves. Either way, get riding immediately to distribute the sealant and allow the beads to settle.

Conclusion

Overall, the milKit Booster is a lightweight, compact and simple solution to roadside or travel tubeless woes. It's cheaper, smaller and less than half the weight of the nearest competitor, the 1.15L 130psi Airshot, now £49.99 at rrp, and can be used as a water bottle with the right cage so utility and storage isn't an issue on bikepacking trips. However, that small volume does mean you need to thoroughly test your setup, and possibly invest in milKit valves to ensure you can retain what pressure manages to get inside your tyres, out on the road or trail.

Verdict

Lightweight and compact way to reinflate your tubeless tyres, with caveats around your setup working with it