Pirelli P Zero SmarTube

The Pirelli P Zero SmarTube is the lightest in its range of thermoplastic polyurethane (TPU) inner tubes. It is exceptionally light, just 39g on the road.cc Scales of Truth, improves ride comfort, and provides better puncture resistance than lightweight butyl tubes. If you are unfortunate enough to puncture, though, a repair is a little more involved.

Using TPU for inner tubes is claimed to increase toughness, gram for gram, and reduce volume – and rotating mass – and while the cost might seem incredibly high for a tube, if you're looking to save weight then the grams saved per pound ratio stacks up well.

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The use of TPU has been growing gradually since Foss brought the technology to the cycling market in 2012; it's been joined by Tubolito, arguably the market leader now, and more recently Schwalbe, releasing its Aerothan late last year.

Pirelli's TPU SmarTubes come in three model areas to cover road, gravel and mountain biking. The Cinturato, for gravel and wider road tyres, is available in four sizes covering 28-45mm tyres and in 650B and 700C wheel sizes; the Scorpion, for mountain biking, comes in three sizes and for 27.5in and 29in wheels; while the P Zero SmarTube on test here is for road riding, and comes in just a single size designed to fit 23-32mm tyres.

Within the Cinturato range, there are certain versions that are classed as reinforced, adding a slight weight penalty but still lighter than an average butyl inner tube. The 28-35mm reinforced version could be an option for road bikes and those looking for a more robust tube than the P Zero version, while still being significantly smaller than a standard butyl inner tube.

The P Zero has a valve length of 60mm (as do all the Cinturato models) and the valve core is glued in, so if you needed a longer valve you'd need an external extender.

Both tubes tested weighed 39g each, making them 4g heavier than the claimed 35g, and they can be used with both rim brakes and disc brakes.

The tubes are from the first batch produced and have "Do not repair" printed on them, but this advice has since changed. Pirelli now says that TPU patches, such as the Tubolito patch kit, are effective and safe. One thing to bear in mind, though, is that a patch can take up to 30 minutes to cure and the process is different to a standard tube – best done at home rather than out on a ride. It isn't possible to use either a normal vulcanised rubber patch or a self-adhesive patch.

To test the tubes I used them to replace a pair of Tubolito inner tubes. The biggest difference is the colour, with Tubolito featuring an orange TPU material and valve, whereas the Pirellis are yellow with a plain black valve. Otherwise, they're incredibly similar – same font, same valve style, both are made in Austria, and the weight is almost identical – so it would be reasonable to assume they're made in the same factory, perhaps to a different thickness and specification.

I used the tubes within Pirelli P Zero tube type road tyres and installation was simple, which was a relief. As I found out when testing the Schwalbe Aerothans, the thin material can be caught and punctured during the process. The tyre/wheel combination used meant no tyres levers were needed.

Comfortable ride

While ride comfort might not be the biggest selling point for Pirelli, for me it's the most noticeable difference on the bike. It's more comfortable than with butyl tubes at the same tyre pressure, and similar to latex tubes in their ability to slightly mute road imperfections – but without the gradual air loss and fragile nature of latex tubes. Air loss over several weeks was minimal, a few psi at the very most.

I tested the tubes using a set of 40mm deep-section rims, so there was sufficient valve outside for easy inflation with a track pump, but the threadless valve design meant the valve rattled on my wheels. It's not an issue unique to Pirelli, and will depend on the exact rim and setup used, but you can get specific parts to prevent this, or use a few wraps of electrical tape on the valve itself.

While testing I haven't had any punctures, which is pleasing. In my experience with TPU inner tubes, they don't rip or tear like butyl tubes when punctured, with slightly slower air loss as a result; even when inflated out of the tyre, the puncture doesn't tear the material, which can happen with both lightweight butyl and latex tubes.

TPU or tubeless?

While the low weight is easy to measure in comparison with butyl or latex inner tubes or a tubeless setup, one area that is far more complicated is rolling resistance; tests have been carried out, but there are too few independent ones currently available to make a definitive and conclusive judgement, and Pirelli makes no claims on this.

And while tubeless adds weight – once you factor in the different tyre requirement, tubeless valve and sealant – where it can win over any inner tube material is the ability to run lower pressures, for improved comfort and, particularly off-road, for better grip, while still offering puncture resistance.

Value

Paying £27.99 for an inner tube will no doubt put off many, but when compared to even a lightweight 90g tube that might cost £4 or £5 it's a pretty cheap way of saving some weight from your bike compared with upgrading your wheels or groupset, for example.

They're on a par with other TPU tubes: the Tubolito Roads are exactly the same price (or £29.99 for the S-Tubo Road), while the Aerothans are slightly cheaper at £24.99 each.

Conclusion

Overall, the improvement in ride quality, low weight and possible improved puncture resistance compared with a lightweight butyl tube make these worth considering, and while they are expensive, it's a pretty cheap way to reduce weight.

The biggest hurdle to overcome is the potential of a puncture, with the tubes requiring a specific patch kit, and the time it takes making roadside repairs less viable. The minimal space they take up in a saddle pack or pocket is appealing, but I'm not sure I'd want to rely on one as my only spare.

If tubeless isn't something you wish to consider, though, the benefits of TPU inner tubes might be worth it – if you can get over the initial cost.

Verdict

Extremely light and gives a very comfortable ride – worth the extra expense and repair faff if you puncture