GCN Tech Clinic: Why do tubeless tyres leak air?

Alex and Ollie are back to unravel all of your questions in the latest GCN Tech Clinic.

It’s been a busy two weeks since the last edition with the Tour de France getting underway in Spain. Cycling’s biggest event is always a hotbed for the latest and coolest tech so we sent Si Richardson over for the start of the race to see what he could discover.

During our two-week absence we’ve also received plenty of your questions, so let’s dive straight in.

Why do tubeless tyres leak air?

Starting with one of the most popular topics we encounter on GCN Tech Clinic: tubeless tyres.

Tubeless tyres, as the name suggests, don’t require inner tubes. Instead, the tyre creates an airtight seal once seated on the rim. Many tyres also require a sealant to help form this airtight seal. But what do you do if, once seated, the tyre keeps leaking air?

It’s a common problem and one Alex recently encountered. He managed to solve the issue by adding extra sealant which helped to form the airtight seal.

Other causes can be an incorrectly fitted valve, damaged rim, or a hole/defect in the tyre.

Can wax be applied to a used chain?

This is a subject close to Ollie’s heart and he’d always avoid applying a hot-melt-wax treatment to a used chain.

It’s a lot of hassle and the benefits of wax are far greater when it’s applied to a new chain.

Need help waxing a chain? Check out our guide below.

Why do waxed chains last longer?

Sticking to the subject, why do waxed chains last longer?

Many people believe that chains stretch over time due to the power put through them, but this is a common misconception. In this scenario, the products applied to the chain would have no influence.

In reality, chains don’t stretch but they do wear over time. We won’t go into too many details here as we don’t want to take away from Ollie’s expert hand demonstration. In essence, wax treatments protect chains against wear better than lubes.

Which tyre width is best?

Selecting the correct tyre width is a matter of finding the right balance between rolling resistance, aerodynamics and comfort.

Ollie recommends 25mm or 26mm tyres if you usually average over 35kph on rides, but 28mm when averaging under that speed.

Can an incorrectly routed chain damage pulley wheels?

When attaching a chain, it’s easy to accidentally route it outside of the derailleur cage on the pulley wheel. It’s something we’ve done ourselves.

Hopefully you’ll notice before riding and, barring a little frustration, will fix the issue without any problems. But what happens if you ride your bike without noticing, will it cause serious damage?

This is one neither Ollie or Alex have tested out themselves but they suspect it’ll only scuff the pulley wheel cage which, in the context of things, shouldn’t be a big issue.

Why don’t carbon seatposts need compression plugs?

As Alex explains, steerer plugs were used long before carbon came along and their main function is to preload headset bearings. With the introduction of carbon, they were adapted to also add strength to the steerer tube.

Seatposts don’t have the added responsibility of preloading any bearings, they just have to handle clamping forces. The carbon layup of seatposts is also optimised to handle these clamping loads, so they don't require compression plugs.

Can an in-line barrel adjuster replace a broken derailleur barrel adjuster?

You’ve broken the barrel adjuster on your derailleur. You don’t want to shed money on a new one. Is it possible to simply use an in-line barrel adjuster instead?

It is, but we’d place this in the bodge category. It’s better to remove a barrel adjuster from a second-hand derailleur (check in with your local bike shop as they may have spare parts) and swap it in for the broken barrel adjuster.