Tubeless inserts, short cranks and track tyres: GCN Tech Clinic

How do tyre inserts work and how to improve your head unit's visibility - these questions and more answered in this week's clinic

Clock11:42, Wednesday 15th May 2024

For the first time in a long time on the Tech Clinic, Alex Paton and Ollie Bridgewood do not have a question about waxed chains. In its place is an interesting question about the rolling resistance of inner tubes, plus the boys look at what defines a climbing bike.

How does tubeless sealant get to the puncture if you use a foam insert and what is the best way to install a foam insert?

Depending on which type of insert you use will vary the answer slightly however, most tyre inserts use a permeable open cell design that can be compared to a sponge. When the tyre is inflated the internal pressure compresses the insert and leaves the sealant plenty of space to circulate around the tyre. As the pressure decreases as a result of a puncture the foam insert will expand to fill the tyre.

When it comes to installing the insert the best way to go about it is to fit the insert first and then add the sealant afterwards. It can be a fairly involved job to install the insert and adding sealant to the mix will only make things messy.

Are clip-on lenses for cycling glasses good for people who have impaired vision?

There are a couple of different options to tackle this issue depending on budget and which one best suits your needs. Firstly you can get some sunglasses made to your specific prescription. This is often quite an expensive solution but does offer a sleek finish with no additional clip-on lenses required and a full range of vision at your needed prescription.

If like the person who asked the question, the issue focuses on the ability to read the screen of a bike computer, using a bike computer with a nice big screen can help. Another option is to configure your bike computer screen to include only two or three data fields so that the date on display is nice and clear which should make it easier to read.

What makes a bike good at going uphill?

To a greater or lesser degree, the term climbing bike is a bit of a misleading term. It might have a small benefit over a different type of bike when the road points up but this will be minimal for most people. The typical characteristics of a ‘climbing bike’ is that it prioritises weight over aerodynamics and comes with gearing tailored to riding at the slower speeds associated with riding up hills.

The rider in general will have a bigger impact on how a bike feels riding uphill than the bike itself. Something that can be overlooked is the fact that climbing is a skill and requires a different pedalling technique to ride on the flat as the torque is delivered differently. If you find yourself doing a lot of indoor training work it might not replicate the demands of climbing making it feel difficult when you head out on the road.

How does an inner tube affect rolling resistance when it isn’t in contact with the road surface?

This is a great question as it does seem odd that something inside a tyre can affect how it rolls on the road. The answer lies in energy loss due to deflection which is scientifically known as hysteresis. As the tyre deforms as you roll along, the inner tube inside the tyre also has to deform. The tougher the inner tube material is, the more energy it takes to deform which results in a loss of energy in the form of increased rolling resistance. This means that using a more supple inner tube, like a latex one will result in less energy loss than a thicker butyl tube.

I received some new cranks, however, they are the wrong length. I use 175 and I have been given 170 are these still ok to use?

Although from a purely mechanical perspective, there might be an advantage to using longer cranks, recent studies into the biomechanics of crank length point towards shorter cranks offering some level of an advantage. It is worth fitting the shorter cranks and seeing how you get on with them. The main thing to remember is that your saddle height will need to be adjusted to compensate for the difference. It is a little bit counterintuitive as you will need to raise your saddle if you are fitting shorter cranks.

Do track cyclists use tubeless tyres or are they still using tubular tyres instead?

There are a small number of riders who have made the move over to using clincher tyres with inner tubes however, the overwhelming majority of track racers still use glued-on tubular tyres. The reason behind this is that tubular tyres can be pumped up to super high pressures and on the ultra-smooth surface of a velodrome this does offer an increase in efficiency.

The other reason we are not seeing riders use tubeless tyres on the track is partly due to the rules regarding no liquids on the velodrome. This is why we don’t see riders taking on water during track races as any spillages would make the surface incredibly slippery and likely cause a mass pile-up. The same could happen if a tubeless system punctured as the sealant would spray onto the track's surface.

Does an aero bike still present an advantage if you are riding deep in a group?

The short answer to this is yes. Regardless of where you are positioned, aerodynamics are always at play. It might not be as pronounced as when you are sitting on the front or riding on your own however riding in an aero position and using aero equipment will still save you watts even if there are 10 riders in front of you.

If you have any tech-related questions that you need answering, head over to this week’s Tech Clinic video on the GCN Tech YouTube channel and add your question to the comments along with #ASKGCNTECH. Or leave your question in the comments below.

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