Calculating watts, café locks and CO2 flats – GCN Tech Clinic

Alex Paton and Ollie Bridgewood are back in the clinic to put to bed some of your burning bike-related questions. From how best to leave your bike at a café to tubeless setups, there is no question that we cannot answer.

If you’ve got a tech question that you need answering, don’t forget to leave it in a comment below one of our YouTube videos along with the hashtag #ASKGCNTECH.

What sort of lock is best to carry for use at the café stop that won’t impact weight or aero too much?

There are a couple of things that you can take with you to act as a deterrent that will prevent any opportunist thief from walking off with your bike. Brands like HipLok make small locks that work like a zip tie with a combination lock that can fit in a jersey pocket or around your frame without any real penalty.

The reality though is that for anyone who is set on taking your bike, none of these locks will put up much of a fight. As a lock's strength increases so does its bulk and weight as it has to use heavier-duty materials to withstand an attempted theft. If you are riding in a group it is better to take turns to head into the café to get your coffee and cake so that the bikes are never left unattended.

Another option is to choose your café wisely and avoid stopping in a busy location. Instead, head to a quieter café where the likelihood of running into a thief is greatly reduced. Positioning your bike so it remains in sight whilst you are in the café can also put your mind at ease.

Is there a way to calculate a power output based on distance and speed?

There are a few ways that you can reverse-engineer the data to get a power figure, however these will always be a rough estimation with a significant margin of error as there are so many variables at play. The more accurate the data that is used for the calculation, the more reliable the calculations will be so having as much information as possible will massively help.

By using an online software such as mywindsock.com you can input all the data that you know and select a specific course and it will calculate the specific power required to ride at a given speed.

For historical rides, having all of the data needed for an accurate calculation could be tough as things such as the rolling resistance of the tyres, total system weight and the coefficient of drag of the whole system aren't always readily available. As long as you accept that the calculated wattage is open to a fair bit of error and take it more as a ballpark figure, this method can provide some level of insight into your efforts.

Why are tyre inflation canisters filled with CO2 and not air?

Carbon dioxide molecules are smaller than that of nitrogen and as a result, CO2 escapes quicker from a tyre or inner tube than air would. As the question rightly asks, wouldn’t it make more sense to fill the canisters with air, as it would also have a slight performance benefit over carbon dioxide?

In reality, the difference in molecule size is not that significant and wouldn’t actually present a measured difference. The reason pure CO2 is preferred over plain air is down to the ability to compress the gas. CO2 can be compressed to a higher level than air can be, this means that a greater volume of the gas can be compressed into the canister.

During the manufacturing process, CO2 is actually poured into the canisters as a liquid and then sealed in. As the temperature of the liquid CO2 increases it returns to a gas and pressurises the canister. Due to this process, it is a lot easier to do with a single gas rather than a cocktail of different gasses that make up air.

Are heavier riders more susceptible to perineal numbness on a turbo trainer?

The short answer to this is yes. Generally speaking, a rider's sit bones fit into a fairly narrow band of widths. The heavier you are as a rider, the more force goes through your sit bones and surrounding area. This increase in pressure can result in perineal numbness.

Due to the static nature of indoor training, there is no rest bite from this fixed position, which will result in numbness. When out riding on the road, changes of gradient, bumps in the road and changing between a seated and standing position all naturally alleviate the pressure on the perineum.

How can I clean my bike without access to a hose or a car washing station?

If you find yourself without easy access to a hose, there are other options when it comes to cleaning your bike. First of all, there is the option to use a bucket and sponge. It might not be as effective as being able to hose your bike down but it can work especially for cleaning your drivetrain and getting the worst of any dirt off your frame.

Another option that can replace the need for a hose is to put your bike in the shower. Obviously, this will depend on the size of your bike and the size of the shower but having a contained area to shower your bike off can be a great solution when in a squeeze.

Why did Ollie use 80ml of sealant per tyre with his new Canyon Aeroad?

In a recent video where Ollie went through exactly how he has set up his new Canyon Aeroad, he revealed that he had used 80ml of tubeless sealant in each tyre. For the 28mm wide tyres that he is using, this equates to around double what the recommended amount would be.

The reason behind this is to maximise puncture protection whilst out on everyday rides. The more sealant in the tyre, the quicker a puncture can be sealed. Of course, there is a slight weight penalty for setting the bike up like this but the trade-off is worth it in Ollie’s eyes. As far as rolling resistance is concerned, the added sealant would have very little impact on the rolling performance of a tyre.

If Ollie were to optimise his bike purely for performance, that is when he would eithrt reduce the volume of sealant or use a TPU inner tube instead to save those precious grams.

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.