GCN Tech Clinic: Frozen brakes, gravel suspension and watt calculators

Alex Paton and Ollie Bridgewood find themselves back in the GCN Tech Clinic, and on the menu this week is an eclectic array of topics, including power meter accuracy, how to store your bike for a long period, and whether suspension forks are a good component to upgrade on gravel bikes.

I’ve always found that crank/pedal-based power meters read higher than hub or indoor trainer power meters. Is this because of drivetrain efficiency losses?

This is a tough question to unpack definitively. The short answer is yes, in perfectly controlled conditions where all data could be trusted and everything was calibrated equally, you would expect to see a small difference between a pedal or crank meter and a hub meter. This would be attributed to the losses through the drivetrain.

The issue is that most of the time the readings have a greater level of discrepancy than drivetrain losses can account for on their own. Typically a range of 5-10 watts can be lost through the drivetrain with 10 being a very inefficient system. If you are using a waxed chain and keep a good chain line the difference is far more likely to be closer to 5 watts. If you are consistently seeing an over-read on the pedal or crank meter it could be that they are calibrated slightly off from the hub or trainer meter.

We have looked at this topic in the past and Ollie is a firm believer that indoor trainer power meters are more accurate than pedal/crank-based meters. Something else to consider if you’re using a single-sided pedal or crank meter is that the reading is susceptible to biomechanical asymmetry whereas a hub or trainer meter is measuring the total output at that point of the drivetrain.

Are there any good calculators for working out how power/weight can affect performance over a course or climb?

If you have watched any of Ollie's particularly nerdy videos, you’ll know that he loves to take a real deep dive into the maths behind what a change in power, weight or aerodynamic efficiency translates to out on the road. For those looking to dig into the data that little bit more, there are a few websites that do offer calculation tools. However, for the most reliable and accurate ones you will need to get your wallet out and pay for access.

Ollie's personal favourite site for this is mywindsock.com but there are others such as goldencheetah.org that also offer calculations based on existing data. It is important to use meaningful data when looking to use calculators like this as it needs to be controlled and repeatable with the data as unaffected by external factors as possible.

For example, using a calculator on a Sunday club run will provide little benefit as there are so many variables that remain unaccounted for such as where you rode in the group, how much traffic there was, did you move from the drops to the hoods a lot, etc. All of this makes any deductions redundant. Going out for a ride on a known course with as many variables stabilised as possible will be the best way to input data to then use in calculations.

I have an entry-level gravel bike with a suspension fork with no lockout, would it be better to upgrade my fork to a rigid carbon fork or upgrade my wheels and keep the suspension fork to make the bike faster, especially uphill?

If it was our bike, we would be looking to replace that suspension with something rigid, ideally a carbon fibre fork. Not only will this shed a significant amount of weight from the bike it will also have an immediate impact on the climbing efficiency of the bike. The rigid fork will also allow for a better transfer of power especially when out of the saddle as there will be no energy lost to the spring of the fork.

By upgrading the bike to have a rigid carbon fork it will have a great chassis for future upgrades such as the wheels. With the loss of the suspension unit, fitting some wider tyres or playing around with some lower tyre pressures will give added traction and comfort to compensate.

What do I need to do before storing my bike for a prolonged period where it will not be touched?

Before storing a bike for a long time, it is important to give the bike a good clean and get all the dirt and debris off the bike. It is important to pay particular attention to the moving parts around the bike such as the drivetrain, wheels, and brakes/discs. When the bike is appropriately clean, the most crucial thing to do is to make sure that the bike is dried. This is what can cause the most damage to a bike whilst it is being stored. Any moisture left on the bike can lead to rust or corrosion and can ruin bearings by the time you go to use the bike again.

How you store the bike can also play a role in how it fairs for long-term storage. Ideally, the best place to store the bike would be in a temperature and humidity-controlled environment however if that isn’t the case then taking some time to cover the bike with an opaque sheet can help to protect the more delicate areas of the bike. Things such as bar tape, lever hoods and tyres can all be damaged by UV exposure so covering the bike with a barrier can help to prevent these areas from degrading.

Are there any safety pitfalls from using an inner tube in a tubeless tyre and wheel?

As far as safety is concerned there are no issues with using an inner tube in a tubeless-ready system. Tubeless tyres and wheels are all compatible with inner tubes which is great as sometimes fitting an inner tube is the only puncture repair that will get you home if you get a big hole whilst using a tubeless setup.

If you have tubeless rims make sure you check whether they are hooked or hookless. This has to do with the internal wall profile of the rim. Modern carbon wheels are more commonly hookless as they allow for cheaper and lighter rim construction. What this means is that regardless of whether they are set up tubeless or not they have a maximum tyre pressure limit of 73psi.

Do I need to use a winter-specific hydraulic brake fluid when the temperature drops to -10 Celsius?

Hydraulic disc brakes use either a mineral oil or a DOT fluid to actuate the calliper. Both of these fluids have freezing points considerably lower than -10 with mineral oil not affected until around -30 Celsius and DOT even colder at around -40 Celsius. If you find that your hydraulic brakes are freezing as soon as the temperature drops south of zero the system has likely been contaminated.

Over time, especially through repeated heating and cooling cycles, moisture from the air can find its way into the brake hoses. The accumulation of this can be enough for a small section of the hose, calliper or lever to freeze. When this happens it can restrict the flow of fluid and prevent the actuation of the pads.

To remedy this issue a full system bleed is needed with a complete replacement of the fluid in the system. If the issue prevails after this it would be worth investigating the points the hose interfaces with the calliper and lever as well as checking the hose itself for small cracks or tears that could be allowing moisture to permeate through.

Can a good quality premium wet lube be a good alternative to a waxed chain treatment?

Keep your eyes peeled for a more detailed run-through of this in the coming weeks as Alex has been getting nerdy and testing different lubes to see how they perform. Ultimately it depends on the wet lube you are looking to use. A high-quality, well-formulated wet lube can be considered a viable alternative to a waxed chain. The quality of the wet lube really can affect both its performance and how well it protects the drivetrain from premature wear. Some wet lubes can act as a grinding paste, attracting grit and grime that can accelerate drivetrain wear.

In very cold conditions a waxed chain is not the best form of chain lubricant as it will harden and lose some of its efficiency as well as longevity. In these cases, a wet lube would always be the preferred choice as it retains its characteristics even at sub-zero temperatures.

Do you have a tech question you want answered? You can leave it under the comments of this YouTube video or in the comments section at the bottom of this article.