You probably already know that cycling on rough surfaces is harder than on smooth surfaces, but research by Joseph Viellehner and Wolfgang Potthast at German Sport University Cologne shows us why and just how much harder. They took a group of trained cyclists and simulated various intensities found during a race, then measured different physiological markers (heart rate, oxygen consumption, muscle activation) with and without vibration being applied to the riders and their bike. The researchers found that although vibration didn't limit the amount of forward propulsion it did increase muscle use in the forearms and triceps as well as the calf muscles. So much so that heart rate increased on average by 6 beats per minute during low intensity efforts and by 10 beats during medium intensity efforts. Note that the efforts in the experiment were only 2 minutes long. Extrapolate that increased heart rate over several hours and it's easy to see that vibration is a significant contributor to fatigue, even if your rides aren't races. Reduce the effect of vibration and you reduce unnecessary fatigue.
The easiest way to reduce the amount of vibration reaching your body on rough roads is through the use of wider tyres and lower air pressures. Yes, higher pressure will be quicker (up to a point) on smooth tarmac. At the other extreme, riding the cobbles of Paris-Roubaix at 25km/h required only 153 watts with tyre pressures of 2.5/3.0 bar. With tyre pressure at 4.5 bar the same speed required a power of 199 watts. The faster you ride, the larger the difference between lower tyre pressure (fewer watts) and higher pressure. As poor as a our roads can be, very few come close to the pavé of Northern France. But just as elite race teams test different pressures, shouldn't we all be experimenting with what works best for us?
We've covered why harder isn't always faster in a previous article. Here I want to touch on some of the other objections people may have to trying lower tyre pressures.
Pinch Flats
Pinch flats are often an objection to lower pressures. If your tyre pressure is too low the bead of the tyre can move over bumps and trap the inner tube between tyre and rim causing a "snake bite" or pinch flat. Tannus Armour for inner tubes sits between the inner tube a tyre sidewall so pinch flats cannot happen. An additional benefit of the Armour sitting between the tyre and tube is that it provides lateral support at low pressure. No squirming or instability during cornering.
Weight
The only cyclists not obsessed about weight are the ones obsessed about aerodynamics. But let's do some maths. A pair of Tannus Armour inserts weights 420g. You could offset some of that by using superlight inner tubes, since very little is going to penetrate 15mm of puncture protection. Or you could calculate how much using inserts is adding to the total weight of rider and bike and see that it isn't making much real world difference. For example, with a rider + bike system mass of 82kg it's adding less than 1%. Wheel manufacturer Swiss Side analysed the data from a one hour circuit race and calculated that a 400g lighter wheel only saved 0.7 seconds due to isolated rotational inertia reduction (the bit attributable to weight). Yes, a heavier wheel is harder to accelerate up to speed but once you've got it there that energy keeps you moving forward. Energy is lost only during braking, and even during the one hour circuit race analysed by Swiss Side, riders were only braking 2% of the time. If you're looking to break competition records then worry about weight. If you're riding sportives, with a club, or just for the love of it, then regularly taking a yoga class to improve your flexibility and core strength will have a far greater impact on your average speed, since you'll be able to hold a more aerodynamic position for longer.
Risk of Rim Damage
Another objection to running lower pressures is the potential for rim damage. Carbon fibre wheels are not cheap and when carbon does decide it's had enough it rarely gives a warning. Here Tannus Armour is not only providing 15mm of puncture protection, it's also providing impact protection. If you run tubeless tyres on a bike that can accept 28mm tyres then the new Tannus Armour Lite (coming May 2024) offers impact protection yet weighs around 50g. That's the same mass as a decent gulp of water and may be the difference between "Oof, this road is rough!" and a long walk home wondering how you will be able to replace your expensive rim.
Lower fatigue, greater protection
Cycling is full of traditions, but the era of marginal gains is constantly challenging many of the assumptions that these traditions are based on. From gearing to nutrition, to training and tyre technology, data has shown us that there are no one size fits all solutions. Maybe it's time to question why you run the tyre pressures you do. It could help you ride further.
