Asymmetry: Life, The Universe, and Rolling Resistance

Welcome to the second episode of Marginal Gains!  In this episode the team delves into asymmetry and asymmetric effects surrounding tire pressure optimization problems for different race conditions.  This episode builds on one of the most popular tech blog pieces ever posted by SILCA on their website (view here) about optimizing pressures for Roubaix as well as more traditional road racing.  

Interesting Links, Sources, and Additional Reading From this Episode


Kahneman and Tversky paper on Prospect Theory:  View paper


In-depth look as Thermodynamic Asymmetry in Time: View paper

View more information on the SILCA blog: View here

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12 thoughts on “Asymmetry: Life, The Universe, and Rolling Resistance

    1. BL, we mirror the concepts from the podcast on the SILCA tech blog so if you are looking for something much more compressed and limited to cycling, subscribe there. We do about 75 days of testing per year with pro teams and athletes and try to distill and share what we can when we can on that site. Marginal Gains is more for those who want to take it next level and go beyond cycling, or just kill an hour on the trainer with something interesting. We are also going to start Q&A episodes of the podcast which will be much more direct, but will not be summarized on the SILCA blog, first Q&A episode will be in 2 weeks.

    1. Yes, much of the core data here is discussed in the 5 part series we did on tire size/pressure/rolling resistance/aero a while back. Much of the data is located here and will be further distilled and built upon in future episodes: https://blog.silca.cc/page/5
      Thanks
      Josh

  1. I’m a bit surprised that a discussion of tire compliance did not include any mention of frame compliance or suspension. Surely the fork on a mountain bike does something to change the energy absorption on rough surfaces? What about the visible vibration I see in a steel fork on an older road bike? Isn’t that on the order of the tire deflections?

    It feels funny to me that after decades of stiffening up wheels and bike frames with carbon the fastest outcome is to make the tire soft. It’s true bike makers now have a lot more design control over where the deflection occurs, but I’m going to guess that compliance in the wheels or frame makes the breakpoint occur at higher tire pressures . Is it possible the steel bikes from 20 years ago were most efficient with tires closer to 110psi?

    1. John, this is a great point and one that comes up on our future episode on Roubaix. Bike designers are continually evolving the vertical compliance of road bikes, but due to the way springs in series behave, since the tire is the softest it dominates the entire system. From this linked page you can read the stories about optimizing specifically for roubaix as well as the system stiffnesses measured on actual team bikes. https://blog.silca.cc/page/5

      To answer your last question, steel forks were more compliant than the last 20 years of carbon forks and likely were more efficient on rough surfaces. This is changing quickly, largely due to the spotlight placed on it by us and others for the last 10+ years. Mountain bike suspension changes the compliance and comfort of the entire system, as the suspension has lower spring rate typically than the tire, however the tire still ends up driving the setup of the suspension as it is the only thing actually touching the ground and it can be changed in spring rate much more readily than the shock.. so you will find offroad pros are far more particular about tire pressure than road pros. Also from a speed perspective, the compression and re-expansion of the tire has far less energy loss than a suspension system and the suspension system has far lower losses than jostling the entire bike/rider up and over the obstacle.

  2. It’s fantastic to be listening to a cycling podcast and encounter Kahneman and Taversky. Michael Lewis’ excellent book The Undoing Project recounts Kahneman’s and Taversky’s work and relationship.

    Regarding symmetry and its appeal to the human eye, how should we consider the Golden Ratio (~1.618) and what photographers know to be the “rule of thirds.” More often than not, the images that catch our eye have the subject positioned 1/3 of the way from the left/right and/or 1/3 of the way from the top/bottom. The symmetry of “subject in the middle” generally doesn’t fare as well.

    1. Jeff,
      Awesome question which hits on some of the points made in the podcast.. while symmetry is considered beautiful and sometimes strong, it isn’t as visually interesting as asymmetry. I like to think of the parthenon compared to a Zaha Hadid building.. the parthenon is quite imposing and beautiful, and something you want to get close in order to observe the details, but the Hadid is completely striking, eye catching, confounding.. take a look at Hadid’s Heyday Aliyev Center in Baku, it very closely follows Fibonacci’s golden ratio and is the sort of thing you just want to stare at whether in photos or in person!

  3. Great podcast! Please do the deep dive on Paris-Roubaix and release before the race to give us more insight when watching it.

  4. Great podcast! I love the thoughtful discussion on cycling related topics, without the normal “do this interval at this intensity to get this result” conversations. My thinking often goes towards what you call marginal gains because those are often the items that don’t necessarily cost a lot of money (in an expensive hobby/sport) but do result in gains over those that haven’t considered the small details.
    That said, I have a question regarding carbon tubulars. Is there a place for them in the marginal gains discussion? I ask because I ride a 2009-ish carbon bike with relatively narrow stays compared to modern bike frames. Many owners of wheels from that era are now selling because they have upgraded, and at fairly attractive price points in the used market. Can I play the tire pressure game with a set of tubulars? I know that a 40-50mm carbon wheel will have an aero advantage over my stock aluminum wheels, as well as weight, but I’m wondering if that gain is nullified by the tubular ‘issues’. Or are there tubular ‘issues’? I really don’t know because I’ve never used them and don’t know any cyclists that have used them.
    Maybe my question is more accurately stated – do clinchers with tubes have an advantage over tubulars on a similar wheel set? Or vice versa? And by advantages I’m referring to rolling resistance and aerodynamics, and not to serviceability or maintanance.

    Thanks for your time, and I look forward to the next episode! Chris

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