Ask Josh Anything #001

Q&A Episode 1 –

Josh answers a dozen questions from our listeners AND THE Robert Chung, inventor of the Chung Method for determining CdA and Crr from field testing, calls in to discuss a topic from last week’s episode.

Interesting Links, Sources, and Additional Reading From this Episode

Got a question you’d like to ask Josh? Text or leave a voicemail at the Marginal Gains Hotline: +1-317-343-4506. You can also email us at, or just leave a comment in this post!

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Chung Method, Golden Cheetah software

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17 thoughts on “Ask Josh Anything #001

  1. Big fan of what you’re doing with the podcast! I have had a serious question for Josh ever since I heard his contribution to the CyclingTips podcast where they walked through and analyzed each TdF team’s time trial set up. He mentioned during the Trek-Segafredo section how he really liked what Trek did with the design of their Speed Concept, specifically in regards to how they “were the first to understand the challenge of a composite spoke wheel.”

    My question is, as someone who owns a Trek Speed Concept and has a HED H3 front wheel, do you believe that the Trek Speed Concept fork blades are suitable to be paired with a composite spoke wheel? Or would a typical 70-90mm deep wheel potentially be a faster option?

    I only ask because I have seen multiple people debate the efficiency of running a trispoke wheel in the latest generation Speed Concept frame, stating that the fork blades are not wide enough (in comparison to the Pinarello Bolide for example)

    1. Garret, a good rule of thumb is that if you can hear it making that ‘thwump-thwump’ sound when it is spinning, you are losing some watts.. to make sounds requires energy, so that’s your legs powering a small sound machine. Trek was definitely the first to really start addressing this and Pinarello has taken it one further on the Bolide. It always helps to do your own testing to be certain as there are so many complex interactions in these systems that the answers are rarely clear cut. Having said all of that, you are probably talking a couple of watts either way, so the gains or losses will be rather small.

  2. Hello,

    I was recently at a track cycling world cup and noticed that the teams were selecting their gearing around 14 and 15 tooth cogs.

    From sprinters 14T to IP riders 15 tooth cogs seem to be the jam. (Ashton Lambie’s WR pursuit I usually ride a bigger gear, so I went with a 111.6 (62 x 15) for the qualifier, and 113.2 (63 x 15) for the final since it was a little warmer – PezCyclingNews. (He also didn’t have aero TT-sculpted extensions and his chainring looked more spider like than an aero chainring.)

    If chainring flex was an issue surly track sprinters would have stayed small.
    My understanding is that they track riders limited by the chainring size, as larger (say 70×16) would hit the chain stay. Maybe dropped track chain stays (like gravel bikes) and larger rings are the future??

    This makes sense to me. Less “chain wrap” around the cog. Better leverage of the chain and reduced chain bending and friction….
    I am not into buying custom rings, so I have built my track bike’s gearing around a 14t cog.

    Extrapolating this to road.
    For normal riders would 42×54 chainrings with a 12-32 cassette not be more efficient than 11-28 with 36×52?

    This brings me to SRAM.
    is a 10t cog not heading in the direction of less efficiency?
    (Motivated by being non-compatible with all others and forcing users to commit 100% to the SRAM ecosystem from wheels up)

    Thanks for your podcast,


  3. Hi Guys,
    Loving the podcast. My question is about chain lubes and temperature. Does a particular chain lube operate more effectively in high temperatures versus low? For instance comparing Adelaide during the Tour Down Under (40C) to the Spring Classics like Milan San Remo where it regularly snows (5C). Would a low visosity chain lube work better at low temperatures and a wax lube at high temperature?

    Keep up the great work.

  4. Thanks for this episode. I realize that making these Q and A session takes up a lot time in addition to your ‘regular’ job. I also loved your take on rim brake vs disc on the Cyclingtips podcast. That inside look at how and where the industry is spending money was very informative and I would love to hear more about that in future installments. Bummed to hear about the lubricant issue but, as always, you offered solutions not just laments.

  5. Josh, I’ve been thinking about your question would you rather have 10% more power or 10% lower drag, and I’m afraid that after thinking about it I don’t understand why the lower drag is better. To me it looks as if speed scales as (P/CdA)^1/3 for the limiting case where drag dominates. In this case I don’t see how it makes a difference if the ratio of (P/CdA) increases by a change in power or lowering of CdA*. On the other hand, if we consider the other retarding forces (rolling resistance, drivetrain losses, and gravity) increasing power will have a benefit while lowering drag will have no effect. To me this looks lowering drag is at best equal to increasing power and probably less effective. What am I missing? Thanks.

    * Unless you were thinking raising power by 10% increases the ratio to 1.10 whereas lowering CdA by 10% raises it to 1.11111.

    1. Tony, you are totally correct, you’ve caught me conflating Drag force with CdA.. something my brain still hasn’t settled after a career of utilizing direct balance force data in the wind tunnel!! We will cover this, and why I would still take the CdA over the power in Q&A#2 going live on March 26th
      Nice catch!

  6. Great poscast! Live the level of analysis, which is beyond basics, and focuses on first principles of understanding. Here is a question, and a possible future episode topic… tires. Why do the pros stick to tubulars? Modern tubeless and clinchers are getting do good on a crr level. Are tubulars still showing an edge with impedance? It it flat tolerance? Habit? Or are the tubulars supplied specifically for racers still edging out what we can buy (thinking continental)?

  7. Josh, you mentioned previously that you are unable to make NFS lube anymore because one of your suppliers is no longer selling you an ingredient. You made it sound like they still make the ingredient, but Silca specifically was put on a naughty list. Was there any reason given why? Did they see you as a competitor, did they not approve of how you were using the ingredient, or what?

    1. Thanks Mark,
      We don’t exactly know why we can’t get it anymore, but the timing is a bit suspicious.. one week after NFS appeared on Cyclingtips as the winner of their big lube shootout and the test lab guy saying that cyclists should “either use hot melt wax or SILCA NFS’ for minimal drag and extended chain life, they let us know that they were going to stop selling this ingredient.. that’s all we know. Time will tell if they are doing their own bicycle lube or what the whole story it, but in the mean time, Josh at NFS has a barrel of the goods remaining and is continuing to sell until he is out, so you can find him here:

  8. I use a Garmin Virb Ultra 30 and/or a GoPro Hero to record my rides, and to make videos of my races (road, mostly crits) Neither of these cameras are remotely aero, so I recognize I am paying a penalty to get interesting video for my dozens (maybe) of viewers.
    I have a few locations where I can mount the camera. Aesthetic considerations aside, which location exacts the least aero penalty:

    Skewer mount front wheel

    Skewer mount back wheel

    Under my Garmin on an out front mount (K edge or BarFly)

    Under the saddle facing backwards

    Mounted on a bottle mount on the seat tube.

    If it matters, I’m riding a Giant Propel with aero bars and 55mm wheels.

    If you have time for a 2nd question, why don’t camera manufacturers make an aero camera? Surely it wouldn’t be that hard to design something that was more aero than a square box!

    I’m enjoying the podcast, and look forward to hearing my question in a future episode. Feel free to use my name if you want.



    Barry Bean
    Bean & Bean Cotton Company
    Peach Orchard, MO

    1. Ooooh, this is a good question! The next Q&A was recorded last week and goes live tomorrow, but definitely will drop this one into the next episode as it’s a great question and something I have some pretty strong feelings about on a couple of levels!

  9. Hi guys!
    two quick questions:
    1) how important is to be aero in the climbs? Can you give an estimate at what speed does an average rider use the same power for overcoming drag and meters climbed? (I’m 85kg, pushing 250W up my local 8% climb so you can start from there)
    2) I saw some coaches analyse ironman bike split data using W/kg. I don’t understand why is this metric relevant – when riding mostly flat terrain at mostly constant speed doesn’t total mass have a relatively small impact on speed in comparison to drag?

    1. Zlatko, awesome question and we will get it into the next Q&A!
      The answer is complicated so we’ll try to do our best to cover all the bases.. stay tuned!!

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