Ask Josh Anything #006

The ongoing “Ask Josh Anything” series is back from Summer vacation and we’ve got a fun — and surprisingly informative — set of questions for Josh, including: 

  • What marginal gains are made by following the TTT instructions in a pre-TdF video by Team EF?
  • When you’ve got a tailwind, is it better to still make yourself as small as possible, or should you sit up and try to take advantage of the wind behind you?
  • What’s going on when the dish changes the first time a tire is mounted on a new wheel?
  • Some riders claim their bike feels faster and lighter on climbs when they move their bottle to their jersey pocket. Is there any merit to this, or is the effect in fact the opposite? Or neither?
  • FFWD claims to have made the fastest wheel ever. Is it possible to legitimately make this claim?

All this and an in-depth discussion of what happens to your aero-ness when you grow a beard (with a side discussion on types of beards), in the show that makes a big deal about the little things, and how those little things can be a big deal.

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

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16 thoughts on “Ask Josh Anything #006

  1. Hypothetical question: (Thinking back to the early days of triathlon for example, where wheels as small at 24″ were used with success)

    If you could start from scratch with no legacy, what would be the best road bike wheel size? Where does the optimum balance of aerodynamic drag, lift, weight, rolling resistance and bump compliance lie?

  2. Hi,

    Another mechanical engineer here LOVING your podcast. Rated 5 stars and telling my friends.

    A question I’ve been wrestling with in my head lately relates to power demands based on grade, with the motivation behind the question pertaining to gear selection during training on an indoor trainer in ERG mode. My theory is that all watts are not created equal, my logic is below.

    In short:
    1. How is power actually calculated?

    Of course, strain gauges in the crank arm measure strain in the material, so that Force -> Torque -> Power can be calculated. Sampling this strain many times over the duration of one revolution of the crank gets you your force vs. angle measurement. Averaging that can get you your average power, or something like that.

    2. How do the power demands within a single pedal stroke change with respect to grade?

    You spoke in one of the recent podcasts about micro accelerations. When climbing, you’re fighting these micro accelerations a lot more than if time trialing or riding on a downhill. My thought is that 300watts at 90rpm climbing is physiologically different than 300watts at 90rpm time trialing or descending, because you have to overcome these micro accelerations (FBD shows this concept easily as positive grades have a higher net deceleration in the absence of a pedaling force). Again, my theory is that all watts are not created equal. 300w @ 90rpm climbing must be different thatn 300w @ 90rpm descending.

    3. If we now understand the physiological differences between power demands at various grades, what gear should we be training in in ERG mode on an indoor trainer?

    The root of my question is cycling on a trainer in ERG mode. Gearing must matter in my opinion. A low flywheel speed (small chainring up front, large cog in the rear) simulates climbing with micro accelerations (higher braking force on the flywheel, lower flywheel speed). A high flywheel speed (large chainring up front, small cog in the rear) simulates a TT or descent (lower braking force on the flywheel, higher flywheel speed). 300W in erg mode in different gear selections must be physiologically different, right? All watts are not created equal, right!?

    Can you please explain the physics behind the phenomenon I’m wondering about? Help me sort out this confusion that I have!

    1. i think what you’re asking about is related to crank inertial load. Even at the same power, cadence is related to crank inertial load, though the strength of the relationship varies from individual to individual. Since the power is the same but the cadence varies, crank torque (or pedal force) must also vary. In general, crank inertial load is low when in a low gear climbing a steep hill, and CIL is high when in a high gear while on the flat or descending.

  3. During hot gravel endurance races my shins/knees/biceps will become crusted in gravel dust. Basically anything that is a leading edge in the wind & sweats eventually develops a thin crust of gravel dust.

    I always use a little bit of water to clean this off because I think it inhibits cooling. CONSENSUS is not to waste water by pouring it on yourself & a coat of gravel dust doesn’t inhibit evaporative cooling from sweat anyhow.

    This isn’t really Josh’s bailywick but what does he think? Does a Crust of Dust inhibit evaporative cooling?

  4. Regarding beards and Aero: a few years ago specialized put the beard to the test in their tunnel. It showed less than a watt of difference over 40K, so pretty nominal. i suppose if you havea full mountain beard, the difference could be larger. thank you

  5. I have a question for Josh. In addition to cycling, I also compete in inline speed skating. My events are usually marathon distance races (26.2 miles) on paved roads.

    The general rule of thumb has always been that harder urethane wheels are faster than softer wheels. This thinking probably comes from the mind equating vibration to speed (something Josh has touched on before).

    Since we don’t have power meters for our inline skates, it’s a difficult concept to field-test. I think a roll-down test is somewhat inconclusive for skate wheels because a good wheel needs to do more than just roll well. The way we propel ourselves on skates causes the wheel to frequently change the degree in which the wheel contacts the ground (from left edge to right edge and back) and as we push down into the ground, it seems as though the wheel slightly compresses and rebounds.

    In Josh’s opinion, would a softer wheel that vibrates less be a faster option than a harder wheel? Would you suggest going with the hardest wheel that still feels smooth as it rolls across a surface?

    Aside from picking fast wheels and bearings, what other marginal gains should i be looking for? I wear an aero-road helmet and skinsuit. I’m thinking maybe some of the trip-strip socks would help. Body position seems important. Hands behind the back with arms pulled as tight into the body seems like the logical best option and feels fast, but I’m open to other suggestions.

    I’m a huge fan of Silca and this podcast. My SuperPista Digital is one of my favorite cycling-related purchases. Who would have guessed that I would ever look forward to pumping up my tires every day? Keep up the great work!

    1. Love your question Rob. I will bring it up with Josh. In the meantime, have you considered trying the “Chung Method” to test your wheel compound theory? – Hottie

      1. Thanks Hottie. The problem with the Chung Method is that it requires Power as an input, and I don’t think a power meter currently exists for inline skates.

  6. Uhm If a pencil is worth 5 watts…how much energy am I losing by strapping a number plate flat to the front of my bike and how should it best be fitted to reduce drag (without messing w the magnetic strip)?!

  7. With the latest generation of road tubeless tires now on the market from Continental, Vittoria and Specializes supposed tubular killer yet to be released. Is now the time to go tubeless as far as rolling resistance is concerned compared to each company’s comparable tire with a latex inner tube? I have seen some data comparing the GP5000TL and GP5000 with butyl tube but no data yet with latex tubes. If I did the math correctly figuring a 3 watt savings per tire with latex tube over butyl it is still marginally faster to run latex tubes in a GP5000 over a GP5000TL.

  8. To go along with the discussion concerning wheels, in particular the problem of differential spoke tension between Drive and Non-Drive side on a rear wheel; I am curious what Josh’s thought are concerning a 2:1 lacing pattern? Fulcrum, Shimano, and the now defunct brand American Classic have all used the 2:1 lacing on some of their wheels over the past decade. I own a few sets with 2:1, and have had really good longevity with them. Alternatively, I just bought a high dollar wheelset in the last 12 months with a standard lacing pattern, as I was looking to get something wide and tubeless compatible so that I could run 28mm tubeless tires on a new road bike (I also changed to disc brakes). They came out of dish after less than 1000 miles of use. I checked the spoke tension when they came out of the box, and they were all well over 100 kgf to start, probably to account for the de-tensioning expected from mounting the tire. When I discovered the wheel was out of dish, the non-drive spokes were basically at 0 tension. I shipped them back to the manufacturer and they re-laced the wheels with new spokes. I’ve put well over 1500 miles on them since I got them back with no problems, but I’m keeping a wary eye on them now. I also just re-laced a buddies standard laced rear wheel that came out of dish, but attributed that to high mileage. Meanwhille, the 2:1 wheels just keep rolling along.

  9. Why are tire manufacturers not making 23mm tubeless tires? The new minimum (e.g. Conti GP5000TL, new Schwalbe Pro One) seems to be 25mm, which seems likely to cause aero losses and handling problems in high yaw conditions.

    Some time ago, you published the ‘rule of 105’, in which “the rim must be at least 105% the width of the tire if you have any chance of re-capturing airflow from the tire and controlling it or smoothing it.” (I understand why this is, but won’t repeat it here).

    According to my calculations, a 25.0mm nominal tire (measured on a 19mm internal width rim) will expand to 25.9mm on a 21mm internal width rim, such as my HED Jet Plus. That’s 104%. 🙁

    A 23mm nominal tyre (again measured on 19mm internal rim) would expand to 24mm, giving 112% rim/tyre ratio – much better.

    Is this a market decision (everyone wants wide, because ‘wide is good’), or is there a technical reason for doing this?

  10. Cyclocross question. Not sure if it counts as a marginal gain if you aren’t using the best tech – which would be tubulars. But for clinchers, is tubeless or latex tubes the way to go?

  11. I have to ask this question, what are your thoughts on the youtube channel Hambini? He is an aeronautical engineer who has tested many wheels and claims many manufactures testing result to be utter rubbish especially Zipp. I’d love to know your thoughts on his testing results.

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