Ask Josh Anything #007

We’re back with a new set of questions for Josh, digging deep into the topics super-nerd cyclists care deeply about. We talk about the products that intrigued Josh most at Eurobike, find out what size (diameter and width) he’d make road wheels be if he could start from scratch, speculate on whether the very aero-looking Ceepo Shadow-R is actually aero, consider marginal gains in gravel races, ask whether it’s better to wrap cables together or keep them separate, ponder the age-old question of tubeless vs latex tubes, and…ponder marginal gains opportunities in inline skating. (Hey, rollerbladers need marginal gains love, too.)

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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11 thoughts on “Ask Josh Anything #007

  1. It’s possible to determine Crr (and CdA) for a bike without using a power meter, so it would be possible to do so for inline skate wheels without a power meter. It’s a hassle to do but if you’re desperate enough …

  2. I was re-reading the article on tire pressure and Roubaix and the optimization between pavement and pave. As noted a 5 psi drop of pressure is typically not a deal breaker, but in this optimization I assume the regular loss of pressure over the course of the race is taken into consideration as well? Since in this type of race each sector is important and different that may be a factor but what about the end of the race when you might really need those couple of watts in the velodrome? Sounds like a pretty complex problem but how is pressure loss during the race factored into the optimal tire pressure at the start of the race? How much is lost in a typical race? and is Roubaix a worst case scenario for the pressure loss over the day?

    1. Ha!! Yes, that is a beautiful example of the power of aero.. one the body is horizontal the CdA goes WAY down and you can see that he just begins accelerating! Of course they don’t do this in the pros because it’s too dangerous and leaves the rider with too little control of the bike. There is enough talk about maybe penalizing riders for some of the extreme positions being used while clipped in, so I’m sure this would be banned by UCI straight away.. Thanks for sharing, love that video!
      Josh

  3. Hi all, a question for Josh, prompted by the final hour record podcast and the comments about Boardman’s frame I his Merckx record.

    I love my steel bike. Old fashioned round tubes. Simple diamond shape. Caliper brakes. Is it worth my while having my old CX-ray Mavic Open Pro wheels rebuilt with something cheap and ‘aeroish’ like alu Kinlin 31. Will I feel more benefit from the aero gains or the rolling resistance improvements or perhaps not that much at all?

    Thanks for keeping my brain ticking in my dotage.

    “Oh no! Not again”

    1. Awesome! My road bike is an Eddy Merckx MX-Leader built up with modern Campag.. my love for steel bikes runs deep!
      You aren’t going to see much difference until you get to 40+mm rims and ideally something that falls under the rule of 105%. I’m running 303’s on my Merckx and they are sublime in ride quality and quite fast. Something like the Kinlin 31 will not provide any noticeable difference over your Open Pro’s you would be better off spending the money on some really fast tires and latex tubes, with $$ to spare.
      Best
      Josh

  4. Awesome episode as always !

    Couple of questions regarding the 105% rule and CRR.

    1) 105% rule :
    – does it matter where the widest section of the rim is relative to the tire widest section ? Firecrest for example has its widest section close to spoke bed but pretty far from tire and is actually narrower than most tire at brake track… creating kind of peanut shape more than an airfoil shape… so should the 105% rule be at brake track or external part of the rim in case of a disc brake rim since brake track does not apply (even if it means a toroidal shape that is actually 120% widh of tire width somewhere in the middle and 105% at brake track) or should it be 105% somewhere on the rim but it does not matter where?
    – Zipp 858 NSW is a different beast with the 18h rim (front rim brakes) being 24.4mm max width and the 24h rim (rear rim brakes & front and rear disc brakes) being 23.7mm max width… meaning all tires even 700×23 are going to be wider than the rim with the 17mm internal width. So what do the Zipp engineers know which allow them something that does not respect the 105% rule at all ?

    2) CRR
    – when doing aero testing I’m trying to be as precise as possible regarding all parameters but it’s almost impossible to know what’s the correct CRR is on the road I use for testing. Do you have any advice to calculate CRR properly ?

    Thanks again, looking forward to the next episode(s).

  5. I would be interested in an update on pulley wheels since the Friction Facts data I have is getting old. Have the newer drivetrain offerings (eg. r8000) improved in this area (over the models tested in 2013) or can similar gains still be found by moving to ceramic bearings and/or OSPW? In summary,have these gains become more marginal? Thanks.
    I have enjoyed every episode, so I hope you all continue to find this platform rewarding enough to continue for years to come.

    1. Thanks Andrew, we will try to get this into a future episode, but OSPW is a 1.5-2.5 watt savings at higher chain tensions depending on setup, brand, etc

  6. This might be my new favourite podcast. Awesome!

    2 questions and a comment.

    Comment
    1) I have read in a few places that the high heat absorption of dark colours also means dark colours let go of heat faster and as a result, the wind convention effect at around 22kph or higher means dark colours are cooler than light colours at that speed (or faster).

    Questions
    1) Aero over weight.
    Using best bike split, this looks very clear. But when you add in the extra element of riding in a 50 rider size bunch on the flat…..are the aero gains of an more aero, but heavier wheelset or frame mitigated to the point where weight starts to matter more when you have a main climb in the race or course? Assuming you never take a turn on the front of the peloton. Does this explain why marquee climbers still stick with light bikes over aero bikes in the pro tour?

    2) If you have aero data on a wheel, tested in a tunnel, presumably on it’s own or as the front wheel, what is the general consensus of the type of aero performance reduction would you expect for the back wheel (behind a frame, churning legs and crank etc)? All companies would post aero data of a front wheel hitting the clean air, so you wouldn’t just double that for 2 wheels, or would you? Or does it vary so wildly that there’s not a typical range?

    Thanks for the shows! Love them.

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