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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22 thoughts on “Ask Josh Anything #007

  1. Arguing against some wheel size is just silly. Take a custom bike that looks “perfect” that rides “perfectly” for some person (whatever their arm/leg/torso length). Scale that person up or down and the optimal should be a bike that’s scaled the same in all dimensions, including hub width to maintain bracing angles.

  2. It had been a few years since I read the Friction Facts report on pulley/jockey wheels. Would improvements by the drivetrain manufacturers (SRAM/Shimano/Compag) with newer series have narrowed the gap with the aftermarket offerings? Ie is R8000 better than the Ultegra version tested at the time?

  3. Hi Josh, Hi Fatty, Hi Hottie,

    Another awesome Q&A !

    Here are a couple of questions for Josh for Q&A episode 8 (that I’ll obviously listen as soon as it’s out there !) on the topic of aerodynamics and rolling resistance :

    1) Rule of 105% is now very well known thanks to you Josh and has really helped a lot of people understand modern wheels design. There are two things I’ve always wondered though :
    – Many rims including Firecrest won’t have its widest part at the brake track area. It’s pretty common to see “aero” rims that are 105% the width of the tire pretty far away from the tire with a brake track (not a correct name when talking about disc brake rim but I know you get the idea) width that actually narrower than the tire, giving the whole assembly kind of a “peanut shape”… so even though the 105% rule is somehow respected, shouldn’t it be 105% as close as possible to the tire ?
    – On the same topic, Zipp which is a company very aware of that 105% rule launched 858 NSW with a max width of 24.4mm for the 18 holes rim (front 858 NSW rim brakes) and 23.7mm for the 24 holes rim (rear rim brakes and front/rear disc brakes), that’s with a 17mm internal width. Even a 700×23 GP5000 with latex tube at 90psi is going to be wider than 23.2mm (24.4/1.05) on that wheel and I don’t see anybody running something narrower these days. Do they know something we don’t ? Does biomimicry rim design or does HexFin ABLC dimples change the rules and 105% is not relevant in that case ?

    2) All the articles talking about rolling resistance on the Silca Blog (my favorite being : part-4b-rolling-resistance-and-impedance) are awesome and very eye opening, I do happen to do some aero testing on my spare time and it’s ok to plug in a number for Crr and just don’t change it as long as you don’t test anything wheels related and you always test on the same road on a same day, then you can compare your results for different setups. Doing that : fixing Crr, fixing mechanical losses, etc. is not a problem at all for comparisons purpose. Now my question is : if I wanted to get a CdA number I can trust (not just for comparisons between different setups but really to keep that number) what would be a good testing method for measuring actual Crr on my testing road ?

    Thanks a lot and looking forward to listening to the next show and many more after that !

  4. Hey josh, I’m a national level time trialist in Australia. For The past few seasons I’ve been riding a plasma 10 but am looking to upgrade. I’ve almost settled on a giant trinity TT (needs to be UCI compliant). Is this the best TT bike available at the 3500-5000 per frame price point?

  5. Hey josh, I’m a national level time trialist in Australia. For The past few seasons I’ve been riding a plasma 10 but am looking to upgrade. I’ve almost settled on a giant trinity TT (needs to be UCI compliant). Is this the best TT bike available at the 3500-5000 per frame price point?

  6. Great Podcast and you are making my daily commute a bliss!

    As we are approaching winter in NE temperatures will change from 80F to 32F
    Assuming same:
    bike with same tyres and wheels ,
    rider (hopefully at the same weight),
    route and so on

    Question: Should I use the same pressure in the winter as in the summer ? Are the temperature effects in tyre material negligible?


  7. 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 …

  8. 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?

  9. I am building my first dream bike which would also be used for daily commute. I plan to put full fenders on it for daily commute, and pair it with Enve 4.5AR wheels and 700x28mm tires so I can go fast. I know there is some amount of aero penalty associated with fenders. What is the interactions between the full fenders and the aero wheels? Could the fenders extend the aero wheels “depth?” If not, would the fender’s aero penalty be offset by the aero wheels or is it a waste of money to install the aero wheels? Are there other ways to offset the fenders’ aero penalty? Thank you.

  10. Foam tire inserts (Nube, Tubolight, Pepi’s) in tubeless tires are getting a lot of traction in the popular press as an upgrade for XC and cyclocross racers. They’re supposed to allow lower air pressure (say 17 psi versus 22 without an insert) due to protecting the rim while providing sidewall support so they’re not squirmy. Nino Schurter and other top XC racers have been reported (and seen) to be using them this year. People are suggesting that the extra weight (from 100 to 200 grams for both wheels) can be made up by going back to narrower tires like 2.1 or 2.2s. And there have been reports of improved rolling resistance. But all reports have been anecdotal as far as I’ve seen with no controlled testing, and it would be great if you’d comment on the idea and any theoretical advantages (or lack thereof).

    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!

  11. 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.

  12. 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).

      1. Thanks Josh,
        I missed that answer and thought my messages were coming as SPAM to you or something… so tried with two different email adresses… sorry about that.

        Anyway, so looking forward to hearing your answer about the Zipp 858 in a future episode… maybe in ask John episode #10 ! 🙂

        And thanks for providing the link to Chung Method, have read it before will do again until I find how to get proper CRR numbers, for now with Golden Cheetah I’m able to play with the correct elevation and make CdA pretty relevant but that’s when fixing a CRR value, so I’ll try and get smarter with that.

        Thanks again !

  13. 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

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

    2 questions and a 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).

    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.

  15. Hi Josh. You have just given credibility to my aversion to riding tubeless tires. Like you, I cannot be bothered to deal with sealant.

    It would be cool if tire manufacturers find a way to enclose a thin layer of sealant in the tire carcass. So you get the hole plugging benefit of sealant without the slop inside the tire.

  16. A nit to pick about the “mantis” position as referenced by Antonio in the podcast… while hands are trending higher than in the past, this is really not exactly similar to what Floyd did way back when. UCI rules limit length, but triathletes are not constrained by those rules. The hands are higher, if done properly, because reach and stack are added, with the intent of improving comfort, power, and the Cd of the overall fit, and not necessarily the watts +/- of higher hands. This is also why the tilt is required. As a fitter and reasonably average athlete, even if the net effect was a loss of watts, it’s still the preferred method for long course triathlon fit due to the efficiency and other ancillary benefits.

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