Dan Empfield: Slowtwitch, Quintana Roo, Tri Hall of Fame...and Marginal Gain


You've no doubt heard Josh mention Slowtwitch.com many times on this show.  It's one of the key places he goes to share ideas and get feedback. But Slowtwitch is more than just a place. It’s a person too. The site was founded by Dan Empfield in 1999, and remains publisher to this day. 

But before Slowtwitch even existed, Dan was a competitor. He did his first Triathlon in 1978 and competed in the first Ironman Kona in 1981. You may also know Dan as the man behind Quintana Roo. That stack and reach thing we all use now: that came from Dan’s work. We get into all of that and more with our guest this episode:Tri Hall of Famer, Slowtwitch founder and Publisher Dan Empfield.


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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  • Wilbert

    Hi MarginalGains,

    Would like to ask some details about the rule 105 in relation to the Discus 45|40 + 32mm GP 5000 combo.

    1. Is the rule 105 applicable mainly on the front wheel? Or is it also applicable for the rear wheel where air is disturbed by the bike and rider?

    2. Would the surprising aero results of the Discus 45|40 + 32mm GP5000 also translate to the narrower Discus45|32 + 28mm GP5000? They seem to have similar ratio of tire and rim depth.

    Thank you!

  • Willie Hatfield

    Hi from Willie Hatfield at Bike Friday, a US manufacturer like Silca. Our tagline is Performance that Packs, and we’ve been building lightweight road and touring bikes with small diameter wheels for 31 years. (451/406mm BSD)

    I’d love to hear Josh’s thoughts on the effects on a bike of wheel diameter. Specifically, assuming the same tire construction, rim cross-section, wheel system stiffness,etc., except for diameter, how will the rolling resistance of the tire change? Will casing losses remain the same, but impedance change? Might impedance be proportional to the ratio of surface roughness to wheel diameter?

    From skateboard wheels of 90mm to 36ers with 900mm diameters, there is a large range of human-powered wheels on the road today. Could Josh ball park, or walk through how he’d estimate the Rolling Resistance wattage differences between these extremes?

    That’s a lot of questions, sorry. Please answer whichever you wish! Love your show!

    For cycling,

    Willie Hatfield
    Bike Friday Engineer
    Eugene, Oregon

  • Julien Van den Brande

    Hey Guys,

    I’ve been a fan of your podcast for a few years now and I have been adapting my Belgian kermesse race setup with your tips.

    I have a few questions on the topic of the Giro:

    -What is the penalty in watts of a single speed chainring? As there is more tension on the chain by the rear derailleur and the narrow-wide chainring also gives more friction then a traditional chainring, certainly on the extreme gears.

    -Does the helmet change and unzipped tt suit cost overall victory to Geraint Thomas?

    Bonus question:
    How good is WD40 on a totally degreased chain in comparison with lubricants?

    Kind regards

  • David


    Silca tire pressure calculator: I run 25mm in the front and 28mm in the back. Love that Setup, but I cannot use the calculator with Mixed tire sizes. Can I Just Run the calculator for 28mm and 25mm tires and then use the respective Front and rear Numbers? That would leave me with around half a bar Higher pressure in the front than in the rear.

    Or is there more to it when mixing tire sizes?


  • Robert Chung

    What a fun listen.

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