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The next marginal aero gain? Gels up you sleeves
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Marc Hirshi today putting gels up his sleeves in the TT, ostensibly to close the gap between your arms.

I presume it's the same principle as a bottle down your shirt? E.g. limit the air going by your chest and into the groin area vs forcing it around the body?

https://twitter.com/...xBKO7Gkjkpw&s=19
Last edited by: timbasile: Sep 23, 23 14:00
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Re: The next marginal aero gain? Gels up you sleeves [timbasile] [ In reply to ]
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Yup. I've only been saying it for 20 years, here but mostly elsewhere. Pressure and interference drag is where it's at, and understanding how these change with speed.

The general principle of interference drag is if you can't space it wide enough, close it up.
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Re: The next marginal aero gain? Gels up you sleeves [timbasile] [ In reply to ]
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Here in Indiana back in the late 80's on the duathlon scene dudes were slipping on tricep fairings in T1 that were made by Paul Lew if memory serves correctly. USAT banned them pretty quickly. lol
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Re: The next marginal aero gain? Gels up you sleeves [Runorama] [ In reply to ]
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Runorama wrote:
Yup. I've only been saying it for 20 years, here but mostly elsewhere. Pressure and interference drag is where it's at, and understanding how these change with speed.

The general principle of interference drag is if you can't space it wide enough, close it up.

RE: Aero changes with speed, especially for things as sensitive as cylinder width/spacing.

The current strategy is to have a refined aero position for flat roads, on the bullhorns for climbs, and tucked on the bullhorns on descents for stability. There's a wide range of flat roads though with pro TT speeds between 20-35mph. Surely the optimal arm/head position is not the same at 20 and 35. In theory a rider could have a few positions each optimized for a narrower range of speeds. Maybe forearm supports that have a few 'slots' of padding at the correct height and width for each range. That way there's no moving parts that would run afoul of the regs.

Even just a high speed/low speed setup, one slot wider and higher than the high speed slot that is narrower and lower.
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Re: The next marginal aero gain? Gels up you sleeves [mathematics] [ In reply to ]
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Based on what I understand of interference drag in between the arms, the relationship would not change materially with speed. Any spacing larger than two diameters and lower than 4 is bad.

How Cd changes with speed for a cyclist mostly has to do with the fact the overall positioning and resulting shape of the cyclist can enable flow to become critical over certain areas (most noticeably the lower back), at which point the separation angle will start for go from 10-15 degrees all the way to 40-50 degrees.
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Re: The next marginal aero gain? Gels up you sleeves [timbasile] [ In reply to ]
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Is it enough of an aero gain to offset the aero loss of his sleeves not being flush with his arm anymore (presuming tight clothes are better than loose clothes for aero purposes)?
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Re: The next marginal aero gain? Gels up you sleeves [timbasile] [ In reply to ]
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I noticed the bottle down the shirt thing was big in Finland, among pros & AGers alike. Wouldn't mind seeing some rules on this stuff.
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