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What was the thinking behind having a bigger rear wheel on a TT bike back then?

The barbie bike

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The rear wheel is normal size (700), the front wheel is smaller (650). It was for aerodynamic reasons. By lowering the torso of the rider, the frontal surface of the rider became smaller.

The configuration appeared first in triathlon and was later banned by the UCI in road and track events. Both wheels must now be of identical size i.e. 700.

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    In addition to lowering the profile of the rider and the bike, I'd bet the smaller front wheel is not only more aerodynamic than a larger wheel, it's also less affected by crosswinds.
    – Andrew Henle
    Commented Jul 18, 2020 at 17:32
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    @AndrewHenle yes - and though not possible in a TT, a smaller front wheel lets you draught closer to the rider in front for more gain.
    – Criggie ♦
    Commented Jul 18, 2020 at 21:55
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    @Criggie: Individual TT it was, no drafting permitted there!
    – Carel
    Commented Jul 19, 2020 at 7:35
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    Can you add why it was banned to your answer?
    – End Antisemitic Hate
    Commented Jul 19, 2020 at 8:20
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    @Criggie: A smaller wheel is also less stable due to the smaller gyroscopic effect.
    – Carel
    Commented Jul 19, 2020 at 20:01

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