If we're talking specifically about tri/TT bikes, most have the same BB drop across the entire size range, so it matters even less. So in this case, our theoretical pro who decides to size down his Shiv from XL all the way down to XS, but decides to keep the 175mm cranks, still has the exact same cornering clearance as before...

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"I'm thinking of a number between 1 and 10, and I don't know why!"

I would think that the crank arm length for a TT fit would probably be in the range of 150mm to 165mm.

Also, I would never pedal through a corner. Problem solved.

Should be, but on most production tri bikes they're still spec'ing 170-175.

If you've got 155mm cranks on a bike with a BB drop suitable for a crit racer with 175s, why not hammer through the corners...?

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"I'm thinking of a number between 1 and 10, and I don't know why!"

You are correct. The bottom bracket height for the new Shiv is 265 mm for all frame sizes, and the height for the old Shiv is 258 mm for all frame sizes. The crank length varies from 165 to 172.5 mm for the new Shiv and 165 to 175 mm for the old Shiv.

Looking across a number of triathlon bike brands, I don't see any crank lengths specified smaller than 165 mm regardless of the frame size.

A proper bike fit would probably have a crank length around 155mm.

That crank length limitation is a product of available OEM lengths rather than ideals

I measured my fixed-gear track bike. Pedal strike during turns is an important consideration for fixed-gear bikes because the pedals are always turning. My fixed-gear bike has crank arms that are 165 mm and a bottom bracket height of 285 mm. I checked the specifications for some other fixed-gear bikes and found they were similar.