Originally Posted by
zzyzx_xyzzy
They ride bikes with quite short chainstays for whatever reason. When you shorten the chainstay you also have to shorten the front center to keep the weight distribution from getting too rear biased. So short TT/long stem.
This doesn't make sense. The chain stay length doesn't change as the frame size goes up. For example all Cervelo R3SL's have 399 mm chainstays regardless of the lenght of the top tube from 48cm to 61cm. By your theory the larger frame sizes would be horribly out of balance.
Moreover the weight distribution is going to be the same regardless of whether the reach to the bars is made up of 56cm of TT and 12cm of stem, or 58cm of TT and 10cm of stem.
What is different is that the bike with the 56 cm top tube typically has a shorter head tube, and than the bike with 58cm top tube.
Hence my point, the smaller frame tends to facilitate a more aero position, i.e. more drop from seat to bars.