Ah, the power of the internet is astonishing.

One thread with one question, and several answers that all sound pretty definitive.



I agree that several reasons for the change are probably appropriate since things rarely change in an industry for one single reason.

However, I must throw in my vote for the origins. I strongly suspect that they were originally horizontal simply for adjustability and chain tension. They appear to me to be a hold over from when everything was single speed...

Not to adjust wheelbase, not to increase aerodynamics, not to change bb height...

Could people through the years have individually tweaked their wheel positions to accomplish these things to some degree? Sure! But i strongly suspect that none of these were factors in the original design decisions.