@suboptimusprime I'm a bit of a jerk, but this is in no way intended to come across that way. Serious question. I actually started this thread but have very little seat time over the last 15 years (just look at my Zaskar in the first post for proof!). I've noticed the trend of dropping the top tube lower on the seat tube over the last few years. Can you, or somebody, explain the significance of that, please? My mind always goes to something like this...
View attachment 2014404
(***not ACTUALLY
@stevezero 's bike, but only because Santa Claus didn't like him in 1975.)
EDIT: I DO have a bandana to match that seat, and I DO wear it on occasion. Well, it doesn't have the weird yellow discoloration in the middle, but it's similar.
My experience (being a USA cycling coach since 1990, World Cup director sportif and worked closely with Kestrel, Ritchey, Specialized, Rock Shox and others) the frame design began changing with the advent of exotic metals, carbon fiber and engineering principles that required stiffer frames due to the materials and higher loads the materials were being put under. Please remember those traditional frames are made from butted steel tubing brazed together into lugged head tube/seat tube/bottom brackets, very thin steel tubing. Then came aluminum, titanium, carbon opening engineers minds to what a bicycle frame could look like.
Dropping the top tube to meet the down tube, making stronger “triangles”, particularly when the need to have a top tube meet the down tube at/near the seat where the top of the down tube, where the seat is mounted, takes very little lateral load.
Most significantly, this frame change also allowed manufacturers to accommodate a larger buyer population with fewer frame sizes. Back when I rode bikes, frames came in single centimeter sizes, such that frame manufacturers had to make many different sizes to accommodate the variety of human sizes. Additionally, the tooling costs for making so many varieties of frame sizes were additional costs, where now most manufactures make 3, maybe 5 sizes if they include women.
Next step came the advent of dual suspension, where the additional frame loads and stress points of frames brought the triangles tighter and many more to help with rigidity in the bottom bracket and rear suspension pivots.
Working with Kestrel and their monocoque carbon frames, where they eliminated the down tube on their road bike, allowed them to effectively design the carbon layers such that the top tube became a suspension beam where the down tube/chain rails became a rigid, unflexible platform where all the energy from the rider was applied to the pedals/cranks/chain/wheel. I was part of testing where lateral flexion was measured at the bottom bracket and the Kestrel, without a down tube, measure the least deflection.
Sorry to go on so long, really just an engineering/cost reduction over time. Thankfully, the industry didn’t get stuck and moved forward with the times...
