What replaced the level top tube.
Monsoon Cycles, Colorado Springs · Updated August 21, 2026
Effective top tube (ETT) is the horizontal distance from the head tube's top center to the seatpost line, measured level, regardless of where the actual top tube goes. It exists because top tubes stopped being level in the 1990s and the old "22 inch frame" way of talking suddenly described nothing.
ETT is a decent first read on how long a bike will feel in the cockpit, because it includes what the seat angle does to your position. Two frames with identical reach but different seat angles will feel different lengths once you are on the saddle, and ETT captures that where reach alone does not.
Where it fools you: ETT moves when the seat angle moves, so comparing ETT across bikes with different seat angles quietly mixes two variables. That is exactly the confusion stack and reach were invented to fix. The working rule at this bench: compare frames by stack and reach, then use ETT plus seat angle to think about the saddle-to-bar picture, and never buy a bike off ETT alone.
The Frame Lab shows ETT, stack, and reach live as you drag the seat angle, which makes the relationship click faster than any paragraph.