"Front End Length": This is the theoretical horizontal distance (parallel to the ground) from between two vertical lines (perpendicular to the ground), one intersecting your BB and the other the top of your head tube. WHY ? Because it takes out the variables of both seat tube height and seat tube angle. Road bikers care a lot where their seat is. BMX and DJ don't because you're standing all the time. Before you say who cares, this is bull**** geek stuff, read the following description from the empirebmx website: Example from empirebmx.com : "Fly Bikes Tierra frame 19.8", 20.6", and 21" TT, 13.25" CS, 75 HA, 71 SA, 4.65 lbs; the seat tube is offset 0.4" towards the back, so the actual TT length is 0.4" longer than how the bike will truly feel (21" rides like 20.6", etc.) " A 0.4" longer when your choices between different $350 frames are based in 0.5 increments . . . . What you want to know is where are your feet/knees are in relation to your hands. (Knee gonna hit your bars?) A frame with a laid back seat angle will have a longer top tube than one with a more vertical seat angle--but the bikes will feel exactly the same to ride. Companies are telling you numbers that are easy for THEM to measure because the bike is in their hands. But it doesn't help us compare 2 different frames we haven't ridden unless you're going to do some Trig. (calculating the seat angle factor). The distinction between "actual" versus "effective" TT lengths is also irrelevant to BMX and DJ. This comes from road biking where old school road bikes originally had top tubes that were parallel to the ground. When they started slanting them down (and intersecting lower on the seat tube), they got shorter, even though your seat is still in the same place. For example see here: http://www.somafab.com/geometry03.html Heh heh. Now maybe I'll get back to work. No wait, it's lunch time.