Hindsight is 20/20, they say. Mountain bike geometry has taken a big leap forward in less than five years. One of those improvements - steep seat tube angles - has inspired much ridicule about old-school mountain bike designs. "How did anyone ride those things?" Compare the performance of a modern trail bike to any vanguard design from or before the year 2000 and you might believe an alien race had recently intervened to alter the course of our sport.
Spend a day climbing on a bike with a 76- or 77-degree seat tube angle and you'd wonder how anyone managed that task with anything slacker. How could early bike designers miss something so obvious? To discover the answer to that question, one need only perform the following test:
Roll up to a steep, challenging descent aboard your Pole Machine. Extend its 170-millimeter dropper post all the way to the top and give it a go. I'll take a risk here and say you'll completely understand the remainder of this article in less than 20 meters. With the seatpost fully extended, the steep-angled seat tube positions your saddle exactly where your body needs to hover. Nearly every effort to control the bike is impeded by the saddle's location.
Turns out that you can't have a steep seat tube angle without a proper dropper seatpost. First, steep seat tube angles position the saddle much taller over the bike - awkward! Further hindering the rider is the fact that the difference between your seated and standing position over the saddle narrows dramatically as the angle arcs upward as it nears vertical. If you haven't put two and two together, it was the widespread acceptance of the dropper seatpost that made steep seat tube angles possible.
Before the dropper post was included in the mountain bike equation, slacker seat tube angles offered a mechanical solution. For the same leg length, the slack seat angle's saddle sits significantly lower over the bike. When the rider stands to descend, the forward and upward movement away from the seat creates three to five inches of free space for maneuvering the bike. Without a dropper post (or an Allen wrench in hand to manually lower it), 74 degrees was the upper limit for seat angles before the saddle's position at
full extension became a serious handicap on the downs. The old-school, 73-degree seat tube angle offered a compromise between climbing and descending when dropper technology was not available.
So you have the Gravity Dropper, not modern frame designers or an alien master race, to thank for steep seat tube angles and the wonderfully improved climbing performance this simple improvement has bestowed upon today's trail bikes.