Originally Posted by
Darth Lefty
Slanted top tubes were first commonplace on mountain bikes. They'd already dropped the top tube for more stand-over and raised the bottom bracket for more ground clearance. That made the head tubes very short, but when the suspension fork was added they needed more room underneath, so the whole head tube moved up. Several things were tried, like Cannondale's Killer V. The slant was just the simplest. The road bikers adopted it because it gave them a stiffer triangle for pedaling at the same time as a long seat post for more comfort. It also goes along with threadless stems, which also came from MTB because quill stems would slam down into the steerer, but don't provide much added stack.
The steeper seat tubes are a new development and they are a compromise of designing the bike with a long front center and long reach and slack steering, so a standing rider is in the middle of the bike and not OTB.
This blog post by Peter Verdone describes the basic idea. This is pretty much a done deal on mountain bikes. Some people have tried it on gravel bikes (
Evil Chamois Hagar is an example) but it seems for now that gravel bikes will remain pretty much just armored-up endurance road bikes.
how does the Chamois Hagar manage to get away with such an aggressive drop in chainstays without the pedals hitting the ground? Clearly, getting the geometry right has more to do with what is best suited to your personal needs. For me personally, I find that I lean forward slightly which puts enough weight over the front axle to cause a fair bit of understeer. I find that I have to be extremely gently during turn in, especially on gravel. My front wheel just plows. I'm planning to try using a wider and more aggressive front tire in the future.
I'm a taller and bigger rider, which may have something to do with the fact that I prefer a very upright riding position. But if I did manage to use some sort of swept back handlebars to achieve that stable rear biased handling im looking for, there just won't be enough weight over the front axle during steeper climbing. I think some sort of stem which you can adjust on the fly would be a nifty idea.
Would you mind explaining the difference in stability/ versus precision trade off when comparing the head tube angle to fork rake? Can you achieve handling which is both stable and precise, especially at speed by contrasting these two measurements?