Originally Posted by
veryredbike
With seat tube angle, it has a lot to do with your position relative to the cranks. As you come forward you put more weight on your hands.
With head tube angle I'm a bit out of my depth, but I think it has more to do with the style of riding. If you're making a comfortable bike, you don't make the steering aggressive and twitchy, you leave that for "more pain equals more gain" crowd ;-) It'll affect the relative handlebar position... but that's something correctable with the stem length and top tube length... so yeah, I think it has to do more with what you're aiming for steering wise.
This is OTM. And just to follow on from my last post, the steeper the headtube angle, the more upper body weight is thrown forward onto the handlebars, which itself creates a twitchier ride. It also means less fork rake is required to hit the trail sweetspot (which again will vary depending on the type of ride you're aiming for) which in turn pulls the front axle back towards the cranks - this of course shortens the wheelbase, resulting in a more responsive ride (a good thing on a track bike), but it also places your hands/weight further over the front axle, which also effects handling (to what degree I'm not so sure), and the only way to shift that weight back would be to shorten the stem, which would undoubtedly effect a further increase on the twitchiness of the ride.
So designing a frame/fork set i always think is kinda like filling in a jigsaw puzzle - sometimes the bits don't quite fit perfectly, in which case it's about compromising in a way that will least jeopardise the type of ride you're aiming to achieve.