Originally Posted by
jimmuller
It has always struck me that ST angle is more important to a builder than to a fitter. Have a bike with steeper ST? Then move the saddle back on the rails, and your saddle-BB position will be the same.
ST angle matters to a builder because it constrains chain stay length. A steeper ST angle places the point of closest approach between wheel and ST lower and allows the BB to be closer to the DOs. When the rider then moves the saddle back to compensate it moves the rider's weight back toward being over the wheel. So you end up with a different weight distribution and a tighter rear triangle, both seemingly significant.
You nailed it. The current fad is short chainstays/short wheelbase. I think the marketing people have found that they can make a bike sound fast with too short chainstays. They tell us that we will corner a lot faster with a short wheelbase. They're just selling numbers. Unfortunately for us, chainstay length/wheelbase does't have a significant effect on cornering ability until you go to extremes like a cargo bike. Cornering ability happens at the front end, primarily with trail. In the real world, the back end just follows the front end and small changes in wheelbase are transparent to most of us. Where short chainstays fail is in out of the saddle climbs or sprints. For some reason, short chainstays allow the back wheel to fishtail more easily than a longer bike when the rider is hammering out of the saddle. I imagine that most of us would agree that scrubbing the back tire sideways across the road does not contribute to getting down the road faster.
So, back to the OP's question. Seattube angle doesn't matter as long as you can get the saddle where you need it. Or, if you are a marketing manager at a big bike company, it helps you sell bikes for all the wrong reasons.