Agreed. But what is optimal? As a short man I don’t need my seat super far forward to prevent looping out on steep climbs. I have read many times that a steeper seat tube angle is more efficient but I’ve never read why it is so or seen any real data about that. I have read some studies of road bike position that indicated that a steeper seat tube angle was more efficient because it allowed the riders to engage their leg muscles better and for greater parts of the pedal cycle. But on a road bike riders are already more bent forward at the waist. I think that there is an optimal torso femur angle that will be most efficient which of course will differ from rider to rider. What that angle is I don’t know. One thing I read years ago was that bolt upright is not good at all. Like the old guy on a three speed Raleigh pumping back and forth. What that rider is doing is trying to engage his gluteus muscles. You need to have some angle between the upper body and upper leg to get those muscles working well.
Certainly too slack a seat tube angle with a squatting full suspension bike for long legged riders will loop out more easily. I’m not convinced that simply steepening the seat tube angle is the best solution to that but a combination of steeper seat angle and longer rear centre for taller riders makes sense.
As reach on bikes has increased I sense that designers have steepened seat tube angles more to maintain cockpit length. At the same time that allows more room for suspension movement so that they can make all frame sizes with the same dinky chain stays. It’s far cheaper I’m sure to make all rear triangles one size. What would the ride characteristics of this GeoMetron be if the bottom bracket were mover forward a couple cm but all other dimensions remained the same? Would that provide better fore aft balance though weighted pedals when descending? Worse?
My own little experiment with my size small Chameleon is that the longer chain stay position climbs better but I really can’t feel much difference descending. That bike with a the 150 36 has a static head angle of 65° and static seat tube angle of 71°.
I find it all very interesting but I don’t have a great feel for how all these things work.
Oct. 8, 2019, 12:44 p.m. - Andy Eunson
Agreed. But what is optimal? As a short man I don’t need my seat super far forward to prevent looping out on steep climbs. I have read many times that a steeper seat tube angle is more efficient but I’ve never read why it is so or seen any real data about that. I have read some studies of road bike position that indicated that a steeper seat tube angle was more efficient because it allowed the riders to engage their leg muscles better and for greater parts of the pedal cycle. But on a road bike riders are already more bent forward at the waist. I think that there is an optimal torso femur angle that will be most efficient which of course will differ from rider to rider. What that angle is I don’t know. One thing I read years ago was that bolt upright is not good at all. Like the old guy on a three speed Raleigh pumping back and forth. What that rider is doing is trying to engage his gluteus muscles. You need to have some angle between the upper body and upper leg to get those muscles working well. Certainly too slack a seat tube angle with a squatting full suspension bike for long legged riders will loop out more easily. I’m not convinced that simply steepening the seat tube angle is the best solution to that but a combination of steeper seat angle and longer rear centre for taller riders makes sense. As reach on bikes has increased I sense that designers have steepened seat tube angles more to maintain cockpit length. At the same time that allows more room for suspension movement so that they can make all frame sizes with the same dinky chain stays. It’s far cheaper I’m sure to make all rear triangles one size. What would the ride characteristics of this GeoMetron be if the bottom bracket were mover forward a couple cm but all other dimensions remained the same? Would that provide better fore aft balance though weighted pedals when descending? Worse? My own little experiment with my size small Chameleon is that the longer chain stay position climbs better but I really can’t feel much difference descending. That bike with a the 150 36 has a static head angle of 65° and static seat tube angle of 71°. I find it all very interesting but I don’t have a great feel for how all these things work.