Originally Posted by
guy153
Was going to post this to the other thread but the discussion seems to have got a little warm and it's been closed by a moderator.
Anyway was thinking about this style of fit and discussing it a bit on uk.rec.cycling.moderated. The general philosophy seems to be a straighter back, less weight on the hands, and a high seat (with probably a toes-down pedalling position) because this avoids stressing the knees. Pressing hard with bent legs is bad for knees.
The downsides of this position are aero, the high centre of gravity, and a lot of weight on the seat. The high CoG limits braking on dry roads especially downhill. More weight on the seat is not a problem in itself-- after all it might be better than putting all that weight on your hands-- but it does mean you want a wider, squishier seat, perhaps sprung, and this can get in the way of pedalling.
The solution to all of these problems is a slacker seat-tube angle. It gets the centre of gravity lower and further back, so braking is safer. It means you can have a wider seat without it disrupting pedalling since your legs aren't fighting with the sides of the seat. It means you can put your foot down easily when you stop in spite of the long seat-tube. It's even slightly more aero.
It turns out that there are not "upright" bikes and "recumbent" bikes but that it is actually a continuum, a bit like LGBTIQ. See
RANS Bikes for some interesting frame (and seat) designs. Old Raleighs from the 40s and 50s also had a much slacker seat-tube angle, perhaps 68 degrees or so, and sprung seats, and a swept-back handlebar. I see no reason why a bike like this should not be very comfortable over long distances although a bit slower for aero reasons. I wonder to what extent this could be mitigated by the addition of a small fairing.
One disadvantage of the full recumbent design is that you can't stand up on the pedals a bit when you hit a bump or a pothole, especially important for off-road or gravel. The sweet spot may be around 68 degrees or so. Playing around with frame designs I realized that if you go slack on the seat tube you start to need very long chainstays. So why not make the back wheel smaller? Then it occurred to me that this is a hack you could do without even making a new frame. I didn't see this at first because for me the fun is always making a new frame. Throwing a 26" wheel on the back of frame intended for 700c, which an equivalent low-profile, i.e. road, tyre, should slacken the seat tube and head tube by about 4 degrees. This should keep the steering geometry manageable without needing a custom fork, especially if you start with something with quite a steep head-tube angle. Then you'd add the big wide seat. The handlebar is automatically higher at this point but you might want to find one that is more swept back. Maybe this is something Moisture could try out.
You brought up some really good points here.
I've noticed my preference towards slacker seat tubes. I find that it sets me weight rearwards for better stability. I read somewhere that adjusting the angle of your saddle should chsnge the "effective" seat tube angle of your bike. I noticed that my saddle is set to be at roughly the same angle as the seat tube itself, although this is probably also due to the design of the saddle.
pedalling with even slightly less than optimal leg extension definetely can be very hard for your knees. As for the way im set up currently with the strap ins, this will definetely change around your "effective" frame reach figure versus having the heel of your foot all the way forward on the pedal. This is also going to noticeably change your balance on the bike.
If i am dealing with a lot of wind for example, pedalling relatively hard up a mild hill in a low gear, I found this situation to be very hard on my knees in fact, some of the most stress I've ever felt on my knees in such a short period of time. I definetely feel like my quadriceps are being taxed harder as well, but thats largely due to muscle imbalance and poor posture such as pelvic tilt.
while I dont think the seat is high enough above baseline currently to dramatically affect handling, I just don't think its worth sacrificing the extra effieincy of my strap ins to be able to lower the seat - and the stem - to baseline. Nonetheless, I acknowledge that in the future this will have to improvise. I think the main reason why this position causes more weight in the saddle is because jt might be harder to centre your weight through the cranks with just your toes. If you have strong toe flexors and calves to support this style, you can sort of flick down with one foot while lifting up and into the strap on the other side. I can pedal faster, more efficiently and use a wider range of low gears. I can take advantage even further with my reverse oriented biopace rings, which I find have a super smooth and natural feeling.
However, for me at least,.the poorer centre of gravity with the higher seat would cause slightly more weight in my handlebars if anything, at least if I didn't have such a high rise stem to compensate for all of this.
As I am now continuing to increase my core strength, I am decreasing my stem height in small increments as I get better and better at biasing my weight into the cranks rather than the handlebars and saddle. The way I see it, these should be looked upon more as contact points which provide the rider with more information regarding road surfaces, not to keep your weight in (the saddle)
When I Changed out my stem from a 60mm to 40mm, being able to slide my saddle almost all the way back on the rails, that extra 8mm or so to stretch out space over the rear chainstays greatly improved my ability to feel the terrain through the saddle and get more leverage over that rear axle. My typical riding conditions involve a lot of bumpy rough sidewalks,.badly damaged pavement, gravel, dirt, snow, even with slick tires, I can feel both ends of the bike working together to provide wonderfully balanced handling.
Despite my high saddle and super upright riding position, i still get wonderfully smooth ride quality without the need for a suspension seat or anything like that. Its actually remarkably how stable and fluid the bike is over such terrible pavement by simply biasing my weight into the cranks.
Another think to note, that with my inseam, I need around 185 or maybe 190mm crank arms .
You mentioned using a 26" rear rim. You mean while leaving the front a 700c, correct? Or making both wheels 26", if you still had the ability to stop properly? This would be good for centre of gravity, but would certainly bring my bottom bracket too low to the ground even with crank arms too short for my legs.
As you might know, im riding with a 26" front rim right now, and while i did like the slightly steeper angles, the bike is clearly not designed for the geomtery of a wider /smaller tire. The biggest problem was the difference in rim diameter between front versus rear. I've done this before on my gt - using a 700c rim front and leaving a 26" rear - its not good for the geomtery of the bike at all.
I have a touring saddle that is fairly thickly padded while still being on the stiff side. It has really good ergonomics though, good comfort without being super cushy and wide enough to allow you to steer with the insides of your legs on slippery surfaces without letting it get in the way of your pedalling. I still have my seat slightly lower than full leg extension with the toe to pedal concept, so that when I am sprinting, im motivated to keep my weight off the saddle and minimize bouncing.
Longer chainstays versus a slack seat tube seems like a very fine balance. My stays are 435mm. I think I'd prefer them slightly shorter because I do a lot of low speed riding grinding through wind.