I'm relatively new to the bike world and I'm surprised how much there is to learn about basic bike geometry. Today's challenge is my wife's seat post on her Electra ebike. Her combination of seat tube angle, seat post design, and desired saddle angle are the issue. Her saddle adjustment is of the "two bolt" variety, with one forward and one aft bolt as shown below (this is a google image, not her seat post). In order to adjust her saddle angle to her liking I had to put a shim between the cylindrical mating surfaces in the seat post - only then could I adjust her saddle nose low enough for her. The geometry at the head of the seat post seems to be the issue:
View attachment 198371
Specifically, the angle shown in red seems to be working against me here. When I "middle" the two bolts, i.e. set the saddle angle at the center of the adjustment range, the nose of the saddle points up at a ~10 degree angle. When I fully loosen the rear bolt, and fully tighten the front bolt, i.e. set it to the extreme nose-down end of the adjustment range, the saddle is about horizontal - but she wants the nose down ever-so-slightly more. To accomplish this, I inserted an aluminum shim, and that did the trick - it added just enough additional range, that she is happy. However, I am not so happy to have a shim here - I would rather have a seat post that does not require a shim.
When reading about seat posts, I see the specifications given for length, minimum insertion, and offset, but I never see specs for the angle shown in red above. I would think, ideally, the red angle here should be complimentary to the seat tube angle on the bike - i.e. if the bike has a 57 degree seat tube, this red angle should be 33 degrees (57 + 33 = 90, the definition of "complimentary"). Maybe bikes in general don't vary in seat tube angle that much, so this just usually isn't important?
I'm wondering if anybody else has faced this, and if there are "two bolt" seat posts that might offer a larger range of adjustment than hers, or if there are other seat post designs that might accommodate a larger range of adjustment? I did try a serrated one-bolt design, which did seem to have more adjustment range, but the stepped nature didn't allow me to dial it in exactly.
I also saw somewhere a seat post that offered an eccentric bolt for the saddle angle adjustment, similar to how options for
breast augmentation NYC provide precise customization, but I can't find it now—has anybody seen one of these before?
TIA!
