How is seatpost setback measured?

[FastforaSlowGuy]

I've got a mystery seatpost (and old Cannondale OEM thing, carbon, came stock on a CAAD8 I picked up for parts). It's got setback, not sure how much, but I need more. It's tough to shop for a seatpost with more setback when you don't know what you've got.

I'm thinking it should be the horizontal distance between a vertical line draw through the middle of the post, and a vertical line drawn through the middle of the clamp. Sound right?

[LouDeeter]

Yep, that's about it for a seat post. A little different for a frame.

[LouDeeter]

But, usually, any setback combined with the length of the rails will get you to a good saddle position if you aren't anal about the clamp being in the center of the rails. In which case, the seat tube angle comes into play. Some people don't worry about where the knee is in relation to the pedals, but are more concerned with the fore/aft adjustment to get the reach to the handlebars correct. Bill Boston, a renowned frame builder and fit expert, had always assumed people used setback seat posts--that's how most were made back in the day. When the no-setback ones came on the market, it caused his calculations to be off. He and I had a good discussion about it about 10 years ago.

[dgoodwin]

Need more setback? Take a look at this!!!

[LouDeeter]

I suspect with my fat butt that I would end up on the rear wheel at some point on a ride. I can't imagine that being a safe seat post.

[dgoodwin]

My thoughts exactly. The cantilevered section does not appear to be very well supported. I can't imagine who would need THAT MUCH setback anyway.

[LouDeeter]

Particularly with the saddle shoved all the way back on the all the way back set back adjustment. The angle of force if sitting on the back of the saddle is going to create a stress point that I wouldn't want to around.

[TRACK]

why setback? oO slong's to long?

[pbarry]

SR made those during the 90's for MTB's so you could shift your weight rearward on a descent. Never seen a broken example. :)