[Uncle Jam's Army]

I am trying to determine whether I will need a setback/offset seatpost for a custom frame I am getting. The framebuilder recently sent me the proposed geometry and he has indicated a 72.5 degree seat tube angle. I have never had a frame with such a shallow seat tube angle. My two frames I have are 73 degree, and I use a 25 mm setback/offset seatpost, with the seat sitting squarely centered on the post (neither jammed up forward nor back). My setback (tip of the saddle to center of bottom bracket) is 91 mm.

As I have the opportunity to purchase a hard to find seatpost, I am trying to determine if I will need a setback seatpost with such a shallow seat tube angle. Does 1/2 degree make that much difference on setback?

Many thanks in advance for any insight you can offer.

 

[wooglin]

You're shelling out for a custom frame, which means you're also shelling out for the framebuilder's expertise. So why don't you ask him this question?

 

[Uncle Jam's Army]

You're shelling out for a custom frame, which means you're also shelling out for the framebuilder's expertise. So why don't you ask him this question?

I already did over a week ago, but he has not yet responded and I need to make a decision in the next two to three days. By the way, the seatpost in question is the 3T Dorico Team in White, which is a very limited run and very hard to find.

 

[Uncle Jam's Army]

Nevermind..... the framebuilder just answered my question. A 25mm setback post it is.

 

[terry b]

Nevermind..... the framebuilder just answered my question. A 25mm setback post it is.

That's an interesting response because with -.5 degrees you're going to have to push the saddle forward by about 5mm to get the same fit.

Setback post will of course work just fine, but the saddle will not be exactly centered, as it is now. NTTIAWWT.

 

[m_s]

Other elements of the fit could compensate for the lengthened reach though of course it won't feel exactly the same otherwise. Perhaps the builder simply feels the OP should have a more laid back seat position than what they are currently riding?

 

[terry b]

Other elements of the fit could compensate for the lengthened reach though of course it won't feel exactly the same otherwise. Perhaps the builder simply feels the OP should have a more laid back seat position than what they are currently riding?

You're right, if part of this project is to change the basic contact points then sure - a setback post on a slacker STA would accomplish that. Could also be that no one really cares about exact centering of the seat on the post clamp.

In either case, the post will work just fine.