Serotta's "Calculated Setback"

[Needs Help]

Hi,

Can anyone tell me how Serotta's "Calculated Setback" on their Master Design Template is measured?

Thanks.

[Kevin]

I don't know. But why don't you ask the fitter that is measuring you for the new ride? Which Serotta are you getting?

Kevin

[Dave]

Normally, frame setback is measured horizontally, along the center of the top tube. It's the distance from a vertical line through the BB center to the intersection point of the seat tube and top tube centerlines.

To calculate the setabck, knowing the seat tube angle and the c-c frame size, it's simply the cosine of the STA times the c-c frame size.

In the drawing I've linked, it is the Sc dimension. For example, the 540 x 540 frame has a c-c frame size of 520mm and a STA of 74 degrees. cos74 x 520 = 143mm. Also, 143/520 = cos74.

http://www.trialtir-usa.com/2005-colnago/colnagoinfo/colsizecharts.htm

[Needs Help]

Thanks for the response Dave.

I was wondering how Serotta's Calculated Setback works with sloping top tubes. Is it the Sc measurement in the diagram you linked? In other words, do they calculate it by measuring the setback with a virtual horizontal top tube? Or, is it the Scs measurement?