Originally Posted by
dddd
Don't be fooled by the frame's short top tube measurement.
These frames have really steep angles, up north of 76 degrees on my example (and which adds several cm to the frame's reach dimension!).
A longer stem will calm the quick steering though, so perhaps best to keep an open mind about stem length choice, on account of the radical geometry.
A similar situation occurs with PX10E and LE models from around 1973-1975, again where the ST angle is 76+ degrees!
Right you are. I hadn't paid any attention to the angles, but the bubble level app on my phone suggests the STA is right around 76° and HTA might be pushing 77°. I am completely ignorant of stack and reach. Is that a simple calculation for our vintage frames knowing angles and tube lengths? (I see an online calculator at
https://www.bikegeo.net/ but it would seem to require at least a frame with an installed headset...)
I wonder about the (lack of) saddle setback with such a steep angle. My plan was to start with a nominally a straight seatpin-style seatpost, Brooks-stye clamp and prolly an Ideale 80 saddle. The extra 3° or so of STA is going to push me (and my knees) quite a bit forward. If I did my math right, for a 60cm seat tube, a 76° STA moves the top of the seat tube forward about 3cm compared with a 73° STA. That, coupled with the short top tube is going to necessitate a longer stem to provide the same cockpit length, yes?