ColonelJLloyd
05-21-2020, 10:06 PM
I've been thinking about a hypothetical custom frame and have a question regarding frame geometry. Specifically, I want to know if and how a frame's geometry (ST and HT angles, bb height) can remain fixed with either of two forks that have differing axle-to-crown measurements.
The hypothetical bike has a 44mm head tube. I want to use fork A, but I also want the option to use forks B or C at some point in the future because they have cage/light/fender mounts that fork A does not.
Fork A: 383mm A-C. 47mm offset. 1 1/8" straight steerer. Integrated 45° crown race.
Fork B: 393mm A-C. 50mm offset. 1 1/8" straight steerer. Integrated 45° crown race.
Fork C: 395mm A-C. 55mm offset. 1 1/2"-1 1/8" tapered steerer.
Could I keep the frame's geometry effectively* fixed if I used an external cup lower headset with fork A, but used an integrated/zero stack lower headset with fork B?
But in order to use fork C, I would have to use an external lower cup, which would raise the front end ~10mm compared to using an external lower cup with fork A?
* I realize a mm or two difference in fork offset, A-C, or lower headset cup stack height are probably inevitable, but I want to minimize the difference.
The hypothetical bike has a 44mm head tube. I want to use fork A, but I also want the option to use forks B or C at some point in the future because they have cage/light/fender mounts that fork A does not.
Fork A: 383mm A-C. 47mm offset. 1 1/8" straight steerer. Integrated 45° crown race.
Fork B: 393mm A-C. 50mm offset. 1 1/8" straight steerer. Integrated 45° crown race.
Fork C: 395mm A-C. 55mm offset. 1 1/2"-1 1/8" tapered steerer.
Could I keep the frame's geometry effectively* fixed if I used an external cup lower headset with fork A, but used an integrated/zero stack lower headset with fork B?
But in order to use fork C, I would have to use an external lower cup, which would raise the front end ~10mm compared to using an external lower cup with fork A?
* I realize a mm or two difference in fork offset, A-C, or lower headset cup stack height are probably inevitable, but I want to minimize the difference.