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I got number blind looking at that, but what gravel frame are you getting with a 73mm shell? Most outboard BBs end up at the same width whatever, with spacers compensating for the lack of width on as 68mm shell for MTBish cranks or just 68mm and no spacers allowed for road/grav cranks. I've not played often or in depth with the cranks you mentioned but a quick Google of the Middleburn suggest road only so no 73mm shell frames.
snottyotter
launchpadboi
i'm about to build a new gravel/bikepacking frame, which i'd still need a crankset for. i've narrowed the shortlist down to middleburn ro2 and white industries a30. not entirely sure if the middleburns fit with a 73mm bb, but assuming they do with certain spacers.
i'd like to keep the q factor as narrow as possible and made some highly theoretical calculations on the crank arm clearance using my road bike's current setup as a reference. ta'da:
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reference road bike with 2010 sram force 110bcd cranks (68mm bb)
q factor: 145.2mm
outer stay width @ 19cm (from middle of axle to the outer edge of crank arm on 170mm cranks): 103mm
gap between crank arm edge and chainstay outer edge: 12mm
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middleburn ro2 (q factor stated online as 153mm, i've added 2.5mm to compensate for the 73mm bb)
q factor 155.5mm (5.15mm wider per side vs. the reference sram force)
new frame outer stay width @ 19cm: 120mm
gap calculated against the reference: 12mm - 8.5mm + 5.15mm = 8.65mm
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white industries a30 (stated q factor 163.5mm with a 73mm bb)
q factor 163.5mm (9.15mm wider per side vs. the reference sram force)
new frame outer stay width @ 19cm: 120mm
gap calculated against the reference: 12mm - 8.5mm + 9.15mm = 12.65mm
if the calculation is in any way valid, the conclusion would be both models clear the stays easily while the middleburns give a slightly narrower q factor. i've got a chris king bb, which i'd use either the hollowtech kit (middleburn) or the 30mm axle kit (wi) with. not sure if and how this variable changes the calculation.
perhaps someone more knowledgeable can confirm what did i miss and advise how this kind of situation is best approached :D thanks!