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TvH
@Emyr
Cotic's geo chart for 120mm forks says they assume 531mm static length and 25% sag, so I've used 501mm as the A-C in my model.
Using their 120mm large geo, the numbers work out pretty well (unlike OnOne's for example), suggesting their EC44 lower headset adds 10.6mm to the stack. BB height on 749mm tyres (29x25") is 314.5mm, 45.4mm fork offset, 117.07mm trail. (headangle provided is 66)
To get the same BB height on 736.4mm (27.5x3.0") tyres with a 45mm fork offset, the sagged A-C needs to be 520.1mm, the trail becomes 120.7mm, headangle 65.2. Stack increases 609.4 to 616.3mm, reach shortens 486mm to 477.2mm. Assuming the same fork design, that means a 140mm fork at 22% sag.
Isn't maths fun?