I think it’s a pretty obvious difference but I’m rather the royal with the legume problem when it comes to geometry.
However, it’s easy to change the head angle, either through fork length or headset – you can go up to 2 deg either way with Works headset, 1.5 deg either way with a Cane Creek, whilst the rest of the geometry is more fixed.
My old hardtail was a Cotic Soul, briefly with 100m forks, then 140mm for years and years. I replaced it with a Bird Zero AM which in the stock configuration (150mm fork) is longer, lower and a bit slacker. I’ve ridden it with a -2 deg Works zero stack headset and 130mm fork and Cane Creek -0.5 deg external cup headset and 140mm fork (64.3 and 65 deg static respectively). The latter setup gave the same as stock geometry but 1/2 deg slacker whilst the former was lower BB and longer reach and steeper seat angle and even slacker, and that combination was too extreme for my local trails.
Have a look at the BB height/drop, the seat angle, and the reach too. I’d say they’re the other three most critical numbers. Personally I think the Bird Zero AM is pretty dialled so I’d consider that – and see how those other two compare.
