If, for example you were to take a Yeti 575 with a 150mm RS revelation and the resulting static head angle would be 68deg & the BB height be 13.3" (according to the Yeti website)
If you were to fit a Works Components head angle reducer head set thingy and slacken the HA by 1deg (the maximum according to WC), all things being equal [i]i.e.[/i] the fork remains static / unsagged as does the rear shock how much lower would the BB be?
It's basically a maths question, but to work it out I'd need the A"C of the fork & the stack height of the lower head set cup, so I thought I'd ask on here 😉
The Cat Sat On An Orange And Howled Horribly
Very little. Have a play round on BikeCAD is probably the easiest way to work it out.
Sind(68) = 0.927
Sind(67) = 0.921
(0.927-0.921)*510mm = 3mm
So thats your headtube 3mm lower with a 510mm fork, so about 1mm at the BB.
If you want a lower BB try offset bushings rather than offset headsets, just be carefull they dont cause clearance issues.
TINAS - there's also the effect of a (possibly) different lower headset cup stack height - in any case it's still going to be minimal.