Originally Posted by
deepakvrao
I think what he means is that the newer disc brake bikes, have a taller fork, to allow for larger tyres, and that affects stack. Much as you have also explained.
I have a road bike and a gravel bike, both with 16.2mm headtubes, but the stack is about 2.5cm more on the gravel bike.
Ok, but I don't think this matters because that same newer bike will also have a 'taller' rear end as well for the same wider tires. Yes, stack can be affected though if you put a 40mm tire in the front, and eg. a 28mm tire in the rear.
And as you realized stack is measured from the BB, not the ground.