****, I see there's a different formular for cylinders. Well, since it's done we'll see what it sounds like. So how did you manage to get your cu. ft. you stated? You used 5/8" right? What is your ring thickness? and how many rings? What is your inner diameter and height?
So I'm looking at your pics...are you using the factory spare tire 'cause it looke like you have your aftermarket wheel back there? Is that how you're getting more cubic space? If you're using 5/8" and you have 6 layers, then your internal height is 2.5" correct? Which means your internal diameter needs to be at least 17.5"? Is this how wide your box is?
I'm also comparing the pics of our two boxes, and our top boards look pretty much the same size. My top piece was like 17" and there's no way to get that to sit at the bottom of the wheel. So you've got a different wheel back there right?
Worst case scenario, if this 10" sounds awful, I can pull the top board off and put a new one on and swap the 10" for an 8" since the 8" meets this 0.25 spec.