Quote: "no actuall scietist knows why they are so much bigger than their parents"
They do. The growth control gene is not inherited from either parent, resulting in an animal that grows to it's naturally sustainable size. And most hybrid animals have sterile males, which is believed to be nature's way of saying "no more!"
A second generation Liger would be unlikely to be any bigger than it's parents.
It's also illegal to breed a Liger / Tigon. They are usually a result of accidental mixing in Safari Parks. In the wild they would never mix, although there are a couple of reported cases.
Oh yes...I'm a huge Panthera Tigris fan
I didn't just decide to research this because I saw a thread.