AssassinsMace
Lieutenant General
It wasn't that big. It was fighter size.
I find something interesting; the landing gear's doors of the J-20 are similar to those the the J-8II but the later are much smaller.
Landing gears for land-based airplanes, especially those smaller airframes of fighter jets, don't need to be fancy. They are too light and runway lengths are more than sufficient to need a big and complexed landing gear like those on the new J-15.