How do you measure the dimensions?

My axels are about 3 1/2" from the bottom of the fuse to the axels center. With no weight on it. It sags when sitting ready to fly. ITs kind of a low rider, I dont mind.
The bottom of the fuse is 3 1/4" wide. And the tires center to center about 15" apart.

I need something about 4" from bottom of fuse to center of axle.....(give or take a little) and kinda wide. (wing span is 60 something)

I have not abused the gear, but it seems like its getting lower and lower to the ground. LOL!