springRatio increases the mass the wheel can support. damperRatio counters bounciness from spring decompressing. The tweakble sliders, range 0.05~2, most likely are multipliers to the values in the config file. Unfortunately there's dynamic adjustments going on in the suspension module and it's very hard to get any predictable behaviour out of them. I have no idea why the lower tier stock wheels are configured as they are.
You don't want to set suspension all the way down, there are extra colliders in the wheels to prevent them from clipping into the terrain when the wheel is on its side. When you reduce suspension all the way down, you increase the chance the extra collider rubbing against the ground and popping the wheel up.
you might want to give GoSlash's stock landing gear fix a try.
nli2work's post in Does anyone know just quite what spring strength and damper actually do? was marked as the answer