Alrighty, Tech threads.
Spring Rates; listed in either Imperial (500LB/in) or Metric (10kg/mm) is the amount of weight needed to compress the spring by the desired value. A 500lb spring needs 500lbs to compress the spring 1 inch.
The higher the value, the more weight it takes to move the spring. Now, the shock also matters, because when the spring gets compressed, there is energy that is built up inside of the spring that needs to get released.
Without a strong enough shock, the spring will 'over-power' the shock's ability to dampen and you get that whole 'floating' issue. (think 1980s oldsmobile driving down the highway with the front suspension bouncing around).