Is a coil spring load consistent up to coil binding?
I presume it would be after the initial load is applied from the unloaded situation.
I must admit that I struggle to rationalise the spring rates combining in this situation. That being the case though and with the rebound spring unloaded, as the stub moves down - inner wheel on a corner - then as the main spring decompressed and the rebound begins to compress, presumably the rate is at a minimum, and this is why some owners have found an initial roll when turning in?