Just in process of upgrading suspension on my new to me Z 2012. My local supension specialist has stripped and rebuilt the rear shock and improved the shim stack for better damping, added a heavier duty spring and replenished oil and gas. Also forks now have Hagon Progressive springs, in the smallish progressive end of thre new sping is in itself stiffer than the standard spring and off course the rest is stiffer. Heavier Fork oil has been added. We did look to source a linear spring but were very happy with the springs from Hagon and the spec sheet supplied. Even with these springs fitted my mate tells me it has left some adjustment capability. Interestingly, even with the low miles on my bike the Fork oil looked well passed its best and the internals and seals needed cleaning/replacing.