For anyone interested, here is what Sachs, Italy says about the stock shock's spring:
SPRING Rate:
K1= 8 kg/mm from 0+/-54 mm F1= 432 Kg
K2= 10,5 kg/mm from 54+/-90 mm F2= 810 Kg
And their recommendation for a rider of 170 pounds is to increase 2 mm preload over stock and adjust 2 clicks rebound.
If anyone has thoughts on whether the above is or is not a suitable spring rate for a 170# rider on an M620, please weigh in.
I;ve been told the 748 Showa's spring is pretty soft in comparison (and my butt shock dyno agrees although I don't have preload set properly yet). I think I'm going to swap the sachs spring to the showa shock body and see where we go from there. I'm also going to add in one of those Traxxion preload roller bearings to allow easier adjustment of preload. Its such a pita to get at, anything you can do to make it easier to adjust seems like a good idea...
The 748 shock certainly feels a bunch better than the stock sachs did -- I can actually feel both sides of bumps now instead of being launched over them. If the spring swap works well, this is a pretty cost effective modification for newer monsters....
mike