Where to start...
There is no "proper" spring rate.
Contrary to popular belief, bodyweight has very little, if anything to do with spring rate selection. For example, a buddy of mine weighs 135lbs and at some tracks uses springs "designed" for someone who weighs 220lbs. If someone has absolutely NO idea what springs to use, then sure, get some for your bodyweight as a very basic starting point. But I can honestly say that
we haven't checked the sag on any of my race bikes in 8 years. What matters is how it acts on track. I like a certain feel and stability from the front end, I don't like to use all of the fork travel (some people do), etc. Those things matter.
Bodyweight is a factor in how the bike acts on the brakes, because the bike is trying to slow more weight, but bodyweight isn't necessarily the reason for selecting certain springs.
But even then, the necessary spring rate will change depending on the track. Bike setup changes for every track, including spring rate. That is why we have a suspension guy we work with all the time, they are constantly making changes.
dpapavas said:
I can't see why this process has to be magic. In theory one should be able to estimate, both a) what sort of stiffness and preload are currently installed, based on easily performed measurements of sag, as well as b), what sort of springs to install so as to be able to achieve either the desired free and race sag, or some other parameter, such as natural frequency.
You seem to have this idea that there is "a" proper setup, and you seem to think that achieving the proper sag is the goal. It isn't, like i said, we haven't checked the sag on any of my bikes in years, and i get around the track pretty good.
Getting the bike to handle properly and have good tire wear is the goal. I think that is where the confusion is coming in. Bike setup is a living thing that changes track to track, day to day, maybe even morning to afternoon depending on the weather.
Here is an example. The season opener was the first time I ever rode the 1299S. They set it up with a good baseline based upon how they did my other bikes. We struggled with setup all weekend. At first the tire wear was great...as in TOO great for the abrasive track we were at. It was because I was sitting at the top of the stroke and just spinning. So he changed the rear shock spring to a softer one (ended up changing it again later, so we ended the weekend at 2 rates lower than what we started). Then it had better drive grip, but it was trying to wheelie too much coming off apex (it makes 202hp and 105ft/lbs of torque on race fuel). So we had to play with the wheelie control. That helped the wheelies, but then it was trying to push me wide and wouldn't finish corners on the gas. Not to mention i was bottoming out the forks under hard braking. By the end of the weekend we ended being 2 spring rates lower on the rear, 2 spring rates higher in the front, added a total of 20cc's of oil to the forks, and had altered the geometry several mm on both ends. Not to mention all of the playing he did with rebound, compression, and preload.
The next weekend was at Road Atlanta. I was hitting the rev limiter in 6th gear on the back straightaway and running out of top end, so we had to drop 2 teeth on the rear sprocket. That wheelbase change sent us back to the drawing board and we spent all weekend chasing a "Road Atlanta setup". We made more spring rate changes, preload and geometry changes.
For another example, I run completely different geometry and springs at Jennings than I do Road Atlanta. Obviously my bodyweight hasn't changed, but the track has changed. Different tracks require different setups.
I run different spring rates on the R6, RSV4, 675R, and 1299S. Even at the same track, the spring rates will vary for each bike.
Something else that is interesting. A few years ago me and a buddy were riding the exact same bike, with the exact same motor build, on the exact same tires, with the exact same parts, with the exact same suspension components, and we were running damn near the exact same lap times........but we had DRASTICALLY different setups. That is something else you aren't considering...riding style and/or rider preferences. Setup isn't all mechanical and it isn't all about numbers and equations. Like I said, it is a living thing that changes all the time.
Every time I come off the track, especially since we are chasing setup on the Panigale, Livengood will ask how it felt, if there were times I couldn't get on the gas like I wanted to, how stable the front end is, he will look at tire wear, check the zip tie on the forks, etc. And he will make changes. You cant think of spring rates or setup as one entity that you just plug and go. It just doesn't work like that.
How much riding/racing experience do you have? To be honest, it seems to me like you are WAY over-thinking this. You are asking questions that either don't need to be asked, or are completely irrelevant.