suspension /spring rate - preload and sag

[Fencer]

I am setting my sag on my new (to me) GSX-R It has a Penske?? on it.

I just droped the spring out to see what is was rated for. 500lbs

I am now setting the sag to my fat arse (230) and am cranking a lot (IMO) of pre-load. Is there a rule of thumb of when to go up in spring rate?

 

[03silverbullet]

I am setting my sag on my new (to me) GSX-R It has a Penske?? on it.
I just droped the spring out to see what is was rated for. 500lbs

I am now setting the sag to my fat arse (230) and am cranking a lot (IMO) of pre-load. I am running about 3 inches down from the collar. Is there a rule of thumb of when to go up in spring rate?

The front should drop a total of 35mm and the back 25mm with you on it.

These measurements are from both ends being fully extended.

The spring seems awfully light especially for a guy your size. I think a 750 - 800 lbs spring would be in order.

 

[HaulinAshe]

I am now setting the sag to my fat arse (230) and am cranking a lot (IMO) of pre-load. I am running about 3 inches down from the collar. Is there a rule of thumb of when to go up in spring rate?

Yes, when rider sag (static sag with fully-geared rider) exceeds 25% of total suspension travel with preload adjusted at 5% static sag (bike weight only).

In other words...

If you adjust preload so that the rider sag does not exceed 25%, and then measure how far the bike settles under its own weight, AND that settling is significantly less than 5%, it means you have too soft a spring and had to crank too much preload to compensate.

Ideal average setting is 5% bike sag and 20-25% rider sag. Again, we are talking VERY general here. Different bike models vary.