Natural Frequency Balance and Spring Rates

[Mach3M3]

Originally Posted by 135

The 9" spring will become loose at full droop so an 8" spring will become loose even earlier though the range of droop.
As @rac said, it depends on the ride height but I would expect an 8" spring to still be loose during droop, irrespective of the ride height.

My 8" spring definitely becomes loose at full droop, but a 9" might not. I am also not aware of what negative consequences this would have on the car's behavior. I run a clutch type LSD so i dont have any power down issues associated with that. I also think the rear sway bar is doing some work in keeping the tire in contact with the ground.

[bbnks2]

Your magic number is going to depend on application.

I personally believe a lower front roll couple is better for autocross. The courses are tight and front end grip is really important for being able to navigate around tight turns without understeering everywhere. Making the rear a bit more loose allows you to drive the course using rwd to your advantage with throttle application (or dumping the throttle to shift weight forward and plant the front wheels) for rotation. I have seen many others say the complete opposite of this... but maybe because they are driving miatas or whatever and focus more on transient response. I've been able to get pretty quick locally running 450/896lb springs. I am now running the Ohlins dedicated track setup at 672/1008 and tbh it feels too front biased in autocross. Understeer is back after not having to deal with it for a long time.

Road-course is where you might want more front roll couple. The inertia going into the corner at higher speeds biases things forward more under decel and turn-in. I have not been on track yet with the dedicated track setup but I would bet the car feels more comfortable to push hard at high speeds than when I ran 3-450 lb spring setups up front and the rear end would get loose as the front end dived.

Just my 2c anyway. I think context and application matters Magic number being application specific... but yeah you should be aiming to fall within that "standard" window of 55-70% or so. if your spring rates and bars land you at 70%+ front roll couple then you know you'll have excessive understeer especially so at low speeds. Knowing how this all works really allows you to cut down on the guess and check.

Whether or not an 8" or 9" spring is loose at full droop is going to be completely dependent upon how long the rear strut is when full extended. People's answers are going to vary here too. Wedge a longer spring than needed into the rear and your ride height is going to increase. If the spring is loose, make the damper body shorter (if you can) but know that this also affects the wheels position in the wheel well and your primary concern should be ensuring that the wheel does not contact the fender lender at full bump.

[rac]

Originally Posted by 135

The 9" spring will become loose at full droop so an 8" spring will become loose even earlier though the range of droop.
As @rac said, it depends on the ride height but I would expect an 8" spring to still be loose during droop, irrespective of the ride height.

my ride height adjusters (tckline) are basically at maximum extension and the 8" becomes slightly loose full droop. i could go lower in ride height but i like some rake forward, somewhere far down the to do list is machine a spacer ring to take up the extra few mm I need.

[Dieselboy]

Originally Posted by rac

my ride height adjusters (tckline) are basically at maximum extension and the 8" becomes slightly loose full droop. i could go lower in ride height but i like some rake forward, somewhere far down the to do list is machine a spacer ring to take up the extra few mm I need.

What about using helper springs in this case to keep some compression on the spring at full droop?

[Driven5]

I forgot that Ohlins dampers aren't length adjustable. In that case, yes you probably want to either run a helper spring or devise some type of droop limiter.

[rac]

Originally Posted by Dieselboy

What about using helper springs in this case to keep some compression on the spring at full droop?

Could do.