Keep in mind the spring rates for coilovers are not the same
As example for base and Z51 C8 Corvettes
The base Corvette has 180-lb coil-over springs in the front and 217-lb springs in the rear,
whereas the Z51 gets 226-lb coil-over springs in the front and 263-lb springs in the rear."
This is not a quick decision of which ones to install as the wrong rates may change deeply how the car ride is and
may not be correct for the type of driving people do and may work well for street but not for track or other way around
Use the above stock spring rates as baseline to decide what you want for the new ones.
The stock coilovers that allow adjustment allow a maximum from low to highest just about 1 1/2 inches.
The shock can as you see does not have a lot of thread depth for spanner to move up or down
There is two types of spring designs, some info might help choosing your replacement coilover springs
Progressive Springs are used on non-adjustable units.
Example being, a standard OEM assembly or a mere simple lowering spring.
This means there is no exact spring rate number.
The spring is designed to fluctuate as the driving force and pressure are applied.
This would be more for a generic setup where performance is not the key upgrade intent.
Linear Spring rates are set numbers.
This means the weight needed to compress that spring under load does not change.
This setup delivers much higher performance but comes with a stiffer ride.
Linear type springs are found on the most common coilover setups.
Spring rates can get pretty technical when calculating.
The stiffer the spring, the less travel the suspension will have.
Weight and driving type must also be taken into consideration.
Street, Drifting, Drag racing, Circuit, Rally, Autocross etc, all have different requirements.
Most commonly seen is a spring rate given in KG/mm or LBS/in. This means the weighted force / the space traveled.
For example, 700LB/in would mean 700 pounds will compress that spring only 1”.
This can also be read as 12.5K/mm (12.5kg to compress spring 25mm).
Below is a simple chart of just a few spring rate conversions.
Spring Rate Conversion
Approx 1KG/mm = 56LBS/inch
700 lb/in = 12.5 kg/mm
650 lb/in = 11.6 kg/mm
600 lb/in = 10.7 kg/mm
550 lb/in = 9.8 kg/mm
500 lb/in = 8.9 kg/mm
450 lb/in = 8 kg/mm
400 lb/in = 7.1 kg/mm
350 lb/in = 6.2 kg/mm
300 lb/in = 5.3 kg/mm
250 lb/in = 4.5 kg/mm
Other facts is you want a spring to have a height that installed leaves spring at correct rate but still has enough to allow adjusting height up/down