Looking to increase the front spring rate on my NB (500-550lb) , from what I gather the Tein Street Flex uses a 70mm ID coil spring. Has anyone successfully used a 2.5" or ~63.5mm spring? 70mm springs are less common and can cost twice as much.

 

Frsport has the Tein brand 70mm springs for a reasonable price.
12Kg/mm (670lb/in) SA120-01150 $56.99 each