How the spring fits on the spring cup is very critical, ie the spring diameter to the spring cup seat diameter. If the fit is loose the spring will slide around when being compressed and will change the setting of the pod. Other than that any spring cup will work. If my spring is loose on the cup I squeeze the last coil to fit better. After doing this I found my pod settings repeated extreemely well. :thumbsup:
I have also found how loose the spring cup is when seated against the ball cup has a similar negetive effect. Again any ball cup will work but take into consideration these small differences when building your car.
The racing has gotten SO competitive that the tiny things matter more and more.