I'm new to using these and the series I run basically only allow a 1/2 inch rubber. To clarify this is a modified are running but I thought I'd get better answers here. We went to a 400lb rf spring and driver said he couldn't get off the corner. We were running a 3-12 shock and I don't know if we need more rebound to stay into the bump or less with a softer spring. Does anyone have any starting recommendations with these?