Caltrac springs - ride height recommendation

[Cruzin]

 

I'm preparing to order a set of mono leaf springs from Calvert Racing.  This is on a '73 Challenger.  The decision is between a "0" or a -1 spring.  Those who have been faced with the same decision please chime in. 

I'm using a 28" tall tire and don't mind a slight rake.  Just wondering if the "0" or the -1 is the way to go???

Photos are helpful.

 

[challengerx]

73 challenger with 0 calvert springs and shocks

[Cruzin]

Thanks, ChallengerX.  What size tires are those?

[challengerx]

275-60-15