That is because the mazdaspeed rear had .500" shafts. Eibach has since remedied this with a .625" shaft, with a one piece seal head instead of the old two and three piece ones.

 

I was not going to point that out.

 

Yeah... this is just a problem in the NASA "Performance Touring" class which uses the same rules as time trial. The shock asorber rules have been problematic. They USED to do it based upon the retail price of the shock asorber. The director then found that certain shock asorber manufactures were lowering their prices to be just under the limit the rules allow (hey... not a bad deal from my consumer standpoint!). So he came up with the current rules that seem to mainly just distinguish based on wether the shock is remote reservoir or not. Certainly a flawed system. We'll see if it changes...