Im looking for a new DE/HPDE tire to replace my R888's with. Everyone says very good things about these Direzza Sport Z1 Star Spec's. I looked on both tire rack and Dunlops site and neither of them list a 275+ in 18's for the rear. Im running a 305 R888 on my rear right now.

 

Don't believe they do. I read great things about these in Grassroots mag but no sizes for a 997.

 

star specs are not to replace r888. I use them as rain tires and as street tires. on dry track they will not be best choice to sustain full level of heat.

if you use 8"/10" wide 18" rims then you simply get 235/275 tires they have. that is what I got on stock rims now. IMHO those tires are great for a street. if you want faster tires for dry to run in stock street AX class with SCCA - look at hankook r-s3. thy tolerate heat a bit better but they need to be warmer than star specs to get to optimal grip level - thet is why star specs are better for street as they get to full grip almost immediately. but r-s3 are worse in rain than star specs. another usual choice is potenza re11.

someone tried new michelin super sports after R888 and said it was almost there, so you have this option now as wel, but it will be good $600 on top of star specs price in kinda same size, not sure if it makes much sense.

good sizing for C2 is to get 9/12 18" rims and get 255/315 R888 on them.

star specs are good tires, very good indeed but they are STREET tires. R888 are r-comps.