I am looking at buying 18" rims (not sure which ones yet). Does the offset depend on what rims you get or the tires? New to the whole rims/tire upgrade.

 

It is a specification for the wheel - tires have nothing to do with offset

 

No. Offset is the distance from the wheel mounting surface to the physical center of the wheel. It has no relation to wheel diameter. I have several offset threads with diagrams and examples. Search is your friend.

 

This may help:

http://www.rims-n-tires.com/rt_specs.jsp

 

Thanks for the link. When I have been looking for rims, they have offsets already...should i just follow those? Some rims say they come with no offset (gram lights 57 magnum18") but then others have a 35mm offset (o.z. crono HT 18"). just go with what they come with?

 

Ok the calculator say that the wheel combination I want to run stick out toward rim 28 mm further than the stock wheels I am running now. I did search for stock offset and I think it is 33 rear and 30 front, but I maybe mistaken. Will the +20 offset from the 18x9.5 Ruff rims rub the fender of my 06 ZR. Its not lowered but plan to lower it on Nismos soon. Any help appreciated. I hope since this is on the same topic it is not a high jacked thread, but didn't think the same question needed two threads.

 

Some retailers offer wheels specifically for the 350Z. They know the car and proper offset, but no recommendation is 100 percent guaranteed. Always compare the OEM wheels to the new wheels to be sure.

 

An addition 28mm should be OK. The 350Z has plenty of room between the tire and fender. Note of caution: make sure that the car tracks wider in the rear than in the front.