Will the 21mm offset fit on the front in an 18X9.5? I know it will clear just fine on the inside, I'm worried about fender rubbage. I have some negative camber in the front and rear from lowering about 1.25" so that will help a bit.

These are made for a Mustang so I'd have to get hub rings from 70.5 to 66mm.

I am going to use these for autocross use only with Hoosiers AS303's and AS304's when they are available.

Unfortunately SSR only offers the competitions in 18X9 and 18X10.5 for the Z in a 31 offset front

 

Back when I was searching for new wheels I had a hell of a time trying to figure the proper offset. I like my wheels to just barely fit inside the fender... I hate the inset tucked look.

I determined that the wheel "front spacing" or the distance between wheel mounting surface and inside of the outer bead of the rim, needs to be about 3.1 to 3.9" in order to keep the wheel just inside the fender with enough clearance for hard cornering and bumps.

So....

Here's the formula to determine where your wheel will sit.

Take the width (in inches) and multiply by 25.4 to get mm.

Then divide by 2 to find the centerline of the wheel width.

Add the offset

then divide that sum by 25.4 to bring the number back into inches.

subtract this last number by the wheel width to determine "front spacing"

if the number is less than 3.9 I guarantee you will have no issues with rubbing... even with 1" drop.

here's an example

19x9.5 +21mm offset)

9.5 x 25.4=241.3

241.3/2 =120.65

add offset of 21

120.65+35=141.65

divide by 25.4 to get inches

141.65/25.4=5.57 (btw, this # is your approximate backspacing)

now subtract 5.57 from wheel width of 9.5

9.5 - 5.57 = 3.93

3.93" is the wheel front spacing. it slightly exceeds the sweet spot of 3.3 to 3.9 ..... but it'll be fine.

Remember.... you have to add about .5" to this to get the dimension from the wheel mounting surface to the outer most edge of the wheel lip because wheel widths are not measured outside to outside, but rather bead to bead.... but for our purposes we are concerned about the tire clearance... not wheel clearance. As far as I know no one is so low that they are tucking rims in the Z...

As some of you have seen, my new wheels are just inside the fenders by about .3" and my numbers fall right within the sweet spot range.

remember..... 3.1 to 3.9 is the sweet spot... you can go less but be carefull about going more... especially if you drop your car more than 1"