Flyin_Ryan

Hi sorry if this has been answered already I couldn't find any threads.

Anyways I have a '93 Z28 that I would like to put 18x9 or 18x10 torq thrust 2 wheels on.
They have to be custom made so I want to ensure I will have the proper dimensions to provide them for backspacing/offset etc...

Thanks.

Injuneer

For the 9" wide wheels, specifying a 41mm offset will produce approximately the same results with regard to the outside edge of the wheel/tire as shown in these photos:





Backspace and offset are mathematically related, so you only need to specify one of them. Note that the calculation requires an assumption of the thickness of the flange on the wheel that holds the tire bead on the rim (stated wheel width is measured inside of the flanges, where the tire beads sit), so without knowing that exact dimension, I can only give you an approximate number. Using my assumption of the flange width, if the dimension is similar to the wheels above, the resulting backspace will be 6.57" and the "frontspace" will be 3.33". You may want to review that with AR to let them tell you what offset will achieve the desired frontspace.

If you go to a 10" wide wheel, there will be no problem in the rear, but you may have an issue in the front with the inside edge of the tire being too close to the steering knuckle or the outside edge of the tire being slightly outside the edge of the fender. Using a 54mm offset, the frontspace would remain at 3.33", but the backspace will increase to 7.57" which may be too much for the front.

My current front wheels are 17x9.5 56mm offset, which yields a 7.42" backspace, and the tire is very close to the steering knuckle. However, with an 18" wheel you may gain some additional room, as the knuckle is tilting inwards as you go upwards. Again, in the back, no problem. Rear will easily accommodate up to 7.75" backspace. To keep the tire from appearing too deep in the wheel well, you might want to run a 45mm offset in the rear with 10" wheels. But now you have an issue with ability to rotate the wheels/tires. It's only a 1/3 of an inch so you could even consider 45mm all around, and have the outer edge tire locations as shown in the photo moved out by 1/3th inch.

Probably be good if someone who actually owns the TTII's responds, but there doesn't seem to be much traffic on Wheels and Tires.

Flyin_Ryan

Yeah it would be helpful for someone with these wheels to reply. Seems like a tough answer to find... American Racing doesn't offer much help and I can't find any correct number, lots of variance. Never knew it was going to be this tough, thought I would order out of a catalog and be done.

Injuneer

Looking at the AR catalog, they use 0.50" for the flange width. Recalculating (my spreadsheet is based on 0.45") you get:

9.0" wide: 43mm offset puts the outside of the wheel/tire exactly where they are in my photos (3.33").

10.0" wide: You will need additional input.
OFFSET - BS - FS
55mm - 7.67" - 3.33"
50mm - 7.47" - 3.53"
45mm - 7.27" - 3.73"
40mm - 7.07" - 3.93" (FS limit to keep rears under fender, but outside front fender)