PLEASE HELP! 15x8 wheels

[Black Yaris]

Originally Posted by Nimble

That's incorrect, a 225 sitting on a 15x8 ET38 will not sit in the same place as a 225 sitting on a a 15x7 ET38, what tire shop did you work at again? A 1" wider wheel will put roughly 13mm's more on either side of the tire, both on the shock side and the fender side.

smoke another one because the tire will be sitting in the same spot, and that is what I said... THE TIRE WILL BE SITTING IN THE SAME SPOT

since the tire is 225 mm wide (8.9in) wich is wider than either wheel the tire is going to sit in the same position regaurdless... you need to figure out TIRE clearance, not wheel clearance in this case and that is what I did with the +38 offset

[largeorangefont]

Originally Posted by Black Yaris

smoke another one because the tire will be sitting in the same spot, and that is what I said... THE TIRE WILL BE SITTING IN THE SAME SPOT

No, not quite. The mounting pad of the wheel will be in the same place relative to the wheel centerline on a 8 inch. vs a 7 inch rim with the same offset. But the mounting pad would be in a different location relative to the inner and outer wheel lips, and this change the position of the wheel in the wheelwell. The only time this relationship would not change is if the wheel was 0 offset, meaning the mounting pad was in the dead center of the wheel. Then you would increase equal distances on the outside and inside, and relative position would stay the same.

The +38 is a fixed number. That means 38 MM from the center of the width wheel to the mounting pad. That distance has to stay the same, regardless of rim width, but the width still grows. Because the offset is favored to one side of the wheel (not 0 offset), one side protrudes furthur than the other as width grows.

That is why the wider wheel you go the less offset you have, because you have to account and compensate for uneven growth on both sides of the wheel centerline.