Lower Control Arm Rubbin'

[Renegade]

Then please, enlighten this former ASE master tech and suspension/alignment shop manager. Feel free to get as technical as you'd like.

Out of respect for Binfordtools, and forum decency, I will keep this technical, and not personal. I do feel that erroneous information in forums has to be clarified or corrected though, so people who reference them in the future get accurate information.

1. You stated, "If a 4.5" offset clears, a 4.5" offset clears on every wheel in every size and any similarly sized tire."

Offset is measured in millimeters, and not inches. It's industry standard. While you COULD measure an offset in inches, it would not match up to manufacturer published wheel specs. Further, a measured 4.5" offset is mathematically the equivalent to +114 (mm) offset, which isn't reasonable to a Jeep application, if one even actually exists.

2. You further stated, "Offset requires the wheel width to be known before it solves OP's problem."

Actually, the opposite is true. Backspacing requires the wheel width to be known in order to identify where the center plane of the tire is located in the wheel well. With offset, the center plane of a tire is always in the same location when a different width wheel of the same offset wheel is used. For example, 0 offset wheels with widths of 7", 8", 9", and 10" all locate the tire in the exact same position. The only thing which changes with the width of the wheels is the tire section width, and bead mounting width. The contact patch of the tire stays in the exact same location. Because tire tread edges (edge of contact patch) is most often the point of contact with Jeep control arms, this is often the most applicable wheel spec consideration. There are times when brake or other suspension component clearance to the wheel itself (or tire sidewall) is more important than that of tire edge/control arm contact. In these cases, backspacing becomes a more valuable consideration.

As I read your post, it seems like you may have transposed the terminology, and are actually thinking along the same line as I am, but maybe not. In any case, I wish you well with your Jeep endeavors.

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[LostWoods]

Out of respect for Binfordtools, and forum decency, I will keep this technical, and not personal. I do feel that erroneous information in forums has to be clarified or corrected though, so people who reference them in the future get accurate information.

1. You stated, "If a 4.5" offset clears, a 4.5" offset clears on every wheel in every size and any similarly sized tire."

Offset is measured in millimeters, and not inches. It's industry standard. While you COULD measure an offset in inches, it would not match up to manufacturer published wheel specs. Further, a measured 4.5" offset is mathematically the equivalent to +114 (mm) offset, which isn't reasonable to a Jeep application, if one even actually exists.

2. You further stated, "Offset requires the wheel width to be known before it solves OP's problem."

Actually, the opposite is true. Backspacing requires the wheel width to be known in order to identify where the center plane of the tire is located in the wheel well. With offset, the center plane of a tire is always in the same location when a different width wheel of the same offset wheel is used. For example, 0 offset wheels with widths of 7", 8", 9", and 10" all locate the tire in the exact same position. The only thing which changes with the width of the wheels is the section width, and bead mounting width. The contact patch of the tire stays in the exact same location. Because tire tread edges (edge of contact patch) is most often the point of contact with Jeep control arms, this is often the most applicable wheel spec consideration. There are times when brake or other suspension component clearance to the wheel itself is more important than that of tire/control arm contact. In these cases, backspacing becomes a more valuable consideration.

As I read your post, it seems like you may have transposed the terminology, and are actually thinking along the same line as I am, but maybe not. In any case, I wish you well with your Jeep endeavors.

Ok I'll eat #1, as you noticed I crossed terms going back and forth. If a 4.5" backspace clears, a 4.5" backspace clears on every wheel in every size and any similarly sized tire. This is speaking to a problem like OP is having but really, any rubbing can be universally defined with a maximum backspace given any one overall dimension of the wheel/tire assembly.

On #2, you are so close to getting it and I think I see exactly where your bad assumption is. If the tread itself was a perfect width every time then we're arguing a distinction without a difference. In that perfect world, offset does make a lot more sense.

But it's not a perfect world and because wheel widths are generally narrower than the tread, the tendency is for wider wheels to create a more square cross-section compared to their narrower coutnerparts. You move the beads outward which reduces tread roll at the edges and maximizes sidewall height. In short, the shoulder typically moves very little relative to the edge of the wheel as long as you're dealing with reasonable sizes and not crazy stretching.

With two wheels having an identical backspace, this is nearly irrelevant because all that is added is to the outboard side and clearance to the inside of the tire remains unchanged. With two wheels having an identical offset, however, you are adding equally to each side so those wider shoulders are now closer to the metal bits and can frequently cause issues. This is why you need to understand wheel width alongside the offset spec.

 

[Renegade]

On #2, you are so close to getting it and I think I see exactly where your bad assumption is.

Let’s just agree to disagree on some of the technical details. See you out on the trail.

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