Backspacing questions

[veedubtuner]

I'm familiar with offsets and how they work. But backspacing I'm not and I'm not too sure how much it matters for picking wheels for "trucks and offroad" applications. I've never really delt with backspacing with the cars I've built.

I currently have the Black appearance package wheels 18x8 55 et backspacing unknown. With 265-60-18. I was originally looking at the Ford Performance wheels for that "Tremor" look I wanted, which are 17x8.5 et 55 with a 177.5mm backspacing. I want to run a 275x70x17 tire, but I'm not liking how close that is to the struts. And I'm sure the closeness pictured in the diagram is not real world accurate lol.

So I found some other wheels I like that are specked better at 17x8.5 et25 (with 5.73" I assume is the backspacing) This website I use doesn't take backspacing into account so I'm wondering how much of an issue it might be?

I'm trying to do as much research as possible so I don't get wheels that don't fit properly. As a side note I am planning a slight lift/level and changing out the intrusion bars for added clearance.

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[Colo_Ranger]

Backspacing and offset are the same thing, just measured differently.

Backspace is the back lip of the wheel to the mounting surface. Offset is the front lip to the mounting surface.

Also, as long as the top of the tire is not touching the strut when you are stopped, you will be fine. Tires deform at the bottom because the weight of the vehicle is on them. The top of the tire will not change at all, since there is no outside force to deform them. I've run tires that were 1/16" from the strut and they NEVER made contact. Even aired down, they deform at the bottom.


Edit: Part of this is wrong - Offset is mounting surface to wheel centerline, not the front lip.

 

[veedubtuner]

Backspacing and offset are the same thing, just measured differently.

Backspace is the back lip of the wheel to the mounting surface. Offset is the front lip to the mounting surface.

Also, as long as the top of the tire is not touching the strut when you are stopped, you will be fine. Tires deform at the bottom because the weight of the vehicle is on them. The top of the tire will not change at all, since there is no outside force to deform them. I've run tires that were 1/16" from the strut and they NEVER made contact. Even aired down, they deform at the bottom.

Thank you for that explanation.

 

[Colo_Ranger]

Thank you for that explanation.

Also - I crossed in my head. Offset is the mounting surface to the true center line of the wheel, not the front lip.

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