Need help understanding Offset & Backspacing

[RandysWay]

I'm beginning to hate Metric with a passion. The way that was explained to me today, as well as on many websites, which makes complete sense..

Let's say that the rim has a Backspacing of 5 inches and the rim is 8.5" Wide. Now, let's cut the rim in half: 4.25" Wide. With a 15 mm offset, I translate that to 0.59 inch - a little over half an inch. 4.25" + 0.59" = 4.84 inches. I'm 0.16 inches short of the 5 inch Backspacing.

Here's another example. The rim is 9.5 inches wide with a Backspacing of 5.84 inches. Now let's cut the rim in half: 4.75 inches. With a 15 mm offset, I translate that to 0.59 inch - a little over half an inch. 4.75" + 0.59" = 5.34". I'm off a half inch.


What in the heck am I doing wrong?! I'm beating my brains out over here trying to figure this out... even searched Google for an explanation and it says what I already know, yet nothing adds up.

Also, what is the Stock Offset on an R/T Daytona? What width rim would you recommend? 8" or 8.5" Wide for a 20" Wheel? What Offset would be a HAIR inside the fender with an 8" or 8.5" or MORE Wide Rim?

Thank you.

[RandysWay]

I THINK I DID IT! If I take half the rim width and add a half inch, I am coming up with CONSISTENT offset's. Am I doing it right!?? Did I do it!?! But, I still need help with the last part of the question on the recommended offset as well as the stock offset. Thanks again!

[done]

I THINK I DID IT! If I take half the rim width and add a half inch, I am coming up with CONSISTENT offset's. Am I doing it right!?? Did I do it!?! But, I still need help with the last part of the question on the recommended offset as well as the stock offset. Thanks again!

Offeset is the relative position of the mounting surface to the centerline of the wheel. + when the centerline is closer to the car and - when the centerline is farther away from the car. The offset is designated for a particular vehicle to maintain even loads on the bearings and to maintain the suspension geometry.

So a wider rim with the same offset will split the extra width between the inside and ouside of the wheel well. If you vary the offset and the width, then you have to calcualte the change.

The standard offset for a RWD is 24 mm. In general, most people who change rims will increase the width of the rim. Since there is more rrom to the outside than to the inside, a 14mm offset will work ok.

[VanillaRT4me]

Forget having to learn and calculate backspacing. It was the old way of doing things and it wasn't very accurate at that.

By the way, the part you're missing with back spacing is that every wheel is overall wider than the stated width for mounting a tire -- that's where the additional .5" is coming into play.