Tire Offset vs Backspacing, can someone help with my misery?

[Ethan]

Hi,

After looking at the following chart, I am kinda confuse and frustrate. I think I am interpreting it in the wrong way. /ubbthreads/images/graemlins/frown.gif

https://www.galantvr4.org/docs/backspacing.htm

What I understand is,
At first chart, let's assume I have 7" wide wheel with +40mm offset. It show I have 5" backspacing.
When look at the second chart, 7" wide wheel with 5" backspacing give +25mm offset. /ubbthreads/images/graemlins/frown.gif

So, can someone help me out, please?

 

[RedTwo]

All of the wheel widths in that second table appear to have an extra inch added to them before doing the calculation. 7"/2 does not equal 4" :/

 

[Ethan]

What I understand is....

Backspacing - Centerline = Offset

Centerline for 7 inch wheel... is it 3.5 inches?

If that wheel has 5 inches of backspacing,
5 - 3.5 = 1.5" (38mm)

According to chart I mention, VR4 should have 35mm to 40mm of offset for 7" wheel. So, it fit? Am I right? /ubbthreads/images/graemlins/uhh.gif

 

[iceman69510]

Stated wheel "width", such as a 7" wheel, is measured at the bead. The wheel from outside to outside edges is wider than that, often as much as 1 inch because of the general flange design. This is why the backspacing versus offset is not just a simple subtraction.

 

[Ethan]

Awww...

So, I have to measure individual wheel, and calculate as follow to get the offset. Right?
Backspacing - Centerline = Offset

Right? /ubbthreads/images/graemlins/smile.gif

 

[iceman69510]

Actually, offset is a wheel design feature. It is the distance from the centerline of the wheel to the wheel mounting surface.

For positive offset wheels (typical for all front wheel drive and now more common on rear wheel drive) is it indicated as +, and indicates the mounting surface is further out from the wheel centerline.

For negative offset wheels it is indicated as -, and indicates the wheel mounting surface is further in from the wheel centerline.

Backspacing is basically one-half the actual wheel width (not bead width) plus the offset. I'm sure the tire rack site has some illustrations of this.

Zero offset wheels have the wheel mounting face at the centerline of the wheel.

 

[iceman69510]

Quoting Ethan:
Awww...

So, I have to measure individual wheel, and calculate as follow to get the offset. Right?
Backspacing - Centerline = Offset

Right? /ubbthreads/images/graemlins/smile.gif



Long answer above, but yes I think your basic formula is correct.

 

[Ethan]

Thz alot, iceman69510 /ubbthreads/images/graemlins/smile.gif

I am finding 17" wheel for My JDM GVR4. And, in our country, wheel market is ... how should I say, it is like... "this room is full of wheel, look around and take what u want". Can't ask abt offset or whatever. And, 17" wheels with 4 lug RWD pattern are so rare too.

So, I am reading about fitment and backspacing for GVR4 , saw this chart and confusion appear.

Thz for your help. /ubbthreads/images/graemlins/smile.gif

P.S ; This is my first exp for changing wheel. I used stock at former rides and other rides. /ubbthreads/images/graemlins/grin.gif

 

[ktmrider]

Great link: click

 

[Ethan]

Thz. ktmrider.

Ya link is so cool. /ubbthreads/images/graemlins/smile.gif