Wheel offsets, backspacing and info: Explanations:

[Tim240z]

For information purposes:

 

Wheel Terminology:

 

 

How to measure PCDs:

 

 

How to measure backspacing:

 

 

Offset:

To calculate offset you'll need the following measurements:

Wheel backspace

Wheel Width

Wheel Center line (outboard flange to inboard flange measurement / 2)

 

Subtract:

Wheel center line from Wheel backspace to get offset.

If backspace is less than the wheel centerline the offset is negative

If backspace is greater than the wheel centerline the offset is positive

 

Tip:

To convert from inches to mm multiply by 25.4

To convert from mm to inches divide by 25.4

 

[z-ya]

Tim,

 

Can you make this post a sticky? Lots of great info on a subject that always seems to come up.

 

Pete

[Drftn280zxt]

uh I think you have your offset calculations backwards. If the offset were negative 19mm it would be a deep dish rim. You actually subract the centerline from the backspacing. Hondas (for example) have a 7" wheel I think. 8"wide (flange to flange). 4" centerline. +45offset (+1.77"offset)( the bolts are further out on the outside of the car).So in this scenario you have X-4"=1.77.......X=5.77" backspacing.

 

so the equation is really Backspacing-Centerline=Offset

 

deep dish would be like this. Lets use a 9inch wheel for example. The true width like you said is an inch bigger being 10". Divide by two and the centerline is 5". Okay now lets say I have 3.5" of backspacing. Now lets work the math.

3.5"-5"=-1.5" or -38.1mm offset

 

deep dish is always negative!

 

Just wanted to fix your mistake the schematic and everything else was right though.

[hanomon]

Great info Tim, Thanks!