Rim Offset - How to measure it and get it right

[MudRunnerTD]

I answered this in a thread and thought i would put it here for all to view, hope it helps.

Firstly this is a Nissan Patrol Forum so note that the standard offset on a Nissan Patrol is +10 or positive 10.

Your offset choice will determine where the wheel sits in your wheel arch and whether it stick out of your guards at all.

On a Nissan Patrol it is very common to increase the offset into the Negative to bring the wheels further out to the edge of your wheel arches to give a wider track and stop bigger tyres from scrubbing on the inner guard.

OK so to get the right measurement you are really going to need a rim off the car or your spare off the door if it is the same. You need to measure the back space of the rim centre to figure out the offset. Offset equals how much the centre of the rim is away from the middle of the rim...

from the diagram below you can see how important it is to know the exact width of your rim. stop into a tyre joint and they will throw a calliper on it for you if you have time or you can figure that out.

Once you have the width of the rim then you halve it to determine the centre of the rim. Offset is how far from the centre of the rim is the centre mounting plate.

OK. You need to lay something across the back side of the rim outer edge of the bead to outer edge of the bead. Then measure the distance from that line to the back of the centre plate of the hub to determine where it is in relation to the rolling rim.

on an 8 inch rim i think they are 200mm wide (you should measure to make sure as every rim is different). zero offset would measure 100mm. Negative 22 offset (considered Toyota offset by most) would measure 78mm to the back plate. Standard Nissan offset of +10 would measure 110mm to the back plate.


wheel_dimensions1.jpg

^^^^ Now that is a pic of an Alloy Mag wheel. the front of the rim is to the left of the pic and the back is to the right.

or we can get a little technical

wheel-offset-backspacing.jpg

wheel_guide.jpg

wheel_terms.jpg

Measuring Wheel 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


An that is that.. Hope that helps you.

Cheers MR