Offsets Question

[Bart]

I'm looking at getting some new wheels but am struggling to get my head around offsets. Does anyone have any easy way of explaining this? I'm basically looking at getting a set of sportmax wheels. I want them to sit flush with stock guards. Can anyone help a brother out?

Cheers Bart

[Clinton]

flush guards on a KE70? or an AE86?

http://www.tirerack.com/images/wheels/tech/offset.gif

The offset of a wheel is the distance from its hub mounting surface to the centerline of the wheel. The offset can be one of three types.

ZERO OFFSET

The hub mounting surface is even with the centerline of the wheel.

POSITIVE OFFSET

The hub mounting surface is toward the front or wheel side of the wheel. Positive offset wheels are generally found on front wheel drive cars and newer rear drive cars.

NEGATIVE OFFSET

The hub mounting surface is toward the back or brake side of the wheels centerline. "Deep dish" wheels are typically a negative offset.

[shinny]

offset calculator (http://www.1010tires.com/WheelOffsetCalculator.asp) might help as well

[marvis]

Ewwww sportmax. 15 x 8 0 offset will be fine, Don't go anything smaller or positive offset. Actually on the front it will sit well inside your guards.

[Bart]

Cool as. Thanks for the info!! Im assuming offset is measured in mm? Is there a proper way of measuring this or is it a case of pulling the old ruler out?

Oh and its on an AE86.

[Clinton]

1) measure the overall rim width of the wheel.
2) measure the backspace, which is the measurement from the hub surface contact area to the outside of the inner rim.
3) divide the overall rim width by 2 which gives you the center line.
4) subtract the center line (overall rim width divided by 2) from the backspace.
5) a negative answer means the wheel has a negative offset and a positive answer means the wheel has a positive offset

[Chairs with flares]

To throw a spanner in the works, clearance has to be calculated with wheel width and tire section width in consideration.

i.e. a 15x7J +15 wheel will sit out further than a 15x6 +15 wheel. It will sit 13mm/half inch further out because of the extra width (half inch wider strut side and half inch street side).

HOWEVER; the edge of the tire (assuming no stretch) will sit exactly the same on either wheel, it will just apear to have less bulge on the 15x7J wheel.

In my experience, I found ran 205/50 R15 tires non stretched. With the same tires, I went from a 15x7J +24 wheel to a 15x6J +13 wheel. The outer lip of the wheel sat pretty much the same with the new wheel as the extra offset was cancelled out by the wheel being narrower. But the tire tread sat out an extra 11mm since where the tire tread sits can be deduced from offset alone (assuming no stretch).

Cliff notes:
- Offset numbers will dictate where your tire tread will sit.
- Where your wheel edge will sit will need to take wheel width into consideration.