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[nks_bb]

What's the difference between a High Positive Offset and a Medium offset.

I'm looking at specifically

120mm High Positive Offset
120mm Medium Offset

[CombatNinja]

Wrong forum. Go to www.tirerack.com for a complete explanation of offsets.

[wahooooman]

Originally Posted by CombatNinja

Wrong forum. Go to www.tirerack.com for a complete explanation of offsets.

^^this +100
Many people don't realize there is a dedicated forum for this!

[VMRWheels]

120mm is the bolt pattern. IE: 5x120. High or low offset determines how far or close your wheels will sit relative to your wheel hub.

[jphughan]

OP, you generally don't want to stray too far from the OEM offsets even if you're changing your wheel size slightly. A positive offset means that the wheel attaches to the car that many millimeters closer to the outside of the wheel from the wheel's centerline, so a wheel with a high positive offset would have less (or no) creep inward at the center of the wheel's face. A negative offset would mean that the wheel mounts to the hub that many millimeters closer to the INSIDE of the wheel from the wheel's centerline; so-called "deep dish" wheels have high negative offsets.

The total wheel width (WIDTH, not diameter) and the offset combine to determine your car's track width on that axle, which in addition to influencing handling also affects appearance. Here's the basic way to figure out the expected change for appearance:

1. Find out the width (again, NOT diameter) of your current wheels; stock BMW wheels will generally have different widths front to back. Divide that by 2. Since width is usually in inches and offsets are in millimeters, convert that number from inches to millimeters. That will tell you how many millimeters you have from the wheel's center to its edges.

2. If you have a positive offset, SUBTRACT the offset from the value you just got above. If you have a negative offset, ADD the offset from that value. That will tell you how far the wheel protrudes in the outward direction from the car's hub.

Now when looking at aftermarket wheels if you want to figure out how well they'll match your car's stock appearance, repeat that formula for the aftermarket wheel widths and offsets you're looking at. If you get a higher value at the end than stock, your wheels will be farther out than stock by that marginal difference, and vice versa with a negative value.

Calculating track width changes is easy since track width is just the distance from the center of one wheel to the center of the other wheel on the same axle -- so regardless of what wheel size you choose, any additional positive offset on the new wheel compared to the OEM offset will DECREASE your track width by double the amount of the additional offset (since you're losing width on both sides), and less positive offset will INCREASE your track width by double that margin.