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Understanding Offset Fitting a set of wheels with the correct offset is most important. Yet, because there are two commonly used (but different) methods for measuring offset, much confusion reigns. At Speedy Wheels we understand both the "backspace method" and the "centreline method", so a short explanation of each may assist you in selecting the correct offset wheels. Backspace Method: Measure from the inside rim edge to the high point of the bolt hub. Distance "A" in millimetres. Centreline Method: Measure the overall width of rim (Distance “X”), halve this measurement to find centreline then measure backspace (Distance “A”). Subtract “A” from “X/2” and you now have the centreline offset, which in Australia is written 35P or 10N to denote either positive or negative centreline offset. In Europe, centreline offset is usually written ET35 or ET10 etc. NOTE: The centreline offset measurement is “rim width dependant”, ie. as the width of the rim changes, so does the centreline offset, eg. if you have 14 x 6 wheels with 47P offset and would like to fit 14 x 7 alloys, then the same offset in 14 x 7 is 35P. In both instances, the backspace remains at 135mm.

P.C.D. (Pitch Circle Diameter) The P.C.D. of a wheel refers to the diameter of an imaginary circle drawn through the centre of the nut/stud holes in the mounting face of the wheel. An example of a P.C.D. is 5x120, where 5 indicates the number of holes (for studs/nuts) and 120, a diameter of 120mm.

Hub Location The hub hole is the hole in the centre of the wheel which mates with the centre hub of the car. The centre bore must locate on the centre hub as the car’s load must be directed through this point. Locating wheels on the studs/nuts is not the correct way to locate a wheel onto a car. The studs/nuts merely prevent the rim from spinning around the hub axis, and holds the rim to the vehicle. By not locating a wheel on the cars’ centre bore, the vehicle can sometimes encounter vibration problems, which can lead to either loosening of the studs/nuts, broken studs/nuts, or at worst, rim failure. All Speedy wheels are either supplied with centre bore locating rings or are machined to be a perfect fit with the vehicles hub to completely eliminate any of the above mentioned scenarios.