Hi All, I have just been offered a set of 10x15 and 8x15 wheels - anybody know what offset I should be looking at? The tires that are on need replacing, so if the wheels are OK any recomendations on tire size. I am also considering swapping out to 17 inch wheels again any suggestions/advice would be appreciated .
At the end of the day I want to fill the arches with tires...
Thanks
Steve
First, the Buick Big cars use a 5 X 5" bolt circle pattern, not the smaller car 5 X 4 3/4" pattern, so make sure whatever wheels you buy have the correct bolt pattern.
Second, It's really important to understand the terms offset and backspacing. They are not the same.
The 1971 Buick Riviera Chrome Rallye Wheel was 15" X 6" wide. The back spacing for that wheel was 3 7/8". Back spacing is measured from the back EDGE of the rim to the mounting surface of the wheel. That same wheel has + 3/8" offset. Offset is measured from the CENTER of the wheel width to the mounting surface. In addition, offset can be + or -. Wheel width is measured between the bead surfaces. The wheel measured from EDGE to EDGE is actually 1" wider, so a 6" wheel is actually 7" when measured EDGE to EDGE. Therefore, the CENTER of 6" wheel is actually 3 1/2" measured from either EDGE. Positive offset moves the wheel in, negative offset moves the wheel out. 3 7/8" back spacing means the mounting surface is 3/8" from the wheel CENTER, and is positive offset since it moves the wheel in.
Proper backspacing and offset keep the wheel centered in the wheel well.
The center of an 8" wide wheel would there fore be 4 1/2", and adding the +3/8" offset would mean a back spacing of 4 7/8"
The center of a 10" wide wheel would be 5 1/2", and adding the +3/8" offset would mean a back spacing of 5 7/8".
Back spacing is much easier to measure than offset. Simply rest the wheel on a flat surface and measure from the inside edge down to the mounting surface. Use a straight edge across the inside rim edge.
