- Joined
- Sep 12, 2023
- Messages
- 1,607
- Location
- Charlotte, NC
- Vehicle Details
- '95 Thunderbird with '18 TF 5.3L - SVO Engine
Backspace is the distance from the inside of the mounting hub to the inside of the wheel. Essentially, it's the space that hangs back into the wheel well.
For instance, a 17 x 8" wheel with a backspace of 4" will have an offset of 0, since the mounting surface is right on the center-line. If it has a backspace of 5" it will have an offset of 1". If it has a backspace of 3", it will have an offset of -1" (negative offset wheel). As you can see, offset is a useless measurement without knowing the width of the wheel. Backspacing can tell you at least how much the wheel will protrude into the wheel well.
A 17 x 8" wheel is actually 9" wide because wheel backspacing goes to the outside edge so a 17 x 8" wheel with a 4" backspace is actually 1/2" negative.
Tire guys measure wheels from inside to inside, whereas wheel guys measure from outside to outside hence the confusion.
Wheel Offset:
Offset is the distance that the mounting surface is offset from the center-line of the width of the wheel. You need to factor in that wheel lip (usually around 1") when determining backspacing from offset.
This is why you need to know both the offset and backspacing.
You also need to convert to millimeters because wheel manufactures post their specs in mm.
Example: A 17 x 9" wheel with 26 mm offset = 6" of backspacing
Our Professional Recommendations:
For 17" x ? Rims:
Front:
Rear:
For 18" x 9" Rims:
Front: 245 or 255 / 45 / 18
REAR 275 /45 / 18 or 285 / 40 / 18
For instance, a 17 x 8" wheel with a backspace of 4" will have an offset of 0, since the mounting surface is right on the center-line. If it has a backspace of 5" it will have an offset of 1". If it has a backspace of 3", it will have an offset of -1" (negative offset wheel). As you can see, offset is a useless measurement without knowing the width of the wheel. Backspacing can tell you at least how much the wheel will protrude into the wheel well.
A 17 x 8" wheel is actually 9" wide because wheel backspacing goes to the outside edge so a 17 x 8" wheel with a 4" backspace is actually 1/2" negative.
Tire guys measure wheels from inside to inside, whereas wheel guys measure from outside to outside hence the confusion.
Wheel Offset:
Offset is the distance that the mounting surface is offset from the center-line of the width of the wheel. You need to factor in that wheel lip (usually around 1") when determining backspacing from offset.
This is why you need to know both the offset and backspacing.
You also need to convert to millimeters because wheel manufactures post their specs in mm.
Example: A 17 x 9" wheel with 26 mm offset = 6" of backspacing
Our Professional Recommendations:
For 17" x ? Rims:
Front:
Rear:
For 18" x 9" Rims:
Front: 245 or 255 / 45 / 18
REAR 275 /45 / 18 or 285 / 40 / 18
Last edited:
