View Full Version : Wheel backspacing

09-05-2006, 05:00 PM
Okay, I assume this has been addressed here before, but I am fairly new to the forum thing and have not seen it the short time I have been here.
I want to replace the wheels on my Champ pickup (1/2 ton). I want to put 16" steel wheels on it. I would like to leave the front the stock width (It is hard enough to turn now, I don't need to make it any more difficult.), but I would like to go wider on the rear. What is the backspacing on stock truck wheels and how wide can I go on the rear of my truck?
Thanks, Joe Roberts

09-05-2006, 07:51 PM
Start here ... I only know the passenger car offset.;)



09-05-2006, 10:49 PM
What is the passenger car off set and back-spacing? Two different animals I've heard. jimmijim

09-06-2006, 08:20 AM
Take a rim and lay it on a flat surface. Using a straight edge, measure from the surface (inner plane) to the outer plane of the rim. That's, obviously, the entire width of the rim.
Offset is measured using this width. Where the mounting area inside of the rim contacts the brake drum/rotor, in relation to the exact center of the total width, is considered your offset. If the mounting surface is closer to the outside of the rim, then you have positive offset. If it's closer to the inside of the rim, then it's negative. Offset is usually given in millemeters (mm) FWD cars usually have zero or negative offset. RWD cars usually have positive offset ( +20, +35, etc)
Backspace is measured from the inside plane to the mounting surface and is usually described in inches.
Here's the kicker, though. if you have a 15X6 rim, the "6", is measured inside the bead seat, where the tire bead sits. There's a bit more meat to the rim, as there's the lip that holds the side of the bead in place. Both sides generally total about an inch, so your 15X6 rim is really 7 inches wide. Using this figure as a rule, will give you a better idea on where your offset is, in relation to the backspace. IE, 15X6 = 7 inches wide. Zero offset is at 3.5" backspace. A +15mm offset on the same rim will give you 4 1/8" backspace and place the rim farther under the fender, than a zero offset.

09-06-2006, 08:41 AM
Thanks for your explanation. jimmijim