main-wheels1 "Backspacing" and "Offset" are two words that probably don't come up in a casual conversation, unless you're a Jeep or 4X4 fan. These two relate to specs when choosing a wheel and  / or tire for your vehicle. They are more of a type of measurement than anything  else. But they're important to getting the right wheel, and in the end, the right tires, to get you where you want to go and set your Jeep up for the style driving you have in mind. Let's take a look at these terms and their use: The first term we'll start with is: BACKSPACE The measurement determines how far inboard the hub (where the holes are for bolting on the wheel) are from the outside end of the wheel. For instance, if you lay a flat yard stick or steel ruler across the edge of the wheel, you can measure from that to the hub to determine the backspace. NOTE: you do this on the BACK of the wheel, the part of the wheel facing the vehicle. The reason this is important is you want to place the tire (mounted on the wheel) at a certain distance away from the end of the axle. Why? You don't want the edge of the tire to hit or rub up against any suspension parts on the back side. But you also want to help make sure it doesn't touch any of the body, exhaust, or any other number of parts on a Jeep. You are also making sure the wheel will clear the caliper or brake drums, or any other related brakes or parts. If the rotor and caliper stick out 4-inches, you need to make sure the inside of the wheel spacing will accommodate that. By changing your backspace on the wheels you use, you can move the tire itself in and out of the wheel wheel area as needed. The width of a rim is measured from the two sides, the two lips outside of where the tire in mounted in the middle. A rim might be 10 inches wide let's say. You can have two 10 inch wheels, one with a backspacing of 2 inches, and one with 3 inches. Even though the wheel itself is the same width, the offset will determine how far the wheel (and tire) will extend outside from the end of the axle. Meaning, the 3 inches of backspacing will allow the tire to be closer inboard (towards the vehicle). (the Offset can effect this measurement -  see more below). Backspace-ermahgerd It's an easy and quick measurement to make if the wheel is off the Jeep. Just lay the wheel with the outside facing down, and measure on the back (and maybe use a towel or something to protect the face of the wheel from scratches while you're doing the work). The second term to look at is: OFFSET There are actually three terms of Offset.
  • Negative Offset - (sometimes called "Deep Dish") is a case where the back of the bolt pad (where the wheel bolts up)  is closer to the inside of the wheel. Meaning, the mounting surface is inboard of the rim's centerline (the center of the wheel, looking at it from the side).
  • Positive Offset -  is a case where the back of the bolt pad (where the wheel bolts up)  is closer to the OUTSIDE of the wheel. Meaning, the mounting surface is outboard of the rim's centerline (the center of the wheel, looking at it from the side).
  • Zero Offset -  This is when the hub is exactly centerline, and in the middle of the wheel.
  For instance, the wheel below, seen from the side, has a positive offset.

wheel offset diagram

  Offset on a wheel does much the same thing as backspacing. It's a visual clue to make sure the wheel won't interfere with other axle and brake parts. But it can also help when choosing how wide of a rim to use. When you measure the backspacing, you want to note if the hub (where the bolt holes are)  is inboard the centerline, or outside it.  Now you will know if it has a negative or positive offset. When choosing a wheel, the wheel manufactures normally mention these specs, so you can easily chose a correct wheel based on you measurement and observations. At Morris 4x4 Center, we carry a wide variety of wheels to fit almost any kind of backspacing or offset combinations. We also carry the best and most popular brands as well, including: See you on the trails!