How do you measure backspacing on a wheel

Diameter of Hub Center Required if wheels are hub centric C. Wheel Stud Diameter Required along with bolt circle D. Height of Hub Center E. Modular Wheel Leak Detection So your tires keep going flat, before you blame those leaky slicks, check your wheels for leaks. The easiest way to measure backspace is to lay the wheel face down onto the ground so the backside of the wheel is facing up.

Backspace to Offset Conversion Chart The table on the right is q quick reference for finding offset, pick the rim width and follow the row over to the backspace of your wheel. Suggestion: Start your search for new wheels by picking the tires first.

Note: Always refer to Owner's Manual for proper factory specifications that take precedence over the listed recommendations. Bead-Loc A device which captures the tire bead between it's flanges, usually secured by bolts to keep tire bead from dismounting. Usually used in dirt circle track or off road applications where low tire pressures are used and hitting ruts or other vehicles are common. Left: An example of a Bead-Loc wheel.

After thoroughly cleaning all mating surfaces with an appropriate cleaner, add a thin skim coat of silicone sealant to these surfaces, assemble wheel and torque bolts to recommended torque Install a new valve stem Add a thick coat of silicone sealant to the drop center area of the wheel and let it cure for 24 hours before initial use.

Wheel offset. Perhaps the most important factor in choosing and installing new wheels is the proper handling of wheel offset. Offset also can be one of the most difficult factors to get right when replacing wheels.

However, it is important to get it right, because getting the offset wrong risks badly damaging the replacement wheels and tires as well as suspension components, and can put the driver at serious risk of a blowout. Offset, scrub radius and contact patch are the only three technical terms we need to understand. However, offset might be easier to visualize with a few simple drawings that focus on the tire contact patch. When the surface of the mounting flange is exactly aligned with the center of the tire contact patch, offset is zero.

If the flange is inside the center of the contact patch closer to the center of the car , offset is negative. If the flange is outside the center of the contact patch closer to the curb , offset is positive see Figure 1. On most OEM wheels, offset is positive contact patch slightly inboard , and it can have a major effect on steering feel and stability during acceleration and braking.

To visualize this, lay a pen on the table and hold the top end still. The radius of that arc is the distance between the pivot point that you are holding and the tip that moves through the arc. Now make another drawing to put that arc on the car.

Looking at the car head-on, imagine a line drawn from the upper strut mount or upper ball joint and down through the lower ball joint, and then on down to the road.

If the line touches the road inboard of the contact patch, scrub radius is positive. If the line touches the road outboard of the contact patch, scrub radius is negative see Figure 2. The point where that line meets the road is the steering pivot point, same as where you held one end of the pen. As the wheel is steered, the point at the center of the contact patch moves through an arc around that pivot point.

The arc can be inboard negative scrub radius or outboard positive scrub radius of the pivot point, and the distance between the arc and the point might be just a few millimeters, but that small distance makes a big difference in what the driver feels in the steering wheel.

Technically, offset is the distance from the hub mounting flange to the centerline of the wheel between the mounting beads. Measure the distance from the floor to the straight edge and divide by two. That calculates the centerline of the wheel. Conversely, an offset of mm is the opposite, 50 millimeters to the inside of the centerline, yielding a deeper "dish" in the wheel. When bolted up to your car this means that a lower offset wheel will stick out farther.

Obviously, a negative offset works the same way. A mm wheel replaced with a mm wheel will move 1" outward as well. Also worth noting are bolt circle and center bore. Bolt circle refers to the diameter of a circle drawn through the center of the wheel studs. On a four or six-lug car, this is easy to measure, simply go center to center on the holes or studs. Five lug wheels and hubs are more common to the cars that we love, and the odd number can make them a bit tricky to measure.

To quickly measure on the wheel, center the measuring tape or ruler on one hole, skip a hole, then measure to the outside of the next hole. This is the best way to measure bolt circle without a template. Measure from the outside of one stud to the center of the stud across from it. There are also plenty of bolt circle templates available, such as our part These make it easy to measure bolt circle quickly and accurately.

Also critical is the center bore. This is the hole through the center of the wheel, and if it's smaller than the protruding part of your hub or axle, the wheel will not fit.

Check out our Wheel Bolt Pattern Guide to learn more about measuring all types of wheel bolt patterns. The most important takeaway here is not to confuse offset and backspacing.

With that established, you can make an informed decision when selecting aftermarket wheels for your car. Don't forget that there are tools available that can help you reach a decision. If you have your tires already, these Wheel Fit kits are handy to have because they allow you to actually install the tires on the car to check clearance. Shop our extensive inventory of wheels.