Backspacing? ...4+3? ...Huh?
Ever wondered what in the world an “offset” means? More importantly, why do we need them.. and how does a +10mm or -47mm offsets really apply or affect my vehicle/machine? This thread is dedicated to help you better understand and make sense of this very easy but very important factor in wheel manufacturing. As an ATV wheel fan, you may be used to things being explained in backspacing* which looks like this: 5+2 or 4+3. While this version of offset is easy to understand on a basic level, it lacks the details and specifics that a +/-mm offset provides, which can mean the difference between wheels rubbing, sticking our too far or just plain not fitting. If the offset of the wheel is not correct for the vehicle, the handling can also be adversely affected. When the width of the wheel changes, the offset also changes numerically. If the offset were to stay the same while you added width, the additional width would be split evenly between the inside and outside. Read below for the basics of what offset means and then use the diagram below to put it all into prospective and make your wheel shopping a little easier to understand. Questions? Give us a shout: (800) 734-4890
Lets talk Offset - the details
Lets make this easy on all of us. The offset of a wheel is the distance from its hub mounting surface to the centerline of the wheel. The whole point of an offset is for the end user of the wheel to know how much in inches (4+3) or in the case of millimeter offset, how many mm the wheel will stick out or suck in from the mounting surface of the hub. Remember, even a couple of millimeters can affect performance, ride quality, the look/stance of your vehicle and more important than anything, how safe the setup is.
Because you are reading this, you have probably spent some time trying to figure out how to get your machine to run as true to stock as you can. Although we completely understand this effort as stock means safe, you must understand that the other reason you are here is because you want nice, custom looking wheels. A stock wheel, no matter what OEM manufacturer, is going to run a +high offset, typically in the +30mm to +40mm range. This allows the wheel to “suck-in” under the vehicle more, keeping your center of gravity under the cockpit and reducing overall machine width. The problem with a +30mm and higher offset is that the hub is so close to the front of the wheel, the design of the wheel is going to suffer tremendously. The deep lips and steep spoke drops just cant happen within 2 inches of room. Reverse the offset (-47mm) and you now have 5 inches of design space for swooping, dramatic spokes and just 2 inches for hub clearance. The basics: The offset can be one of three types (measured in millimeters).*
The hub mounting surface is even with the centerline of the wheel (dashed line to left).
The hub mounting surface is toward the front or “wheel side” of the wheel. Positive offset wheels are generally found on front wheel drive cars and newer rear drive cars. An example of a positive offset wheel is the Polaris RZR 1000 which comes stock with a +38mm offset. Higher offsets restrict design and leave the wheel looking flat, with little to no depth in spoke design/lip.
The hub mounting surface is toward the back or brake side of the wheel. “Deep dish” wheels are typically a negative offset and benefit the design process by allowing sharp angles, deep spokes and incredible layering.
How to measure a wheel backspace:
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. Take a straight edge and lay it diagonally across the inboard flange of the wheel (like picture above). Take a tape measure and measure the distance from where the straight edge contacts the inboard flange to the hub mounting pad of the wheel. This measurement is backspace. Backspacing, similar to offset, is the distance from the hub mounting surface to the inside lip of the wheel (measured in inches).
How to measure a wheel offset:
To calculate the wheel offset, you will need the following measurements:
Wheel backspace (see above)
Wheel centerline (outboard flange to inboard flange measurement, divided by 2)
Once you have these measurements, you need to subtract the wheel centerline from wheel backspace to get the offset.
If backspace is less than the wheel centerline, the offset is negative
if backspace is greater than the wheel centerline, the offset is positive
To convert inches to millimeters, multiply inches by 25.4
To convert millimeters to inches, divide mm by 25.4