Wheels of Destiny – Wheel Sizing (Part Two)
When you go to order your custom wheel you will be asked a few questions that pertain to the fitment for your Ford Truck. You’ll be asked things like the diameter you’re looking for, the offset or backspacing you need, the hub center bore and wheel bolt pattern, or if you are running aftermarket brakes or not.
Many wheel manufacturers do have experience in fitment for your vehicle, however if you go to a wheel maker that hasn’t had any experience with domestic trucks they may require you to measure out things to help them pick the right size you need.
There is a wheel fitment tool that makes this very easy, but unless you plan on opening a shop or go through wheels more than you do shoes the investment isn’t very wise. That shouldn’t stop you from finding the right measurements, though.
Grab a yard stick, a couple of rulers, and a dial caliper as it’s time to go measure what will actually fit. First, measure the hub center of your wheel using the dial caliper and be sure to measure the thickest part that will contact the wheel as this will determine your wheel center bore and don’t forget to find your wheel bolt patter at the same time. There are databases for wheel bolt patterns, but you simply measure from two opposite wheel studs to find your bolt pattern.
From the center of the hub measure out to the bottom of the caliper, this will let the person helping you find your wheels know how tall the wheel hub will need to be or if your calipers will clear it.
You’ll also want to measure from the face of the wheel hub to the widest part of the caliper going towards the wheel face. While you’re still at the wheel hub, measure the center of the hub out to the tallest point of the caliper; if that is a brake line fitting or bleeder cap that will be the part you measure to. That takes care of the inside of the wheel.
You’re not done, though, as you will still need to determine how wide or what backspacing you’ll be able to run. With the front wheels straight, you’ll want to measure from the hub face to your shocks and springs as these will be the closest components with the wheels in a straight line.
However, if you notice any other component that sticks out beyond the shock or spring, take that into account as well. You’ll then turn the wheel and measure from the hub face to the frame and any suspension components that could hit the wheel as you turn it.
You’ll do that for both left turn and right because of steering Ackerman, which is the angle of the wheels while you turn. The wheel of the inside of a turn will have a greater steering angle and is why measuring the left and right turn of each front wheel is important. We’ll dive into steering Ackerman and more in a future steering article, so we won’t explain it further here.
Now that you have all of those measurements, you can give them to person helping you pick your wheels! However, a quick note about offset and backspacing; in a general sense, they are the same thing. They are both a measurement of where the wheel mount is in relation to either the back of the wheel, in backspacing, or from the center of the wheel, as in offset.
Backspacing will almost always be a positive number where offset will be negative, positive, or zero. A negative offset is the same as a low backspace number and will push the wheel face towards the outside of the wheel well. Zero offset is dead center of the wheel as measured between the bead seats. A positive offset is the same as a high backspacing number and will pull the wheel face towards the inside of the wheel well.
However, unlike backspacing, offset will not be the same on every wheel despite a similar number. For example, a positive eight offset on an eight-inch wide wheel will not be the same as a positive eight offset on a ten-inch wheel. The positive eight offset on the nine-inch wide wheel will have a backspacing of 4.8-inches where the ten-inch wide with positive eight offset will be 5.8-inches. A five-inch backspacing on either the eight or ten-inch wide wheel will always be a five-inch backspacing.
Click here for the conclusion of Wheels of Destiny – Forged vs Flow Formed vs Cast (Part Three)
In case you missed it, read Design (Part One) here.