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If you're tired of hearing, "Those wheels won't fit on your truck," or if you're considering a billet wheel that can be custom-built to fit your special lug-tucking needs, then this tech is for you. We put together a how-to guide that will help you use the simplest of tools to measure your own backspacing and wheel offsets, and how to use those measurements to find a wheel that will tuck deeply into your fenderwell.
Using the backspacing measurement, you can order wheels from your local wheel store without paying attention to the salesperson ranting and raving that there is "no way in hell you're going to fit a 22-inch wheel on that S-10." We decided to see if we'd be able to fit a set of Boyd Coddington 19x8-inch wheels on a '93 Toyota and take the guesswork out of wheel purchasing. Boyd Coddington Wheels offers a service that allows you to test-fit wheels so you can get the exact backspacing you need. Not every wheel manufacturer offers this service, so we'll shed some light on finding the optimum backspacing for your mini.
Offset Equation
Using a 10-inch-wide Niche Over Ride wheel as an example, we can easily find the offset using the backspace measurement.
Measurements needed: Wheel centerline (wheel width divided by two) and backspacing
Equation: Backspacing minus wheel centerline equals offset
Note: If the answer is negative, then you have a negative offset; if it's positive, you have a positive offset. A 10-inch-wide Niche Over Ride has a wheel centerline of 5 inches and the backspace is 6-1/2 inches
Offset: 6-1/2 (backspace) minus 5 (wheel centerline) equals 1-1/2 inches (positive offset)
Most wheel companies have offset charts by wheel width, so the main measurement you need is the backspacing. To find the backspacing, you'll need a straightedge, a tape measure, and a weighted bob.
1. The first step in measuring backspacing is to understand exactly what that measurement represents. The backspacing of a wheel is the distance from the inboard flange to the back of the hub mounting pad. The easiest way to measure this is to lay the wheel face down (without the tire) so that the backside of the wheel is facing up.
2. Lay a straightedge across the inboard flange of the wheel.
3. Measure the distance from the hub mounting pad to where the straightedge contacts the inboard flange of the wheel. As you can see, this wheel has a 6-1/2-inch backspace.
4. Using the Nitto 215/35ZR19, the od (outside diameter) is 25 inches, so by turning the wheel lock-to-lock and taking down a few measurements, we figured that the firewall will need to be tubed and the inner fenders will need to be cut, but the frame and other trouble spots wouldn't pose any problems.
5. We can now get back to measuring the backspace. To make things easy to visualize, we used a plumb bob to mimic the drop line of the inside fender edge.
6. Measure the distance from the hub assembly to the drop line of the weighted bob and record your findings. Our measurement was 4-1/2inches. To create what we call a no-rub zone, subtract 1 to 1-1/2 inches from that number. We subtracted 1-1/4 inches just to make things simple, giving us a whole number of 3 inches. This number is the maximum amount of outboard space for our wheels.
7. The width of the Boyd wheel is 8 inches and using a no-rub zone, we only have 3 inches of outboard space, leaving 5 inches of inboard space. Therefore, our backspace is 5 inches, which will allow us to tuck the wheel deep once the firewall is tubed for the body drop. Stay tuned to see this truck laid on the ground tucking 19s.