Buying wheels online means reading spec sheets full of numbers and abbreviations. If you don't know how to read wheel specs, you risk ordering wheels that don't fit your truck, rub on suspension components, or sit too far in or out from the fender. Every number matters, and this guide explains what each one means in plain language.
Wheel diameter is measured in inches from bead seat to bead seat — not from the outer edge of the lip. A 20-inch wheel has a 20-inch bead seat diameter where the tire mounts.
Common truck wheel diameters:
Smaller diameter wheels allow for taller sidewall tires, which absorb more impact and provide better off-road comfort. Larger wheels require lower-profile tires, which look sleek but sacrifice cushion here.
Wheel width is the distance between the inner bead seats, measured in inches. A spec of 20x9 means 20-inch diameter, 9-inch width.
Width determines which tire sizes fit the wheel. Every tire has an approved wheel width range — mounting a tire on a wheel that's too narrow or too wide is unsafe and will cause handling problems.
Common truck wheel widths:
Offset is the single most important spec after diameter and bolt pattern. It determines where the wheel sits relative to the fender and suspension components.
Offset is the distance in millimeters from the wheel's mounting surface (where it bolts to the hub) to the centerline of the wheel. It comes in three types:
A wheel with -12mm offset will sit about a half-inch further out than a wheel with 0mm offset. A wheel with -25mm offset will poke out roughly an inch past a zero-offset wheel.
Too much negative offset causes tires to rub on fenders during turns or suspension compression. It also places additional stress on wheel bearings and ball joints because the load is further outboard. Too much positive offset tucks the tire inboard where it may contact control arms or brake components here.
Backspacing measures the distance from the back edge of the wheel to the mounting surface, in inches. It's an older way of expressing the same information as offset but can be more intuitive.
A wheel with more backspacing sits further inboard. A wheel with less backspacing sticks out more. Many off-road wheel manufacturers still list backspacing alongside offset.
To convert: Backspacing = (Width / 2) + (Offset / 25.4)
Bolt pattern is expressed as two numbers: the number of lug holes and the diameter of the circle they form (bolt circle diameter, or BCD). For example, 6x135 means 6 lugs on a 135mm bolt circle.
Common truck bolt patterns:
Mismatched bolt patterns simply won't mount. Always verify your truck's bolt pattern before ordering.
The center bore is the hole in the middle of the wheel that fits over the hub on your axle. Hub-centric wheels have a center bore that matches your hub diameter exactly, centering the wheel precisely.
If the center bore is larger than your hub (common with universal-fit wheels), hub-centric rings fill the gap. Running wheels without proper centering can cause vibrations at highway speed.
Every wheel has a load rating — the maximum weight it can safely support. This is especially important for heavy trucks, towing applications, and trucks with heavy bumpers and accessories.
Stock truck wheels are rated for the vehicle's GVWR. Aftermarket wheels may have lower load ratings, especially lightweight cast wheels. Always verify the load rating meets or exceeds your truck's requirements, including the weight of any accessories you've added.
A typical wheel spec reads: 20x9, 6x135, -12mm offset, 87.1mm center bore, 2,500 lb load rating
This tells you: 20-inch diameter, 9-inch width, fits Ford F-150 (6x135 bolt pattern), sits slightly outboard of center (-12mm), needs an 87.1mm hub bore, and supports up to 2,500 pounds per wheel.
Wheel fitment involves more than matching numbers — tire size, fender clearance, suspension travel, and brake caliper clearance all factor in. At Redline Auto Creations in Tampa, we've mounted thousands of wheel-and-tire combinations across every major truck platform. We measure your truck, account for your lift and accessories, and recommend setups that fit perfectly.
Call (813) 544-4009 or visit 11626 N Florida Ave, Tampa, FL 33612 for expert wheel and tire consultation.
At Redline Auto Creations, we specialize in crafting custom vehicles with precision and passion. From wheels and tires to suspension, performance upgrades, and custom designs, we bring your vision to life. Contact us today and transform your ride.
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