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A Guide to Making Sure Your New Rims Will Fit Your Truck

kmc modelWill those sexy new rims fit your vehicle? You’ve spent hours drooling over thousands of gorgeous images of sexy new rims and you’ve finally seen the style and design that you want. You have to have them, nothing else will do… but there’s one thing that could ruin everything; will they fit on your vehicle? Understanding a Wheel’s Specs For those sexy new rims to fit correctly they have to match the pattern of your vehicle’s lug nut studs and clear the inside wall of the wheel wells. To tell if they will or won’t fit you’ll first need to read the wheel’s specs.

Generally a wheel’s specifications will be listed in this format: 15x8, 5x4.05  OS: -12mm BS 4.03”

Understanding these numbers is easy and will allow you to determine if a particular wheel will fit on your vehicle.

bolt patternTypical bolt patterns The first set of numbers (15x8) is the wheel’s physical size in inches, listed diameter first and depth last. So in this case the wheel is 15 inches in diameter and 8 inches deep, front to back.

The next set of numbers (5x4.05) indicates the bolt pattern – the positioning and spacing of the lug nut bolts. The first figure is the number of  individual lug nut studs (5) and the second figure gives the size of the circle the arrangement of studs makes. 4.05 would be a 4.05 inch diameter circle.

Bolt patterns can also be in millimeters; 5x102. The third figure (OS: -12mm) refers to the wheel’s offset. The offset is the distance from the wheel’s hub mounting point to the wheel’s centerline, which will be either a positive offset, negative offset, or zero offset.

A figure with a minus sign before it indicates a negative offset, meaning the hub mount is closer to the inside edge (the brake pad side) of the wheel. The spokes of these wheels are recessed deeper within the wheel when viewed from the outside and are often referred to as ‘deep dish’ wheels.

A positive figure indicates a positive offset and the hub mount will be closer to the outside edge (the road side) of the wheel, giving a flatter profile when viewed from the outside.

wheel diagramAn alloy wheel’s specs explained The figure 0 indicates a zero offset wheel. The hub mount that is in line with the wheel’s centerline and has a traditional or ‘neutral’ appearance when fitted to a vehicle.

The fourth and final  figure (BS 4.09”) is the backspace, which is the distance from the hub mounting surface to the inside or inboard edge of the wheel. It can be given in either inches or millimeters.

From these simple figures you can determine whether those new rims you’re lusting after will fit your vehicle or not. Making Sure a Wheel Will Fit A wheel with a large positive offset will sit deeper within the wheel well and may cause the tire to foul on the inner wheel well wall. Conversely a wheel with a lot of negative offset might protrude too far out and rub upon the outer wheel arch.

Use the offset and backspace figures to measure and see if your dream wheels will sit too far in, too far out, or just right. If they are going to hit the inner wheel well wall you can get a spacer to compensate for that, and if they are too wide then fender flares might remedy the problem.

wheel offsetPositive, zero and negative wheel offsets The bolt pattern is often the stumbling block when buying new rims. A 4-stud hub is never going to work with a 5-hole wheel, and if the diameter and spacing of the studs don’t correctly line up it won’t fit either. However, a bolt pattern adapter can adapt a vehicle’s existing hub arrangement to accept the shiny new rims you’ve set your heart on.

Lastly, double check that your dream wheels will fit over your vehicle’s axles. Most aftermarket wheel manufacturers make the central hole sufficiently wide in the knowledge that their wheels will be fitted to a variety of trucks, 4x4s and cars, but it doesn’t hurt to check before you buy. Once again, if it looks like there might be a size issue, spacers and adapters can usually be employed to sort things out.

By John Bone
Posted on August 26th, 2013

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