Why Does Wheel Size Matter?

March 18, 2021

 

When it comes to picking out a set of wheels there are many more things to consider than just how they look! Today we are giving you guys the formula on how to get the perfect size wheel the first time. Get the most out of your wheels and make sure they fit!

 

WHEEL / TIRE PACKAGES

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Table of Contents

  1. Diameter

  2. What is Offset?

  3. Backspacing

  4. Inside Diameter of the Barrel

  5. The Overall Width

  6. Section Width

  7. Center Hub Bore Size

 

Wheels

 

Diameter

 

The majority of us, who use our vehicles for more practicality and functionality over form, especially for off-road purposes, are going to stay in that seventeen to twenty-inch wheel diameter size range. Some still prefer the fifteen or sixteen-inch sizes because they are cheaper or they already have tires for that wheel size. These smaller wheel sizes allow for more tire sidewall which is more useful and safer off-road. 

 

Off-Road Wheels

 

A good rule of thumb is to not go any smaller in the wheel diameter than what your rig came with from the factory as you might run into clearance issues with the wheel not fitting over the brake caliper or even possibly the tie-rod ends.

As you get larger with your wheels and tires keep in mind that they will get more expensive. 

 

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Rims

 

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What is Offset?

 

Another important measurement is your wheel offset. The offset of a wheel is the distance, measured in millimeters, from the wheel hub mounting surface to the centerline of the wheel and will be one of three different measurements. 

Zero offset means that the wheel mounting surface lines up exactly with the center of the wheel itself. 

 

Wheel Offset

 

Having a positive offset will tuck in your wheels and tires more towards the frame of the vehicle and are more commonly found on passenger cars, crossovers, and SUVs. 

Having a negative offset will push your wheel and tire out away from the vehicle giving you a wider stance or more poke of your tire. Negative offset pushes out and positive offset sucks them in. 

 

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Offset

 

It is important to know what your factory offset is before purchasing your next set of wheels.  The best way to find out what your factory wheel’s offset is by removing the wheel from your vehicle and searching the backside of one of the wheel’s spokes for the E.T. number. 

 

ET Number

 

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Backspacing

 

Backspacing is easily measured with the front of the wheel facing down and is the measurement from the hub, or wheel mounting surface, to the inner flange of the wheel where the tire bead sits. To measure the backspacing, take a straight edge and lay it across the inner flange on the back of the wheel, then take a tape measure or ruler and place it flat on the wheel mounting surface and measure to the straight edge and that will give you your backspacing measurement. 

The lower the backspacing measurement is the more your wheel and tire is going to be pushed out away from the vehicle and away from your steering and suspension components as well. 

 

Backspacing

 

This is especially important when increasing the size of your tires and upgrading your steering to larger components. When turning sharp, or from full steering lock to steering lock, larger diameter tires will be much more likely to hit on your inner wheel wells, frame, leaf-springs if you have them upfront, and even your shocks if you are flexing out your suspension, they’ll end up hitting the upper part of the shock unless they are inboarded far enough.

 

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Wheel

 

But, also keep in mind that the more your wheels and tires are pushed out, the more negatively it will affect your on-road handling and performance, and the more wear and tear it will put on your driveline components like your ball joints and wheel bearings.

 

Rim

 

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Inside Diameter of the Barrel

 

What is the barrel of a wheel? The Barrel is the overall round structural component of the wheel and is this part of the wheel between the outboard face and inboard rim edge. The barrel is shaped to create the tire mounting surfaces such as the drop center and the rim flanges. When the tire is mounted, the outer surface of the barrel closes off the open end of the tire, enabling the tire to hold pressure.

 

Aftermarket Wheels

 

Even if the overall diameter of the wheel and the barrel consists of more mass and is thicker than your vehicle’s factory wheel is, this can cause the inner diameter of the barrel to be smaller in circumference and may not allow the wheel to fit over the top of your brake caliper causing you to have to return your wheels.

 

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Wheels

 

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The Overall Width

 

A wheel has two different measurements for the width and the most commonly referred to number is what’s known as the Overall Width. This is the number that you’ll see when the width is listed alongside the diameter of the wheel. The overall width is measured from the outside of the rim on the backside to the outside of the rim of the wheel on the front side.

 

Wide Wheels

 

The rim is designed for the tire bead to sit up against to keep the tire bead in place and keep the air from wanting to escape and it also prevents the tire from being knocked off of its bead seat when being pressed or hit up against obstacles. Which, for practicality and safety reasons, selecting the right wheel width is also pretty important. 

 

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Wheels

 

A wheel that is too narrow and on some tires, the bead of the tire is going to interfere too much with the rim of the wheel and won’t allow the tire bead to seat properly, if the tire bead isn’t seating all the way then air will be able to pass under and around the bead, preventing it from being able to hold air.

 

Wheels

 

And if the wheel is too wide, then you’ll run a much greater chance at popping the tire bead off of the rim and the bead seat every time you air down as the natural physics of the tire is going to want to pull the tire beads together unless you’re running a super-wide tire that is proportionate with the wheel width. 

 

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Wheels

 

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Section Width


Then the other wheel width measurement is known as the section width or rim width. This is the measurement from the inside of the rim on one side to the inside of the rim on the other side. A narrow rim width can balloon the tire and create more of a donut-shaped tire contact patch and affect the traction.

 

Rims

 

A rim width that is too wide and now the center of the tire tread can become a bit concave and can also affect the traction performance. So it’s important to ensure that you’re matching the right size width of the wheel along with the proportional width of the tire to ensure you’re maximizing the performance of the tire both at street pressure and when aired down on the trails. 

 

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Wheels

 

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Center Hub Bore Size

 

And our last important measurement to know for proper wheel fitment is going to be the size of your hub. The hub bore in the middle of the wheel fits nice and snug over the hub if it is a hub-centric wheel, which the majority are. If not, and the hub bore of the wheel doesn’t fit over the hub on your vehicle, then you’ll have to go through the costly process of shipping the wheels back and all the time lost in doing that.

If the hub is smaller than the hub bore of the wheel, but you want a tight fit around the hub, then you can use hub-centric rings to fill in that hub void.

 

Rims

 

In most cases, having the center of the wheel fit tightly around the hub bore will help increase the overall stability of the wheel as it helps distribute some of the weight off of the lug nuts themselves and through the hub as well as in a severe-load situation or application can also help in preventing the wheel studs from getting sheared off and losing a wheel at highway speeds is something you definitely don’t want to have happen.

So make sure when selecting the perfect size wheel for your rig that you also keep in mind the hub measurement as well.

 

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Wheels

 

Something else to keep in mind is your bolt pattern. 

Check out our gallery for any fitment questions you may have. And be sure to add your own rig to the gallery

Like always, when you get a wheel and tire package, you will get free shipping, mounting, and balancing. We also offer as low as 0% APR financing for those who qualify do you can build now and pay later.

What wheels are you picking up? Let us know in the comments below!

 

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