Offset: The Art of the Flush and Functional
Wheel offset seems to be one of those things that you either pick up immediately or are baffled by from the get-go when you’re looking at purchasing a brand new set of wheels. Whether you’re looking for a set of Wheels for a BMW or Wheels for a Scion FR-S, Offset is critical to the fitment of your wheels, and unfortunately, many people don’t even bother to pay attention to this very important measurement when they make their wheel purchases.
The truth is, offset can make or break both the fitment and stance of your car. Whether you’re seeking a conservatively fitted daily driver or a hellaflush hardparked show car, offset is the ultimate master over whether or not you will be able to tuck those wheels and tires into your fenderwells. Unsure of what offset is or what it does? Don’t worry, we’re here to help you realize that offset isn’t really as intimidating as it may seem… if you pay close attention to the information below.
So What Is It?
Okay, so your first question may be: What the heck is offset anyway? And why does it matter? To make the concept as simple as possible, imagine that you’ve got a wheel in front of you. The barrel of the wheel is the dish or cylinder that sits around the face of the wheel. A zero offset wheel would have the contact surface (the part of the rear of the face that makes contact with your hub) perfectly centered in the middle of the barrel.
For example, on a 10 inch wide wheel this centerline would be at the 5 inch mark on the barrel. So when you are shopping around for a new set of shiny round things, if you see ET0 next to the measurements, that means the back of the faces of the wheels are literally 0 millimeters away from the center of the barrel. But that is only the first step to understanding the sneaky ways of the offset measurement.
Offsets can come in both positive and negative numbers. When an offset number is positive (PAY CLOSE ATTENTION TO THIS. IF YOU DON’T REMEMBER THESE RULES, YOUR WHEEL SAAVY FRIENDS MAY LAUGH AT YOU.), it means that the contact point on the back of the face is moved forward to the OUTSIDE of the wheel. So if the wheel was on the car and you looked at it from the side, the face would be closer towards your direction on the barrel than the inside of the barrel.
This ultimately would bring the entire width of the rim (and tire) closer into the inside of the car because of the hub having to move further into the wheel to mount it. Compared to a zero offset wheel of the same width, a wheel with positive offset would be considered having more conservative fitment because of being more “sucked inside” the wheel wells.
When an offset number is negative, the story is exactly the opposite. The contact point of the face is located behind, or toward the inner side, of the barrel’s centerline. Having a negative offset on any width wheel is generally considered a very aggressive offset. This is so because of the more inward location of the contact point causing the wheel as a whole to poke more outward than a zero offset wheel of the same width would. This gives your car a much wider stance and fills the wheel well gaps a little more nicely than a positive offset wheel would. Negative offset wheels are generally used for sports car or widebody applications because of their bulging fenders and wide track. But there are dangers involved if you want to go too aggressive or conservative with the fitment of your vehicle’s wheels and tires.
Limitations to Offset: To Alter or Not to Alter
There are limits to having high positive or low negative offsets. You can’t just slap on the most aggressive wheels you can find onto your ride without thinking about what that can do to your fitment. For example, let’s say you have a car that can fit 8 inch wide wheels that are between +30 and +50 offset safely in the wells without causing any side effects or major changes in ride quality. If you decide that you want to get a bunch of grip but keep a relatively stock looking stance, you would go with a wheel that is a bit wider than stock (Say 9 inches wide) with an offset more close to the +50 side (but not exactly +50 because you have to account for the extra inch in width you have gained = +25.4mm, or +12.2mm on each side of the wheel) of your car’s fitment spectrum. But what if you get a wheel that is too wide? Or what if you get a wheel with an offset higher than +50? Well then you start to go into the danger zone.
There is a problem with getting a wheel that is too wide and has too high of an offset for your specific car. Since the wheel gets more and more sucked into the wells as the offset gets higher, you will start to experience rubbing on the inside of the tire. Inside rub is a much worse problem to have than outside rub because of how limited your options are to correct or alter your car to fit the wheels you have chosen. You can have a professional installer air hammer the inside of your wheel well to free up more space. You can also buy the recommended spacers for your specific car, wheel width and offset to push the whole wheel out a bit more and avoid tearing up the inner part of your tire and wheel well/components (electrical, fuel/brake lines, etc.). Just make sure you are very careful and precise with accounting for width changes and offset before you buy your wheels because some positive offsets simply cannot fit because of brake clearance or wheel well size.
Now say you go on a forum. You see this drool-worthy car that is running a wheel setup that is wider and more aggressive than belief. You look at the wheel specs and see they are 20 inches in diameter, 13 inches wide, and -2,000,000 offset… well maybe a LITTLE less aggressive than that. But anyway, you want the exact look that the car has so you decide to buy those exact wheels. STOP RIGHT THERE! No no no… no no no…………. no no. Don’t you click that Add to Cart button yet! You’ve got to understand that running a super aggressive setup requires a lot of work – and compromises in other areas. I know you want to fulfill your 2-lane wide sports car dreams, but you haven’t taken into account how much work and trial-and-error that person has gone through to make those wheels fit in just the perfect way. Now would be a good time to decide whether or not you really have the stomach (and the financial wearwithall) for the amount of effort you need to fit these wheels safely and reliably. For example, check out our write-up on what it takes to run super-aggressive Forgestar F14 Super Deep Concaves on a E92 BMW 335i.
Earlier we mentioned that negative offset moves the face of the wheel closer to the inside of the wheel well, therefore pushing the entire wheel’s width out of the car. If you get a wheel with an offset that is too negative for your car, prepare yourself for some careful and precise work. If the lip of your wheel starts to poke out of the fenders, depending on your fitment preferences, you may want to roll and stretch your fenders to compensate for the possible fender scrapeage you will get from the travel of your suspension. Do you want scraping? Absolutely not! It can damage both your wheels and your fenders- a sharp metal fender will slice right through a spinning tire’s sidewall like a hot knife through butter.
So what is fender rolling and stretching, and why would you do it? Well, you can get the whole story on Fender Rolling here, but here’s the reader’s digest version: Rolling a fender can involve a couple things. Did you ever notice that there is a bit of an overhang of fender material when you look into the wheel wells of your car? Well with more aggressive fitments, your wheel and tire setup tends to hit this material when you hit things like bumps and potholes… especially when your car is lowered (P.S. Ride height is also a HUGE factor in the way your wheels and tires fit into the wells, but I will go over that further into this article). Rolling a fender is when you bend that overhang up into the backside of the fender in order to prevent that bumping. On certain cars, the same thing is done on the circumference of your wheel well because of other miscellaneous metal strips poking out enough to cause fitment obstruction. But sometimes rolling by itself is not enough.
The more negative the offset, the more alterations you have to do to get the fitment you want. This is where fender pulling comes in. Pulling a fender is an art in itself. It’s when the edge of a fender is pulled out a specific length to snugly tuck your tire under the fender and prevent rubbing. The reason most people are scared to pull fenders is because of the fear of pulling unevenly on all four corners of the vehicle and ruining the look of their fitment and symmetry. That is why I recommend going to a professional fender puller if you want the best and cleanest results.
Camber: Making Impossibly Wide Setups Possible
So you got some aggressive wheels, rolled and pulled your fenders. Now what? Camber is what. Without camber (the tilting of your wheel on a horizontal axis parallel to the side of the car that is located where the ground and the tire meet), rolling and pulling your fenders is useless. Since your fenders will be coming out at a slant, a tire and wheel setup with 0 degrees of camber will still rub during bumps or potholes. That is why you must apply a negative tilt (one that directs the top of the tire more inward) in order to prevent rubbing and a large part of your tire from poking out at the top of your fender.
This can be achieved through multiple methods of camber adjustment. The first, and probably most simple, is buying a set of coilovers that are fully adjustable and come with camber plates. Camber plates are pretty much adjustable slots that are moved inward and outward to change the camber of your wheel and tire setup. These slots are located at the top of your shock tower where the coilovers are bolted to the wheel well tubs.
But there are limitations to camber plates. They only allow for a small amount of camber adjustment. So if your wheels are only poking out from the stretched fenders a little bit, camber plates may be the only thing you need to achieve that flush fitment. But if you’re going for a setup that needs some major camber (i.e. hovercraft fitment), you’re probably going to need some adjustable control arms to really scoot the bottoms and tops of those soon-to-be sideways wheels. Keep in mind, the wider the setup you’re going for, the more camber adjusting parts you will need. But some people don’t like to see a good majority of their tread pattern sticking out from the fender in plain sight, and camber can also cause some very costly tire wear because of all the weight of the car being burdened onto a smaller patch of contact surface with the ground. So what do you do to get nearly straight up and down fitment but still use tires and wheels wide enough to put F1 cars to shame? Read on my brothers and sisters in fitment, read on!
You No Want the Tilty? Widebody It!
So you’ve come to the conclusion that you want a functional wide setup, not a cambered out show car. Well there are a few options that can provide you with an aggressive stance and very high track performance potential.
The first is fender flares, a sort of bolt-on mini fender system you can add to your existing fenders to create a new, wider edge for your tires and wheels to flush up to. The great thing about fender flares is that they are very cheap and don’t take much time and effort to install. You can either rivet them right on or smooth them out with bondo and match them to your paint for a cleaner look. Some more extreme (and expensive) examples of fender flares would be the Rocket Bunny Widebody kit for the Scion FR-S. With more aggressive fender flares, like the Rocket Bunny ones, there will be some cutting of the OEM fenders involved (I know, so sad!). But the extra clearance and width will definitely allow you to run super low offsets on your wheels and still maintain a track-ready stance.
The second option, if you want a more smooth look, is overfenders. These are wider fenders that completely cover and mold over your OEM fenders. There will definitely be some bondo and smoothing work to do with a complete overfender system to get the look you desire. The advantage of this type of system is that the fender still looks like it is one piece, and you can typically get much wider fenders than if you would have installed fender flares.
The third method to getting an unearthly amount of width and race-ready stance is the full replacement widebody system. This is when you completely replace the OEM fenders (and sometimes bumpers) of your ride with some more bulgy, sexy and functional curves while. Some also come with sideskirts to match. A WIDEBODY KIT IS THE ULTIMATE IN AGGRESSIVE LOOKS AND TRACK PERFORMANCE. This step in wheel fitment and track width is what makes everyone on the side of the road/track drool with envy. You know why? Because it looks absolutely spectacular! And there are so many benefits to a full replacement widebody. It cuts down installation time and difficulty compared to overfenders (but yes, you still may have to cut and sand to get that perfect fit). It allows for the widest and most sturdy fenders and bumpers in the industry. And you don’t have to live with the guilt of hurting your baby’s OEM fenders. You get wider. You get grippier. You get faster. It’s as simple as that!
Where Do I Find Wheels That Dang Wide?
Sometimes it can be hard to find a way to get wheels with low enough offsets to flush up to the mile wide fenders of your widebody. Wheel companies like Forgestar, HRE, BC Forged, SSR and Volk offer completely custom forged and cast wheels that will be wide enough for most widebodies. But what if you don’t want to spend that much for tires or even the wheels themselves?
Well to save on both, you can get spacers to compensate for that missing width in your setup. It may just be my personal opinion, but every time I hear the words spacers and widebody together, it kind of makes me die a little inside.
Spacers, being the pieces of metal that they are, are usually not perfectly in balance when you receive them and can be the weak point of your unsprung mass, especially on a widebodied car. If you are going to spend the money to get a widebody, I suggest that you don’t cheap out on your unsprung setup. If your spacer cracks or, God forbid, breaks, your wheel can fly right off and do significant damage to you and your car. We don’t want that do we? That is why you should run a longer control arm and axle setup if you are going to be running skinnier tires and wheels on a widebody. It may be more expensive in the short run, but at least you won’t have runaway wheels on the track when you’re hammering it in the corners. It’s also why ModBargains only offers high quality spacers manufactured by H&R. You can read our whole writeup on Spacers in detail here.
Ride Height: Will it Fit or Will it Function?
With all of the suspension technologies coming out today (fully adjustable coilovers, airbags, air cups, etc.), it is becoming easier and easier to fit your wheel and tire setup. Yes, if you are a show car person, fitment will be the only thing you are concerned about. But others will need to know what height their car needs to be at to avoid rubbing during turning and the compression of their shocks. Honestly, the only way to really know is to experiment. Adjust your coilovers or air system increments at a time while driving your car as you normally would over bumps and through turns. If it rubs, you can either raise it a little and try again, or you can make alterations to your car to have a functional setup at the ride height you want.
Fitment Alterations Continued
This can include fender rolling and pulling, air hammering the wells (like I stated above) or even completely replacing the fender wells with custom deeper ones. The possibilities are endless with fitment actually. If someone is determined enough to tuck 6 inches of their 20’s in the back wells, there is definitely the possibility of getting a functional setup. They can change camber and caster settings, ride height, choose a more conservative offset, get a lower wheel width, widebody the car and many many other things. As you can see, just about anything is possible with fitment; you just have to know how much money you want to spend and what your vision of perfect fitment is for your car.
So yeah, this was supposed to be an article discussing offset. I kind of went on a long tangent there, but it was a necessary tangent I promise! Offset may be a simple measurement (the distance in millimeters of a wheel’s contact surface on the back side of the face from the centerline of the wheel), but it affects so many things and can save you a huge headache in the future. If you pick the right offset wheel now, you won’t have to worry about extensive alterations later.
When you know exactly what the end goal is for your vehicle’s fitment, that is the perfect time to pick the offset of your wheels. With the knowledge of fender widths, hub location, wheel well clearance and other measurements on your vehicle in its finished state, you will be able to accurately order the right offsets and prevent too many complications in the future. Of course there will be alterations needed for more extreme fitments, but it is well worth it when you get to step back after all your hard work and see the dream car you’ve been waiting for this whole time. Fitment isn’t just how well your wheels fit your car, it’s a process that makes your car unique and satisfies every car enthusiast’s inner perfectionist.
ModBargains is the perfect place to go for advice and making an order for your new set of wheels. If you don’t know what offset you need, our Experienced Modification Experts are ready to help out. We have the tools and knowledge to get you the exact fit you want. So if you’re interested in any of our wheel brands or have any sort of questions regarding sizing, give ModBargains a call at 714-582-3330. Happy wheel hunting!