So you think you’d like to put a large set of wheels on your ride and you want to know what you’re getting into. Sure they look good, but how practical are they? There are lots of opinions on the matter and lots of industry data as well. This article touches on the big differences between smaller factory wheels and larger aftermarket wheels.
There are two different approaches with larger wheels. The first is standard plus sizing. This is where the diameter of the wheel increases and the meat on the tire decreases. The overall diameter of the wheel tire combo stays the same as factory sizing. The second approach involves increasing or decreasing the overall diameter of the wheel tire combo. When you do this, it changes the physics of multiple components throughout the entire vehicle. At this point, you can expect more dramatic performance differences. We will cover those a little later.
Plus Sizing and Overall Diameter Change
For this article we’re going to focus on cars, trucks and SUVs that can support wheels of at least 20″ diameter. Why? Because Diablo does big. Our wheels go from the realistically sized 20s to eye popping ginormous 32s. If you want to know the impacts of going from 15s to 16s, then you drive a Prius and Diablo might not be right for you.
Standard plus sizing is the most common form of wheel swapping. Let’s say your Camaro came with 19″ factory OEM wheels. The different factory makes that year have 18″, 19″ or 20″ wheels. You’re right there in the middle of factory standards and want to know how going to 20s or 22s will affect things. Most of the statistical data you’ll find on performance will be based on factory fitments. Data for larger wheels needs to be found in independent studies or drawn from comparisons in other tests.
Almost everything can be figured by the sidewall left on the tires. Every inch added to the wheel diameter takes half an inch of meat off of the sidewall of the tire. Several things are affected by this reduction. This includes weight, stability, braking, gas usage, noise levels, smoothness of ride, surface grip and durability.
All are important subjects, but not all will be super important to you. With everything there are tradeoffs. If you’re in a muscle car, you don’t park in the electric car spot and you don’t care. You do probably care how fast you can move through corners and how fast you can get off the line. Well this is what standard plus sizing means to you.
Wheel Size Factors
So what goes into deciding to get bigger wheels? First and foremost is the subjective. Larger wheel diameters just look better. This is how your ride struts versus blends in. Visual appeal is the first thing all opponents to larger wheels dismiss because it’s the 100% true factor that they can’t discount. They will always downplay the subjective though. These are the same guys that insist tofu is just as good as steak or that it’s not the size that matters, but how you use it. Mmmhmm…
Fine. They can stand there in their Jesus sandals with socks and tell you looks don’t matter. They say it’s all about how it affects your gas to performance ratio. So let’s move on to the tangible and talk about weight, braking and gas usage. Larger wheels weigh more than smaller ones. The bigger the diameter the more weight added. This is no surprise. The more weight you carry around, the more gas you’re going to burn. It takes more energy to move more weight. Heavier objects in motion take more opposing force to stop. All of this is true. Anyone who’s been to the gym knows this.
Take two cars with different wheel diameter but otherwise exactly the same specs and place them side by side. The one with larger wheels will start and stop slower while burning more gas. This is true, but how true? When accelerating or slowing down, you need to move the mass as a whole. Your car weighs thousands of pounds. The weight of the wheels is important, but they are only one of many factors. Typically the difference between a set of 19s and 20s is between 20 and 40 pounds total. Ten gallons of gasoline weights about 60 pounds. Big Moe who usually rides shotgun tips the scales at 275. Do you notice the acceleration, braking or gas efficiency when you’re rolling with an almost empty tank or Big Moe is chilling at home? The differences are there, but unless you are dragging for pink slips, they are no different than carting home some groceries.
How about stability and surface grip? The height of sidewalls on your tires determine much of your driving experience. The taller the sidewall, the ‘spongier’ your ride. Your side to side drift on corners decreases when you have larger wheels and smaller sidewalls. That is because there is less give in the sidewall as the vehicle mass pulls out of the turn via centrifugal force. The tires grip the road as your car pulls out and away.
When you accelerate, brake or turn, the more of the tire’s surface that makes contact with the ground the better. This is how force is distributed from your ride to the road. While this is the tire’s job, the wheel size has a direct relationship with the tire’s structure. As wheel and tire width increases the surface area increases. This gives more grip area. For performance vehicles, this is key. The give in the sidewall impacts the force on the edges of the surface. So the diameter of the wheel affects the grip as well. Studies vary from tire to tire, but in general the more rubber you put on the road, the more ability you have to accelerate, brake or turn.
Larger wheels with less meaty tires require more care. There is less padding between the vehicle and the road. You will ‘float’ more with taller sidewalls. This gives more impact resistance which translates into a smoother ride. Like your shocks, the rubber of the tires absorbs uneven surfaces and dissipates the displacement. This reduces both energy and noise. The more sidewall you take away, the less the tire can dissipate. Good springs and shocks will compensate for this, but where they can’t help is with extreme surface change. Plus sized wheels without a lot of tire do not like potholes. They are more subject to impacting the wheel. This can damage the wheel’s surface and in some cases even bend the wheel itself.
Another thing to consider is that when there is less meat on the side of the tire, the wheel’s lip tends to stick out farther than the rubber. This means that if you rub up against a curb, the wheel will scratch before the tire hits. You will grind the finish of your pristine wheels. That goes directly to driving skill, but it is not fun damaging your pride and joy. Ouch…
That is about it with standard plus sizing. So overall you will have a better looking, better handling, slightly heavier, less spongy ride. You will need to be less reckless with broken roads and potholes. That plus you should develop a small fear of curbs. If that all sounds fine to you, I say upsize. We spend a lot of time in our cars. They define you as much as the clothes we wear or the music we enjoy. Why not treat your ride to some individuality?
Beyond Factory Wheel-Tire Dimensions
At some point individuality becomes the most important factor. That’s when both the car and its wheels take on personalities of their own. Trucks with lift kits, slammed rides, or donks all change the physics of the factory settings for a vehicle. Everything mentioned above applies, but many other factors come into play.
Springs and shocks are altered for anything that changes the height of the vehicle. This impacts not only the way your car reacts to changes in the surface of the road, but also in the outward stability in turns. Trucks and jeeps often deal with this by widening the wheel base, but donks tend to be less stable on the curves. Force and gravity always win.
We love 32s, but they truly are massive. When you add that much weight and mass, you are changing the base functionality of your ride. First off it is almost guaranteed that you will need to physically alter the vehicle’s wheel wells to accommodate the size.
When you increase the outside diameter of the wheel-tire combo, you change the ratio with the relationship between how many times the tire has to rotate to cover a distance. Basically bigger diameters spin fewer times than smaller ones to cover the same distance. That means the odometer on your car needs to be adjusted for the larger set.
The mass will also make it harder to stop. Earlier we talked about the difference between 19s and 20s. The difference between 20s and 32s is between 50 to 60 lbs per wheel. It also changes the weight distribution of the car by elevating the main mass. This multiplies the demands on the brakes because it moves the heavy elements away from the axels.
So why alter your ride to these extremes? Because individuality and the ability to alter things are always necessary. We need outlets for creativity and the automobile industry is an excellent place to express ourselves. Sure you have to be careful when you drive a mustang on 30s. You wouldn’t expect anything else. There will be hundreds of people talking about how crazy your ride is and how slow it must stop. Grumpy bastards will talk about the extra gas you burn. Haters will say that you tricked out a beauty. The reality is, they all paused and took note. With millions of cars on the road, only a handful cause that to happen on a regular basis. That is why we do it. We demand to be expressive and unique.
Weight, mass, and handling are all conditions. If you are aware of them and willing to accept the impacts they make on your driving experience, you get the one thing that all haters can’t dispute. You win the subjective battle and prove once and for all that bigger is better.