Wheels & Tires 101
Choosing a high-performance wheel and tire combination can be simple. For the wheels, select a style, color and finish that suit your taste; for tires, you can simply purchase a size that fits. The main consideration in this scenario is to purchase a combination that you can afford. However, selecting the best wheel and tire combination for your needs takes a little more effort. Your entire car is a system where no component can be added without having an effect on the other components. Knowing what to look for in a wheel and tire combination can go a long way toward maximizing the full potential of your system.
There are several advantages to using a lightweight performance wheel. One of the major advantages is improved acceleration and braking thanks to reduced rotational inertia. Rotational inertia is defined as the resistance to change in the rate of rotation. It is a function of a rotating object’s rotational speed and mass, as well as the specific distribution of mass in the rotational object. So, with all other elements in the function being equal, a lighter wheel (one with less mass) will have a lower rotational inertia. For example, there is a specific amount of energy required to turn a 20-pound wheel from a dead stop, and another amount of energy (braking force) to bring that wheel turning at 50 MPH back to a dead stop. If that same wheel design had a weight of just 15 pounds, it would require less energy to bring that wheel to speed from a dead stop and less braking force to slow it down. This lowered effort in accelerating and decelerating is due to the lower rotational inertia present in the similarly designed 15-pound wheel.
In addition to overall weight, the specific design of the wheel also affects its rotational inertia. Wheel designs where most of the wheel’s weight is closer to the center of the wheel will have a lower rotational inertia than those with more mass on the outer edges or the barrel section. Hence, not all 15-pound wheels have the same rotational inertia.
The unsprung weight of a lighter wheel also benefits the vehicle’s suspension system. As the system compresses to handle road or track irregularities, the lighter wheel transfers less kinetic energy to the suspension components. This allows the suspension to react faster to the bumps and dips, keeping more of the tire’s contact patch on the ground. The lower amount of kinetic energy transferred also allows for a “softer” spring, shock or shock valve setting, resulting in a smoother ride on the street.
Wheel rigidity is sometimes considered more important than overall lightness by performance suspension tuners. Unwanted wheel flex under hard-driving conditions can upset finely tuned suspension settings, affecting the car’s handling and grip. The end result could be slower lap times. The problem is exaggerated even further when sticky compound tires are used in these conditions.
The two most common methods of wheel manufacturing are casting and forging. Most OEM wheels are cast since they are easier and less costly to produce. There are two major types of casting (gravity and low/high pressure) that are most commonly used. Gravity-cast wheels are made from molds in which molten aluminum is simply poured in. Without pressure, the chance for the molten liquid to form air pockets is increased, resulting in a casting that may contain voids (areas inside the wheel where no alloy is present.) As additional material needs to be added to increase strength requirements, gravity-cast wheels often weigh more than wheels cast with a low/high pressure method. With regards to RAYS, their manufacturing process takes traditional casting to higher levels, adding in robotically controlled pouring machines, using varying angles to pour, which reduces potential air pockets. RAYS molds are high-tech and are cooled internally, further reducing air pockets simultaneously by precisely controlling the temperature of the setting molten aluminum.
In the low/high pressure method the molten aluminum is forced into the mold with applied pressure. This method increases the density of the aluminum and decreases the likeliness of the occurrence of voids in the metal. As a result, the finished wheel is able to meet or exceed strength requirements without using as much material, keeping the weight lower than a similarly designed, gravity-cast wheel. Some manufacturers use different casting techniques that allow them to design stronger wheels that still retain a low weight. Expect to pay a premium for these special and often proprietary casting techniques, but expect to get more in terms of performance.
The wheel forging process involves, essentially, squeezing a billet into the shape of the desired wheel. The high pressure and heat applied to the billet material changes its internal structure, creating a more compact and dense material with a superior grain flow. In the case of a RAYS forged wheel, their forged wheel manufacturing process involves the highest class of forging: Mold Forging, also known as Net Forging where sets of molds and dies are used simultaneously to add pressure to the top and bottom of the wheel while elongating the rim section into one seamless process. This type of 3D forging is patented by RAYS and gives the wheel a superior grain flow compared to other forged wheels. Because of this process, the enthusiast who chooses to use these wheels on their vehicle will gain the ultimate combination of lightweight, durability and stiffness, which leads to maximum performance and safety.
DIFFERENCES IN WHEEL MANUFACTURING
FORGED: produces the strongest wheels; forged monoblock designs are usually the lightest; sometimes available as multi-piece design; the best track/competition wheels available; most costly manufacturing process
FLOW FORMED: good wheel strength; reasonably lightweight, slightly heavier than forged; sometimes available as multi-piece design; good for street/track; modest manufacturing cost
GRAVITY CAST: least durable process; often heaviest; sometimes available as multi-piece design; not recommended for racing/competition; least expensive to manufacture
One, Two or Three Piece?
Multi-piece wheels separate the manufacturing of the wheel face and barrel into separate structures (two or three pieces) in order to offer a wider range of offsets, diameters and widths for a particular design. This is beneficial for the purpose-built project, but adds nothing but “style” points to a vehicle that uses a standard width and offset and spends most of its time on public highways. For racing, a multi-piece wheel is another tool in the builder’s arsenal to further tune the suspension and chassis components to exacting parameters.
You now know enough about wheel design and construction to make an educated choice, based on where and how you will be using your vehicle. The next step is to choose a set of performance tires that will allow you to maximize the potential of your vehicle once they’re mounted to your wheel choice.
From Molten Metal To Burning Rubber
Knowing how you will use your vehicle will determine the type of tires you have mounted onto your wheel selection. The Federal Government has implemented a series of tire performance ratings to help consumers understand how they should expect a particular tire to perform. Under the Uniform Tire Quality Grading (UTQG) standards, tires are assigned values in three categories that attempt to indicate treadwear, traction rating and temperature rating of a particular tire.
Treadwear relates to how long the tire treads will last. A tire with a treadwear of 200 should last twice as long as a tire with a treadwear of 100. Keep in mind, however, that this rating is based on testing in a controlled environment and does not necessarily demonstrate real world performance. Expect spirited driving and hard launches to reduce the estimated life of the tread. Also, it’s important to note that some manufacturers underrate their tires for marketing purposes. A lower treadwear rating tends to add to a tire’s performance credentials; softer, stickier compounds tend to wear faster than hard, less-grippy ones. This underrating helps in marketing the tire as a performance tire, although it may not necessarily be factual for comparison purposes. When researching your high-performance tire, remember that some racing series designate classes based on the tire treadwear rating.
The UTQG traction rating also addresses the wet traction capabilities of a tire. Testing for this consists of straight-line deceleration, so the performance enthusiast who expects to use this number as a determination for acceleration and turning traction is easily misled. Likewise, the temperature ratings found on a tire’s sidewall are not very informative. In these tests, the tire is inflated to spec and subject to load. The tires are then tested for a minimum ability to accept heat from friction (extended use and/or loading) before showing a functional loss or destruction of the tire. Minimally pass g tires are graded with a C, while those that exceed certain levels of federal standards receive B’s and A’s respectively.
The speed rating is probably more important and pertinent to the racing enthusiast rather than the street-only tire and wheel buyer. Letters are assigned to specific speeds, which correlate to the highest sustainable speed possible with the tire in question. US street-only enthusiasts are subject to a maximum federal speed limit of 70 MPH, but tire manufacturers print these numbers anyway to aid performance- minded drivers in their tire selection.
The Numbers Game
Deciphering the format of the alphanumeric soup on a tire’s sidewall is relatively easy. Aside from the manufacturer or federally mandated ratings (treadwear, traction, and the like), the tire’s size will also be printed in a form similar to this: 205/45ZR16. In this example, the first number is the section width (in millimeters) of the tire. Our sample shows a 205mm wide tire. The second number, 45, refers to the height of the sidewall as a percentage of the width. So, the sidewall on this tire is 45 percent of 205mm, or 92.25mm, tall. The first letter in the last combination of the tire indicator denotes the tire’s speed rating (Z-rated for 149 MPH continuous operation) while the second indicates that it’s a radial construction tire. The last number, in our sample, 16, refers to the mounting diameter; this is what you’ll answer when someone asks what size wheels you have.
All of the choices you make in your selection of wheel style, diameter and offset, as well as the tire dimensions and compound you select, are going to have an effect on your vehicle’s chassis dynamics, whether you want them to or not. For example, a sticky tire compound will increase the chances of wheel flex, which can affect your suspension alignment settings under standard conditions, essentially contributing to slower laps or elapsed times. Similarly, that same sticky tire mated to a wheel with a design that promotes or enhances brake system cooling may save you from having to switch to larger brakes.
Choosing the right tires isn’t as daunting as it might seem. With an understanding of the difference between tire models and their intended purpose, you’ll be lapping the track or making trips down the strip in short order.
TIRE HEIGHT CALCULATION
Section Width (mm) x Aspect Ratio + Rim Diameter (in) = Overall Tire Height in) 1270
TOTAL SIDEWALL CALCULATION
Overall Tire Height (in) – Rim Diameter (in) = Total Sidewall (in)
PLUS SIDEWALL CALCULATION
Total Sidewall (in) – Rim Diameter Increase (in) = Plus Sidewall (in)
PLUS TIRE SIZING CALCULATOR
PLUS Sidewall (in) x 1270 = New Section Width (mm) New Aspect Ratio
*Choose a New Aspect Ratio that is lower than original
RAYS WHEELS BUYER’S GUIDE
RAYS Variance Versus V.V.10S
Colors: Black Machined, Bicologrigio
Includes: Variance center cap, RAYS valve stem, long adapter
Sizes: 19x8, 19x9 (various offsets); 20x8.5, 20x9.5 (various offsets)
Volk Racing G27
Color: Pressed Black Clear
Includes: G27 center cap, metal valve stem
Sizes: 19x8.5, 19x9.5, 19x10.5 (various offsets); 20x8.5, 20x9.5, 20x10.5 (various offsets)
Volk Racing G50
Colors: Dark Purple Gunmetal, Prism Dark Silver
Includes: G50 center cap, metal valve stem
Sizes: 19x8, 19x8.5, 19x9.5, 19x10.5 (various offsets)
For pricing and more info, contact: Mackin Industries, 562/946-6820, mackinindustries.com
(Story: Aidan Spraic and Arnold Eugenio)
(Photos: Courtesy of DSPORT staff, and by Danny Nguyen/JDMZipties)
A Little More About This R35 GT-R…
You can find Jimmy Yang’s GT-R most often at two of Southern California’s elite shops: Signature Autobody, where precision care is given to making vehicles look their best, or Evasive Motorsports, the masters of tuning, aero and track development for street and race cars. At the time of shooting, the VR38DETT had been modified slightly with a few parts from COBB Tuning (downpipes and an intake), HKS (mid-pipe) and a GReddy exhaust but have been upgraded further with a HKS GT570 racing package—altogether this is now producing 740hp with 660lb-ft of torque to the crank. Being a Signature demo car, the paint and aero are of the utmost highest quality, silky smooth and glossy, it’s almost easy to miss how great the paint condition is. The N-Tune and NISMO accents are really touches as well.
Alas, the GT-R is one of the greatest specimens to showcase one of Volk Racing’s most timeless—and popular—wheels: the TE37. However, this Nissan supercar is deserving of a more special version, the TE37 Ultra. This 20-inch variant has special U-shaped forged spokes, making it much stronger and lighter than a standard issue TE37. More over, the TE37 Ultra has a center hub featuring an overhang that’s carved out for weight reduction and additional rigidity; the Volk logo is also 3D-machined onto the spokes. On Jimmy’s GT-R, he only wanted the best, opting for a set in Hyper Red, the perfect color offset for this pure black monster. Here you get a picture perfect reason why Volk Racing is at the top of the game when it comes to premium wheels for both street and motorsport use.
(Story by Jonathan Wong; Photos by Danny Nguyen/JDMZipTies)
2009 NISSAN GT-R
Owner: Jimmy Yang
Hometown: Orange, CA
Occupation: Marketing Director, Signature Autobody
Engine: 3.8L VR38DETT; ’12 OEM turbo inlet pipes; COBB Tuning downpipes and Big SF intake system; Denso 265lph fuel pumps; GotBoost Flex Fuel kit; HKS resonated mid-pipe, actuators and spark plugs; GReddy Supreme Titanium 94mm exhaust
Engine Management: COBB Tuning Accessport with custom tune by Evasive Motorsports
Suspension: Swift Spec R springs
Wheels: 20x10" +30/20x12" +20 Volk Racing Hyper Red TE37 Ultra wheels; Project Kics R40 lug nuts
Exterior: N-Tune front bumper, front carbon fiber lower diffuser and carbon fiber side skirts; 2012 DBA rear conversion; OEM NISMO red accent kit; 2015 OEM headlights, taillights and fender grills
Interior: Zerek Fabrication roll bar; GT-R Black Edition headliner; Specialized Performance LED interior
Special Thanks: Evasive Motorsports, Signature Autobody, Dr. Mobile Detailing