Register Your Tires Warranty Understanding Your Tires FAQ Contact Us Customer Survey find a dealer Service Bulletins Tire Care Reading Your Tire Construction Customizing Tire and Rim Association (TRA) Yearbook >Performance Tire and To maintain consistency in specifying a tire's measurements, representatives of all Wheel Relationship major tire companies and most minor brands formed The Tire and Rim Association >Plus Sizing (TRA) in the United States. The TRA has established technical specifications that are >High Performance based on engineering principles and approved practices. Every year they publish the Wheels TRA Yearbook, which contains all TRA standards and related information approved >Aspect Ratio by the Association. These standards include: Calculator ● Tire Designations >Rim/Wheel Width ● Tire Load Ratings >Installation ● Dimensions Glossary ● Approved ● Rim Widths ● The Design Rim or Measuring Rim Standards for Metric tires are established through a similar association called the European Tire and Rim Technical Organization (ETRTO). The approved rim width range for each tire size has also been carefully selected by the TRA and ETRTO organizations. For example, the P255/50VR16 tire is approved to be mounted on wheels ranging from 6-1/2" to 10" (refer to pg. 44). Past experience and engineering practice has shown that wheel widths outside these ranges will stress the tire in a manner that may result in poor service and potential tire failure. It is important to note that there are some differences between P-Metric and Metric approved rim width ranges (in general, Metric tires have a slightly narrower range). The TRA also has developed a measuring rim for each tire size that enables all manufacturers to measure their tires on the same size wheel. For 50-series tires and higher, the measuring rim width is 70% of the tire's section width rounded off to the nearest 0.5." For example, a P255/50VR16 tire, which has a design section width of 10.04", is measured on a 7" wide wheel. Mid-Range Rim Widths Provide a balance between handling capabilities and ride quality. The wheel's width influences handling and ride quality. Always choose a rim width within the range of the tire's acceptable rim width specification. For tires that have an aspect ratio lower than a 50-series, the measuring rim is 85% of the tire's section design width. Therefore, a 255/40ZR17 tire with the same 10.04" section width would be measured on an 8.5" wide wheel. The measuring rims for Yokohama tires are listed with their dimensional data in this guide. As mentioned previously, the actual dimensions of a tire are dependent on the rim on which it is mounted. The dimension that changes the most is the tire's section width—a change of about 0.2" for every 0.5" change in rim width. For an A032R in the P255/50VR16 size, Yokohama's dimensional data indicates a section width of 10.2", an overall diameter of 26.0", and a tread width of 9.1" when mounted on a 7.0" wide wheel. While the tire size designation indicates that this is a 50-series tire, let's see how the tire's aspect ratio is calculated. A tire's aspect ratio is the relationship between its section height and section width. Since the section height is not provided, we must calculate it. Determine the section height. Subtract the rim diameter from the overall tire diameter and divide by 2 as shown in the following formula: (Overall Diameter - Rim Diameter) ÷ 2 = Section Height To determine the section height of a P255/50VR16 tire: Note: More than one dimension may vary with a change in rim width; however, the Yokohama tire dimensions listed in this guide are accurate for the measuring rim widths specified. © 1994-2006 Yokohama Tire Corporation. All rights reserved. Register Your Tires Warranty Understanding Your Tires FAQ Contact Us Customer Survey find a dealer Service Bulletins Tire Care Reading Your Tire Construction "Inch Up" To Plus Zero, Plus One & Plus Two Tire Size Applications Customizing >Performance Tire and Wheel Relationship >Plus Sizing >High Performance Wheels >Aspect Ratio Calculator >Rim/Wheel Width >Installation Glossary What's "Inch Up"? "Inch Up" is the process of mounting a lower aspect ratio tire and larger diameter wheel on your car. This creates a larger contact patch and a shorter sidewall. Why "Inch Up"? "Inch Up" to improve your vehicle's performance and appearance. ● Increased Steering Response ● Improved Dry Handling ● Enhanced Cornering Ability ● Aggressive Good Looks "Inch Up" may be done in several ways. The most popular are: "Inch Up" to improve your vehicle's performance and appearance. 1. Plus Zero This method utilizes the same wheel diameter as OE, but incorporates a tire with a larger than OE section width and smaller than OE aspect ratio. For example, replacing an OE 175/70R14 tire (on a 5.5-inch wheel) with a 195/60R14 tire would be a proper Plus Zero fitment. Note that this may require a replacement wheel to maintain proper rim width for the new tire. 2. Plus One This method utilizes a one-inch larger diameter wheel, in conjunction with a tire of a one-step lower aspect ratio. An example of an appropriate Plus One fitment is to replace an OE 175/70R13 tire (23-inch overall diameter) with a 185/60R14 tire (22.9-inch overall diameter). Note that this method always requires a replacement wheel. 3. Plus Two This method utilizes a two-inch larger diameter wheel, in conjunction with a tire of a two-step lower aspect ratio. An example of an appropriate Plus Two fitment is to replace an OE 175/70R13 tire (23-inch overall diameter) with a 195/50R15 tire (22.8-inch overall diameter). An independent research company recently conducted a test to determine the effect Inch Up has on handling. Included here is an abbreviated summary of the test results. The vehicle used for this comparison was a 1989 Mazda RX-7 SE. The original equipment tire is a 185/70HR14, and is mounted on a 5.5-inch wide wheel. The test was conducted on a dry asphalt surface. As the results from the lateral acceleration and handling course indicate, each successive plus size led to a noticeable increase in handling performance. This fitment guide recommends several Inch Up applications for both import and domestic vehicles. If the desired Inch Up application is not listed, the guidelines listed on the next page should be utilized to evaluate its appropriateness. Warning: When changing to a non-OE tire size, always consult the load/inflation charts to determine proper inflation pressure to maintain OE load-carrying capacity. © 1994-2006 Yokohama Tire Corporation. All rights reserved. Register Your Tires Warranty Understanding Your Tires FAQ Contact Us Customer Survey find a dealer Service Bulletins Tire Care Reading Your Tire Construction Selling high performance tires provides a great opportunity to include high performance wheels as an important and profitable part of your business. High Customizing performance wheels are available for most applications to both improve the appearance >Performance Tire and of a vehicle and complement the performance of replacement tires. Wheel Relationship >Plus Sizing To assure correct fitment, proper replacement wheel size, dimension and load-carrying >High Performance capacity are critical. Always consult the wheel manufacturer/distributor's literature to Wheels verify that the desired wheel and tire combination is an acceptable application for the >Aspect Ratio vehicle. Calculator >Rim/Wheel Width >Installation Wheel Width Glossary Choosing the wheel's width is important to assuring customer satisfaction. In addition to correct fitment, the wheel's width also influences handling and ride quality. Always choose a rim width within the range of the tire's acceptable rim width specifications. ● Choosing a wider rim: increases vehicular stability, steering response and cornering ability. A rule of thumb is to use a rim width 90% as wide as the tread width (not section width) of a performance tire for street applications. This provides a good balance between performance and ride quality. Always be sure that the chosen rim width is within the tire's range of acceptable rim width specifications. ● Choosing a narrow rim: results in an improvement in ride quality, but may sacrifice the tire's ultimate performance capabilities. ● Choosing a mid-range rim width: provides a balance between handling capabilities and ride quality. An example of a proper application would be to use a 15" x 6" wheel for a 205/70VR15 tire. Never attempt to mix millimetric wheels and tires with standard inch wheels and tires. An improper application would be mounting a 200/60R390 size tire on any 15" wheel. A 390mm tire is designed to fit on a wheel with a diameter of approximately 15.35" with a non-standard bead seat. Warning: According to RMA guidelines, there is danger in installing a tire of one rim diameter on a rim of a different rim diameter. Always replace a tire on a rim with another tire of exactly the same rim diameter designation and suffix letters. For example: a 16" tire goes with a 16" rim. Never mount a 16" size diameter tire on a 16.5" rim. While it is possible to pass a 16" diameter tire over the lip or flange of a 16.5" size diameter rim, it cannot be inflated enough to position itself against the rim flange. If an attempt is made to seat the tire bead by inflating, the tire bead will break with explosive force and could cause serious injury or death. High Performance Wheels The following are various high performance wheel measurements that play an important role in determining tire and wheel fitment: Wheel Backspace This is the distance from the back edge of the wheel to the hub mounting surface.