Modifying the tires on your Lexus IS does not have to be an overwhelming task. By performing the necessary research and identifying your individual needs, you can purchase the tires that will give you optimal performance and the best look for your vehicle.
Typically there are three types of tires to choose from, the first being summer tires, which are the standard Lexus OEM. Then there are all weather drive (AWD) tires, and finally, pure snow tires. Depending on the specifications of your Lexus IS and the driving conditions you encounter, you will have many different choices for your vehicle.
Step 1 - Determining tire need
Purchasing the right tires for Lexus IS should initially be dependent upon the driving conditions you encounter on a daily basis. Many Lexus IS owners will have two sets of tires based on summer and winter climates. However, if you are living in a warmer climate and can maintain summer tires on your vehicle all year long, you will get the best performance. Not all all weather tires will work on every Lexus IS, and you will need to check the specifications to ensure you are getting the right tire for your vehicle. The same can be true for standard snow tires; not all will fit each Lexus IS, however, the sizing guide below should help you with understanding tire size. There are also many online resources to assist you as well.
Figure 1. Check the tire specifications for your IS.
Step 2 - Understanding tire sizes
Understanding different tire sizes is important for determining the correct size for your vehicle. Tire size will impact both performance and appearance.
Figure 2. Tire dimensions and terminology.
The Lexus IS 250, with the wheel size of 17 inches, comes with the stock wheel size of 225/45R17. This size is used for the following calculations:
The first number (225) is the tire's section width in millimeters, measured from sidewall to sidewall. If you would prefer to calculate this dimensions in inches, it can be converted into inches by dividing it by 25.4. For example: 225mm / 25.4 = 8.86". The second number (45) is the tire's aspect ratio. Aspect ratio represents the percentage of a sidewall’s section height to the tire’s section width. Section height can be calculated by multiplying the section width by the aspect ratio percentage. The answer will be the height of the sidewall.
For example:
225mm x 0.45 = 101.3mm
8.86" x 0.45 = 3.99"
The last number (R17) is the diameter of the wheel or rim in inches. The Lexus IS is typically equipped with 17 or 18 inch rims, but modifications to 19 and 20 inch rims are possible. To calculate the overall diameter of a tire in inches, you would need to add the top and bottom sidewall, and the rim size. Generally, this is the determining factor in the aesthetic look of the tire for your Lexus IS.
For example:
3.99" + 3.99" + 17" = 24.98"
Step 3 - Picking and mounting the right tires
The Lexus IS series typically comes with 17 or 18 inch wheels or rims. It is not necessary to upgrade your wheel size in order to get a new look, or bigger wheels for your Lexus IS. Upgrades to 19 and 20 inch rims are possible; however, performance issues, most noticeably rubbing, may occur with the larger wheels.
Depending on the final look that you desire, and the final wheel size that you choose, you need to be aware of the mounting issues that may occur that can also change the look and performance of your tire.
Types of Offset
Causes
Zero Offset
Occurs when the hub mounting surface of the tire is even with the center line of the wheel.
Positive Offset
Occurs when the hub mounting surface of the tire is toward the front of the wheel.
Negative Offset
Occurs when the hub mounting surface is toward the brake side of the Lexus IS. This is the most technically difficult way to mount the tires, as you have a greater risk of rubbing.
Figure 3. A wheel with a positive offset moves the tire closer to the frame. A wheel with a negative offset moves the tire further away from the frame.
Step 4 - Final considerations
If you purchase a bigger tire for your Lexus IS, your odometer and speedometer may not be calibrated correctly to your new, bigger tire. There are two options in case of this situation. The first is to bring your Lexus IS to your dealership to have the speedometer and odometer re-calculated. The second is to perform a self calculation by driving your Lexus IS between mile markers on the highway, and re-calibrating based on time and distance. Additionally, it is important to notify any subsequent buyers of your Lexus IS that the speedometer and odometer are not correctly calibrated, and to give them the correct information.
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