How do I know my alloy wheel size?
To know your alloy wheel size, you need to look for the size information printed on the existing wheels or in your vehicle's owner's manual. The wheel size is typically expressed in a format like "17x8J" or "18x8.5ET35", which provides details about the diameter, width, and offset of the wheels.
Understanding Alloy Wheel Size Specifications
Alloy wheel sizes are typically expressed using a few key measurements:
- Diameter - This is the diameter of the wheel, usually measured in inches. Common sizes are 16, 17, 18, 19, and 20 inches.
- Width - This is the width of the wheel, also measured in inches. Typical widths range from 7 to 10 inches.
- Offset - The offset is the distance from the mounting surface of the wheel to the centerline. It's measured in millimeters (mm) and can be positive, negative, or zero.
The full wheel size specification will look something like "17x8J" or "18x8.5ET35", where the first number is the diameter, the second number is the width, and the letter/number combination after indicates the offset.
Finding Your Wheel Size
To determine your current wheel size, you can check the following places:
- Look on the existing wheels - The size information is usually stamped or printed on the inside or outer edge of the wheel.
- Check your owner's manual - Your vehicle's owner manual should list the factory-installed wheel size.
- Inspect the tire sidewall - The tire size, which includes the wheel diameter, is printed on the sidewall of the tire.
Once you know your current wheel size, you can use that information to find compatible replacement alloy wheels that will fit your vehicle properly.
Are rims marked with size?
Yes, rim size is marked on the rim itself, usually on the back of the spokes or the inside surface. The markings often look like "17x8" where "17" is the diameter in inches and "8" is the width in inches, but other numbers like offset (ET) and a flange profile letter (e.g., J) will also be present.
How to find the size on the rim
- Look for a stamp: The size is typically cast or machined into the metal on the rear face of the spokes or the inside of the barrel.
- Understand the numbers: A common format is Diameter x Width, for example, 17x8.
- Diameter: The first number is the wheel's diameter in inches (e.g., 17).
- Width: The second number is the wheel's width in inches (e.g., 8).
- Look for other markings: You may also find other information, such as:
- Offset (ET): A number in millimeters that indicates the wheel's position relative to the hub mounting surface (e.g., ET38).
- Flange profile: A letter that describes the rim's flange (e.g., "J").
What if you can't find the markings?
- Check the door jamb: Some cars have a sticker on the driver's side door jamb that lists the original tire and wheel size.
- Use your tire's sidewall: The last two digits of your tire's size designation indicate the rim diameter it's designed for (e.g., a tire with "R20" on the sidewall fits a 20-inch rim).
What does 4.80 4.00 mean?
The numbers 4.80/4.00-8 read like this: 4.80" is the tire width, 4.00" is the tire section height (from the inside of the donut hole to the outside) and the 8" is the wheel diameter. Finally, the numbers 4.80-8 read like this: 4.80" is the tire width and "8 is the wheel diameter.
What does +35 mean for rims?
On car wheels, +35 refers to a positive offset of 35mm, which indicates the wheel's mounting surface is 35mm toward the front (or outside) of the wheel's centerline. This measurement determines how far the wheel sits inside or outside the fender, with positive offsets pushing the wheel further out compared to zero or negative offsets.
How it works
- Offset: This is the distance, measured in millimeters, between the wheel's hub mounting surface and its geometric centerline.
- Centerline: You can find the centerline by measuring the wheel's total width and dividing it by two.
- Positive Offset (+35positive 35+35): The mounting surface is on the "front" or "street" side of the centerline. The +35mm measurement means the mounting surface is 35mm out from the centerline.
- Other types:
- Zero Offset: The mounting surface is exactly at the centerline.
- Negative Offset: The mounting surface is on the "back" or "brake" side of the centerline, making the wheel stick out further. A wheel that is "deep dish" often has a negative offset.
Why offset is important
- Fitment: The correct offset is crucial for ensuring the wheel and tire clear the vehicle's suspension, brake calipers, and fenders.
- Handling: An incorrect offset can negatively affect handling, steering, and suspension components by putting extra stress on parts like wheel bearings and tie rods, and can even cause tires to rub.
How do I tell what size my wheels are?
You can find your wheel size by looking at the tire's sidewall for a code like "R15," checking the driver's side door jamb sticker, or inspecting the back of the wheel itself for size markings like "18x7½". The number after "R" on the tire or the "diameter" number on the wheel indicates its size in inches.
On your vehicle's tires
- Look for a code like P215/65 R15 95H on the sidewall of your tire.
- The number after the "R" is the wheel's diameter in inches. In this example, the wheel size is 15 inches.
On your vehicle's door jamb or in the owner's manual
- Open the driver's side door and look for a sticker on the door frame or jamb.
- This sticker often lists the original tire and wheel size, including the wheel diameter.
- You can also find this information in your car's owner's manual.
On the wheel itself
- Turn the wheel to look at the back of the spokes.
- You may find the size directly stamped on the wheel, typically as a diameter and width, like 18x7½.
- In this example, the wheel has an 18-inch diameter and a 7½-inch width.
