The correct spare tire cover is sized by the tire’s overall diameter. To ensure a proper fit, measure the tire’s outer diameter and, if needed, the mounting depth and any protruding hardware. Then choose a cover that matches or slightly exceeds that diameter and accommodates the mounting location.
Key factors that determine fit
Spare tire covers are typically sold by diameter and are designed to fit circular tires. While the sidewall size printed on the tire provides a quick reference, the actual outer diameter can vary with tread depth and manufacturer. The installation location on your vehicle (rear door, hatch, or undercarriage) also matters because some covers need extra clearance around hinges, spoilers, or mounting brackets.
Step-by-step measuring guide
Use these steps to measure the spare and select the correct cover size.
- Locate the tire size on the spare’s sidewall (for example, P215/70R15). This information helps estimate the tire’s outer diameter.
- Measure the tire’s outer diameter across the center of the tire: place a tape measure vertically at the tire’s midline and measure from the topmost point to the bottom. If direct measurement is difficult, wrap a flexible tape around the circumference and divide by pi to obtain the diameter.
- Determine the mounting depth: measure how far the tire sits from its mounting surface (how much it protrudes from the spare carrier or hatch). This affects how thick the cover must be.
- Check the installation opening: measure the diameter of the opening or frame where the cover sits to ensure it will slide on and off without obstruction.
- Match to a cover size: choose a cover with a diameter equal to the tire’s outer diameter or slightly larger (typically 1/2 inch to 1 inch extra for a snug fit). Avoid a cover that’s smaller than the tire.
If measurements are tricky, bring a photo and the tire sidewall size to a retailer or consult the manufacturer’s sizing chart for your specific spare tire model.
Common sizing guidelines
Most spare tire covers are offered in standard diameter sizes. Use the outer diameter you measured to pick the closest size, aiming for a snug but easy-on fit. If you’re between sizes, ask the retailer about stretchable or adjustable options.
- Diameter up to 28 inches: choose a 27"–28" cover (check the exact product range).
- Diameter around 29"–30": look for 29"–30" covers.
- Diameter 31" and larger: select 31"–32" covers or larger depending on your tire.
These guidelines help ensure the cover seals well and provides protection against dust, moisture, and UV exposure.
Summary
Measuring for a spare tire cover begins with determining the tire’s outer diameter. Use the sidewall size as a starting point, then verify with a center cross-measure or circumference calculation. Consider mounting depth and opening clearance, and pick a cover that matches or slightly exceeds the measured diameter for a secure fit. When in doubt, consult the retailer’s size chart or ask for guidance to ensure compatibility with your specific spare tire and mounting setup.