Understanding your wheel size: reading the sidewall marking

Understanding your alloy wheel size means reading three numbers moulded on the tyre sidewall — an essential step before ordering any alloy wheel protector.

Whether you have just clipped a kerb or are simply looking to fit your wheels with suitable protection, knowing the exact diameter of your alloy wheel is the first step. This figure is not found in the vehicle handbook but directly on the tyre sidewall, encoded in an alphanumeric sequence that most drivers do not know how to read. Here is how to decipher it in under two minutes.

The sidewall marking: decoding the full sequence

On any approved tyre, you will find a sequence such as 225/45 R17 91W. Each segment corresponds to a specific measurement:

• 225: section width of the tyre, in millimetres
• 45: sidewall height, expressed as a percentage of the width (here 45% × 225 = ~101 mm of sidewall)
• R: radial construction (standard on modern cars)
• 17: inner diameter of the tyre, i.e. the alloy wheel diameter, in inches
• 91W: load and speed rating, unrelated to alloy wheel protection

The key figure for choosing an alloy wheel protector is this 17 (or 18, 19, 20…). It determines which AlloyGator profile size fits your wheel.

Where exactly do you read this marking?

The marking is moulded on the outer sidewall of the tyre and is visible without removal. On modern vehicles fitted with low-profile alloy wheels (sidewall below 50%), it is even easier to read, as the sidewall is short and the marking clearly exposed. If you are unsure about legibility, the sticker on the driver's door pillar often shows the original fitment — however, bear in mind that a previous owner may have changed the tyres. Always rely on the marking of the tyre currently fitted.

Size guide and AlloyGator compatibility

The AlloyGator profile is fitted between the tyre and the alloy wheel around the entire circumference of the rim. Compatibility depends on the alloy wheel diameter. Here are the most common sizes on vehicles in France:

The set of 4 AlloyGator alloy wheel protectors covers all of these diameters. Fitting is carried out by a network approved fitter in approximately one hour, with the set priced at €134.90 and fitting from €99 depending on the installer — wheel removed, profile crimped, tyre reinflated.

If you own an Audi or BMW fitted with large low-profile alloy wheels, compatibility can be checked directly on the dedicated model page on the website.

FAQ

Is the alloy wheel diameter always the same on all four wheels?

On the vast majority of standard production vehicles, yes. Some sports cars, however, use an asymmetric setup with wider rims at the rear — check the markings on each axle before ordering. The tyre markings for the front and rear may differ in width (the first figure) without the diameter changing.

Can I rely on the door jamb sticker rather than the tyre sidewall?

The door sticker shows the manufacturer's original tyre pressure and fitment specifications. If the current tyres do not match that reference (following a tyre or wheel change), only the markings on the sidewall of the fitted tyre are authoritative. If in doubt, an approved fitter in the network can confirm the size in a matter of seconds.

Does an alloy wheel protector fit any rim profile (deep-dish, flat, multi-spoke)?

The AlloyGator profile sits on the outer edge of the rim, regardless of the spoke design or bowl depth. The determining variable is the diameter in inches, not the aesthetic style. Ford or Hyundai owners with complex alloy wheels can consult the model-specific pages to check compatibility for their vehicle.