Understanding your rim size means reading three figures moulded into the tyre sidewall — an essential step before ordering any wheel protector.
Whether you've just clipped a kerb or are simply looking to fit your wheels with proper protection, knowing your exact rim diameter is the first step. This figure doesn't appear in your vehicle handbook — it's found directly on the tyre sidewall, encoded in an alphanumeric sequence that most drivers don't know how to read. Here's 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: tyre section width, 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, therefore the rim diameter, in inches
- 91W: load and speed index — not relevant 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 corresponds to your wheel.
Where exactly should you look for this marking?
The marking is moulded onto the outer sidewall of the tyre, visible without removal. On modern vehicles fitted with low-profile tyres (sidewall below 50%), it is even easier to read, as the sidewall is short and the marking is 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 rim around the entire circumference of the edge. Compatibility depends on the wheel diameter. Here are the most common sizes on French roads:
| Rim diameter | Example of a tyre marking | Typical models |
|---|---|---|
| 15 inches | 195/65 R15 | City cars, entry-level |
| 17 inches | 225/45 R17 | Compact saloons, compact SUVs |
| 18 inches | 235/40 R18 | Premium saloons, SUVs |
| 19 inches | 245/35 R19 | Sports cars, high-end SUVs |
| 20 inches and above | 275/30 R20 | Premium SUV, GT |
The set of 4 AlloyGator alloy wheel protectors covers all of these diameters. Fitting is carried out by an approved fitter in the network in approximately one hour, at a typical price of around €99 including labour — wheel removed, profile crimped, tyre reinflated.
If you own an Audi or BMW fitted with large low-profile wheels, compatibility is verified directly on the dedicated model page on the website.
FAQ
Is the rim diameter always the same on all four wheels?
On the vast majority of standard production vehicles, yes. However, some sports cars use an asymmetric fitment with wider wheels at the rear — check the marking on each axle before ordering. The front and rear tyre markings may differ in width (the first figure) without the diameter changing.
Can I rely on the door jamb label rather than the tyre sidewall?
The door placard shows the pressure and the manufacturer's original fitment. If the current tyres do not match this reference (following a tyre or wheel change), only the marking on the sidewall of the fitted tyre is 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 fits around the outer edge of the rim, regardless of the spoke design or bowl depth. The key variable is the diameter in inches, not the aesthetic style. Ford or Hyundai owners with complex alloy designs can check the model-specific pages to verify compatibility for their vehicle.
