Tire Number Guide: Understanding Manufacturer OE Markings Like Star, MO and AO

The short answer

A manufacturer-specific marking on a tire's sidewall is a short letter code or symbol showing that the tire version was jointly developed and validated with a particular vehicle brand for its vehicles. Common examples are a star for BMW, MO for Mercedes-Benz and AO for Audi. OE stands for original equipment: tires the vehicle manufacturer selected and approved for installation at the factory.

Two conditions change how you should read a marking. First, it identifies an automaker-approved version, not proof that a particular tire came on a car from the factory, because marked tires are also sold as replacements. Second, it does not by itself mean the tire fits your vehicle. Your vehicle's specified size, load index and speed rating still apply, and a marking from one brand says nothing about suitability for another brand's vehicles or for every model within the same brand.

What the marking actually represents

When a vehicle manufacturer works with a tire maker on original equipment, the tire can be tuned for that brand or model. The development work can target handling, ride comfort, noise and efficiency. The resulting version carries the automaker's marking so it can be told apart from other versions of the same tire line.

This automaker approval is separate from regulatory type approval. Regulatory approval concerns whether a tire meets the legal requirements of a market. An automaker marking concerns whether a vehicle manufacturer validated that version for its vehicles. A tire can meet regulatory requirements without carrying any automaker marking.

Because two tires can share the same model name and size while only one carries an OE code, the marking can be the only visible difference between two builds that may differ in how they were tuned.

Common markings by manufacturer

The table below lists examples of markings used on tires developed with specific vehicle brands. It is not a complete list for each brand. Some manufacturers use additional variant codes, and codes can change over time, so confirm the marking that applies to your vehicle with its documentation or an authorized dealer.

Marking	Vehicle manufacturer
★ (star symbol)	BMW
MO	Mercedes-Benz
AO	Audi
N-series codes such as N0	Porsche
K1, K2, K3	Ferrari
T0, T1, T2, T3	Tesla
VOL	Volvo

Where to find the marking

Look on the sidewall for a short letter code or symbol separate from the main size and service description. It is often molded near those numbers but can appear elsewhere on the sidewall. In retailer listings and product databases, the code is usually appended to the product name.

The marking is read alongside the standard size and service description, which describes dimensions, construction, load capacity and speed capability. For example:

225/45R17 94W

225  section width in millimeters
45   aspect ratio: sidewall height as a percentage of width
R    radial construction
17   rim diameter in inches
94   load index (a coded maximum load per tire)
W    speed rating (a coded maximum sustained speed)

The load index and speed rating are codes that correspond to values in standardized reference tables. Convert them with the tire maker's published specifications or a current standards reference rather than estimating.

Reading a listing such as "E Primacy A *MO"

Product names in listings and label databases often combine a tire model line with OE codes. In a name such as Michelin E Primacy A *MO, "E Primacy" is the model line, and the star and MO match the BMW and Mercedes-Benz markings in the table above. Listing formats are not standardized, though, and the extra characters in a product name do not have a fixed meaning across retailers. To know which approvals a specific tire carries, check the markings molded on its sidewall or the tire maker's product data for that exact size.

Searches for a tire's "labels" usually lead to regulatory performance labels, which are a different thing from OE markings:

• EU tire label: grades fuel efficiency (rolling resistance), wet grip and external rolling noise.
• US UTQG (Uniform Tire Quality Grading): a treadwear number plus traction and temperature grades, molded on the sidewall of applicable passenger tires.
• Other markets, including Korea and Thailand, use their own energy or eco labeling schemes with their own rating systems.
• Label grades can differ between sizes and between versions of the same tire line, so check the label for the exact version and size you are considering.

Using OE markings when you replace tires

Michelin recommends keeping the originally approved marking where possible while following the vehicle's specified size, load and speed ratings. A practical sequence:

• Record the full sidewall code from your current tires, including size, load index, speed rating and any manufacturer marking.
• Confirm the specified size, load index and speed rating in the vehicle's tire placard or owner's manual, since the current tires may not be the originals.
• Narrow replacement options to tires that meet those specifications.
• Among those, check which options carry the same manufacturer marking as your vehicle's approved tires.
• If you are unsure which marking applies to your model, year and market, ask the vehicle manufacturer or an authorized dealer for the tire brand you are considering.

Illustrative example: a shopper finds MO on the current tires and compares two replacement listings with matching size, load index and speed rating. Only one listing also carries MO. Size, load and speed are the fitment basics; the MO code is a separate selection detail that tells the shopper which option is the Mercedes-Benz-developed version.

Whether a manufacturer requires or only recommends OE-marked tires on a given model is set by that manufacturer, and an unmarked tire with the correct specifications is not automatically unsuitable. For a definite answer on your vehicle, rely on its documentation or a qualified tire professional rather than the marking alone.