A Mercedes tire size like 225/45R18 decodes as: section width 225 mm, aspect ratio 45 (sidewall = 45% of 225 mm = 101.25 mm = 3.99 in), on an 18-inch rim, giving an overall diameter of 18 + 2 x 3.99 = 25.97 inches. Mercedes-Benz USA lists this as the standard front size on the 2026 C 300 4MATIC, with 245/40R18 (25.72 in) at the rear, a difference of 0.96% (calculated). The Mercedes owner manual asks for tires of the same type and make, and the same size on each axle, on 4MATIC cars; it does not publish a percentage. MO marks Mercedes-Original approved tires, MOE adds Extended Mobility (run-flat), MO1 and MOS are further Mercedes-specific approvals.
QUICK EXAMPLE
A 2026 C 300 4MATIC leaves the factory on 225/45R18 front (OD: 25.97") and 245/40R18 rear (OD: 25.72"), according to Mercedes-Benz USA. That staggered pair differs by 0.96% in rolling diameter, the larger of the two front and rear gaps among the Mercedes pairs listed here (the GLC 300 Coupe pair is 0.48%). An owner who swaps the front to 235/45R18 (OD: 26.33") widens the gap to 2.37% against the factory rear, well beyond what Mercedes itself ships. Use the Compare tab to check any proposed swap against your current size before buying.
Decode Any Mercedes Tire Size
How to Use This Calculator
- 1Tab 1 - Decode Size: Enter any Mercedes tire code (e.g. 225/45R18, 245/40ZR18) or click a preset button. Click Decode to see overall diameter in inches and mm, sidewall height, circumference, revs/mile, revs/km, a proportional SVG profile, and the full worked formula using your exact values.
- 2Tab 2 - Compare Two: Enter Size A (current/OEM) and Size B (proposed replacement). The calculator shows a side-by-side SVG visual, a full dimension delta table, a 4MATIC rolling-diameter badge, the general 3% fitment status badge, and a speedometer correction table from 30 to 120 mph.
- 3Tab 3 - OEM Lookup: Filter by model or search by tire size. The table shows the standard front and rear sizes Mercedes-Benz USA lists for each model year, the staggered flag, wheel size and tire type.
- 4Tab 4 - MO / MOE Guide: Review the Mercedes tire markings (MO, MOE, MO1, MOS) as described on the Mercedes-Original Tires page, and what Mercedes-Benz says about replacement tires.
- 5Tab 5 - Pressure & Wheels: See where Mercedes prints your exact tire pressures (door pillar or fuel flap label), how to convert kPa to PSI, and where to confirm wheel fitment with a Mercedes-Benz parts specialist.
Mercedes Factory Tire Sizes: From Mercedes-Benz USA
| Model | Years | Front OEM | Rear OEM | Front OD" | Rear OD" | Tire Type | Note |
|---|---|---|---|---|---|---|---|
| C 300 4MATIC Sedan | 2026 | 225/45R18 | 245/40R18 | 25.97" | 25.72" | All-season, Extended Mobility | Staggered, per Mercedes-Benz USA |
| E 350 Sedan | 2027 | 225/55R18 | 225/55R18 | 27.74" | 27.74" | All-season, Extended Mobility | |
| S 500 4MATIC Sedan | 2027 | 255/45R19 | 255/45R19 | 28.04" | 28.04" | All-season, Extended Mobility | |
| GLA 250 4MATIC SUV | 2026 | 235/55R18 | 235/55R18 | 28.18" | 28.18" | All-season, Extended Mobility | |
| GLB 250 SUV | 2026 | 235/55R18 | 235/55R18 | 28.18" | 28.18" | All-season, Extended Mobility | |
| GLC 300 4MATIC SUV | 2027 | 235/55R19 | 235/55R19 | 29.18" | 29.18" | All-season | 2026 model lists 235/60R18 |
| GLC 300 4MATIC Coupe | 2027 | 235/55R19 | 255/50R19 | 29.18" | 29.04" | All-season | Staggered, per Mercedes-Benz USA |
| EQS 450+ Sedan | 2027 | 255/45R20 | 255/45R20 | 29.04" | 29.04" | Range-optimized summer | Electric |
Sizes are the standard wheel and tire listed on Mercedes-Benz USA (mbusa.com) model pages for the model year shown. Only models whose page listed a tire size are included. Overall diameters are calculated from the metric size, so real tires vary by brand. Trims and option wheels carry other sizes, so check the placard on your car.
Full Dimensions of the Factory Sizes
| Size | OD (in) | OD (mm) | Sidewall (in) | Circumference (in) | Revs/mile | Fitted To |
|---|---|---|---|---|---|---|
| 225/45R18 | 25.97 | 659.7 | 3.99 | 81.59 | 777 | C 300 4MATIC front |
| 245/40R18 | 25.72 | 653.2 | 3.86 | 80.79 | 784 | C 300 4MATIC rear |
| 225/55R18 | 27.74 | 704.7 | 4.87 | 87.16 | 727 | E 350 |
| 255/45R19 | 28.04 | 712.1 | 4.52 | 88.08 | 719 | S 500 4MATIC |
| 235/55R18 | 28.18 | 715.7 | 5.09 | 88.52 | 716 | GLA 250, GLB 250 |
| 235/60R18 | 29.10 | 739.2 | 5.55 | 91.43 | 693 | GLC 300 SUV (2026) |
| 235/55R19 | 29.18 | 741.1 | 5.09 | 91.66 | 691 | GLC 300 SUV (2027), Coupe front |
| 255/50R19 | 29.04 | 737.6 | 5.02 | 91.23 | 695 | GLC 300 Coupe rear |
| 255/45R20 | 29.04 | 737.5 | 4.52 | 91.22 | 695 | EQS 450+ |
All values computed from ISO metric size formula. Circumference = OD × π. Revs/mile = 63,360 ÷ circumference (in). Verify against the tire maker's published dimensions for precision applications.
Mercedes Tire Pressure: Where to Find Yours
Mercedes-Benz prints the correct cold pressures on a label on the door pillar or the inside of the fuel filler flap, and they depend on the model, tire size and load. We do not publish a pressure chart because the label on your car is the only figure that matches your exact trim. Check pressures cold, and never bleed a warm tire down to the cold figure. To convert the label value between units, multiply PSI by 6.895 for kPa, or use our kPa to PSI converter.
Mercedes Tire Size Formulas & Reference
1. Reading a Mercedes Metric Tire Code (e.g. 245/45R18)
First number → section width in millimetres (245 mm). Second number → aspect ratio, the sidewall height as a percentage of width (45%). R → radial construction. Third number → rim diameter in inches (18").
2. Overall Diameter (OD) from Metric Code
Sidewall (mm) = Width × (Aspect ÷ 100) Sidewall (in) = Sidewall (mm) ÷ 25.4 OD = Rim (in) + 2 × Sidewall (in)
Example: 225/45R18 (2026 C 300 4MATIC front): sidewall = 225 × 0.45 = 101.25 mm = 3.99". OD = 18 + 2 × 3.99 = 25.97" (659.7 mm).
3. Circumference
C = OD × π
225/45R18 example: C = 25.97 × 3.14159 = 81.59" (2,072.4 mm).
4. Revolutions per Mile
Rev/mile = 63,360 ÷ C (in)
225/45R18 example: 63,360 ÷ 81.59 = 777 rev/mi.
5. Revolutions per Kilometre
Rev/km = 1,000,000 ÷ C (mm)
225/45R18 example: 1,000,000 ÷ 2,072.4 = 483 rev/km.
6. OD Delta % (comparing two sizes)
Δ% = (New OD − Old OD) ÷ Old OD × 100
Example: replacing 225/45R18 (25.97") with 235/45R18 (26.33") gives Δ% = (26.33 − 25.97) ÷ 25.97 × 100 = +1.39%.
7. 4MATIC Rolling-Diameter Guideline
Mercedes-Benz owner manuals ask for tires of the same type and make, and the same size on each axle, on 4MATIC cars. No percentage is published. Mercedes' own staggered pairs differ by 0.48% (GLC 300 Coupe) and 0.96% (C 300 4MATIC) front to rear (calculated). Continental advises keeping rolling circumference within 3% of the original for speedometer accuracy.
8. Speedometer Correction
True speed = Indicated speed × (New OD ÷ Old OD)
Example: 100 km/h indicated, swapping 225/45R18 (25.97") for 235/45R18 (26.33"): true speed = 100 × (26.33 ÷ 25.97) = 101.4 km/h, so the speedometer reads about 1.4% low.
9. Staggered Fitment - OD Matching
For the 2026 C 300 4MATIC (225/45R18 front / 245/40R18 rear, per Mercedes-Benz USA): front OD = 25.97", rear OD = 25.72", a delta of 0.25" (0.96%).
10. Run-Flat (MOE) Note
MOE means Mercedes Original Extended: a run-flat tire that can be driven a limited distance at reduced speed after pressure loss. The exact distance and speed limit are in your owner manual and on the tire maker's data, so check them for your car rather than relying on a general figure.
11. Tire Pressure Conversion
PSI → kPa: × 6.895 kPa → PSI: × 0.14504 PSI → bar: × 0.06895 bar → PSI: × 14.504
Examples: 35 PSI = 241 kPa. 250 kPa = 36.3 PSI. 36 PSI = 2.48 bar. 2.5 bar = 36.3 PSI. Your required pressure is on the label on the door pillar or fuel flap.
How to Read a Mercedes Tire Size
Every Mercedes tire sidewall carries a three-part metric code: for example, 225/45R18 on the 2026 C 300 4MATIC. The first number (225) is the section width in millimetres. The second (45) is the aspect ratio: the sidewall height is 45% of 225 mm = 101.25 mm = 3.99 inches. The R denotes radial construction, and 18 is the rim diameter in inches. Overall diameter is therefore 18 + 2 × 3.99 = 25.97 inches. This mixed metric/imperial system is a legacy of 1960s standardisation: the width went metric while rim diameters stayed in inches, and the convention persists across all manufacturers to this day. On the same sidewall you will also find the load index (e.g. 95), speed rating (e.g. Y), and the Mercedes OE marking (MO, MOE, or MO1) if applicable. The load index chart and the speed rating lookup decode those two codes.
MO vs MOE vs MO1: Why the Marking Matters More Than the Size
Most owners focus on the size code and overlook the OE marking. According to Mercedes-Benz, MO (Mercedes Original) tires are developed, tested and adapted to individual models. MOE (Mercedes Original Extended) tires have reinforced sidewalls that let you keep driving after a loss of tire pressure, and must be used with a tire pressure monitoring system. MO1 tires are made specifically for AMG models, and MOS tires carry a foam insert to reduce noise on select S-Class cars. If your car came with MOE tires and no spare, replacing them with standard tires removes that run-flat protection, so keep the marking your car shipped with.
Mercedes 4MATIC Front and Rear Sizes
Mercedes-Benz owner manuals ask 4MATIC owners to use tires of the same type and make, and the same size on each axle. Mercedes does not publish a percentage tolerance. Mercedes' own staggered pairs are a useful reference: the C 300 4MATIC 225/45R18 (25.97") front and 245/40R18 (25.72") rear differ by 0.96%, and the GLC 300 Coupe 235/55R19 front and 255/50R19 rear by 0.48% (calculated). A front 235/45R18 (26.33") against the C 300 rear would be 2.37% apart, which is further than the factory ships. Use the Compare tab to see the difference for your own sizes, and ask a Mercedes-Benz dealer before going beyond the factory sizes.
Staggered Fitments on Mercedes: What You Cannot Do
Staggered fitments, where front and rear tires are different sizes, give the rear axle a wider tire. On the Mercedes-Benz USA pages we checked, the 2026 C 300 4MATIC Sedan (225/45R18 front, 245/40R18 rear) and the 2027 GLC 300 4MATIC Coupe (235/55R19 front, 255/50R19 rear) are staggered. Because the front and rear tires are different sizes, they cannot be swapped between axles during rotation, so wear on each axle is tracked separately. For a 4MATIC car the front to rear diameter difference can be checked with the same percentage tool used for other AWD makes, and the staggered fitment calculator lays out the two axles side by side.
MO / MOE Marking Quick Reference
| Marking | Full Name | Run-Flat | Flat Distance | Flat Speed | Description |
|---|---|---|---|---|---|
| MO | Mercedes Original | No | Not a run-flat marking | N/A | Developed, tested and adapted to individual Mercedes-Benz models |
| MOE | Mercedes Original Extended | Yes | See your owner manual | See your owner manual | Models listed with Extended Mobility tires |
| MO1 | Mercedes Original 1 | No | Not a run-flat marking | N/A | Made specifically for AMG models |
| MOS | Mercedes Original Silent | No | Not a run-flat marking | N/A | Select S-Class, foam insert for lower noise |
Descriptions follow the Mercedes-Original Tires page on Mercedes-Benz USA. Flat-driving distance and speed limits differ by model, so use your owner manual. If your car has MOE tires and no spare, replace them with MOE or another approved run-flat tire.
4MATIC Tire Size Note
Mercedes-Benz owner manuals ask 4MATIC owners to use tires of the same type and make, and the same size on each axle. No percentage is published. Mercedes' own front and rear pairs differ by 0.48% to 0.96% in rolling diameter (calculated). We have no Mercedes-Benz statement about what happens beyond that, so we make no claim about driveline wear or stability control.
Use the Compare tab above; the 4MATIC badge shows whether the OD delta is larger than the Mercedes factory pair gaps. Always verify with your Mercedes-Benz dealer before fitting a non-OEM tire size on a 4MATIC model.
Frequently Asked Questions
Disclaimer:Factory tire sizes and MO/MOE descriptions come from Mercedes-Benz USA (mbusa.com) pages. Diameters, circumferences and percentage differences are calculated. Mercedes-Benz publishes no 4MATIC tolerance percentage. Always verify against your vehicle's door jamb sticker, owner's manual, or an authorised Mercedes-Benz dealer before purchasing replacement tires or wheels. Tire fitment can vary by trim level, production date, and regional market. tirecalculatorhub.com is not affiliated with Mercedes-Benz AG or Daimler Truck AG.