What does 225/40 R18 mean, and how low is the sidewall?
225 is the nominal width in millimetres; 40 gives sidewall height as a percentage of width. The calculated sidewall height is therefore 90 mm. R means radial construction and 18 is the wheel diameter in inches. You also need the characters that follow: 92Y XL differs from a version with a lower load rating or a run-flat designation.
Understand tyre size92 XL or 88: why does this matter with a loaded car?
Load rating 92 represents 630 kg and 88 represents 560 kg per tyre under the specified conditions. XL identifies a reinforced version. Check vehicle requirements and axle loads, not simply kerb weight divided by four. If 92 XL is required, a cheaper 88 does not replace it. Higher tyre capacity does not increase your car’s permitted payload either.
Michelin · Load and speed ratings92Y in summer, 92V in winter: have I searched incorrectly?
Not necessarily. Y represents 300 km/h, W 270 and V 240 under the defined conditions. Offers may have different ratings depending on the season. The version you may use depends on your vehicle and its winter-equipment requirements. A Y on a summer offer is not a blanket requirement for every winter set, and V is not automatic approval.
Michelin · Load and speed ratingsGolf GTI, Leon, Audi A3 or BMW 1 Series: is the model enough?
Not enough to order. Check the generation, engine, brakes and approved wheel-and-tyre combination. Even a sporty model badge does not replace those details. If your documents specify 225/40 R18, also check load and speed ratings and any special markings. Our offers are grouped by size, not presented as universal fitment approval for every version of these vehicles.
Understand tyre sizeBMW star marking or run-flat: what matters when replacing tyres?
The star identifies a BMW-specific version. Run-flat describes extended mobility after pressure loss; XL indicates reinforced load capacity. These are three different features. Our six examples are not a selection of BMW-approved star-marked tyres. If your current set has a particular specification, compare it fully before ordering and discuss any conversion with your vehicle or fitting specialist.
BMW Switzerland · Star marking and run-flat225/40 R18 at the front: do I really need four of them?
Not with every wheel combination. A staggered setup may specify a different width, aspect ratio or version at the rear. Read both axles and check the documents. Our four-tyre price helps compare a matching set; it does not mean you should order four identical tyres for your car. With all-wheel drive, the manufacturer’s combination requirements also matter.
Understand tyre size18 or 17 inches: what changes compared with 225/45 R17?
The nominal sidewall of the 225/40 R18 is 11.25 mm lower. Calculated outside diameters are nevertheless close: 637.2 versus 634.3 mm. For more comfort, compare an approved complete 17-inch wheel setup rather than only looking for a softer 18-inch tyre. Tyre model, version and vehicle matter too. Similar overall diameter alone does not make two wheels interchangeable.
Understand tyre sizeCan I choose 225/45 R18 to make the car more comfortable?
Not on a guess. With the same 18-inch rim, the calculated outside diameter rises from 637.2 to 659.7 mm, around 3.5%. That is a different size, not a comfort version of the same tyre. First establish whether the complete wheel-and-tyre combination is approved for your vehicle. For replacement in the existing size, stay with 225/40 R18.
Understand tyre sizeSporty summer tyres or all-season tyres: which suits me?
If you enjoy a winding road in summer and need to use the car reliably in winter, we would start by comparing two seasonal sets. For straightforward lowland driving where you can avoid difficult winter trips, an all-season set is a genuine buying option. Sporty-looking 18-inch wheels do not force you to choose a sports tyre; your journeys should guide the choice.
Which all-season tyre suits my routes better?
Our Pirelli recommendation focuses on everyday dry and wet roads. We would compare the Continental if a more balanced spread across the seasons matters to you. Those different strengths in the TCS model comparison come from 225/45 R17. For the 18-inch versions offered here, we therefore show the VANTIQ Index and their own label values, not a transferred test grade.
TCS · 225/45 R17 · 2025 · PDF DEHow do I compare the cost of a complete set?
Start with matching specifications: season, suitable ratings and any run-flat or manufacturer markings. Then calculate the quantity you actually need. Depending on the offer, add fitting, balancing, valves, TPMS service and disposal. A small unit-price difference may matter less than expected in the overall package. The four-tyre prices above cover tyres only.
FittingWhat pressure does a 225/40 R18 need?
Size alone does not give a target pressure. Use the vehicle manufacturer’s figures for each axle, load and wheel combination. Check cold where possible, particularly before a fully loaded trip. Do not reduce pressure on your own initiative for comfort or deflate warm tyres to the cold target. Repeated pressure loss calls for a professional inspection.
Michelin · Tyre inflationThe steering wheel vibrates after fitting: is the tyre poor?
That symptom alone cannot establish the cause. Have the fitting and balancing of the complete wheel-and-tyre assembly checked first. The rim, runout or damage may also matter. One-sided wear or an off-centre steering wheel is a reason to check alignment too. Ask what the fitting price covers; do not rush to buy another set to solve an unexplained problem.
Michelin · Balancing and alignmentWet grip A and few decibels: is that enough to choose?
The EU label helps compare the exact version. Its noise figure describes external noise, not directly the quietness inside your car. Wet grip alone does not describe the full aquaplaning behaviour, wear or winter performance. Combine label values with the VANTIQ Index and your use. When opening the product page, check that you stay with your chosen specification.
EU tyre label
