2018 Cadillac Tire Fitment Guide

2018 Cadillac vehicles use 13 sizes across four model lines. ATS uses 225/45R17, 225/40R18, 255/35R18, and 275/35R18; CT6 uses 235/50R18, 245/45R19, 245/40R20, and 265/45R18; CTS uses 245/45R17, 245/40R18, 275/35R18, 255/35R19, 265/35R19, and 295/30R19; XTS uses 245/45R19 and 245/40R20. Rim diameters span 17, 18, 19, and 20 inches, and rim-width ranges vary by size, from fixed 8-inch and 8.5-inch drag-radial applications up to broader fitment ranges such as 9.0 to 11.0 inches for 275/35R18.

That means a 2018 Cadillac owner needs more than the year and brand to choose correctly. Start with the exact model, then confirm the wheel diameter already on the car, and finally compare the tire size on the sidewall to the wheel package you are replacing. Shared sizes like 275/35R18, 245/45R19, and 245/40R20 can cross between two Cadillac models, but most of the lineup’s sizes are model-specific.

On a 2018 Cadillac tire, 225/40R18 is a modern metric radial size. The 225 is the nominal section width in millimeters, 40 is the aspect ratio, meaning the sidewall height is 40 percent of the section width, R identifies radial construction, and 18 is the wheel diameter in inches. For 2018 Cadillac applications, this size belongs to the ATS and mounts on 18-inch wheels with product fitment ranges centered around 7.5 to 9.0 inches of rim width.

Understanding the code helps separate tires that may look similar at a glance but are not interchangeable. A 225/40R18 ATS tire is much different in overall proportions from a 225/45R17 ATS tire, even though both begin with 225. If your car wears 18-inch wheels and the sidewall calls for 225/40R18, stay with that exact format unless you are intentionally reworking the full wheel-and-tire package.

No. 2018 Cadillac models do not share one common tire size across the lineup. ATS, CT6, CTS, and XTS each use their own combinations, with only a few overlaps: 275/35R18 is shared by ATS and CTS, 245/45R19 is shared by CT6 and XTS, and 245/40R20 is also shared by CT6 and XTS. Every size in the lineup is radial, but the spread in width, profile, and wheel diameter is broad enough that model identification matters immediately.

That practical difference becomes important when replacing just one pair or correcting a mixed set. A CTS can use 17-, 18-, or 19-inch fitments, while an XTS stays with 19- or 20-inch sizes, so assuming any 2018 Cadillac sedan tire will fit another is a fast way to order the wrong diameter. Check the model badge and the sidewall together before narrowing your choices.

Most 2018 Cadillac tire sizes are available in blackwall form, which matches the understated look expected on modern Cadillac sedans. One exception is 245/40R20, where both blackwall and raised white letter options are available. The blackwall choices appear across BFGoodrich, Nitto, M&H Racemaster, and other performance-oriented selections, while the RWL version adds a more overtly performance-styled appearance.

For a factory-looking presentation on ATS, CT6, CTS, or XTS, blackwall is usually the safer visual match. Raised white letters create a different attitude that can suit a personalized build, but they will look less stock on a late-model Cadillac luxury sedan. If appearance matters as much as size, compare the sidewall treatment before choosing among otherwise similar 20-inch products.

2018 Cadillac tire sizes are covered by BFGoodrich, Nitto, Pro-Trac, and M&H Racemaster, depending on the size. BFGoodrich and Nitto appear across most of the metric radial street sizes, including ATS, CT6, CTS, and XTS applications. Pro-Trac appears in 245/40R20, while M&H Racemaster covers 245/45R17 and 245/40R18 with drag-radial style products aimed at a more specialized use case.

Brand choice for a 2018 Cadillac is less about year-correct restoration than about how you use the car. A CT6 or XTS owner may focus on conventional street radial options in shared luxury-sedan sizes, while a CTS owner might also encounter more aggressive niche products in certain 17- and 18-inch fitments. Narrow the correct size first, then compare which brands actually serve that exact application.

In 275/35R18 for 2018 Cadillac ATS and CTS applications, BFGoodrich and Nitto overlap in blackwall radial street tires but differ in some published details. BFGoodrich offers W-rated and Y-rated versions, while Nitto’s NT555 G2 appears as a W-rated XL tire with a 1,709-pound maximum load at 50 psi and a 9.0 to 11.0-inch rim-width range centered on 9.5 inches. BFGoodrich options include a 95W all-season style version and a 99Y g-Force Phenom T/A with a 1,709-pound maximum load at 50 psi.

For a 2018 Cadillac owner, that means the comparison is not just brand name but also speed rating, load figure, and intended street character within the same nominal size. If your ATS or CTS already uses 275/35R18, compare the sidewall marking carefully and decide whether you want a W-rated or Y-rated product before moving on to tread pattern or series preference.

Rim-width requirements for 2018 Cadillac tires vary by size. Examples include 225/45R17 at roughly 7.0 to 8.5 inches, 225/40R18 at 7.5 to 9.0 inches, 255/35R18 at about 8.5 to 10.0 inches, 275/35R18 at 9.0 to 11.0 inches, 235/50R18 at 6.5 to 8.5 inches, 245/40R20 at 8.0 to 9.5 inches, 245/45R19 at 7.5 to 9.0 inches, and 255/35R19 at 8.5 to 10.0 inches. Some drag-radial applications are narrower and more exact, such as an 8-inch rim for one 245/45R17 product and an 8.5-inch rim for one 245/40R18 product.

That spread is why wheel diameter alone is not enough. A 2018 Cadillac CTS on a 19-inch wheel still needs the correct rim width for 255/35R19, 265/35R19, or 295/30R19, and a shared size such as 245/40R20 still needs a wheel that falls inside the approved range for the specific tire. Check the wheel width before finalizing a replacement, especially if the car has aftermarket wheels.

2018 Cadillac tires in these sizes are modern radial fitments and do not point toward tube-type collector applications. Some sidewall markings explicitly include TL, which identifies tubeless construction, as seen on certain 245/40R18 products, while the rest follow the same contemporary radial pattern without tube-type markings. Nothing in these Cadillac sizes suggests the kind of tube-required fitment associated with older bias-ply or antique tire designs.

For most owners, the practical step is to treat the wheel and tire as a tubeless late-model setup unless a wheel-condition issue or a specialized application changes that conversation. Instead of focusing on tubes, put more attention on wheel condition, bead-seat cleanliness, valve stems, and whether the tire’s sidewall marking matches the wheel diameter and service category your 2018 Cadillac actually uses.

Original 2018 Cadillac wheels cannot be assumed to work with all 13 sizes, because the lineup uses four different rim diameters and multiple width ranges. A 17-inch ATS or CTS wheel will not accept an 18-, 19-, or 20-inch tire, and a 19-inch CT6 or XTS wheel cannot take the 20-inch companion size. Even within one diameter, the rim width must still match the tire’s approved range.

The safest approach is to match the existing wheel diameter first and then verify that the wheel width falls within the intended tire’s range. That matters most on wider CTS and ATS fitments such as 275/35R18 and on low-profile 19- and 20-inch luxury-sedan sizes. If the car has changed wheels during its life, confirm the actual wheel dimensions rather than relying on model-year assumptions.

A 2018 Cadillac should be stored on clean, properly inflated tires in a cool, dry, dark space away from direct sunlight, electric motors, battery chargers, welders, and other ozone-producing equipment. Even modern radial tires age faster when exposed to UV, heat, and long static periods on one contact patch. If the car sits for extended stretches, rolling it slightly from time to time or supporting it properly during long-term storage can help reduce flat-spotting.

That matters whether the car is an ATS weekend driver, a low-mileage CTS, or a pampered CT6 or XTS. Modern radials generally tolerate storage better than older bias-ply designs, but they still benefit from stable pressure, a clean floor, and periodic checks. Good storage habits preserve ride quality and help prevent the kind of sidewall weathering that can shorten a tire’s service life before the tread is worn out.

Tires on a 2018 Cadillac should be judged by age as much as tread depth, especially on cars that see limited mileage. A good rule is to inspect them carefully once they reach the five- to seven-year range and to treat about 10 years as the point where replacement deserves serious consideration regardless of miles traveled. The DOT date code on the sidewall gives the manufacturing week and year, which is the key reference for age.

That guideline is especially useful for luxury and performance sedans that may spend long periods parked while still looking visually fresh. A 2018 Cadillac can wear tires with plenty of tread left but still be overdue because the rubber has hardened or begun to crack. Age, storage conditions, alignment, and inflation often matter more than mileage alone when deciding whether a tire is still fit for service.

Tires on a 2018 Cadillac should be inspected before every drive and again before any longer outing. Look for cracking, cuts, bulges, punctures, uneven wear, and signs that the tire is losing pressure, and check the valve stems at the same time. Low-profile sizes such as 255/35R19, 265/35R19, and 295/30R19 deserve especially close attention because shorter sidewalls can hide impact damage until the inspection is deliberate.

A quick walkaround catches issues before they become expensive or dangerous. On a car that spends time parked, pressure loss and age-related sidewall changes can appear long before tread wear does. If your 2018 Cadillac has a staggered or specialty tire setup, regular inspection also helps make sure the right size remains on the right wheel position and that wear stays even across the car.

Yes, the radial tires used on 2018 Cadillac applications are appropriate for highway use when they are in good condition, correctly sized, and properly inflated. The available speed ratings include W, which carries a 118 mph ceiling, and Y, which carries a 186 mph-or-higher ceiling. Those ratings are well above normal U.S. highway speeds, and on a modern Cadillac sedan the vehicle’s condition, alignment, brakes, suspension, and tire age are usually more important than the rating difference during ordinary road use.

The key is to use the right speed-rated size for the wheel package already on the car and to avoid treating old or damaged tires as safe simply because the tread looks decent. A 2018 Cadillac used for regular road miles should have matching tires across each axle, stable pressures, and no visible sidewall or tread issues before any sustained highway trip.

Inflation pressure for 2018 Cadillac tires should follow the vehicle placard or owner’s manual for the specific model and wheel package, then be checked against the tire’s own rated maximum where load information is published. Some examples of tire-rated figures include 1,389 pounds at 50 psi for certain 225/40R18 products, 1,709 pounds at 50 psi for some 275/35R18 and 245/45R17 products, and 1,874 pounds at 50 psi for one 245/45R19 product. Those maximum figures describe the tire’s capacity limit, not the factory cold inflation setting for every Cadillac application.

That distinction matters because a CT6, CTS, ATS, and XTS do not all use the same vehicle pressure recommendation, even when two models share a size. Use the Cadillac placard as the starting point for day-to-day inflation, then verify that the tire you choose meets the load and service needs of the car. Avoid transferring a pressure figure from one size or model to another just because the wheels look similar.

Before a longer drive in a 2018 Cadillac, inspect all four tires and the spare if the car carries one. Check cold inflation pressure, tread depth, visible cracking, cuts, punctures, bulges, and any uneven wear that could point to alignment or suspension trouble. On low-profile ATS and CTS fitments, also look closely for inner sidewall damage from potholes or curb strikes, and make sure the valve stems are sound.

Tires are only one part of the pre-trip routine, but they are an easy place to prevent trouble. A luxury or performance sedan that has sat for weeks can develop low pressure or age-related issues without obvious warning from the driver’s seat. Pair the tire check with a broader review of fluids, brakes, and lighting so the car is as ready mechanically as the tires are visually.