2021 Cadillac Tire Fitment Guide

2021 Cadillac vehicles use six distinct sizes across two models. The CT4 uses 225/45R17, 235/40R18, and 235/35R19, while the CT5 uses 245/45R18, 245/40R19, and 255/35R20. Rim diameters therefore range from 17 to 20 inches depending on the model and wheel package. Where rim width guidance appears, 225/45R17 works across roughly 7.0 to 10.0 inches depending on the tire, 235/40R18 runs about 8.0 to 9.5 inches, 245/45R18 about 7.5 to 9.0 inches, 245/40R19 about 8.0 to 9.5 inches, and 255/35R20 about 8.5 to 10.0 inches.

That means year and make alone are not enough to choose correctly. A 2021 Cadillac owner should first confirm whether the car is a CT4 or CT5, then verify the actual wheel diameter on the car before moving into brand or series selection. This matters especially on cars that may have alternate factory wheel packages or replacement wheels. Once the size is confirmed, the next comparison becomes speed rating, load capacity, and the exact rim width range of the tire being considered.

On a 2021 Cadillac, 225/45R17 is a modern metric radial size. The 225 is the nominal section width in millimeters, 45 is the aspect ratio, the R means radial construction, and 17 is the wheel diameter in inches. In this year and make, that size belongs to the CT4. Available products in that size use 17-inch rims and Blackwall styling, with W speed ratings to 112 mph.

The main takeaway is that every part of the code matters. A 225 width on a 17-inch wheel is not interchangeable with the CT4’s 18- or 19-inch sizes, even though they belong to the same model family. If your car is a CT4 and carries 17-inch wheels, 225/45R17 is the starting point; after that, compare the tire’s approved rim width range and any load information to be sure the exact product suits your wheels and use.

No. The 2021 Cadillac lineup here splits cleanly by model: CT4 and CT5 do not share tire sizes. CT4 sizes are 225/45R17, 235/40R18, and 235/35R19, while CT5 sizes are 245/45R18, 245/40R19, and 255/35R20. Even where both models use an 18-inch or 19-inch wheel diameter, the section width and profile differ, so one model’s tire should not be assumed to fit the other.

That model-specific split is useful because it narrows your choices quickly once the car is identified. If you are comparing sizes across the year and make, think in terms of sedan family and wheel package rather than Cadillac as one uniform fitment. Owners of cars with optional wheels should still check the sidewall on the existing tire or the wheel itself, since the same model can move across several rim diameters within the 2021 range.

2021 Cadillac tire options in these sizes are centered on Blackwall sidewalls. That applies across the CT4 sizes of 225/45R17, 235/40R18, and 235/35R19 and the CT5 sizes of 245/45R18, 245/40R19, and 255/35R20. That sidewall presentation suits the late-model performance-luxury character of these cars and matches the contemporary look expected on modern Cadillac sedans.

For most 2021 Cadillac owners, sidewall choice is therefore simple: the decision is less about decorative sidewall treatment and more about size, series, and speed rating. Blackwall tires keep the appearance clean and factory-appropriate for this era. Once you have the correct size, compare whether you want an all-season leaning product or a more performance-oriented series, and make sure the tire’s rim width range aligns with the wheels on your car.

BFGoodrich and Nitto cover the 2021 Cadillac sizes here. Both brands appear in 225/45R17, 235/40R18, 235/35R19, 245/45R18, and 255/35R20, while 245/40R19 is represented by BFGoodrich. Within those sizes, BFGoodrich appears in g-Force Comp 2 AS, g-Force Sport Comp 2, and g-Force Phenom T/A forms, while Nitto appears in the NT555 G2 line.

Brand choice on a 2021 Cadillac usually comes down to how you want to prioritize use rather than whether one name simply fits and another does not. Once the correct size is identified, compare the series available in that size, then look at speed rating, load capacity where published, and approved rim width range. On CT4 and CT5 applications with larger wheel diameters, that last point is especially important because low-profile sizes are less forgiving of wheel mismatch.

On 2021 Cadillac sizes where both appear, the BFGoodrich g-Force Sport Comp 2 and g-Force Phenom T/A differ in speed rating, load figures, and in some cases weight. In 235/40R18, for example, the Sport Comp 2 carries a 91W rating while the Phenom T/A carries a 95Y rating. In 245/45R18, the Sport Comp 2 is 96W while the Phenom T/A is 100Y, and both share a similar 7.5 to 9.0 inch rim-width envelope. In 255/35R20, the Sport Comp 2 is 97W XL while the Phenom T/A is 97Y.

Those differences matter most when you are comparing products within the exact same factory size rather than trying to change sizes. A 2021 Cadillac owner should first lock in the correct size for the car, then compare whether the available rating and load specification suit the intended use. The Phenom T/A often carries the higher published speed category in these shared sizes, but the right pick still depends on wheel compatibility and the overall role of the car.

Rim width requirements for 2021 Cadillac tires depend on the exact size. 225/45R17 generally spans from 7.0 to 10.0 inches depending on the tire, 235/40R18 runs from about 8.0 to 9.5 inches, 245/45R18 from about 7.5 to 9.0 inches, 245/40R19 from about 8.0 to 9.5 inches, and 255/35R20 from about 8.5 to 10.0 inches. The 235/35R19 size uses a 19-inch rim, and one product in that size specifies an 8.0 to 9.5 inch range.

That is why checking the wheel itself is just as important as checking the sidewall size. Two tires with the same nominal dimensions may share the same diameter but still carry slightly different approved rim-width windows depending on the product series. If your 2021 Cadillac has aftermarket wheels, confirm the wheel width before selecting a tire. Staying inside the tire maker’s approved range helps preserve intended section shape, steering response, and wear behavior.

These 2021 Cadillac fitments are modern radial passenger-car sizes, and the tire markings shown are tubeless-style metric radial markings rather than tube-type designations. No TT marking appears in these sizes, and several products use standard ZR-format modern passenger tire sizing with XL or speed-rating notation. That places 225/45R17, 235/40R18, 235/35R19, 245/45R18, 245/40R19, and 255/35R20 firmly in the contemporary tubeless category used on late-model wheels.

The practical step is to evaluate the wheel and valve hardware rather than assuming the tire alone tells the whole story. A 2021 Cadillac running original late-model wheels should ordinarily remain in a tubeless setup, but damaged rims, replacement wheels, or aged valve stems can still create air-loss issues. When mounting fresh tires, inspect the valve stems, bead seats, and wheel condition at the same time so the complete assembly is ready for dependable service.

A 2021 Cadillac should be stored out of direct sunlight, away from electric motors, battery chargers, welders, and other ozone-producing equipment, and on a clean, dry surface. Keep the tires inflated to an appropriate storage pressure and move the car periodically so one section of the tread does not carry the full weight for long periods. Modern radials resist flat-spotting better than older bias-ply designs, but long static storage can still affect ride quality and sidewall condition.

Good storage habits are especially important on CT4 and CT5 models with lower-profile 18-, 19-, or 20-inch tire packages because cosmetic wheel damage and unnoticed pressure loss can become more of an issue. If the car will sit for an extended season, many owners use tire cradles or stands to reduce sustained loading. A brief visual inspection every few weeks is worthwhile, even when the car is indoors and not being driven.

On a 2021 Cadillac that sees collector-style or lower annual mileage, age often matters more than tread depth. A good rule is to begin more careful evaluation around five to seven years of service and to treat about ten years as the point where replacement deserves serious consideration regardless of remaining tread. The DOT date code on each tire tells you when it was built, and that date should be part of any inspection plan.

Mileage still matters, especially on performance sedans, but it is not the only measure of tire condition. Heat cycles, parking conditions, sunlight exposure, and inflation history all affect how a tire ages. A CT4 or CT5 that spends much of its life parked can still age out its tires before wearing them out. Owners should balance tread depth with sidewall condition, ride changes, and the tire’s age rather than waiting for the tread alone to make the decision.

Tires on a 2021 Cadillac should be checked before every drive, with a more thorough inspection before any longer outing. Look for cuts, impact damage, bulges, irregular tread wear, punctures, and signs of sidewall cracking. Pressure should be verified regularly rather than judged by appearance, especially on low-profile sizes where a meaningful pressure drop may not be obvious at a glance.

That routine is important because CT4 and CT5 fitments can use fairly short sidewalls on 19- and 20-inch wheels, and those packages place more emphasis on maintaining correct pressure and wheel condition. During routine service, have the valve stems inspected and watch for any vibration, pull, or sudden wear pattern changes. Catching those signs early can prevent damage to both the tire and the wheel and helps keep the car driving the way Cadillac intended.

Yes, the 2021 Cadillac tire sizes here are modern radial performance and performance-touring sizes intended for contemporary road use. The products shown in these fitments carry W or Y speed ratings depending on the tire, with W rated to 112 mph and Y rated to 186+ mph. In practical highway use, those ratings are well beyond typical interstate speeds. On a late-model Cadillac sedan, overall vehicle condition, alignment, brake health, and suspension condition are just as important to safe road behavior as the tire’s speed symbol.

The key is not to treat the speed rating as permission to drive at that ceiling. It is a capability marker for the tire under controlled conditions, not a recommendation for public-road use. For a 2021 Cadillac owner, the real safety checklist is simpler: choose the exact factory-size replacement, verify that the wheel width falls within the tire’s approved range, and keep the tires properly inflated and regularly inspected before extended highway trips.

Inflation pressure on a 2021 Cadillac should start with the vehicle’s factory placard or owner’s manual, because recommended operating pressure is set by the car, axle load, and original wheel-and-tire package. Tire pressure figures associated with load capacity on replacement tires are not universal operating targets. Where load figures appear, they are tied to individual products: 225/45R17 reaches 1,477 pounds at 50 psi on one Nitto example, 235/40R18 reaches 1,521 pounds at 50 psi, 245/45R18 reaches 1,764 pounds at 50 psi, 245/40R19 reaches 1,653 pounds at 50 psi, and 255/35R20 reaches 1,609 pounds at 50 psi on one BFGoodrich example.

Those numbers are useful for understanding the tire’s capacity, but they should not be transferred from one size to another or mistaken for the correct cold inflation setting for your car. A CT4 and a CT5 can share similar tire construction but still require different operating pressures because the vehicles and wheel packages differ. Use the Cadillac specification first, then confirm that the chosen tire’s published limits and load capacity are appropriate for the application.

Before a longer drive in a 2021 Cadillac, inspect each tire for cracking, punctures, cuts, bulges, curb damage, and uneven wear, then verify cold inflation pressure. Check tread depth across the full face of the tire, not just the center, and inspect the spare if the car is equipped with one. On low-profile 18-, 19-, and 20-inch fitments, look carefully at the wheel lip as well, since impact damage can affect air retention and balance.

A tire check should be part of a broader trip-prep routine on any modern performance-luxury sedan. Along with the tires, confirm alignment behavior, brake feel, and that the car is not pulling or vibrating. If a 2021 Cadillac has recently had wheels changed or new tires mounted, a quick recheck after the first miles is wise. Catching a slow leak, bent rim, or pressure mismatch before departure is far easier than dealing with it on the road.