390/40R17 Tire Size Guide

The 390/40R17 size code identifies a tire that is 390 millimeters wide, has a sidewall height equal to 40 percent of that width, uses radial construction, and fits a 17-inch wheel. For this size, that works out to an approximate 6.14-inch sidewall and an overall diameter of about 29.28 inches.

Modern metric sizing like 390/40R17 spells out width, profile, construction, and wheel diameter directly in the code. Older numeric and alphanumeric sizes do not always give that much dimensional detail at a glance, so a modern metric code is generally easier to compare when you are checking stance, wheel-opening fill, or possible substitutes.

The 390/40R17 fits a 17.0-inch wheel, which is 431.8 millimeters in diameter. That wheel diameter must match exactly, because a 17-inch tire cannot seat correctly on a different rim diameter even if the tire's width and height seem close.

Wheel width matters just as much as wheel diameter on a size this wide. The fitment shown here uses a 12.00-inch rim width, so buyers should confirm that the wheel matches that width and that the tire has room at the inner sidewall, outer fender, and suspension before treating the size as a workable option.

The 390/40R17 has a section width of 390 millimeters, which is about 15.35 inches. Section width is measured at the tire's widest point from sidewall to sidewall, not across the tread face that actually contacts the road.

Clearance questions usually start with section width because sidewall bulge can reach farther than the tread itself. When buyers compare this size to another low-profile radial, section width is the first number to check against frame rails, wheel tubs, suspension parts, and fender lips.

The 390/40R17 has an overall diameter of about 29.28 inches, or roughly 743.7 millimeters. That is the full mounted-and-inflated height of the tire from the ground to the top, measured through the center.

Overall diameter influences several things at once, including ride height, wheel-opening fill, and speedometer behavior. If you are comparing the 390/40R17 to another performance size, this number helps show whether the vehicle will sit higher or lower and whether gearing feel and cruising rpm may change.

The sidewall height on the 390/40R17 is about 6.14 inches, which equals 156.0 millimeters. That figure represents one sidewall from the wheel's bead seat to the outer tread edge, not the full height of the tire.

A 40-series profile keeps the sidewall shorter than a taller touring or vintage-style radial, which changes both appearance and feel. Shorter sidewalls usually deliver a lower-profile look and a more direct response to steering inputs, but they also leave less sidewall cushion over rough pavement.

The 390/40R17 turns about 688.8 revolutions per mile. That number comes from the tire's circumference, which is approximately 91.99 inches around.

Revolutions per mile become useful when you are comparing this size with another tire that may be taller or shorter overall. A meaningful change in revs per mile affects speedometer and odometer readings, and it can also alter the vehicle's effective gearing enough to change launch feel or highway engine speed.

The 390/40R17 is associated with modern performance and low-profile passenger-car use, especially where a very wide radial footprint is part of the build. It is not a general-purpose vintage numeric or alphanumeric size, and its proportions point more toward specialized traction and stance goals than ordinary replacement use.

Buyers should approach this size as a fitment-driven choice rather than a universal upgrade. Wheel width, backspacing, suspension travel, body clearance, and actual vehicle weight all need to be checked carefully, because a tire this wide can create interference issues even when the rim diameter itself is correct.

Rim width is critical with the 390/40R17 because the fitment shown here uses a 12.00-inch wheel. On a low-profile radial, wheel width directly affects how the sidewall stands, how the tread sits on the road, and how much real clearance the package needs.

A wheel that is narrower or wider than the intended fit can change the tire's shape enough to affect both appearance and function. Before using the 390/40R17, measure wheel width at the bead seat, then compare inner clearance, outer clearance, and overall stance instead of relying on size code alone.

The 390/40R17 is generally better suited to a modern performance-oriented build than to a judged period-style restoration. Radial construction can improve drivability, but authenticity standards on a vehicle being judged for original appearance may call for a different type of tire and a different overall profile.

Restoration-minded buyers should compare the vehicle's original tire format, wheel dimensions, and intended presentation before choosing this size. A very wide 40-series radial changes the visual character of a car quickly, so the decision usually comes down to whether the goal is faithful factory-style appearance or updated road manners and traction.

The 390/40R17 combines radial construction with a wide section and a relatively short 40-series sidewall, so it generally delivers a firmer, more direct road feel than a taller-profile tire. With only about 6.14 inches of sidewall, there is less visual and physical cushion than on a high-profile fitment.

Ride quality still depends on more than size alone. Suspension tuning, vehicle weight, wheel width, inflation setting, alignment, and tire age all influence how the 390/40R17 behaves on real pavement, so buyers should judge it as part of the whole wheel-and-tire package rather than as an isolated number.

A size like the 390/40R17 is built around width and a lower sidewall profile, which usually translates to a more immediate steering response than a taller, narrower tire. Radial construction also tends to give a more settled contact patch in regular road use than older construction styles.

Handling results are still setup-sensitive, especially with a very wide tire on a 12-inch wheel. Alignment, suspension geometry, wheel offset, and available clearance all shape how the vehicle turns in and tracks, and a tire chosen mainly for traction or stance can behave differently from one chosen for balanced street manners.

The 390/40R17 is a modern radial size, so its construction aligns more closely with contemporary driving expectations than an older bias-ply format. Even so, this particular fitment is specialized, and buyers should think in terms of intended use, vehicle setup, and load needs rather than assuming it behaves like an ordinary daily-driver replacement tire.

Modern road use includes heat cycles, freeway speeds, expansion joints, rain grooves, and uneven pavement, all of which can affect a wide low-profile tire differently than a narrower one. Inspect condition carefully, verify the vehicle's weight and wheel specs, and make sure the overall package suits how the vehicle will actually be driven.

The 390/40R17 is available here from M&H Racemaster. In a specialized size like this, brand choice is often narrower than it is in mainstream passenger sizes, so buyers usually spend more time evaluating construction purpose, dimensional suitability, and use case than comparing a long list of interchangeable options.

A specialized performance size should be chosen with the full application in mind. Look at the tire's intended role, wheel width requirement, load rating, and whether the overall profile matches the stance and clearance needs of the vehicle before treating brand name alone as the deciding factor.

Quality in the 390/40R17 starts with correct sizing, consistent construction, and a clear match between the tire's intended purpose and the vehicle's actual use. Because this is a wide low-profile radial, dimensional accuracy and a proper wheel match matter just as much as brand reputation.

Buyers should compare section width, overall diameter, rim width requirement, load rating, and the tire's application before making a decision. A tire can be well made and still be the wrong choice if it creates clearance issues, mismatches the wheel, or does not suit the way the vehicle will be driven.

Yes, sidewall style can matter, especially when the tire is visible as part of the vehicle's finished look. The 390/40R17 fitment shown here uses a blackwall sidewall, which gives a clean, purpose-built appearance that typically suits modern performance and drag-oriented combinations.

Appearance should still be balanced against the practical side of the choice. On a size this specialized, buyers are usually better served by confirming construction type, width, height, and wheel compatibility first, then deciding whether the sidewall presentation matches the overall character of the build.

The 390/40R17 should be inspected regularly for cuts, cracking, bulges, punctures, uneven wear, and air loss, especially because a wide low-profile tire can show the effects of alignment or clearance issues quickly. Checks are a good idea before long trips, after hard use, and anytime the vehicle's handling feels different.

Inspection should include the inner sidewall and shoulder areas, not just the outer tread face that is easy to see. Vehicles using specialized rear-fitment sizes can develop rubbing or irregular wear patterns if wheel position, suspension travel, or inflation maintenance is not kept under close watch.

A lightly used 390/40R17 can still age out before the tread is worn away. Time, heat, sunlight, ozone exposure, storage conditions, and long periods of sitting all affect the rubber and carcass, so tread depth alone is not enough to judge whether an older tire remains a sound candidate for continued use.

Stored vehicles benefit from clean, dry conditions away from direct sun and electric motors or other ozone sources. Even when mileage is low, buyers should inspect the tire carefully for age-related hardening or cracking and consider replacement if condition no longer matches the demands of actual road use.

The 390/40R17 is normally a tubeless fitment. Tube use is still a wheel-and-tire-system question rather than a size question, so the actual wheel design and the tire being used should always be confirmed before deciding whether a tube belongs in the setup.

Wheel condition matters as much as tire format here. If the rim has sealing issues, damage, or a design that changes how the assembly retains air, a qualified tire professional should inspect the combination and confirm the correct approach instead of assuming the size code alone settles the question.

The 390/40R17 should be replaced when it shows cracking, bulges, exposed cords, repeated air loss, impact damage, or uneven wear severe enough to affect road behavior. Age also matters, even when tread looks usable, because rubber and internal structure can degrade over time in ways that are not always obvious at a glance.

Replacement timing should reflect both condition and use. A vehicle that sees highway miles, hard launches, or long-distance travel places more demand on the tire than one that only moves occasionally, so buyers should inspect carefully and consult a tire professional whenever condition or age raises any doubt.

Load rating is essential with the 390/40R17 because each tire shown in this size is rated at 2,000 pounds at 35 psi. That figure needs to be matched against the vehicle's actual axle loads and intended use instead of assuming a very wide tire automatically has more capacity than the application requires.

Load capacity is only meaningful when paired with the inflation pressure attached to that rating. Buyers should confirm that the wheel, tire, and vehicle requirements all align, particularly on heavy rear-drive combinations or cars built for traction-focused use where rear tire loading can differ from an ordinary street setup.

Buyers should verify condition, wheel compatibility, actual clearance, and load requirements before using the 390/40R17 on public roads. A specialized wide radial can fit the wheel diameter correctly and still present issues with sidewall clearance, fender room, suspension travel, or overall suitability for how the vehicle is driven.

Current sidewall markings and local requirements should also be reviewed before road use. Public-road expectations can differ from track-oriented or occasional-use situations, so it is smart to confirm the complete wheel-and-tire package, inspect the assembly closely, and use a qualified tire professional when the application is at all uncertain.