30X6.75 Tire Size Guide

The 30X6.75 size uses a flotation-style format in which 30 refers to the tire's overall diameter in inches and 6.75 refers to its nominal section width. On this size, the measured overall diameter is 30.0 inches and the calculated section width is about 6.7 inches.

Unlike a modern P-metric code, the 30X6.75 format does not spell out every detail in one string the way a size such as 225/75R15 does. It emphasizes overall height and width first, which is especially useful on older vehicles where stance, wheel-opening fill, and period appearance matter just as much as simple replacement sizing.

The 30X6.75 fits a 5.0-inch wheel diameter, which converts to 127.0 millimeters. Because this is a flotation-style size, the first number is the tire's outside diameter, not the wheel diameter.

That distinction is critical when replacing antique or specialty tires, because a 30-inch tall tire does not mount on a 30-inch wheel. Buyers should confirm the actual wheel diameter at the bead seat and then verify width and clearance, since older wheels and restored chassis setups can vary from one vehicle to another.

The 30X6.75 has a calculated section width of about 6.7 inches, which is roughly 170.2 millimeters. Section width refers to the tire's widest point across the sidewalls when inflated, not the tread face touching the road.

Clearance checks should be based on section width because sidewall bulge is what gets close to fenders, steering arms, brake parts, and suspension pieces. Tread width is usually narrower, so relying on tread alone can lead to surprises once the tire is mounted and carrying the vehicle's weight.

The 30X6.75 has an overall diameter of 30.0 inches, or 762.0 millimeters. That figure represents the full height of the inflated tire from the ground to the top, measured straight through the center.

Overall diameter affects more than appearance. A tire this tall influences ride height, wheel-opening proportion, and the way the car sits relative to its original stance. It also matters when comparing substitute sizes, because even a modest change in overall height can alter gearing feel and speedometer behavior.

The 30X6.75 mounts on a 5.0-inch wheel diameter, even though the size begins with 30. In this format, 30 describes the tire's outside diameter, while the wheel fit must be confirmed separately.

Many buyers coming from later tire sizing expect the last number to show wheel diameter, but flotation and antique-style formats do not always work that way. On a restoration or specialty build, confirming the wheel itself before ordering is one of the most important checks you can make.

The 30X6.75 turns about 672.3 revolutions per mile. That number comes from its 94.25-inch circumference and gives a practical picture of how often the tire rotates at road speed.

Revolutions per mile become useful when you are comparing one tire size to another and trying to preserve original driving characteristics. A replacement with a noticeably higher or lower revs-per-mile figure can change speedometer and odometer readings, especially on older vehicles that were calibrated around tall bias-ply dimensions.

The 30X6.75 is closely associated with late 1920s to early 1930s vehicle use, and its tall bias-ply profile suits the look many antique restorations require. For vehicles from that era, the size helps preserve the upright stance and wheel-opening proportion expected from original-style tire fitment.

Authenticity still depends on the full wheel-and-tire package, not the size code alone. Buyers should compare original owner literature, surviving fitment tags, wheel diameter, and physical clearance before treating the 30X6.75 as the right answer for a judged restoration or a historically accurate driver.

The key checks for the 30X6.75 are wheel diameter, overall tire height, section width, and available clearance through the full steering and suspension range. A 30.0-inch overall diameter and roughly 6.7-inch section width can look narrow, but the tire is still tall enough to affect fender, axle, and steering clearance.

Older vehicles often have less predictable spacing than modern cars because wheel offsets, brake conversions, and spring height may have changed over time. Start by confirming the 5-inch wheel diameter, then inspect how much room exists at the fender crown, frame, tie-rod ends, and brake hardware before finalizing a replacement.

Yes, 30X675 and 30 6.75 are common notation variants for the 30X6.75. They refer to the same basic size format, with punctuation and spacing handled differently rather than changing the tire's intended dimensions.

Even when the size is written in different ways, buyers should still verify the actual tire's wheel fit and dimensions before installation. Older and specialty sizing can look inconsistent from one catalog or sidewall marking to another, so it is smart to compare the complete code and the physical measurements rather than relying on shorthand alone.

The 30X6.75 uses bias-ply construction, which typically gives an older vehicle the period-correct steering response and sidewall character expected from its original era. On antique chassis, that can translate to a different on-center feel and more sidewall movement than drivers used to modern radial tires may expect.

Ride and steering behavior depend on more than construction alone. Suspension wear, alignment, wheel condition, inflation setting, and the age of the tire all influence how the vehicle feels on the road. On a properly sorted antique vehicle, bias-ply construction often preserves the driving personality the car was built around.

At 30.0 inches tall, the 30X6.75 is a height-driven tire size that plays a major role in how an antique vehicle sits. That overall diameter helps fill the wheel opening in the way many late 1920s and early 1930s vehicles were originally proportioned.

Diameter also affects the way the vehicle moves down the road because tire height changes how far the car travels per wheel rotation. With about 672.3 revolutions per mile, the 30X6.75 should be compared carefully against any substitute size if you want to preserve original speedometer behavior and visual stance.

The 30X6.75 should be approached as an antique-style bias-ply tire size rather than a modern everyday replacement format. It can deliver the look and general road manners expected of period-correct equipment, but buyers should expect driving feel to reflect older tire design and the limitations of the vehicle itself.

Modern road conditions place more stress on old chassis systems, so tire age, balance, alignment, brake condition, and steering play matter just as much as the size code. Before regular road use, inspect the full vehicle carefully and make sure the tire's dimensions and construction match the way the vehicle will actually be driven.

A good 30X6.75 should match the original format closely in overall diameter, section width, and bias-ply construction. For an antique application, the value of the size is not just that it fits the wheel, but that it preserves the visual proportion and driving character the vehicle was designed around.

Quality selection should focus on dimensional accuracy, consistent construction, and suitability for the vehicle's intended use. On a restoration, a tire that is slightly off in height or sidewall profile can change the look of the entire car, so buyers should compare measurements carefully instead of choosing by size code alone.

Bias-ply construction is often the right choice when the goal is to keep a 30X6.75-equipped vehicle close to its original character. This size is strongly tied to older tall-profile applications, and bias-ply design supports the authentic sidewall shape and period driving feel many restorers want.

Drivability expectations should still be realistic. A buyer building a judged antique car may prioritize originality, while a buyer planning more road miles may weigh consistency, road manners, and the condition of the rest of the chassis just as heavily. The right choice depends on how the vehicle will actually be used.

Full-set consistency matters with the 30X6.75 because tall narrow antique tires have a visible effect on stance and balance. A mismatch in height, construction, or profile from one corner to another can show up quickly on vehicles with open wheelhouses, exposed fenders, or very upright body lines.

Consistent sizing also helps maintain predictable handling and a level appearance. When replacing only one tire, compare its actual dimensions and construction against the rest of the set so the vehicle does not end up with uneven ride height, altered steering feel, or an obviously mismatched period look.

The 30X6.75 should be inspected regularly for cracking, cuts, bulges, uneven wear, and slow air loss, even if the vehicle is driven only occasionally. Antique-size bias-ply tires can age out from time and storage conditions long before tread depth alone suggests replacement.

Focus your inspection on the sidewalls, the bead area, and any signs that the tire has begun to distort after sitting. A collector vehicle that sees limited miles still needs periodic checks because heat, sunlight, ozone exposure, and long stationary periods all contribute to rubber aging.

The 30X6.75 benefits from cool, dry storage away from direct sunlight, electric motors, and other ozone sources that accelerate rubber aging. If the vehicle sits for extended periods, clean the tires first and avoid storing them in contact with standing moisture or contaminated concrete surfaces.

Long-term storage habits matter because a bias-ply tire can develop flat spotting or cosmetic sidewall stress when left parked in one position for too long. Moving the vehicle occasionally, maintaining proper inflation, and keeping the full chassis load in mind can help preserve both appearance and service life.

The 30X6.75 should have its air pressure checked regularly, especially before driving after the vehicle has been parked for a while. Antique and specialty tires can lose air gradually, and a tire that looks acceptable at a glance may still be running below its intended pressure.

Pressure affects wear, steering effort, and how the sidewall carries the vehicle, so checking it is part of preserving both tire life and predictable road behavior. Use the tire's current sidewall markings and the vehicle's actual load needs as your guide, and recheck before longer trips or seasonal use.

The 30X6.75 should be replaced when age-related cracking, sidewall damage, bulges, repeated air loss, or visible distortion appear, even if tread remains. On antique-size bias-ply tires, time and storage conditions can matter as much as mileage because rubber compounds continue aging while the vehicle sits.

Collectors sometimes focus on appearance first, but safe continued use depends on condition, not tread depth alone. Before road use, inspect each tire closely and have any doubtful casing evaluated by a qualified tire professional, especially if the vehicle has been stored for long periods or is returning to service.

The 30X6.75 can be used on the road when the tire is in sound condition and properly matched to the vehicle, wheel, and intended use. Because it is a bias-ply antique-style size, buyers should evaluate it as part of the entire wheel-and-chassis system rather than assuming the size alone answers every road-use question.

Roadworthiness depends on more than tread. Check for sound wheels, proper mounting, stable air retention, and enough clearance through steering travel and suspension movement. Before extended driving, inspect the tire closely and compare its dimensions and construction with the demands of the vehicle and the roads it will actually see.

Before a longer trip on the 30X6.75, verify tire condition, wheel diameter, air pressure, visible sidewall health, and chassis clearance under real driving load. A tall antique-style tire can look fine in the garage yet reveal rubbing, heat buildup, or handling issues once the vehicle is fully loaded and moving at speed.

Trip preparation should also include checking the spare, reviewing wheel condition, and making sure the steering, brakes, and suspension are in proper operating shape. On an older vehicle, the tire is only one part of the safety picture, so the most dependable results come from inspecting the whole system before departure.