A common guideline is to keep the new tire’s overall diameter within about 3% of your original size. Inside that range, speedometer error is small and most vehicles have room for the change. This calculator marks changes up to 3% as safe, 3% to 5% as a caution (check clearance and consider recalibrating the speedometer), and more than 5% as not recommended. Diameter is only part of it: the new size also has to fit your wheel width, clear the suspension and fenders, and meet your vehicle’s load rating.

Plus sizing means moving to a larger wheel while lowering the tire’s aspect ratio, so the overall diameter stays about the same. For example, a stock 205/55R16 is about 24.9 inches tall. A plus-one 215/45R17 is about 24.6 inches (1.0% smaller), and a plus-two 225/40R18 is about 25.1 inches (0.8% larger). You get a sportier look and sharper steering, but a firmer ride, more road noise, and more risk of wheel damage from potholes. Minus sizing is the reverse, often used for winter tires: a smaller wheel with a taller sidewall, which is usually cheaper and rides softer.

Your speedometer counts wheel rotations, so it assumes the original tire size. A taller tire covers more ground per turn, so the speedometer reads low; a shorter tire makes it read high. Your odometer is off by the same percentage. For example, going from 265/70R17 to 285/70R17 makes the tire about 3.5% taller, so when your speedometer shows 60 mph you are actually going about 62. Many trucks can be recalibrated with a dealer tool or an aftermarket programmer after a size change.

A wider tire usually improves dry grip and cornering, and gives a more planted feel. The tradeoffs are slightly heavier steering, more rolling resistance (which can cost fuel economy or EV range), more road noise, and a higher chance of rubbing on suspension parts or fender liners. Wider tires can also be more prone to hydroplaning in heavy rain. Every tire size has an approved range of wheel widths, so a much wider tire may need wider wheels.

The sidewall is the cushion between the wheel and the road. A shorter sidewall (lower aspect ratio or bigger wheel) flexes less, so steering feels sharper, but the ride is firmer and the wheel is more exposed to pothole damage. A taller sidewall rides softer and absorbs bumps better, with slightly slower steering response. Taller sidewalls are also better for off-roading, since you can air down for traction.

Taller tires raise the vehicle and add ground clearance, but they also act like a taller gear: acceleration slows, the transmission may shift differently, and fuel economy usually drops, often more than the weight alone suggests. Check for rubbing at full steering lock and over bumps, since larger tires may need a leveling kit or lift. Big jumps in size, such as moving to 35-inch tires, often call for re-gearing the axles to restore performance. Heavier off-road tires also add unsprung weight, which can affect braking and ride.

These systems read wheel speed sensors, so they work best when all four tires match in overall diameter. A small, uniform change on all four tires is generally fine. Mixing tire diameters between axles on an all-wheel-drive vehicle can strain the center differential or transfer case, which is why AWD owners are usually told to replace all four tires together. Large size changes can also trigger warning lights or change how stability control behaves.

Yes. The new tire must carry at least as much weight as the load index on your vehicle’s door jamb placard calls for. Lower-profile or narrower sizes can have a lower load capacity than the original, so you may need an XL (Extra Load) version of the new size to stay at or above the required rating.

A staggered setup uses wider tires on the rear axle than the front, common on sports cars and rear-drive luxury sedans. The front and rear sizes are chosen to have nearly the same overall diameter. Because the sizes differ, you cannot rotate tires front to back, so the rear tires usually wear out sooner and are often replaced as a pair.

Flotation sizes, common on off-road trucks and Jeeps, list measurements in inches instead of millimeters. In 35x12.50R17, 35 is the overall diameter, 12.50 is the section width, and 17 is the wheel diameter. This calculator converts flotation sizes so you can compare them directly with metric sizes. Use the Offroad option to enter one.