17 vs 18 Inch Tires: Fit and Fuel Economy

What the numbers mean

The last number in a tire size like 225/55R17 is the rim diameter, measured in inches. Under Federal Motor Vehicle Safety Standard 110, rim diameter is defined as the nominal diameter of the bead seat, the part of the rim that holds the tire bead. This number determines which wheel the tire fits. The other figures, section width in millimeters and aspect ratio, combine with rim diameter to set the overall tire diameter. For a deeper explanation, see our guide on tire size explained.

Choosing a 17-inch versus an 18-inch wheel changes the proportions of the tire and wheel assembly. To keep overall diameter constant, a larger rim requires a lower profile tire, meaning a shorter sidewall. For example, a common crossover tire might be 225/55R17 on 17-inch wheels and 225/45R18 on 18-inch wheels. The overall diameter stays close, but the sidewall height drops. This difference is at the heart of the ride and handling trade-off, which we cover in the next sections. Understanding tire aspect ratio helps you see how sidewall height changes with rim diameter.

Fitment and safety

Your vehicle's manufacturer specifies the correct tire and rim sizes on the placard, usually in the driver's door jamb. Federal regulations require that the tires fitted to an axle have a combined maximum load rating at least equal to the gross axle weight rating. For passenger cars, the normal load on a tire cannot exceed 94 percent of its load rating at the recommended cold inflation pressure, as defined in FMVSS 110 and 139. Straying from these recommendations risks overloading the tires and can affect handling and braking. If you are considering changing wheel sizes, start with our plus sizing guide to understand the limits.

Most vehicles built for the U.S. market also come with a tire pressure monitoring system, or TPMS. Under FMVSS 138, the system must warn you if a tire's pressure falls 25 percent below the manufacturer's recommended cold inflation pressure. That warning applies regardless of wheel diameter, so whether you run 17 or 18 inch wheels, maintaining the correct pressure is essential for safety and efficiency. Proper pressure also plays a key role in tire wear and fuel economy.

Ride comfort and handling

The sidewall height, or aspect ratio, is a major factor in ride comfort. A taller sidewall, typical on 17-inch wheels, flexes more as it rolls, absorbing road irregularities and producing a softer ride. A shorter sidewall, common on 18-inch wheels, transfers more of the road surface to the suspension and steering, which can feel harsh on broken pavement but also reduces body roll and sharpens turn-in. Our guide on tire sidewall height and comfort explains the physics behind this trade-off. For a more detailed look at how sidewall height affects ride quality, see tire aspect ratio and ride comfort.

For most commuting and family use, the smoother ride of a 17-inch setup is often preferred. For enthusiasts who enjoy spirited driving, the crisper response of 18-inch wheels may be worth the firmness. The best choice depends on your vehicle, your local roads, and how you prioritize comfort versus performance. If you are replacing tires on your current wheels, consult our best 17-inch tires or best 18-inch tires to see what options are available in each diameter.

Fuel economy

Proper tire pressure is the most direct way to keep fuel economy in check. According to the U.S. Department of Energy, keeping tires inflated to the recommended pressure can improve gas mileage by 0.6 percent on average, and up to 3 percent in some cases. Under-inflated tires can lower gas mileage by about 0.2 percent for every 1 psi drop in average pressure. This applies to any wheel diameter, but it is especially important if you move to a larger wheel, because larger wheels and tires often carry more weight and have higher rolling resistance. Our article on tire rolling resistance discusses how these factors interact.

Wheel weight also matters. Larger wheels are typically heavier, and extra unsprung weight can reduce suspension compliance and fuel efficiency. However, many modern 18-inch wheels are designed to be lightweight, so the difference is not automatic. When comparing 17 and 18 inch sets, look at the actual weight and rolling resistance values published by tire and wheel manufacturers. For everyday driving, the fuel saving from a lighter 17-inch wheel is often small but measurable over thousands of miles. The relationship between tire width and fuel economy is covered elsewhere on this site.

Speedometer and load considerations

Because the overall diameter of the tire and wheel assembly determines how many times the wheel rotates per mile, a change in diameter will affect your speedometer and odometer. Your vehicle's calibration assumes the factory tire size. If you switch to a 17-inch or 18-inch wheel with a different overall diameter, the speedometer may read inaccurately. For more detail, see our guide on tire diameter and speedometer accuracy.

Load rating is another critical spec. The maximum load rating of a tire, defined in FMVSS 139, is the maximum load it is rated to carry at a given inflation pressure. When changing wheel sizes, the new tire must have a load rating that meets or exceeds the original equipment requirement for your vehicle. The placard and owner's manual provide the exact numbers. Our load index guide explains how to read these ratings. Also, review the tire speed rating guide to ensure the new tires match your vehicle's capability.

What to pick for your use

Questions

Can I put 18-inch wheels on a car that came with 17-inch wheels?

It is possible, but only if the overall diameter remains similar and the new tires have adequate load and speed ratings. Changing wheel size can affect speedometer accuracy, clearance, and handling. Consult a tire professional and check the vehicle's specifications before making the change.

Will 18-inch wheels improve handling?

Generally, yes. Lower profile tires on 18-inch wheels reduce sidewall flex, which can sharpen steering response and reduce body roll. However, the effect is most noticeable on smooth roads; on rough surfaces, the firmer ride may be a disadvantage.

Do 17-inch wheels get better fuel economy than 18-inch?

Not automatically. Fuel economy depends on tire weight, rolling resistance, and pressure. A lightweight 17-inch wheel with a low rolling resistance tire can be more efficient, but many 18-inch wheels are also optimized for efficiency. Proper inflation is the most important factor.

How do I know what tire size to buy?

Check the tire pressure placard in the driver's door jamb or your owner's manual. It lists the original tire size and recommended inflation pressure. If you want to change sizes, use a reputable plus-sizing calculator and ensure the new tires meet your vehicle's load and speed requirements.