255/55R18 tires: size explained

A tire size describes the tire's shape and the wheel it fits. It says nothing about load capacity or speed capability, which are printed separately on the sidewall.

No letterEuro-metric

With no letter in front of the width, this is a Euro-metric size (also called hard metric). It has the same dimensions as the P-metric version but is built to a different load standard, so its load capacity can differ.

255Section width

The tire's width is 255 millimeters (10.0 in), measured from sidewall to sidewall.

55Aspect ratio

The sidewall height is 55% of the width. For 255 mm that is about 5.5 in (140 mm). A smaller number means a shorter sidewall.

RRadial construction

R means radial construction, where the internal cords run across the tire from one edge to the other.

18Wheel (rim) diameter

The tire is made for a wheel 18 inches across. Its overall diameter is larger: about 29.0 in (738 mm).

These are nominal design dimensions. Real tires vary by brand, tread depth, wheel width, load and pressure.

These vehicles list 255/55R18 among their verified sizes, by trim. Open one to see all of its sizes.

• 2027 Mercedes-Benz GLC GLC 350e 4MATIC SUV(rear)

Confirm the size on your tire sidewall or door placard first. These links open each store's own search for 255/55R18; prices and stock are on their sites.

Where winter roads call for extra traction, chains and tire socks are two options that fit over your tires. They are made for specific tire sizes, so these links open Amazon searches for 255/55R18. Whether they suit your vehicle depends on its clearance and the local rules.

Paid links to Amazon search results. As an Amazon Associate I earn from qualifying purchases. Read our affiliate disclosure.

Before you buy

• Chains and socks are sold by tire size, so match the size on your sidewall exactly.
• Check your owner's manual first: many newer cars and SUVs limit or prohibit chains, or require low-profile (often called SAE Class S) chains because of tight wheel-well clearance.
• Tire socks are a lighter-duty option; check your state's rules, because some areas only accept chains when chain controls are in effect.
• Put them on the drive wheels (or as your manual says) and follow the maker's speed limit.

These common sizes have an overall diameter within about 3% of 255/55R18. A common rule of thumb is to keep a replacement size within about 3% of the original overall diameter. Confirm any size change with your vehicle's owner's manual or a tire professional.

Side-by-side dimensions and speedometer difference for sizes close to 255/55R18 in overall diameter.

• 255/50R19 vs 255/55R18-0.01% shorter than 255/55R18
• 255/45R20 vs 255/55R18-0.03% shorter than 255/55R18
• 255/40R21 vs 255/55R18-0.04% shorter than 255/55R18
• 235/65R17 vs 255/55R18-0.05% shorter than 255/55R18
• 255/55R18 vs 285/40R20-0.23% shorter than 255/55R18
• 235/55R19 vs 255/55R18+0.46% taller than 255/55R18
• 235/50R20 vs 255/55R18+0.72% taller than 255/55R18
• 225/55R19 vs 255/55R18-1.03% shorter than 255/55R18
• 245/50R19 vs 255/55R18-1.37% shorter than 255/55R18
• 245/65R17 vs 255/55R18+1.71% taller than 255/55R18

See how another size differs in height, width, sidewall and speedometer reading in the tire size calculator.