155/85R18 Tire Size
A 155/85R18 tire is approximately 28.37 inches tall, with a sidewall height of 5.19 inches and about 710.8 revolutions per mile.
Quick facts
155/85R18 Dimensions
| Measurement | Inches | Millimeters |
|---|---|---|
| Overall diameter | 28.37 | 721 |
| Sidewall height | 5.19 | 132 |
| Section width | 6.10 | 155 |
| Circumference | 89.14 | 2264 |
| Wheel diameter | 18 | 457 |
| Revolutions per mile | 710.8 | — |
Prefilled Calculator for 155/85R18
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How to use this tire size page
This 155/85R18 page is meant to be a quick reference before you compare, shop, or change sizes. The first number, 155, is the section width in millimeters. The 85 is the aspect ratio, which means the sidewall height is 85% of the tire width. The R18 means the tire is built for a 18-inch wheel.
The most useful number for comparisons is usually overall diameter. Diameter affects how far the tire travels in one rotation, which is why it also affects circumference, revolutions per mile, and speedometer behavior. A size that is wider is not always much taller, and a size that looks close can still change the driving feel if the height changes.
Use the prefilled calculator on this page to test the size, then compare it against the tire size currently on your vehicle. Before buying, confirm the tire placard, load rating, speed rating, wheel width range, and available clearance. Tire dimensions are calculated from the size code, but real tires can vary slightly by brand, tread design, and construction.
What this size says at a glance
A 155/85R18 is a narrow tire size, often seen on small cars, compact applications, or space-conscious fitments. The 85 aspect ratio gives it a very tall sidewall, so overall height, gearing feel, and body clearance should be checked carefully. Because it fits a 18-inch wheel, it falls into a very common wheel diameter range for cars, crossovers, SUVs, and light trucks.
Calculated from the size code, this tire is about 28.37 inches tall with a sidewall close to 5.19 inches. That sidewall number is useful because it hints at ride feel and wheel protection, while the overall diameter is the number that matters most when comparing speedometer behavior.
If you are considering 155/85R18 as a replacement, compare it against the tire currently installed on the vehicle rather than relying only on the printed width. A tire can gain width without gaining much height, or it can keep a similar width while changing diameter enough to affect road speed. The calculator above gives you the exact starting point for that decision.