A 305/55R20 tire measures 33.2 inches in overall diameter, or about 843.5 mm from tread surface to tread surface. That height—called the overall diameter—is the most critical dimension for checking clearance, keeping your speedometer accurate, and ensuring the tire fits inside the wheel well without rubbing. Those three figures determine height, stance, gearing impact, and whether the tire fits your vehicle at all.
For the full breakdown, see our best 305/55R20 All Terrain Tires guide.
What Do the Numbers in 305/55R20 Mean?
305 is the section width in millimeters—the widest point from sidewall to sidewall when mounted and inflated. That converts to about 12.0 inches, though actual mounted width for specific models often measures 12.4 inches due to different measuring rims and tread designs. The 305 mm width places this tire in the wide light-truck category, giving a substantial footprint for off-road traction and stability.
55 is the aspect ratio: sidewall height is 55 percent of section width. Multiply 305 mm by 0.55 to get about 168 mm, or 6.6 inches. This is height from rim bead seat to tread shoulder, not overall tire height. A lower ratio (45 or 50) would mean a shorter sidewall and smaller diameter; a higher ratio (60 or 65) would make the tire taller.
R20 means a radial tire for a 20-inch wheel. Recommended rim width for most 305/55R20 tires falls between 8.5 and 11.0 inches. The Toyo Open Country A/T III recommends 9.0 to 11.0 inches; the BFGoodrich All-Terrain T/A KO2 lists 8.5 to 11.0 inches. Mounting outside that range can cause poor bead seating, uneven wear, or handling issues.
How the 33.2-Inch Overall Diameter Is Calculated
305/55R20 Tire Height: Real Differences Between Tire Models
Two tires with the same 305/55R20 code can vary slightly in actual diameter, tread width, weight, and load capacity due to different tread designs, casing construction, and measuring rims.
| Specification | Toyo Open Country A/T III | BFGoodrich All-Terrain T/A KO2 |
|---|---|---|
| Overall Diameter | 33.2 in | 33.2 in |
| Tread Width | 12.4 in | 12.4 in |
| Rim Width Range | 9.0–11.0 in | 8.5–11.0 in |
| Revs per Mile | 625 | 626 |
| Max Load (Single/Dual) | 3,640 / 3,305 lb | 3,195 / 2,910 lb |
| Max Pressure | 80 psi | 65 psi |
| Weight | 66 lb | 60.7 lb |
| Load Range | E | E |
Load range, speed rating, and tread depth vary between models. Always check the manufacturer’s spec sheet—size code alone provides nominal dimensions, not the full safety picture. Before mounting, test clearance at full suspension compression and full steering lock; a tire that clears one truck may rub on another.
FAQs
Is 305/55R20 the same as a 33-inch tire?
The difference matters for clearance and lift requirements.
What is the sidewall height of a 305/55R20?
This is distance from rim to tread shoulder, not overall tire height.
Can 305/55R20 tires fit a 9-inch wide rim?
Always confirm with the specific tire model’s spec sheet, as ranges may shift between manufacturers.
References & Sources
- tiresize.com. “305/55R20 Tire Size Specifications.” Provides nominal dimensions, diameter, circumference, and revolutions per mile for the 305/55R20 size.