P345/40R17 Tire Size

All You Need to Know About P345/40R17 Tires

P345/40R17 carries the passenger (P) load designation, meaning load capacity is calculated under passenger-use standards rather than light-truck or commercial rating systems. Its external dimensions are identical to 345/40R17, with an overall diameter of ≈27.9 inches and a sidewall height of ≈5.4 inches.

This page focuses on how the P-metric load system applies to this specialty performance size. For dimensional behavior, fitment characteristics, dimensions in inches, and vehicle applications, see 345/40R17 tires.

At ≈27.9 inches in diameter with a 345mm section width, P345/40R17 represents the upper boundary of P-metric passenger tire construction. The combination of extreme width and a 40-series profile means load is distributed across an exceptionally wide contact patch, which affects how P-metric load ratings translate to real-world operating conditions differently than narrower sizes in the same designation class.

What P Means in P345/40R17

The "P" designates a P-metric passenger tire built under U.S. load-rating standards. While dimensions match a non-P 345/40R17, the load calculation method differs.

At this section width, the P-metric derating carries more practical weight than it does on narrower sizes. When a P345/40R17 is used on any vehicle approaching its load ceiling, including performance vehicles with heavy drivetrains, the approximately 10% load capacity reduction relative to a Euro-metric equivalent of the same size becomes a factor that should be verified against the vehicle's actual axle load before selection.

P345/40R17 vs 345/40R17 (non-P version)

• Dimensions: identical (≈27.9")
• Width: identical (345 mm)
• Difference: load rating system and effective load ceiling under passenger-use standards

Because there is no dimensional difference, substitution between P345/40R17 and 345/40R17 does not raise a fitment issue. Verification must focus on load index, required inflation pressure, and whether the vehicle's axle loads fall within P-metric capacity limits at this width.

P345/40R17 Load Capacity and Pressure Behavior

Load capacity in P345/40R17 is directly tied to inflation pressure within the tire's rated limits. The 345mm section width creates a large internal air volume, which means pressure loss develops more gradually in terms of visible sidewall deformation than in narrower tires of the same aspect ratio.

On an already short ≈5.4-inch sidewall, however, structural consequences of underinflation concentrate quickly in the casing shoulders. The large footprint that defines this size's performance function also amplifies heat buildup under load when pressure falls below specification. Maintaining correct pressure is particularly critical here, where the combination of extreme width and low profile leaves minimal structural tolerance for deviation.

P345/40R17 Fitment Note

For P345/40R17, dimensional compatibility addresses only part of the selection process. Load index relative to axle weight, inflation pressure requirements, and rim width compatibility within the 11.5-13.5" approved range must all be confirmed together - particularly given that P-metric ratings at extreme widths carry a load ceiling that may not align with the demands of high-output platforms this size is typically selected for.