P315/35R17 Tire Size

All You Need to Know About P315/35R17 Tires

P315/35R17 tires use the P-metric (passenger) load standard, in which load capacity is determined by standardized TRA (Tire and Rim Association) pressure-to-load tables and is conditioned on passenger car application. 

P315/35R17 tires are 315 mm wide, with a 35% aspect ratio and a 17-inch wheel diameter, resulting in an overall diameter of approximately 25.7 inches and a sidewall height of about 4.34 inches - identical in physical dimensions to 315/35R17.

This page focuses on P315/35R17 as a load-defined tire size. The companion page for 315/35R17 (Euro-metric, no prefix) covers the same dimensions from a fitment perspective - wheel width compatibility, fender and suspension clearance, and size substitution within the ±3% diameter threshold. 

This page covers what is distinct to the P-metric designation in the P315/35R17 tire size: how load capacity is assigned from TRA tables, how that capacity changes under light truck application, and how the tire's load index should be evaluated against the vehicle's Gross Axle Weight Rating (GAWR).

The P in P315/35R17 identifies a passenger-car load standard. In P315/35R17, that designation does not change section width, sidewall height, or overall diameter; it changes the method used to assign load capacity.

That distinction matters because P315/35R17 must be evaluated by load index and inflation pressure, not by size alone. A 315 mm width and a 25.68-inch diameter do not automatically confirm that a P315/35R17 tire meets the load requirement of the vehicle on which it is installed.

P315/35R17 Load Capacity Is Pressure-Dependent

In P315/35R17, load capacity increases with inflation pressure up to the pressure assigned for the tire’s load standard. For P-metric tires, the industry-assigned pressure used to rate maximum load is typically 35 psi for Standard Load (SL) and 41 psi for Extra Load (XL).

That means the P315/35R17 load capacity is not a fixed number that can be assumed from size alone. The actual load carried by a P315/35R17 tire depends on its service description, whether it is SL or XL, and the cold inflation pressure at which it is operated.

In performance-oriented P-metric tires, the sidewall may also show a 44 psi maximum inflation pressure. In that case, the extra pressure range does not change the size of P315/35R17; it reflects the tire’s construction and pressure capability beyond the assigned pressure used for maximum-load rating.

For that reason, P315/35R17 should be matched by load index first, then by pressure requirement, and only after that by dimensional fit. Where a vehicle places a higher demand on the rear axle, verifying the placard load requirement matters more than the fact that the tire is 315 mm wide.

P315/35R17 Load Capacity: Application and Verification

The load capacity of a P315/35R17 tire is not determined by size alone. Three factors govern whether a specific P315/35R17 meets the load requirement of a given application: 

• whether the vehicle is a passenger car or a light truck 
• whether the tire is Standard Load or Extra Load
• whether the load index stamped on the sidewall meets or exceeds the vehicle's axle load requirement. 

Each factor is independent - a correct size does not confirm correct load capacity.

P315/35R17 in light-truck or high-load use: When a P315/35R17 tire is installed on a light truck or SUV, its effective load capacity is reduced by a factor of 1.10 (≈9-10%) under TRA guidelines. For example, a P315/35R17 with a load index of 109 (≈2,271 lbs at rated pressure) is reduced to ≈2,064 lbs per tire when applied in LT service. This reduction does not apply when P315/35R17 is used on passenger cars.

SL vs. XL in P315/35R17: A Standard Load P315/35R17 (rated at 35 psi reference pressure) carries less load than an Extra Load P315/35R17 (rated at 41 psi reference pressure). In this size, load index values typically fall in the 106-110 range, meaning the difference between SL and XL versions can exceed 200 lbs per tire. Two P315/35R17 tires with the same dimensions but different load types are not interchangeable unless the required load index is still met.

Load index verification for P315/35R17: Each P315/35R17 tire lists its maximum load and corresponding pressure on the sidewall. Because this size is often used on rear axles of performance vehicles, the load carried per tire can be high relative to passenger-car norms. Always verify that the selected P315/35R17 load index meets or exceeds the vehicle's rear Gross Axle Weight Rating (GAWR). A mismatch in load index cannot be corrected by increasing tire size or width alone.

Speed Rating and Load Index in P315/35R17

P315/35R17 tires in this size commonly carry W (168 mph) or Y (186 mph) speed ratings, reflecting their primary use on performance platforms. Speed rating and load index are independent sidewall designations - a higher speed rating does not increase load capacity, and a lower speed rating does not reduce it.

When selecting a P315/35R17 for a performance rear application, both values must independently meet the vehicle manufacturer's minimum requirements. A tire that satisfies the load index but carries an insufficient speed rating does not meet the full service description requirement.

Selecting P315/35R17: What the Size Does Not Tell You

P315/35R17 identifies a physical tire - 315 mm wide, 25.7 inches in diameter, 17-inch wheel. It does not identify load capacity, load type, pressure requirement, or speed rating. Two tires of this size can carry materially different loads depending on whether they are SL or XL, what load index is stamped on the sidewall, and whether the vehicle is a passenger car or light truck.

For fitment questions - wheel width, fender clearance, and size substitution - see the 315/35R17 page. Those geometric constraints apply equally to P315/35R17 and are not repeated here.

For the P-metric size specifically, correct selection means: load index first, speed rating second, SL or XL confirmed, LT deration applied where relevant, and dimensional fit last.