155/70R17 Tire Size

All You Need to Know About 155/70R17 Tires

The 155/70R17 tire is a (T) temporary spare size designed to maintain limited mobility while minimizing storage space and weight.

The T155/70R17 size represents a tire that is 155 mm wide, with a 70% aspect ratio, mounted on a 17-inch wheel, producing an overall diameter of ≈25.5 inches and a sidewall height of ≈4.27 inches.

Compared to narrower spare formats such as 145/80R17, the 155/70R17 increases section width while reducing sidewall height. This results in a broader contact patch but a slightly smaller overall diameter.

Because of this configuration, the T155/70R17 sits closer to compact spare designs than taller temporary spares, prioritizing packaging efficiency over rolling diameter matching.

T155/70R17 Size Quick Specs

• Approved rim width range: 4.0-5.5"
• Typical inflation pressure: ≈60 PSI
• Overall diameter: ≈25.5"
• Section width: 155 mm
• Sidewall height: ≈108.5 mm
• Fits: 17-inch wheels (temporary spare applications)

Note: The calculated overall diameter of 155/70R17 is ≈25.5 inches. Actual mounted diameter typically varies within ±0.1-0.2 inches depending on construction.

T155/70R17 Dimensions in Inches

The 155/70R17 tire is approximately 6.10 inches wide, 25.5 inches tall, and has a sidewall height of ≈4.27 inches.

At this diameter, the rolling circumference is ≈80.1 inches, which determines the distance traveled per wheel revolution.

155/70R17 in Inches: All Measurements

• Overall diameter: ≈25.5"
• Width: ≈6.1"
• Sidewall height: ≈4.27"
• Wheel diameter: 17"
• Circumference: ≈80.1"

T155/70R17 Circumference Difference vs Full-Size Tires

With a circumference of ≈80.1 inches, the 155/70R17 spare is smaller than most full-size 17-inch tires, which commonly range from ≈82 to 90 inches depending on the vehicle.

This creates a rotational difference of approximately 1.8 to 9.8 inches per revolution, or ≈2.2% to 12.1%, depending on the original tire size.

Because the T155/70R17 overall diameter is lower than both 145/80R17 and 135/90R17, the mismatch in rotational speed is more pronounced. As a result, drivetrain components must compensate continuously when the spare is installed.

Axle Placement Requirements for T155/70R17

The 155/70R17 spare should be installed on a non-driven axle whenever possible.

• On front-wheel-drive vehicles, the 155/70R17 tire should be mounted on the rear axle
• On rear-wheel-drive vehicles, the 155/70R17 tire should be mounted on the front axle

Due to its ≈25.5-inch diameter, the 155/70R17 size creates a measurable difference in rolling speed compared to standard tires. Installing it on the driven axle increases differential activity and mechanical load.

Correct 155/70R17 placement reduces continuous compensation within the drivetrain and limits wear during temporary use.

155/70R17 Inflation Pressure Requirements

A 155/70R17 temporary spare typically operates at approximately 60 PSI.

Although the wider 155 mm section of the 155/70R17 tire increases the contact area compared to narrower spares, load support still depends primarily on internal pressure rather than structural rigidity.

A T155/70R17 temporary spare must be kept at its specified inflation pressure (60 PSI) to maintain rated load capacity. Running below the specification causes the sidewall to flex beyond its designed range, which raises internal operating temperatures and accelerates structural fatigue.

Correct pressure is not optional - it is the primary factor in preventing failure during 155/70R17 temporary use.

Most Recommended 155/70R17 Tires

Best tires in 155/70R17 size include: Continental Spare Tire