T155/80D17 Tire Size

T155/80D17 Spare Tire: Higher-Capacity Compact Spare Size Explained

T155/80D17 is a temporary compact spare tire wider than most donut spares, chosen by vehicle manufacturers when greater load-carrying capacity is needed while still fitting in a compact spare storage compartment.

The 155 mm section width gives T155/80D17 more load capacity than narrower compact spare sizes such as T125/70D17 or T135/80D17, making it appropriate for heavier vehicles - larger SUVs, minivans, and trucks where a lighter spare would be undersized.

T155/80D17 Quick Specs

What Each Part of the T155/80D17 Size Means

• T - Temporary spare
• 155 - Width in millimeters
• 80 - Aspect ratio
• D - Diagonal (bias-ply) construction
• 17 - Wheel diameter

Why Is T155/80D17 Larger Than Smaller Compact Spare Sizes?

The T155/80D17 wider section width increases the tire's load capacity. Heavier vehicles require more structural capacity in the spare, even if that spare is only intended for 50-mile emergency use. Manufacturers select T155/80D17 size when the vehicle's curb weight and load distribution would exceed the safe limits of a T125/70D17 or T135/80D17.

The 80% aspect ratio of the T155/80D17 size also helps the overall diameter more closely match the vehicle's OEM tires, reducing drivetrain stress during the short period the spare is in use.

T155/80D17 vs T155/90D17: The Width Is the Same - Diameter Is Not

Both sizes share the same 155 mm section width. The key difference is the aspect ratio: T155/80D17 has a shorter sidewall (80% of 155 mm = 124 mm), while T155/90D17 has a taller sidewall (90% of 155 mm = 139.5 mm). T155/90D17 will have a noticeably larger overall diameter and is fitted to vehicles whose OEM tires are too tall for the 80-series spare to match closely enough. Never substitute one for the other without verifying your vehicle's specification.