255/40R21
Standard MetricFactory Specs, Physical Dimensions & Compatible Vehicle Applications
The 255/40R21 tire size features an overall diameter of 29.03 inches, a section width of 10.0 inches (255mm), and rotates 695 times per mile. It is a standard factory tire fitment on 47+ vehicle models including Alfa Romeo Stelvio.
Physical Dimensions & Specs
Overall Diameter
29.03"
737.4 mmSection Width
255 mm
10.04" wideSidewall Height
4.02"
102.1 mm (40% aspect)Revolutions / Mile
695
Circumference: 91.21"Rim Diameter
21"
Wheel sizeRecommended Rim Width
6.4" - 8.9"
Optimal rim width rangeWhere to Buy & Install 255/40R21 Tires
Looking for 255/40R21 tires? Skip hauling tires in your car—choose direct delivery to a local certified shop or doorstep delivery:
Tire Rack
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Amazon Automotive
Fast doorstep shipping for DIYers or bringing to your own shop.
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Speedometer & Alternate Size Calculator
Testing an alternate size for your vehicle? Compare 255/40R21 against any proposed tire size below:
Visual Tire & Wheel Comparison
Speedometer Variance
| Indicated | Actual Speed | Diff |
|---|---|---|
| 20 mph | 20.4 mph | +0.4 mph |
| 30 mph | 30.6 mph | +0.6 mph |
| 45 mph | 45.8 mph | +0.8 mph |
| 60 mph | 61.1 mph | +1.1 mph |
| 75 mph | 76.4 mph | +1.4 mph |
| 90 mph | 91.7 mph | +1.7 mph |
Fender & Suspension Clearance
Flush fitment. Extends 17.7mm outwards. Check wheel arch clearance under full suspension compression.
Vehicles That Fit 255/40R21 (47+ Models)
Factory standard and optional vehicle fitments utilizing 255/40R21 tires: