Tire Size Calculator
Compare tire sizes, calculate dimensions, and see speedometer/odometer differences.
Current Tire Size
Example: 225/55R17
New Tire Size
Example: 235/50R18
Tire Dimensions
| Current | New | Diff | |
|---|---|---|---|
| Diameter | 26.7" | 27.3" | +0.51" |
| Width | 8.9" | 9.3" | +0.39" |
| Sidewall | 4.87" | 4.63" | -0.25" |
| Revs/Mile | 754 | 740 | -14 |
Compatible Size
+1.9%
Diameter difference (recommend ±3% max)
Speedometer & Odometer Effects
Speedometer ReadingReads slow by 1.9%
At 60 mph indicated, actual speed: 61.1 mph
Odometer ReadingRecords fewer miles by 1.9%
Speed Conversion Table
| Indicated | Actual | Error |
|---|---|---|
| 30 mph | 30.6 mph | +0.6 mph |
| 45 mph | 45.9 mph | +0.9 mph |
| 60 mph | 61.1 mph | +1.1 mph |
| 70 mph | 71.3 mph | +1.3 mph |
| 80 mph | 81.5 mph | +1.5 mph |
Compatible Sizes
205/55R16
24.9"-7.0%
215/55R17OK
26.3"-1.6%
225/55R17OK
26.7"+0.0%
225/45R18OK
26.0"-2.9%
235/50R18OK
27.3"+1.9%
245/45R19
27.7"+3.5%
255/40R19OK
27.0"+1.1%
265/35R20OK
27.3"+2.1%
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Editorial Note
MyCalcBuddy Editorial Team
This page is maintained as an educational calculator reference.
📚
Formula Source: Standard Mathematical References
by Various
🔄Last reviewed: May 2026
✓Formula checks are based on standard references and internal QA review.