Tire diameter change
−0.17%
Smaller diameterThe proposed tire is 1.1 mm shorter.
Plus Sizing Calculator
Explore a larger rim while comparing nominal overall diameter. Enter a specific candidate or choose from a bounded mathematical search—not a vehicle-approved tire list.
Result updated. 225/45R17 → 220/40R18: nominal diameter changes by −0.17% (smaller diameter). The comparison and candidate ranking are geometry only, not replacement recommendations.
Result
225/45R17 → 220/40R18: nominal diameter changes by −0.17% (smaller diameter). The comparison and candidate ranking are geometry only, not replacement recommendations.
Sidewall change
−13.3 mm
Less sidewallNominal profile-height change, not a comfort or performance rating.
Ride-height change
−0.5 mm
LowerHalf the diameter change, before tire deflection under load.
Estimated actual speed
99.8 km/h
Lower than indicatedAt indicated 100.0 km/h, assuming the original tire was the calibration reference.
Details
- Nominal width change
- −5.0 mm
Swipe to view more, if needed
| Candidate | Diameter | Difference | Ride height | Select |
|---|---|---|---|---|
| 220/40R18 | 633.2 mm | −0.17% | −0.5 mm | |
| 255/35R18 | 635.7 mm | +0.22% | +0.7 mm | |
| 195/45R18 | 632.7 mm | −0.25% | −0.8 mm | |
| 250/35R18 | 632.2 mm | −0.33% | −1.0 mm | |
| 225/40R18 | 637.2 mm | +0.46% | +1.5 mm | |
| 200/45R18 | 637.2 mm | +0.46% | +1.5 mm | |
| 260/35R18 | 639.2 mm | +0.77% | +2.5 mm | |
| 215/40R18 | 629.2 mm | −0.80% | −2.5 mm | |
| 245/35R18 | 628.7 mm | −0.88% | −2.8 mm | |
| 190/45R18 | 628.2 mm | −0.96% | −3.0 mm |
Results use nominal geometry and the stated conventions. They are dimensional answers, not a fitment, safety or legality check.
Plus sizing changes the rim, not the target task
Plus sizing increases rim diameter while reducing sidewall height to keep overall tire diameter reasonably close to a reference. The goal is a dimensional comparison, not a guarantee that larger wheels or lower-profile tires will suit the vehicle.
Select a target rim larger than the original. An optional candidate must use that target rim; inconsistent typed values are preserved and flagged, not silently altered. Choosing a mathematical row enters that exact candidate for comparison.
How the candidate search is bounded
The search considers widths within 40 mm of the starting width, in 5 mm increments, and profiles from 10 to 100 in 5-point increments, bounded by the same input limits as the tire engine. It ranks by absolute diameter-percentage difference and displays up to ten matches.
Advanced provides a 0–10% search tolerance. It is only a filter on the mathematical search, not a universal compatibility threshold. If no candidates meet it, the tool says so rather than inventing a tire. Tie-breaking is deterministic: nearest width, then width and profile.
Read the chosen comparison
Diameter percentage uses the original tire as the reference. Sidewall and theoretical ride-height changes explain what keeping a similar diameter does and does not preserve. A larger rim with less sidewall can have nearly unchanged diameter while changing other physical characteristics.
Candidate widths and profiles are generated numbers. Some descriptions may not exist as commercial tires. Confirm manufacturer availability, approved rim width, actual dimensions and load/speed ratings independently; the top-ranked row is not a recommendation.
Example: searching an 18-inch rim alternative
Inputs: Original tire: 225/45R17; Target rim diameter: 18 in; Diameter search tolerance: 3 %. Metric results below are computed by the same engine as the live tool.
225/45R17 → 220/40R18: nominal diameter changes by −0.17% (smaller diameter). The comparison and candidate ranking are geometry only, not replacement recommendations.
Swipe to view more, if needed
| Measure | Calculated value | Meaning |
|---|---|---|
| Tire diameter change | −0.17% | The proposed tire is 1.1 mm shorter. |
| Sidewall change | −13.3 mm | Nominal profile-height change, not a comfort or performance rating. |
| Ride-height change | −0.5 mm | Half the diameter change, before tire deflection under load. |
| Estimated actual speed | 99.8 km/h | At indicated 100.0 km/h, assuming the original tire was the calibration reference. |
Important limitations
Search results rank nominal diameter only. They do not establish market availability, rim approval, brake clearance, body clearance, handling, comfort or suitability for a particular vehicle.
See the calculation methodology and testing and accuracy for precision, unit conventions and the distinction between nominal geometry and physical measurement.