Plus-size tire calculator
Moving to a bigger or smaller wheel? Enter your current tire size and the new rim diameter to see which tire sizes keep the overall diameter close to what you have now.
Sizes on a 20 in rim within 3% of 285/70R17 (32.71 in tall):
| Size | Diameter (in) | Change | Width (in) | Width change (in) | Sidewall (in) |
|---|---|---|---|---|---|
| 295/55R20 | 32.78 | +0.2% | 11.61 | +0.39 | 6.39 |
| 265/60R20 | 32.52 | −0.6% | 10.43 | −0.79 | 6.26 |
| 275/60R20 | 32.99 | +0.9% | 10.83 | −0.39 | 6.50 |
| 285/55R20 | 32.34 | −1.1% | 11.22 | 0.00 | 6.17 |
| 305/55R20 | 33.21 | +1.5% | 12.01 | +0.79 | 6.60 |
| 305/50R20 | 32.01 | −2.1% | 12.01 | +0.79 | 6.00 |
| 285/60R20 | 33.46 | +2.3% | 11.22 | 0.00 | 6.73 |
| 275/55R20 | 31.91 | −2.4% | 10.83 | −0.39 | 5.95 |
| 265/65R20 | 33.56 | +2.6% | 10.43 | −0.79 | 6.78 |
How the list is made
The calculator tries every metric width from 155 to 355 mm (in 10 mm steps) and every aspect ratio from 25 to 85 on the rim you choose. It keeps the sizes whose nominal diameter, from the official sizing formula, is within your limit, then lists the closest first. Sizes with a page on this site are linked.
Not every combination is made. Check that a tire maker lists the size before you plan around it, and check its load index: a lower-profile tire on a bigger wheel often has a different load index from the original.
Plus sizing in short
Plus sizing means a larger wheel with a lower-profile tire, so the overall diameter, and the speedometer, stay close to stock. A shorter sidewall usually gives sharper steering and a firmer ride. The default 3% limit is a rule of thumb, not a regulation; see changing tire size.
Printed from https://tiresizecalc.net/plus-size-calculator/. Figures as published on 2026-11-01. The full working and the official sources are on that page.
Sources
- UN Regulation No. 30 - Uniform provisions concerning the approval of pneumatic tyres for motor vehicles and their trailers (Revision 3). United Nations Economic Commission for Europe (UNECE). E/ECE/324 E/ECE/TRANS/505 Rev.1/Add.29/Rev.3. 2007-03-29. Para 2.15 and 6.1.2.1: nominal diameter of each candidate size. Retrieved 2026-11-01.
- UN Regulation No. 54 - Uniform provisions concerning the approval of pneumatic tyres for commercial vehicles and their trailers (Revision 2). United Nations Economic Commission for Europe (UNECE). E/ECE/324 E/ECE/TRANS/505 Rev.1/Add.53/Rev.2. 2004-04-16. Para 6.1.2.1 and Annex 5 Table B: light truck and inch sizes. Retrieved 2026-11-01.
- Computed by tiresizecalc.net from the cited formula. Sri Murugan Systems. Candidates: widths 155-355 mm in 10 mm steps, aspect ratios 25-85 in steps of 5; change = new diameter / current diameter - 1. Retrieved 2026-11-01.
Last reviewed 2026-11-01. The full source list, with dates and file checksums, is in How the numbers are calculated. To report an error, email contactus@tiresizecalc.net.