Quick Answer
- Rolling radius is the radius a tire behaves as while it rolls: 63,360 / revs per mile / 2 pi. A 225/45R17 has a free radius of 12.49 in and a geometric 808 revs per mile.
- In the Bridgestone and Michelin truck data books the static loaded radius is 90.6% to 94.4% of the free radius and the rolling radius 96.2% to 100.0%.
- No published passenger tire data was found, so use the maker's revs per mile or a measured rollout for exact work.
Enter a tire size such as 225/45R17, 295/75R22.5 or 35x12.50R20 for the free radius and the loaded and rolling radius ranges.
225/45R17
Free radius (calculated)
12.49 in
317 mm, diameter 24.97 in
Static loaded radius
11.32 to 11.79 in
90.6% to 94.4% of free radius
Dynamic rolling radius
12.01 to 12.49 in
96.2% to 100.0% of free radius
Revolutions per mile
Free radius 808, with the data book rolling ratio (mean 97.3%) about 830
The loaded and rolling ranges come from 149truck tire rows in the Bridgestone and Michelin data books. We found no published passenger tire data, so they are indicative for cars. For exact work use the maker's published revs per mile or a measured rollout.
Get a plain-English explanation of your results and what they mean for your vehicle.
Tire Radius and Circumference Chart by Size
Free radius, circumference and geometric revolutions per mile calculated from the size code. A loaded, rolling tire is a little smaller, so compare with the maker's published figure.
| Tire size | Free radius (in) | Free radius (mm) | Circumference (in) | Revs per mile |
|---|---|---|---|---|
| 195/65R15 | 12.49" | 317 | 78.48" | 807 |
| 205/55R16 | 12.44" | 316 | 78.16" | 811 |
| 225/50R16 | 12.43" | 316 | 78.09" | 811 |
| 225/45R17 | 12.49" | 317 | 78.45" | 808 |
| 235/45R18 | 13.16" | 334 | 82.71" | 766 |
| 245/40R18 | 12.86" | 327 | 80.79" | 784 |
| 235/60R18 | 14.55" | 370 | 91.43" | 693 |
| 255/35R19 | 13.01" | 331 | 81.77" | 775 |
| 275/40R20 | 14.33" | 364 | 90.04" | 704 |
| 265/70R17 | 15.80" | 401 | 99.29" | 638 |
| 285/75R16 | 16.42" | 417 | 103.14" | 614 |
| 35x12.50R17 | 17.50" | 445 | 109.96" | 576 |
| 35x12.50R20 | 17.50" | 445 | 109.96" | 576 |
| 37x12.50R17 | 18.50" | 470 | 116.24" | 545 |
Revolutions per mile for any size are on the revolutions per mile calculator, and the speedometer effect of a radius change is on the speedometer error calculator.
Published Static Loaded Radius and Rolling Radius (Truck Tires)
Overall diameter, static loaded radius and revolutions per mile from the tire makers' data books (first model listed for each size). The rolling radius is worked out from the published revs per mile, and both are shown as a percentage of the free radius (half the overall diameter).
| Size | Maker | Overall diameter | Free radius | Static loaded radius | % of free | Revs per mile | Rolling radius | % of free |
|---|---|---|---|---|---|---|---|---|
| 10R22.5 | Michelin | 40.1" | 20.05" | 18.7" | 93.3% | 517 | 19.50" | 97.3% |
| 11R22.5 | Bridgestone | 41.1" | 20.55" | 19.2" | 93.4% | 505 | 19.97" | 97.2% |
| 11R22.5 | Michelin | 41.3" | 20.65" | 19.3" | 93.5% | 502 | 20.09" | 97.3% |
| 11R24.5 | Bridgestone | 43.1" | 21.55" | 20.1" | 93.3% | 482 | 20.92" | 97.1% |
| 11R24.5 | Michelin | 43.3" | 21.65" | 20.2" | 93.3% | 479 | 21.05" | 97.2% |
| 12R22.5 | Bridgestone | 43.1" | 21.55" | 20.0" | 92.8% | 482 | 20.92" | 97.1% |
| 12R22.5 | Michelin | 42.9" | 21.45" | 20.1" | 93.7% | 483 | 20.88" | 97.3% |
| 12R24.5 | Bridgestone | 45.1" | 22.55" | 21.0" | 93.1% | 460 | 21.92" | 97.2% |
| 275/70R22.5 | Bridgestone | 38.5" | 19.25" | 17.9" | 93.0% | 540 | 18.67" | 97.0% |
| 275/70R22.5 | Michelin | 37.8" | 18.90" | 17.6" | 93.1% | 547 | 18.44" | 97.5% |
| 255/70R22.5 | Bridgestone | 36.3" | 18.15" | 17.1" | 94.2% | 572 | 17.63" | 97.1% |
| 255/70R22.5 | Michelin | 37.0" | 18.50" | 17.4" | 94.1% | 558 | 18.07" | 97.7% |
| 285/75R24.5 | Bridgestone | 41.3" | 20.65" | 19.4" | 93.9% | 503 | 20.05" | 97.1% |
| 285/75R24.5 | Michelin | 40.6" | 20.30" | 19.1" | 94.1% | 508 | 19.85" | 97.8% |
| 295/75R22.5 | Bridgestone | 40.3" | 20.15" | 18.8" | 93.3% | 516 | 19.54" | 97.0% |
| 295/75R22.5 | Michelin | 40.2" | 20.10" | 18.8" | 93.5% | 515 | 19.58" | 97.4% |
| 295/80R22.5 | Michelin | 41.3" | 20.65" | 19.1" | 92.5% | 503 | 20.05" | 97.1% |
| 275/80R22.5 | Michelin | 40.1" | 20.05" | 18.7" | 93.3% | 517 | 19.50" | 97.3% |
| 315/80R22.5 | Bridgestone | 42.6" | 21.30" | 19.8" | 93.0% | 488 | 20.66" | 97.0% |
| 315/80R22.5 | Michelin | 42.3" | 21.15" | 19.6" | 92.7% | 491 | 20.54" | 97.1% |
| 385/65R22.5 | Bridgestone | 42.9" | 21.45" | 19.8" | 92.3% | 484 | 20.83" | 97.1% |
| 225/70R19.5 | Bridgestone | 32.4" | 16.20" | 15.1" | 93.2% | 641 | 15.73" | 97.1% |
| 225/70R19.5 | Michelin | 32.2" | 16.10" | 15.2" | 94.4% | 640 | 15.76" | 97.9% |
| 245/70R19.5 | Michelin | 33.6" | 16.80" | 15.6" | 92.9% | 619 | 16.29" | 97.0% |
| 265/70R19.5 | Michelin | 34.0" | 17.00" | 15.8" | 92.9% | 611 | 16.50" | 97.1% |
| 285/70R19.5 | Michelin | 35.2" | 17.60" | 16.2" | 92.0% | 591 | 17.06" | 96.9% |
| 215/75R17.5 | Michelin | 30.3" | 15.15" | 14.0" | 92.4% | 686 | 14.70" | 97.0% |
| 245/70R17.5 | Michelin | 31.2" | 15.60" | 14.2" | 91.0% | 670 | 15.05" | 96.5% |
Sources: Bridgestone Truck Tire Data Book 2023 (Static Loaded Radius, Revs Per Mile) and Michelin Truck Tire Data Book (Loaded Radius, Revs Per Mile). Across 149 rows the static loaded radius is 90.6% to 94.4% of the free radius (mean 93.1%) and the rolling radius 96.2% to 100.0% (mean 97.3%). Three extracted rows with a loaded radius outside 88% to 96% were dropped as column misreads.
Free, Static Loaded and Dynamic Rolling Radius Explained
| Term | Meaning |
|---|---|
| Free radius | Half the overall diameter of the unloaded tire. USTMA defines overall diameter as twice the section height (unloaded) plus the nominal rim diameter. |
| Static loaded radius | The distance from the wheel center to the ground with the tire loaded and standing. Tire makers publish it in their data books (Bridgestone: Static Loaded Radius, Michelin: Loaded Radius). |
| Dynamic rolling radius | The effective radius while rolling: the rolling circumference divided by 2 pi. It follows from the published revolutions per mile, as 63,360 / revs per mile / 2 pi. |
| Rolling circumference | The distance the tire travels in one revolution, 63,360 inches divided by the revolutions per mile. |
Free radius
Rim / 2 + width x aspect / 100 / 25.4. For 225/45R17: 8.5 + 3.99 = 12.49 in.
Rolling circumference from revs per mile
63,360 / revs per mile. For a published 502 revs per mile: 63,360 / 502 = 126.2 in.
Rolling radius
Circumference / 2 pi. For 126.2 in: 20.09 in.
Revolutions per mile from a radius
63,360 / (2 pi x radius). A 19.5 in rolling radius gives 517 revs per mile.
The effective gearing from the radius is on the effective gear ratio calculator and the engine RPM to mph calculator.
How to Use the Rolling Radius Calculator
- 1In Radius from a Tire Size, type a size. You get the free radius and the loaded and rolling radius ranges from the published truck data.
- 2If you have the tire maker's revs per mile, a measured circumference or a radius, open Radius, Circumference and Revs and enter it to convert between the three.
- 3Use the rolling radius or revs per mile for gearing and speedometer work, and the loaded radius for ride height and clearance questions.
- 4For exact work use the maker's published revs per mile or measure the rollout.