Quick Answer
- AWD makers do not publish a percentage tolerance. Michelin says that with no instructions in the manual all four tires must be the same size with circumferences within 1 inch (2.5 cm). Vehicle manuals ask for the same size, circumference and construction on all four wheels, and Ford and Jeep warn that major size differences can disable the AWD system or damage the transfer case.
- To calculate the difference, convert each size to a diameter (rim + 2 x width x aspect / 100 / 25.4), then divide the difference by the smaller diameter. A 225/65R17 against a 235/65R17 is 1.79%.
- Continental's plus-sizing guidance keeps rolling circumference within 3%. That is a general limit, not an AWD tolerance.
Enter two tire sizes (for example the tires on the car and the one you plan to fit) to see the rolling diameter and circumference difference.
225/65R17
28.52 in
89.6 in circumference, 707 revs/mile
235/65R17
29.03 in
91.2 in circumference, 695 revs/mile
Difference
1.79%
0.51 in (13.0 mm), 12 revs/mile
Within 3%, the limit in Continental's plus-sizing guidance for rolling circumference. That is not an AWD tolerance: no manual we checked gives one, so the safe route is the same size on all four wheels.
Michelin says that when the owner's manual has no instructions, all four tires on an AWD or 4WD vehicle must be the same size and have outside circumferences within 1 inch (2.5 cm) of each other. These two sizes differ by 1.6 in (41 mm) of circumference and are not the same size.
Diameter = rim + 2 x (width x aspect / 100) / 25.4. The percentage is the difference divided by the smaller tire.
What Manufacturers Say About Mixed Tires on AWD
Summarized from owner's manuals and manufacturer pages. Most makers publish no percentage, and where they do not, the table says so.
| Manufacturer / system | Requirement | What the document says |
|---|---|---|
| Michelin (all makes, when the manual is silent) | Same size; circumferences within 1 inch | Michelin USA, Changing tire sizes: if no tire mixing instructions appear in the owner's manual, on four-wheel drive vehicles do not mix sizes (all four tires must be the same size), do not mix radial and bias-ply, and keep the outside circumferences of all four tires within 2.5 cm (1 inch) of each other. |
| Subaru Symmetrical AWD | No number published | Owner's manual: same size, circumference, construction, brand and load range, with the same amount of wear on all four |
| Honda AWD (i-VTM4) | No number published | Honda owner's manual (2017 Ridgeline): same size, load range, speed rating and maximum pressure. A different size or construction can make the VSA, hill start assist, AWD and ABS work incorrectly. It is best to replace all four tires at once, otherwise replace the front or rear pair |
| BMW xDrive | No number found; rolling circumference as similar as possible | BMW Australia's tyre FAQ says that on xDrive models all four tyres should have as similar a rolling circumference as possible. We found no official BMW figure for a tolerance |
| Audi quattro | No manufacturer figure found | We could not find a published Audi tolerance, so none is shown. Your Audi owner's manual is the authority, and Audi dealers can confirm the rule for your drivetrain |
| Toyota / Lexus 4WD and AWD | Same brand, size, construction and tread pattern | Toyota owner's manuals (for example the 2008 RAV4): on four-wheel drive models all tires must be the same brand with the same tread pattern, and Toyota recommends replacing all four, or at least both front or both rear tires, as a set |
| Ford AWD | Same original tire size; new and worn mix tolerated | Ford owner's manual: use tires of the same size, load index, speed rating and type. Major size differences between axles can make the AWD system stop working or damage it, but it can tolerate any combination of new and worn tires of the same original size |
| Jeep 4x4 (Quadra-Trac / Quadra-Drive) | Equal size, type and circumference | Jeep owner's manual (2022 Wagoneer): proper operation depends on tires of equal size, type and circumference on each wheel. Any difference will adversely affect shifting and cause damage to the transfer case |
Requirements differ by maker and model year. Verify with your own owner's manual. BMW owners can run a pair through the xDrive rolling diameter check.
Tire Size Difference Examples
Calculated rolling diameter difference for common swaps. Continental's guidance for rolling circumference is 3%; makers of AWD vehicles ask for matched tires.
| Tire A | Tire B | A diameter | B diameter | Difference | Revs per mile gap |
|---|---|---|---|---|---|
| 225/65R17 | 225/65R17 | 28.52 in | 28.52 in | 0.00% | 0 |
| 225/65R17 | 235/65R17 | 28.52 in | 29.03 in | 1.79% | 12 |
| 215/60R16 | 225/55R17 | 26.16 in | 26.74 in | 2.24% | 17 |
| 225/45R17 | 245/40R18 | 24.97 in | 25.72 in | 2.98% | 23 |
| 265/70R17 | 275/65R18 | 31.61 in | 32.07 in | 1.48% | 9 |
| 225/65R17 | 245/65R17 | 28.52 in | 29.54 in | 3.59% | 25 |
For the effect on your speedometer use the speedometer error calculator, and the tire size difference calculator for any pair.
Factory Front and Rear Sizes on Audi AWD Models
Some AWD models leave the factory with different front and rear sizes: Audi's owner's manuals print them, with a calculated rolling diameter gap of 0.00% to 5.50%. This shows what a given system is sold with; it says nothing about how much mismatch a system tolerates when you mix sizes.
| Model | Front | Rear | Diameter gap (calc.) |
|---|---|---|---|
| Audi R8 Coupe / Spyder 2023 | 245/35ZR19 | 295/35ZR19 | 5.35% |
| Audi R8 Coupe / Spyder 2023 | 245/30ZR20 | 305/30ZR20 | 5.50% |
| Audi e-tron GT 2024 | 225/55R19 | 275/45R19 | 0.00% |
| Audi e-tron GT 2024 | 245/45R20 | 285/40R20 | 1.03% |
| Audi e-tron GT 2024 | 265/35R21 | 305/30R21 | 0.35% |
| Audi Q4 e-tron 2024 | 235/55R19 | 255/50R19 | 0.47% |
| Audi Q4 e-tron 2024 | 235/50R20 | 255/45R20 | 0.75% |
| Audi Q6 e-tron 2027 | 235/65R18 | 255/60R18 | 0.07% |
| Audi Q6 e-tron 2027 | 235/60R19 | 255/55R19 | 0.20% |
| Audi Q6 e-tron 2027 | 255/50R20 | 285/45R20 | 0.20% |
| Audi Q6 e-tron 2027 | 255/45R21 | 285/40R21 | 0.20% |
More on mixed front and rear sizes in the staggered fitment calculator.
How to Calculate Tire Size Difference From the Sidewall
Diameter from the size
Diameter in inches = rim + 2 x (width in mm x aspect / 100) / 25.4. For 225/65R17: 17 + 2 x 146.25 / 25.4 = 28.51 in.
Circumference
Circumference = pi x diameter. Rolling circumference sets how far the tire travels per turn, so a difference in circumference means a difference in wheel speed at the same road speed.
Percent difference
Difference divided by the smaller tire, times 100. The same percentage applies to diameter and circumference.
Revolutions per mile
Revs per mile = 63,360 / circumference in inches. The gap between two tires is how many more turns the smaller one makes in a mile.