The short answer
Going from 265/70R17 (31.6 in tall) to 285/70R17 (32.7 in) makes the tire 3.5% taller (+1.10 in). 60 on the speedometer is really 62.1 mph, and the vehicle sits about 0.55 in higher. That is just over the 3% rule of thumb, so check clearance.
Worked example: 265/70R17 vs 285/70R17
| Step | Math | Result |
|---|---|---|
| Sidewall of 265/70R17 | 265 × 0.70 = 185.5 mm ÷ 25.4 | 7.30 in |
| Height of 265/70R17 | 17 + 2 × 7.30 | 31.61 in |
| Height of 285/70R17 | 17 + 2 × (285 × 0.70 ÷ 25.4) | 32.71 in |
| Difference | 32.71 − 31.61 | +1.10 in = +3.49% |
| True speed at 60 | 60 × 32.71 ÷ 31.61 | 62.09 mph |
| Ride height | 1.10 ÷ 2 | +0.55 in |
| 10,000 indicated miles | 10,000 × new ÷ old | 10,349 real miles |
What the verdict means
- Close match: within 3% of the original height.
- Check clearance and speedometer: more than 3% and up to 5%.
- Big change: more than 5%. Expect speedometer, gearing and clearance effects.
The ±3% rule of thumb is quoted by Discount Tire’s tire size calculator and 1010tires. It is a guideline, not a guarantee that a tire will fit or be safe on your vehicle.
Why height, not width, drives the verdict
Height sets the speedometer, the odometer, the gearing feel and the ride height. Width mostly decides rubbing and whether the wheel is wide enough: check it in the table and with the wheel offset calculator.
Always confirm the wheel width range for the tire, clearance at full steering lock and suspension travel, and the load index and speed rating for your vehicle. See how to read a tire size, the load index chart and the speed rating chart.
FAQ
How do I compare two tire sizes?
Convert each to overall height in inches and compare. 265/70R17 is 31.6 in and 285/70R17 is 32.7 in: 3.5% taller.
How much difference in tire size is OK?
A common rule of thumb is to stay within about 3% of the original overall diameter (Discount Tire, 1010tires). It is not a guarantee: check clearance, rim width, load index and speed rating.
Does a taller tire change my speedometer?
Yes. A taller tire covers more ground per turn, so the speedometer reads low. At 60 mph indicated you would really be doing 62.1 mph with 285/70R17 in place of 265/70R17.
Can I type the tire size in any format?
Yes: 265/70R17, P265/70R17, LT285/75R16, 225/45-17, 225 45 17, 225/45R17 94W and flotation sizes like 33x12.50R15 all work.
Does the tool save my sizes?
No. Your sizes appear in the page link so you can share the result, and nothing is sent anywhere.