Tire Size Calculator & Comparison
Compare two tire sizes side by side: diameter, width, sidewall, revolutions per mile and the speedometer change — drawn to scale, in plain numbers. Free, no signup, calculated in your browser.
Current tire on your vehicle now
New tire you are considering
Full comparison
| Measurement | 265/70R17 | 285/70R17 | Difference |
|---|---|---|---|
| Overall diameter | 31.61" | 32.71" | +1.1" (+3.49%) |
| Width | 10.43" | 11.22" | +0.79" |
| Sidewall height | 7.3" | 7.85" | +0.55" |
| Circumference | 99.3" | 102.8" | +3.5" |
| Revolutions / mile | 638 | 617 | -21 |
| Ride height change | — | — | +0.55" |
Speedometer effect
Assuming your speedometer was accurate on the current tire, here is what changes. Bigger tires make the speedometer read low — you travel faster than it shows.
| Speedometer shows | 20 mph | 30 mph | 40 mph | 50 mph | 60 mph | 70 mph | 80 mph |
|---|---|---|---|---|---|---|---|
| Actual speed | 20.7 | 31 | 41.4 | 51.7 | 62.1 | 72.4 | 82.8 |
Before you buy: fitment checklist
- Wheel diameter: SAME RIM Both sizes fit a 17" wheel — no new wheels needed for diameter.
- Diameter change: DIAMETER Diameter changes 3.49% — beyond the ±3% rule of thumb installers commonly cite. Expect speedometer, gearing and clearance effects to matter. The ±3% figure is a guideline, not a safety standard.
- Clearance: WIDTH The new tire is 20 mm wider — check inner clearance at full steering lock and full suspension travel.
- Rim width: CHECK Confirm the new size's approved rim-width range (from the tire maker) includes your wheel's width.
- Load & speed: CHECK The new tire's load index and speed rating must meet or exceed your vehicle's placard (driver's door jamb).
This is a size comparison, not a fitment guarantee. Clearance depends on your vehicle's suspension, wheel offset and alignment — the checklist above covers what to verify.
Popular tire size comparisons
Popular sizes in inches
Questions drivers ask
How much taller is a 285/70R17 than a 265/70R17?
A 285/70R17 is 32.71" in diameter against 31.61" for the 265/70R17 — about 1.10" taller (+3.49%) and 0.79" wider. It raises ride height by roughly 0.55". Try it in the tool above.
Does a bigger tire make my speedometer wrong?
Yes. The speedometer counts wheel rotations, so a taller tire covers more ground per rotation than the gauge assumes. With a +3.49% diameter increase, an indicated 60 mph is really about 62.1 mph. The table above shows the correction at every speed.
What does 265/70R17 mean?
265 is the width in millimeters, 70 is the sidewall height as a percentage of the width (70%), and 17 is the wheel diameter in inches. The overall diameter works out to 31.61".
Can I put a different size on the same rims?
Only if the rim diameter matches and your wheel width is inside the new tire's approved rim-width range. Diameter changes within about ±3% are a common rule of thumb, but that is a guideline, not a safety standard — run through the checklist above before buying.
Are these the exact sizes of real tires?
These are nominal sizes from the standard formula every tire size is built on. A specific brand and model can measure a few tenths of an inch different, and a worn or loaded tire sits lower. Use these numbers to compare sizes, and the tire maker's spec sheet for one exact model.
Method and data notes: how every number here is calculated. Last verified November 12, 2026.