Tire Size Calculator
Compare two tire sizes: overall diameter, circumference, % difference, speedometer error and effective gear-ratio change.
Eskimo Auto & Truck Parts — Tire Size Calculator
https://www.eskimoautoandtruckparts.com/tools/tire-calculator · (780) 473-2424
Reference only — verify against your owner's manual or factory service information before performing any work. Full terms: https://www.eskimoautoandtruckparts.com/tools/terms
Diameter difference
+7.04%
Over ±3% — check clearance & speedo
Speedo reads 100 km/h → actual
107.0 km/h
You're going faster than indicated
Effective ratio (axle )
3.48
Taller gearing — lower RPM, softer acceleration
Current: 265/70R17 — 31.6″ tall
New: 285/75R17 — 33.8″ tall
Ride height changes by half the diameter difference: 1.11″ up.
| Measurement | Current (265/70R17) | New (285/75R17) |
|---|---|---|
| Overall diameter | 31.61″ (803 mm) | 33.83″ (859 mm) |
| Inch equivalent (dia × width) | 31.6 × 10.4 R17 | 33.8 × 11.2 R17 |
| Sidewall height | 7.30″ | 8.42″ |
| Circumference | 99.29″ | 106.28″ |
| Revs per km | 396 | 370 |
Rule of thumb: stay within ±3% of the original diameter to protect speedometer accuracy, ABS/traction calibration, and transmission shift points. Bigger jumps may also rub at full lock or full compression.
Don't know your size? Tell us your vehicle.
We sell used tires by request. Send us the year, make & model and we'll match the size and check what's on the shelf.
How to read a tire size
Every tire carries a code on its sidewall — for example 265/70R17 115T. Here's what each part means:
265
Section width
The tire's widest point, sidewall to sidewall, in millimetres. Not the tread contact width — that is narrower and never printed on the sidewall.
70
Aspect ratio
Sidewall height as a % of the width — 70% of 265 mm here.
R
Construction
R = radial (virtually all modern tires). D = bias-ply.
17
Wheel diameter
Rim size in inches the tire fits.
115
Load index
Max weight per tire — 115 = 1,215 kg. Never go below factory.
T
Speed rating
Max sustained speed — T = 190 km/h. S/T common on trucks, H/V on cars.
Light-truck sizes add an LT prefix (LT265/70R17) and a load range letter (C/D/E) alongside a dual load index (e.g. 121/118S — the first number for single-wheel fitment, the second for dual-wheel). LT tires carry more weight at higher pressures. Flotation sizes like 31x10.50R15state the diameter and width directly in inches, which is what the "inch equivalent" row above converts to.
Found the size you want to run? Request it and we'll check what's on the shelf or source it.
Reference information only, provided "as is" without warranty. Specs vary by exact vehicle, trim, and production date — always verify torque figures, capacities, and fitment against your owner's manual or factory service information before performing any work. Tool Terms of Use.
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