Free tool
Tire size calculator
Compare two tire sizes side by side. See exactly how diameter, width, speedometer reading and ground clearance change before you upsize — in metric or inch sizes.
265/70R17 or 33x12.50R17.
265/70R17 → 245/75R17
Effectively identical
| Spec | Current | New | Difference |
|---|---|---|---|
| Overall diameter | 31.61" | 31.47" | −0.14" |
| Section width | 10.43" | 9.65" | −0.79" |
| Sidewall height | 7.30" | 7.23" | −0.07" |
| Circumference | 99.29" | 98.86" | −0.43" |
| Revolutions / mile | 638 | 641 | +3 |
Calculated from the size specs — real mounted diameter varies a little by brand, load and pressure. Always check clearance on your own truck before fitting.
How to read a tire size
Two formats, same tire. Here's what each number means.
Tread width
The width of the tread in millimetres, across the tire.
Aspect ratio
Sidewall height as a percent of width — a lower number is a shorter sidewall.
Rim diameter
R is radial; 17 is the wheel diameter in inches the tire mounts to.
Inch sizes
Flotation sizes like 33x12.50R17 give overall diameter × width × rim, all in inches.
Tire sizes — frequently asked
How do I read a tire size like 265/70R17?
265 is the tread width in millimetres. 70 is the aspect ratio — the sidewall height as a percentage of the width (so 70% of 265 mm). R means radial construction, and 17 is the wheel (rim) diameter in inches. A flotation size like 33x12.50R17 instead reads as overall diameter (33"), width (12.5") and rim (17").
Will bigger tires mess up my speedometer?
Yes. Your speedometer is calibrated for the stock tire diameter. A taller tire travels further per revolution, so the speedo reads low — you're actually going faster than it shows. This calculator gives the true speed at an indicated 60 mph so you can see the error and recalibrate if needed.
How much bigger can I go without a lift?
As a rough guide, most trucks accept a tire about 3–5% taller than stock without rubbing. Beyond roughly 15% you usually need a level or lift kit and possibly trimming. Always check your specific truck — fender clearance and offset vary.
Does a taller tire change my gearing?
Yes — a taller tire effectively raises your gearing (fewer revolutions per mile), which can dull acceleration and drop your effective final drive. Many people re-gear the axles after a big tire jump to restore performance. The revs-per-mile difference here shows the size of that change.
What does a wider tire affect?
Width changes grip and stance but also rubbing risk on the inner fender and suspension at full lock or compression. Going wider often needs a different wheel offset/backspacing to keep the tire clear.
