Tire Size Calculator
Compare two tire sizes: diameter, width, revs per mile, speedometer error and clearance gain.
Metric (275/65R18, LT285/70R17) or flotation (35x12.50R17)
Try:
Diameter change—
Speedometer at 60 mph—
Axle clearance gain—
| Measurement | Current | New | Difference |
|---|
| Speedometer shows | You are actually going |
|---|
How to use the tire size calculator
Type your current tire size in the first box and the size you're considering in the second. It accepts metric sizes such as 265/70R17 and LT285/70R17 and flotation sizes such as 35x12.50R17. Results update as you type.
What the numbers mean
- Overall diameter is the tire's height, which is what people mean by "33s" or "35s." For a metric size it's the rim diameter plus two sidewalls: rim + 2 × (width × aspect ratio ÷ 100) ÷ 25.4.
- Speedometer at 60 mph is how fast you're really going when the speedometer reads 60 with the new tires and no recalibration. Bigger tires make the truck faster than the speedometer shows.
- Axle clearance gain is half the diameter increase. It's the only way to add clearance under a solid axle's differential; a suspension lift doesn't.
- Revolutions per mile drops as tires get taller, which is why the speedometer, odometer and effective gearing all change.
Fitment is a separate question
A calculator can't tell you whether a tire will rub. Wheel offset, backspacing, lift height, bumpers and steering stops all matter. Check load index and load range too, especially on a truck that tows.
Want the full background? Read how to read a tire size and leveling kit vs lift kit vs body lift.