Tire Size Calculator
Compare two tire sizes. See the difference in diameter, the speedometer error, and whether the new size is close enough to run.
Compare two sizes
- The 3% rule is a guideline, not a regulation. Clearance is what actually decides whether a tire fits.
- Speedometer error assumes the original size was correct for the vehicle.
- Plus sizing changes the sidewall, which changes ride quality and how the steering feels.
- Revs per mile here is geometric. Published figures run slightly higher because a loaded tire squats.
What the numbers on a tire mean
Take 225/60R16. The 225 is the section width in millimeters. The 60 is the aspect ratio, meaning the sidewall is 60% of the width, so 135mm tall. The 16 is the wheel diameter in inches. Add two sidewalls to the wheel and you get the overall diameter, which is the number that actually matters when you change sizes.
The 3% rule
Keep the new overall diameter within 3% of the original. That is the number most shops work to. Inside 3% the speedometer stays close enough, the ABS and traction control keep behaving, and the tire usually clears everything it needs to clear.
Past 3% you start getting a speedometer that reads noticeably wrong and a real chance of rubbing at full lock or over a bump. Past 5% on a stock vehicle, expect problems.
Which way does the speedometer read?
Bigger tires travel further per revolution, so the speedometer under reads. You are going faster than it says. Smaller tires do the opposite. Your odometer is wrong by the same percentage, which matters for warranty mileage and resale.
Plus sizing
Going up a wheel size and down an aspect ratio at the same time keeps the overall diameter close while the sidewall gets shorter. Steering gets sharper. Ride gets harsher. Potholes get more expensive.
Frequently asked questions
How much bigger can I go without problems?
Within 3% of the original overall diameter on a stock vehicle. Beyond that you are into clearance checks at full steering lock and full suspension compression, and a speedometer that reads wrong.
Will bigger tires make my speedometer wrong?
Yes. A larger diameter tire covers more ground per revolution, so the speedometer reads low. At 3% oversize you are doing about 62 mph when the needle says 60. The odometer is off by the same percentage.
Can I put a wider tire on my existing wheels?
Only within the rim width range the tire is rated for. Every tire size has an approved rim width span, usually covering two or three wheel widths. Stretch it outside that and the tread does not sit flat, which wrecks handling and wear.
Do all four tires have to match?
On all-wheel drive, yes, and it is not optional. Different rolling diameters front to rear make the center differential or transfer case work continuously, and that is an expensive failure. Some vehicles run a staggered setup from the factory, which is fine because it was designed that way.
Everything on this page is an estimate worked out from the numbers you entered and typical figures for the conditions you picked. Your vehicle, your parts and your conditions will differ. Check anything you intend to act on against the manufacturer's specification, the service manual, or a qualified technician. Verifying the result before relying on it is up to you.