Tire Size Calculator — tire and wheel size comparison tool
Tire Size Calculator tire comparison · speedometer error

Speedometer error: 225/45R17 to 235/40R18

Estimate speedometer bias moving from 225/45R17 to 235/40R18 using circumference change (~1.72%). Includes GPS verification tips and a link to the full comparison.

Speedometer planning: 225/45R17 → 235/40R18

When Tire 1 is 225/45R17 and Tire 2 is 235/40R18, modeled rolling circumference is about 1.72% larger for Tire 2 versus Tire 1. That percentage is a useful first-order estimate for how wheel RPM maps to true road speed if your vehicle remains calibrated around 225/45R17.

Verify after install

Use the speed table on this site’s calculator, then confirm with GPS on a quiet road. OEM tolerances, tire wear, inflation, and temperature all nudge real-world results.

Legal and safety note

Posted limits apply to true road speed—not what you wish the dash meant.

Full measurements

Open the dedicated comparison page for side-by-side tables and pairing FAQs: 225/45R17 vs 235/40R18.

Frequently asked questions

Is 1.72% circumference change a lot?
It can be noticeable at highway speeds. Treat it as a planning band and verify on your vehicle.
Where is the interactive table?
Use the comparison page at /tire-size-225-45r17-vs-235-40r18 or the homepage calculator with Tire 1 as 225/45R17 and Tire 2 as 235/40R18.
Can recalibration fix the offset?
Some vehicles can be recalibrated for tire circumference—ask your dealer or tire professional for model-specific options.

Try the free tire size calculator

Open the interactive tire size calculator to compare diameters, see a wheel size comparison side by side, and review a speedometer difference table before you buy tires or wheels. It works like a quick tire fitment checker for geometry—not a substitute for a professional install bay.

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Important: Tire comparison results are estimates for planning only. This site does not provide mechanical certification, OEM approval, or on-vehicle clearance guarantees. Confirm final tire fitment, load/speed ratings, and speedometer calibration with a qualified tire professional or your vehicle and tire manufacturer before driving.

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