Will bigger tires make my speedometer read low?

Yes. A larger diameter covers more distance per revolution, so you are going faster than the speedometer shows.

Can I fit any size with the same diameter?

No. Width, load index, speed rating, offset and approval rules also matter.

Tire Size Comparison Calculator

Enter the original and the new tire size to see the difference in diameter and how much your speedometer will be off.

Results

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Reading a tire size

In 205/55R16, 205 is the width in mm, 55 the sidewall height as a % of the width and 16 the rim diameter in inches. Overall diameter = rim × 25.4 + 2 × width × aspect ÷ 100.

Many tire shops use ±3% overall diameter difference as a rule of thumb for alternative sizes. Always check load index, speed rating, clearance and what is legally allowed for your car in your country.

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FAQ

Will bigger tires make my speedometer read low?: Yes. A larger diameter covers more distance per revolution, so you are going faster than the speedometer shows.
Can I fit any size with the same diameter?: No. Width, load index, speed rating, offset and approval rules also matter.

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