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Speedometer error calculator

Adjust indicated speed by replacement circumference ÷ original circumference.

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Speedometer error calculator processes your input in this browser. Inputs and results are excluded from analytics. Recent tools save tool names, visit counts and last-visit times. Saved tools store only their names. Draft saving is optional and stays on this device; delete saved text with the draft controls. Loading text from a URL is optional and contacts that server; its URL and your IP address are visible to the server. An optional “Use in” action keeps a handoff in this tab. The next tool removes it on arrival and ignores it if more than a minute has passed.

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More inputs and assumptions

Answer

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Adjust indicated speed by replacement circumference ÷ original circumference.

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Precision and calculation record
Rounding changes displayed numbers, not the calculation. Text, fractions, matrices and CSV schedules keep their own formatting. Automatic keeps up to 12 significant digits, with money shown to cents where applicable.
Step-by-step calculation
Inputs are substituted below. Each line evaluates the next operation; intermediate values are displayed to 12 significant digits while the calculation uses full precision.
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    Save the current answer, then change an input to compare. This clears when you leave.
    Formula and assumptions
    Assumes the original calibration was exact and wheel speed is unchanged. Does not account for built-in speedometer bias, loading, tire deformation or slip. It is not a compatibility or safety verdict.
    Automatic precision shows numbers to 12 significant digits. Thousands separators such as 1,000 are accepted; use a dot for decimals.
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    Updated 
    Using Speedometer error calculator
    Adjust indicated speed by replacement circumference ÷ original circumference.
    Assumes the original calibration was exact and wheel speed is unchanged. Does not account for built-in speedometer bias, loading, tire deformation or slip. It is not a compatibility or safety verdict.
    Next: Gear ratio calculator
    A worked example
    Example inputs: original rolling circumference = 2, replacement rolling circumference = 2.1, indicated speed = 60. Actual speed at indicated speed = 63.
    Before you use the result
    Assumes the original calibration was exact and wheel speed is unchanged. Does not account for built-in speedometer bias, loading, tire deformation or slip. It is not a compatibility or safety verdict.
    Example results for original rolling circumference
    These examples use Replacement rolling circumference: 2.1; Indicated speed: 60. They are reference calculations, not recommended settings.
    Original rolling circumferenceActual speed at indicated speed
    1126
    263
    431.5
    Cite this page
    ToolOctopus. “Speedometer error calculator.” Updated 2026-09-26. https://tooloctopus.com/speedometer-error-calculator.
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