Speedometer Error Calculator
Compare independently entered original and new rolling circumferences, nominal tire geometry, and both speed directions.
A QUICK WALKTHROUGH
How to use this tool
- Choose the original and new model independently and enter their measurements.
- Choose km/h or mph and enter every speed to compare, one per line.
- Review both ratio directions, signed change, every speed row and the fixed report.
Independent measurements
Each tire can use its own measured circumference or width, aspect ratio and rim diameter. No standard tire size or speed is prefilled.
Two speed directions
For every entered speed the table treats that value once as indicated speed and once as known actual speed. A positive circumference change raises modeled actual speed at the same indicated reading.
Report and scope
The local report records raw and parsed active inputs, models, units, binary floating-point precision and all rows. Editing or resetting removes the previous snapshot.
GOOD TO KNOW
Common questions
Does geometry measure rolling circumference?
No. π times nominal diameter is an unloaded geometric estimate; real rolling circumference depends on operating conditions.
Can I mix measured and nominal inputs?
Yes. Models are chosen independently for each tire and recorded in the report.
Is this a certified speedometer calibration?
No. The tool models a circumference ratio and does not account for existing instrument calibration or establish legal compliance.