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Tyre size Speedo Calculator
Your Tyre Size
Your Car TyreUpsize Tyre% Change
Tyre Diameter0240
Static Radius0-00
Dynamic Radius0120
Rev / Kms0134370
Refernce Speed Kmph 0 20 40 60 80 100 120 140 160 180
Upsize Speedo Error Kmph 0 21 41 62 83 103 124 145 165 186

% Change%3.4

Tyre size speedo calculator is intended to calculate effect of tyre size change on speedo meter reading. Higher the dimensional change will have higher error in speedo meter.

Example : Original size tyre of 205/55R16 if replaced with 215/50R16, the speedo meter will show following difference over various speeds.

Refernce Speed Kmph 0 20 40 60 80 100 120 140 160 180
Upsize Speedo Error Kmph 0 21 41 62 83 103 124 145 165 186

Tyre DiameterThis is the Geometrical diameter of an inflated tyre at the outermost surface of the tread, or twice the inflated section height of tyre plus nominal wheel rim radius. Tyre diameter is dependent on Tyre width, aspect ratio and wheel rim diameter. In service condition tyre diameter increases marginally due to carcass relaxation. The tyre diameter acts just like another gear in your vehicle and matters a lot in defining the economy and vehicle acceleration.
Static RadiusStatic rolling radius or "Static radius" is the distance between wheel center and the point on the circumference of a tyre taking compression into account. It defines vehicle stance and ground clearance in static condition. Due to tyre compression at corresponding load ,tyre static radius reduces from normal geometrical radius.
Dynamic RadiusDynamic rolling radius is the actual radius of tyre when the vehicle is moving. This takes into account the centrifugal force that acts upon the tyre during revolutions.
CircumferenceThe linear distance traveled by a tyre in one revolution. It is derived from from Dynamic rolling radius as it represents the true radius of tyre during motion. It is useful to compute tyre speedometer and odo meter calibration errors.
Rev / KmsMeasured number of revolutions for a tyre traveling one kilometer. This can vary with load and inflation pressures.
Speedo ErrorAny change in Tyre Diameter influences the number of tyre revolutions needed to travel similar distance. This creates error in Speedometer of your car too. Hence any change in tyre size should not be more than 2%.