There are many good tire calculator apps so why choose this one? Most other tire apps allow you to enter two different tire sizes and then provide a detailed numerical comparison of their total diameters etc. TireCalc Free takes a different approach - one that is more suited to the real-world scenario of having existing tires mounted on a vehicle but then wanting to replace the wheels using rims and tires that have different dimensions while preserving the same overall diameter as the existing wheels. TireCalc Free makes this easy by:

• rapid input of the existing tire size using 'spinner-dials' rather than using keyboard entry;
• instantly providing a list of alternative tire sizes that provide a good match the existing tire's overall diameter;
• the list of alternative sizes can be filtered down by specifying a desired rim size and/or maximum allowed difference in diameter (expressed as a percentage): this 'difference percentage' equals the resulting speedometer error.
• Again, the selection of preferred rim size and maximum difference is made easy using convenient spinner-dials rather than by old-fashioned text input.

TireCalc Free also provides additional pages that explain everything you need to know when shopping for new tires:

• explanation of sidewall markings (e.g. 245 / 45 / ZR17 etc);
• definition of 'aspect ratio';
• math formula used to calculate the overall wheel diameter;
• table of speed-rating code letters;
• table of maximum load indices.