Getting the right tire size for your wheel

[EKam]

Link from TireRack.com:
http://www.tirerack.com/tires/tiretech/general/size.jsp

Width x Aspect Ratio = Section Height x 2 = Combined Section Height + Wheel Diameter = Tire Diameter
Example...185/60R14 85H or 185/60HR14

185mm x .60=111mm x 2=222mm + 355.6mm(14")= 577.6mm or 22.74"

The first number is the width of the tire in millimeters, measured from sidewall to sidewall. To convert to inches, divide by 25.4 In the example above, the width is 185mm or 7.28".

The second number is the aspect ratio. This is a ratio of sidewall height to width. In the example above, the tire is 7.28" wide, multiply that by the aspect ratio to find the height of one sidewall. In this case, 185x0.60=111mm or 7.28"x0.60=4.36".

The last number is the diameter of the wheel in inches.

To figure the outside diameter of a tire, take the sidewall height and multiply by 2,(remember that the diameter is made up of 2 sidewalls, the one above the wheel, and the one below the wheel) and add the diameter of the wheel to get your answer.

[yellowbal]

Here is an interactive calculator. It makes it better for experimentation or just plain exploring the possibilities.

http://www.miata.net/garage/tirecalc.html

[2k4CamThrilla]

tirerack does it for you...

[73sport]

All,
Here is another that lets you input 3 or 4 different choices compared to "your Stock" wheel/tire combo. It also contains OEM applications incase you don't know what your care came with originally (like if the door pillar was torn off and you lost the tag)....

Regards,

Randy

http://www.1010tires.com/TireSizeCalculator.asp

Here are some sample results from this calculator.

BUMMER: The web server trashed the table - it is useless - sorry....
Stock Tire - 205/65R15 >Search Tires Tire 1 - 205/60R17 >Search Tires Tire 2 - 225/50R17 >Search Tires Section Width:8.07 in205 mmSection Width:8.07 in205 mmSection Width:8.85 in225 mmRim Diameter:15 in381 mmRim Diameter:17 in431.8 mmRim Diameter:17 in431.8 mmRim Width Range:5.5 - 7.5 inRim Width Range:Unrecognized tire size.Rim Width Range:6 - 8 inOverall Diameter:25.49 in647.44 mmOverall Diameter:26.68 in677.67 mmOverall Diameter:25.85 in656.59 mmSidewall Height:5.24 in133.09 mmSidewall Height:4.84 in122.93 mmSidewall Height:4.42 in112.26 mmRadius:12.74 in323.59 mmRadius:13.34 in338.83 mmRadius:12.92 in328.16 mmCircumference:80.07 in2033.7 mmCircumference:83.81 in2128.7 mmCircumference:81.21 in2062.7 mmRevs per Mile:816.0Revs per Mile:779.6Revs per Mile:804.6Actual Speed:60 mph100 km/hSpeedometer1:57.3 mph95.5 km/hSpeedometer1:59.1 mph98.6 km/hSpeedometer Difference: -Speedometer Difference: 4.669% too slowSpeedometer Difference: 1.416% too slowDiameter Difference: -Diameter Difference: 4.47%Diameter Difference: 1.4%