Tire Size Modifications
The Tire and Wheel Reference Tools

cribbed, not authored, by yours truly


This program is for comparing original equipment tire size to alternate after market tire sizes. All calculations are rounded up. Calculations are to be treated as approximate only, due to variations in how tires are manufactured.

To use this program you need to key in seven (7) pieces of information. The tire tread width, sidewall ratio, and wheel rim diameter from each of the two tires to be compared and a speedometer reading to be used to compute the effect the after market tire size has on your speedometer.

The following is an example to help to decode a tire size like 185/65R14
185 = tire width in millimeters, measured from sidewall to sidewall
65 = sidewall ratio, the ratio of sidewall height to tire width
14 = wheel rim diameter in inches

After keying in the seven (7) pieces of information, click on the "Compare Tires" button below to have the two tire sizes compared.
For information on stock and popular StarQuest tire selections, scroll to the bottom or click here.


Tires Comparison Section

Step 1: Key in the following information from the tires being compared.
Original Equipment Tire Alternate After Market Tire
Tire Width in (mm): Tire Width in (mm):
Aspect Ratio:
Aspect Ratio:
Rim Diameter in (inch): Rim Diameter in (inch):
Speedometer Reading:

Step 2: To compare the above tires, please click on the "Compare Tires" button below.

Step 3: To see the results of the comparison, SEE BELOW:


Tires Comparison Information Section
Original Equipment Tire Alternate After Market Tire
Side Wall Height (inch): Side Wall Height (inch):
Tire Width (inch): Tire Width (inch):
Tire Diameter (inch): Tire Diameter (inch):
Tire+Wheel Radius (inch): Tire+Wheel Radius (inch):
Tire Circumference (inch): Tire Circumference (inch):
% Difference:
Revolutions per mile: Revolutions per mile:
Revolutions per kilometer: Revolutions per kilometer:
Speedometer Reading: New Speedometer Reading:

NOTE: New Speedometer Reading = What speed the car will need to go (with the after market tires on) to be traveling at the same speed if the car had the orginal tires on.

To compare additional tires, go back to the "Tires to be Compared Section" and type over the information you want to change. After making the changes, click on the "Compare Tires" button to recalculate.

To reset this form, click on "Clear Form" button below.


Stock/Popular StarQuest Tires & Rim Specs:

88/89 Tire Sizes
Configuration Front Rim Offset Rear Rim Offset
Stock 205/55VR16 7" 18mm 225/50VR16 8" -10mm
Biggest (?) 225/50VR16     245/45VR16    
Handling Package 225/50VR16 8" 18mm 245/45VR16 9" 0mm
Biggest (?) 245/45VR16     255/40VR16    
86/87 Tire Sizes
Configuration Front Rim Offset Rear Rim Offset
Stock 215/60HR15 6.5"   215/60HR15 6.5"  
Biggest (?) 225/60VR15     245/55VR15    
Intercooled Widebody 205/55VR16 7" 18mm 225/50VR16 8" -10mm
Biggest (?) 225/50VR16     245/45VR16    
84/85 Tire Sizes
Configuration Front Rim Rear Rim
Stock 195/70SR14 6" 195/70SR14 6
Handling Package 215/60HR15 6.5" 215/60HR15 6.5"
14" & 15" Rims are 4-Bolt
16" Rims are 5-Bolt