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1989 Mustang GT and Wheel Diameter Changes

     So you are thinking about getting rid of your stock 15" or 16" wheels and buying some 17" wheels, ever wonder how that will effect the performance of the car.

     Here is the general rule, A taller tire is faster, A shorter tire is quicker. By making the outer diameter of the tire taller, you are essentially reducing the torque your car has. Also note that horsepower is based on your torque. (Horsepower = (Torque X RPM)/5252 )

     Another key point here, is that if you switch to a taller wheel, but use a low profile tire, you probably have not changed the out diameter of the wheel enough to care. A 225/55/16 tire is actually almost an inch taller than a 225/45/17.

The test below is using a stock 1989 Mustang GT, 5-speed.

Test	16"	17"	18"
0-30 MPH	2.2	2.2	2.3
0-40 MPH	3.8	3.2	3.2
0-50 MPH	5.1	5.1	5.2
0-60 MPH	6.5	6.6	6.7
0-70 MPH	9.1	9.2	9.2
0-80 MPH	11.3	11.3	11.5
0-90 MPH	14.8	14.0	14.1
0-100 MPH	18.1	18.3	18.5
1/4 Mile	15.2	15.2	15.2
Trap Speed	91.4 MPH	91.4 MPH	93.4
Top Speed	141	139	137

The test below is using a modified 1989 Mustang GT, 5-speed. Modifications included, TrickFlow heads, Cobra intake, E303 Cam, and exhuast work.

Test	16"	17"	18"
0-30 MPH	2.0	2.0	2.0
0-40 MPH	2.5	2.6	2.7
0-50 MPH	4.0	4.0	4.0
0-60 MPH	5.0	5.0	5.1
0-70 MPH	6.0	6.1	6.2
0-80 MPH	8.0	7.3	7.4
0-90 MPH	9.6	9.6	9.7
0-100 MPH	11.4	11.5	11.6
1/4 Mile	13.3	13.3	13.4
Trap Speed	109.6 MPH	109.2 MPH	108.5
Top Speed	158	160	166