wret
15+ Year Contributor
- 2,931
- 90
- Jul 3, 2003
-
Bel Air,
Maryland
I still cant make sense of the knuckle / tire clearance. Can you simplify it?
Not really but this exercise might help. Below is a 2D graphical model of the clearance between the rear steering knuckle and the tire. The baseline is a 205/55/16 Kumho 712 tire on a stock 46mm offset wheel. To make this really accurate, we need to know a little more about the tire. Many manufacturers post specifications for their tires. What you need to know are tread width and diameter (which you will divide by 2 to get the radius). You will also need to convert all measurements to millimeters (25.4 to an inch).
Specs. For Kumho 712 205/55/16:
Tread width: 183mm
Radius: 316mm
These dimensions are pictured on the illustration in the (0,0) position. Now lets say I am considering a change to a larger tire, Azenis ST-115 245/40/18, and I want to know if it will fit. Dimensions of the ST-115 are available on the Falken web site. They are:
Tread width: 221mm
Radius: 326mm
To find the clearance for the new tire subtract the baseline from the new width. Then divide by 2.
221-183 =38
38 / 2 = 19
19 will be the X coordinate.
Next, Subract the baseline radius from the new width
326 316 = 10
10 will be the Y coordinate.
Place a mark on the chart at (19,10). (19 to the right, 10 up).
Now factor in an offset change by counting back to the left one unit for every millimeter less offset. In my case, offset will go from the baseline 46mm to 38mm, so I will count 8 units to the left. Thats where the closest point of my new tire will be in relation to the knuckle.
Not really but this exercise might help. Below is a 2D graphical model of the clearance between the rear steering knuckle and the tire. The baseline is a 205/55/16 Kumho 712 tire on a stock 46mm offset wheel. To make this really accurate, we need to know a little more about the tire. Many manufacturers post specifications for their tires. What you need to know are tread width and diameter (which you will divide by 2 to get the radius). You will also need to convert all measurements to millimeters (25.4 to an inch).
Specs. For Kumho 712 205/55/16:
Tread width: 183mm
Radius: 316mm
These dimensions are pictured on the illustration in the (0,0) position. Now lets say I am considering a change to a larger tire, Azenis ST-115 245/40/18, and I want to know if it will fit. Dimensions of the ST-115 are available on the Falken web site. They are:
Tread width: 221mm
Radius: 326mm
To find the clearance for the new tire subtract the baseline from the new width. Then divide by 2.
221-183 =38
38 / 2 = 19
19 will be the X coordinate.
Next, Subract the baseline radius from the new width
326 316 = 10
10 will be the Y coordinate.
Place a mark on the chart at (19,10). (19 to the right, 10 up).
Now factor in an offset change by counting back to the left one unit for every millimeter less offset. In my case, offset will go from the baseline 46mm to 38mm, so I will count 8 units to the left. Thats where the closest point of my new tire will be in relation to the knuckle.
