Technical Notes provided by Joe Schaeffer


Rims/Bolt Circle size:
   Measured from stud to stud:
	3.23"=5.5" bolt circle.
	2.93"=5.0" 					
	2.79"=4.75"
	2.64'+ 4.5" bolt circle.

Flotation/Metric Conversion
             Diameter 
Floatation    (inch)   Metric Size
27x8.5R14      26.5     225/75R14
               27.5     215/75R15
29x9.50R15     28.5     235/75R15
30x9.50R15     29.5     245/75R15
31x10.50R15    30.5     265/75R16
32x11.50R15    31.5     295/75R15
33x12.50R15    32.5     315/70R15	
33x12.50R16    32.8     285/75-16

Section width: 
width of the tire between sidewalls NOT the tread width. 	
Usually measured in mm and the first number on a metric tire. 
Such as the "235" on a 235/75R-15 tire.

Aspect Ratio: 
Relationship between section height/width.
Aspect ratio is the "75" or "60" number in a metric rated tire. 
As in  235/75R-15

Tire diameter of a metric tire can be figured using:
	
	tire dia. = 2 x section width x aspect ratio + wheel size
					25.4			   100


Tires/Gears/MPH/RPM

	tire diameter = mph x gear ratio x 336
                        ------------------------
				  rpm

	gear ratio = rpm x tire diameter
                     ---------------------
		         mph x 336

	mph = rpm x tire diameter
              ---------------------
		 gear ratio x 336

	rpm = mph x gear ratio x 336
              -----------------------
		   tire diameter

NOTE: For rpm's other than hwy speeds you need to figure in 
trans gear ratio and x-case ratio. For mph at hwy speeds use 
5th gear OD ratio ie. 072:1 etc.

Actual speed: When changed to new tires and you need the actual 
speed withhout changing speedo drives. Bigger tires cause speedo 
to read slower than true speed. 

	actual speed = new tire dia. x indicated speed
                       --------------------------------
                            old tire dia.

Example: Old tires 28 inch, new tires 35 inch and speedo reading 60 mph
		
		35 x 60 mph = 75 mph true speed
		   28

To figure what indicated speed to run to achieve actual speed use:

	indicated speed = old tire dia. x actual speed
					new tire dia.

Actual new gear ratio with new tires:

		new gear ratio = old tire dia. x old gear ratio
						new tire dia.
 
Gears to install to restore original gear ratio after new tires:

	new ratio to install = new tire dia. x original gear ratio
						old tire dia.

superdawg

SJ 1962 - 1991 -- tech / repair tips -- SJ rigs - photos --

Diesel Jeeps - KJ and WK

FSJ's are Jeep Wagoneers, J-series trucks, and Cherokees made from 1962 to 1992.

the 1996 snowstorm and Old Blue

since September 24, 1998.

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If you can't answer yes to any of the above,
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THE FSJ CHARTER:
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FSJ information:
The list is for the discussion of Full-size Jeeps (FSJ)

An "FSJ" is any vehicle produced in North America,
carrying the "Jeep" nameplate, with 2 or 4drs,
in 2 or 4wd, whose wheelbase does not exceed 132",
nor is less than 108", and whose tread width is
no more than 63" nor less than 57".
--------------------------
This definition is known to include the following models:
Wagoneer: 1963-1983
Gladiator and J-series pickup: 1963-1987
Cherokee: 1974-1983
Grand Wagoneer: 1984-1991
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ALL FULL-SIZE JEEPS HAVE A JEEP MODEL DESIGNATOR OF: SJ
http://JeepMeister.com/ALL-JEEP-TECH/jeep-model-codes.html
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