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A Few Facts About Wheels
Here are a few measurements you will need before you buy wheels for your rod.

  1. Wheel Diameter
  2. Wheel Width
  3. Back Space (also consider tire bulge)
  4. Front Space (also consider tire bulge)
  5. Bolt Pattern
  6. Center Bore Diameter

In addition to the above measurements, it is recommended that you check the clearance on your existing wheels.  Areas to check are;

  1. Outside fender clearance
  2. Inside frame, fender braces and bumper brackets
  3. Suspension and Steering components (turn wheels with steering lock to lock)

Remember, always make sure the wheels are load rated to your vehicle.  Check the GAWR (Gross Axle Weight Rating) of the heaviest axle of your vehicle.  The wheel load rating is based on 50% of the heaviest GAWR of your vehicle.

Measuring Your Bolt Pattern
Here is a simple but accurate way to measure the Bolt Pattern on your Rod.

  1. Remove the existing wheel (the rear wheel is usually the easiest to measure because the hub normally won’t be in the way).
  2. Use a ruler, or tape measure that shows 32nd’s of an inch.
  3. Measure from the inside of one stud to the outside of another stud (see diagram to the right) (4 lug and 6 lug use opposing studs; 5 lug use 2 studs next to each other).
  4. When measuring a 4 lug or 6 lug, the P.C.D. (pitch circle diameter) or bolt pattern diameter will be the distance measured.
  5. When measuring a 5 lug, use the distance measured then refer to the “5 Lug P.C.D. Chart. The chart shows the “Actual Dimension” in a 3 place decimal. The chart also shows the measurement to the “Nearest 32nd of an inch”.
  6. Find the measurement you took on the chart and that will indicate the Bolt Pattern of your vehicle.

In addition to the above measurements, it is recommended that you check both the front and rear to verify they are the same bolt pattern.
Remember, most wheel companies (and ours is one of them) will not accept returned wheels if they have had a tire mounted. Do a fit check on your vehicle to make sure the wheels fit before you have tires mounted.


 

A Few Facts About Lug Nuts
Here are a few facts about wheel fasteners you should know before you bolt up your wheels on your ride.

  1. Matching your lug nuts or bolts to your wheels.

There are 3 basic type fastener seats;

    1. Conical Seat – cone shape
    2. Spherical Seat – round or ball shape
    3. Flat Washer – commonly known as Mag Type

Be sure the fastener seat matches the seat in the wheel.

  1. Proper Thread Size.

There are several different thread sizes used today by vehicle manufacturers;

    1. 12mm X 1.25
    2. 12mm X 1.5
    3. 12mm X 1.75
    4. 14mm X 1.5
    5. 14mm X 2.0
    6. 7/16" X 20
    7. 1/2" X 20
    8. 9/16" X 18

Two other things to remember; 1) do not put oil or lubricant on the threads of either the stud or lugs nuts/bolts, and 2) re-torque the lug nuts/bolts after 25-50 miles.

  1. Proper Thread Engagement.

This is critically important. Make sure you have a minimum thread engagement of the diameter of the vehicle stud (as recommended by SAE). An example is, if the stud size of your vehicle is ½" then you will need a minimum of ½" of threads into the lug nut. If for some reason you do not have this minimum then it is recommended that you use an ET Type nut (Extended Thread) (see illustration). ET Type nuts are useful when using spacers (that will be another subject in a future TECH Stuff).
Proper Torque (tightening)
This is also very important. Over tightening lug nuts/bolts can fatigue the vehicle studs or lug bolts. Use the SAE recommended torque listed below as a guideline for passenger cars and light trucks;
12mm, 7/16", 1/2" = 85 ft/lbs (+/- 5 ft/lbs)
14mm, 9/16" = 115 ft/lbs (+/- 5 ft/lbs)

Types of Aftermarket Wheels
There are several types of construction that are used to make wheels for the aftermarket.  The type of construction does not necessarily mean that one type is better than the other.  Some types of construction allow for more elaborate styling or finishing, others reduce weight, while others are for the purpose of duplicating the original equipment wheels.  In any case, the strength and safety aspects of the wheel are based on the design and manufacturing quality built in by the manufacturer.  Remember, all the wheels sold should be tested to a recognized specification or standard by the manufacturer to assure that they are safe and reliable regardless of what type construction they are.
The following are the most common types of wheels offered by the aftermarket wheel industry.

  1. Steel Wheels – This is where the aftermarket wheel industry got started.  They consist of a steel outer/rim and a steel center.  Chrome plating is very easy on this type because the rim and center are polished and chrome plated separately then pressed together and welded.  Painting is also easy but is done after the wheel is assembled.  Backspacing/offsets can be varied when the rim and center are pressed together.  Trim rings and hub caps finish off these wheels nicely.  Wire spoke wheels would fall in to this category but require much more maintenance in cleaning and runout (balancing). 
  2. Steel/Composite – This method of building wheels was started back in the 60's.  It consists of a steel rim and a cast aluminum center.  This allows for more styling in the center.  The aluminum centers are cast with steel cleats or inserts on the outer edges so it can be pressed into the steel rim and welded just like the Steel Wheels.  These wheels are offered primarily chrome plated.
  3. 1 Piece Cast Aluminum – This is now the most common wheel sold in the aftermarket.  It offers the most variety of styling, sizes and finishes.  These wheels can be painted, machined, polished or chrome plated.  They are offered in sizes from 13" to 26" (28" & 30" are in development).  These also offer a reasonable weight savings over Steel or Steel/Composite.  The disadvantage of the 1 Piece Cast is the backspace/offsets are fixed in the mold.
  4. Forged – This is the type that offers the lightest weight.  Because of the forging process, the wheel can be built using much less material than a 1 Piece Cast.  The styling is limited in comparison to a 1 Piece Cast and the tooling and manufacturing costs are much greater.  These too can be painted, machined, polished or chrome plated.  Because of costs the sizes offered are limited.
  5. 2 Piece Aluminum – Also known as Billet, this type of wheel has been around for about 20 years.  Like the Steel Wheel, it is made of a rim and center.  The rims are rolled or spun and the centers are cast, forged or machined billet aluminum.  The rim and center are pressed and welded together which also allows for a variation in backspace/offset.  Forged and billet aluminum centers are typically stronger than cast centers because of the density of the aluminum.  Finishing is limited to painting, machining or polishing.  Chrome plating is difficult because the welding has problems created by the copper, nickel and chrome from the plating process.
  6. 3 Piece Aluminum – These are also known as a Modular wheel.  The rim is made up of 2 pieces, the front rim section and the rear section which are either spun or formed.  The center can be of a cast, forged or machined billet type.  The 3 pieces are assembled with the center sandwiched between the front and rear rim sections with bolts or rivets securing the pieces together.  Styling is again limited, but finishing choices are like the 1 Piece Cast.

There are a few folks out there in the industry that will say wheels made by forging or from machined aluminum billet are stronger than cast wheels.  That would be true if both wheels were made to the exact same design and dimensions.  However, the strength or load carrying capacity and durability of a wheel comes from the design and manufacturing quality, based on the type of construction.  The biggest advantage gained from forging or billet is weight.  Because they are stronger, less material is needed.  Regardless if it is steel, cast aluminum, forged or machined from billet, the wheel should still meet performance testing standards to be deemed safe and reliable.

 Bolt Pattern Conversion Chart (mm to inches)


                                   BOLT PATTERN CONVERSION  (mm to inches)

COMMON REFERENCE

MILLIMETERS

CONVERTS TO

INCHES

3x112

3x112

CONVERTS TO

3x4.41

 

 

 

 

4x98

4x98

CONVERTS TO

4x3.9

4x100

4x100

CONVERTS TO

4x3.94

4x4

4x101.6

CONVERTS TO

4x4

4x108  or  4x4.25

4x108

CONVERTS TO

4x4.25

4x110

4x110

CONVERTS TO

4x4.33

4x114.3  or  4x4.5

4x114.3

CONVERTS TO

4x4.5

 

 

 

 

5x100

5x100

CONVERTS TO

5x3.94

5x4

5x101.6

CONVERTS TO

5x4

5x108  or  5x4.25

5x108

CONVERTS TO

5x4.25

5x110

5x110

CONVERTS TO

5x4.33

5x112

5x112

CONVERTS TO

5x4.41

5x114.3  or  5x4.5

5x114.3

CONVERTS TO

5x4.5

5x115

5x115

CONVERTS TO

5x4.52

5x120

5x120

CONVERTS TO

5x4.72

5x4.75

5x120.7

CONVERTS TO

5x4.75

5x127  or  5x5

5x127

CONVERTS TO

5x5

5x130

5x130

CONVERTS TO

5x5.12

5x135

5x135

CONVERTS TO

5x5.3

5x5.5

5x139.7

CONVERTS TO

5x5.5

5x150

5x150

CONVERTS TO

5x5.9

 

 

 

 

6x114.3  or  6x4.5

6x114.3

CONVERTS TO

6x4.5

6x127  or  6x5

6x127

CONVERTS TO

6x5

6x130

6x130

CONVERTS TO

6x5.1

6x132

6x132

CONVERTS TO

6x5.2

6x135

6x135

CONVERTS TO

6x5.3

6x5.5

6x139.7

CONVERTS TO

6x5.5

 

 

 

 

7x150

7x150

CONVERTS TO

7x5.9

 

 

 

 

8x6.5

8x165.1

 

Formula for Calculating Tire Dimensions

USING SIZE 235/35-19 FOR EXAMPLE

The dimensions of a 235/35-19 tire are
9.3” wide (section width) & 25.5” tall (outside dia)
The section width is 235mm wide
(There are 25.4mm to an inch)
STEP 1) 235mm divided by 25.4” = 9.25” (section width)
STEP 2) Multiply 9.25 (section width) by .35 (aspect ratio)
9.25 x .35 = 3.24” (section height)
To find the outside diameter
Multiply 3.24 (section height) x 2 then add rim diameter
STEP 3) 3.24” x 2 = 6.48” + 19.0” = 25.48” round out to 25.5”  (outside dia)