Wheel Fitment Guide w/Pics

[Shadow-Warrior]

I thought the forum needed a "Guide" on how to better understand wheels and know what to look for before buying wheels. The following information should help anyone wanting to understand back spacing, off-set, etc.

How to Measure Bolt Patterns




How to Measure Wheel BackSpace

Items required to measure wheel backspace: Tape measure
Straight edge
Wheel w/o tire (preferred)



The easiest way to measure backspace is to lay the wheel face down onto the ground so the backside of the wheel is facing up. Take a straight edge and lay it diagonally across the inboard flange of the wheel. Take a tape measure and measure the distance from where the straight edge contacts the inboard flange to the hub mounting pad of the wheel. This measurement is backspace. The above photo shows three wheels with 2",3", & 4" backspace.

Measuring Wheel Offset

To calculate offset you'll need the following measurements:

Wheel backspace
Wheel Width
Wheel Center line (outboard flange to inboard flange measurement / 2)



Subtract:

Wheel center line from Wheel backspace to get offset. If backspace is less than the wheel centerline the offset is negative
If backspace is greater than the wheel centerline the offset is positive


Tip:

To convert from inches to mm multiply by 25.4
To convert from mm to inches divide by 25.4




Backspace to Offset Conversion Chart
The table on the right is q quick reference for finding offset, pick the rim width and follow the row over to the backspace of your wheel.




Determining Vehicle Fitment



Fitting a wheel and tire package is different for each vehicle, but by following these guidelines your chances for success will be much greater. In most cases you'll have to use the physical dimensions of the current wheel/tire package to determine the dimensions of the new wheel/tire package.
Items which are potential trouble spots:

Tie Rod Ends
A-arms
Brake Calipers
Shocks and Shock Mounts
Inner & Outer Fenders (esp. front tires turned to lock)


We've made two measurements Front Side Clearance
Back Side Clearance

These measurements when used with:

Tire Section Width
Tire Diameter
Rim Width
Rim Backspace


Determine Wheel Caliper Clearance



Ensuring proper caliper clearance inside the wheel is important. The following chart should enable you to have the dimensions required by most wheel manufactures.
A. Caliper Overhang Distance Used to determine if wheel dish is adequate (in some cases a spacer is required for clearance)

B. Diameter of Hub Center Required if wheels are hub centric

C. Wheel Stud Diameter Required along with bolt circle

D. Height of Hub Center
E. Length of Lug and Thread Type (Fine or Coarse) Required to determine if longer studs are necessary

F. Distance from CL of Hub to Caliper Used with A to determine if a spacer is required for proper fitment

G. Width of Caliper Used with F to determine if wheel ID is adequate to clear rotor/caliper package

H. Diameter of Hub Mounting Face Used to determine if hub is adequate to support wheel/spacer






Typical Lug Nut Torque Specifications
Lug Size Ft/Lbs Torque
7/16" 55-65
1/2" 75-85
9/16" 95-115
5/8" 135-145
12mm 72-80
14mm 85-95

IMPORTANT NOTICE: As with all types of wheels retorque lug nuts after the first 25 miles & at 100 mile intervals until lug torque is maintained.
Note: Always refer to Owner's Manual for proper factory specifications that take precedence over the listed recommendations.



Wheel Terminology



Bolt pattern or lug pattern or bolt circle is determined by the number of bolt holes and the bolt circle diameter.

Hub Diameter or center bore is the hole at the center of the wheel.

Rear spacing or back spacing is the distance from the backside of the wheel mounting pad to the outside of the rim flange.

Offset: The distance from the centerline of the wheel to the mounting surface of the wheel.

Negative offset: When the back of the bolt pad is closer to the inside of the wheel; when mounting surface is inboard of the rim centerline.

Positive offset: When the back of the bolt pad is closer to the street side of the wheel; when the mounting surface is outboard of the rim centerline.

Bead-Loc A device which captures the tire bead between it's flanges, usually secured by bolts to keep tire bead from dismounting. Usually used in dirt circle track or off road applications where low tire pressures are used and hitting ruts or other vehicles are common. Left: An example of a Bead-Loc wheel




Modular Wheel Inspection and Maintenance
Two & Three piece modular wheels require periodic maintenance. You'll want to work out your own maintenance schedule, but here's an example of what the manufacturer recommends. Each Season disassemble, thoroughly inspect, clean, re-seal, and re-torque each wheel:
Replace wheel bolts each season
Wheel Bolt Torque: 1/4" bolts 15 ft/lbs. or 180 in./lbs
5/16" bolts 20 ft/lbs.

After thoroughly cleaning all mating surfaces with an appropriate cleaner, add a thin skim coat of silicone sealant to these surfaces, assemble wheel and torque bolts to recommended torque
Install a new valve stem
Add a thick coat of silicone sealant to the drop center area of the wheel and let it cure for 24 hours before initial use.



Mike

[neworleansparrothead]

Wow Mike, VERY NICE write up! This should answer alot of folks questions..

Kudos to you!!!

[Fjamming]

That looks familiar . Looks like it's from the same link in my sig.

https://www.rsracing.com/tech-wheel.html

[Shadow-Warrior]

Yeh, I had it too in one of my old threads I posted for someone. I thought I would post it by it self for everyone that may have a hard time trying to understanding wheel fitment information they hear.


Mike

[redfernsoljah]

props very nice

[Shadow-Warrior]

Thanks


Mike

[DooDooBloo]

Spank you very much.You serious wheelers scare me.I feel like such a pansy.

[Shadow-Warrior]

It's all good

Mike