TECH Stuff #11 Modified Wheels – Safe or Risky?

The original equipment wheels that the factory puts on cars and trucks are designed and tested for use on a specific vehicle.  The wheels that the aftermarket offers are designed and tested to fit a wide range of vehicles.  The range of those vehicles is determined primarily by the load rating or weight of the vehicles.  Both OEM and Aftermarket wheels are designed and tested to a standard and to a maximum load carrying capacity. In TECH Stuff 3, wheel standards, testing procedures, marking requirements and load ratings were discussed.  Using a wheel that was designed, tested and manufactured for a different vehicle carries some risks.  Modifying a wheel to fit a different vehicle than originally intended, carries even larger risks.

 Here are some examples of modifications that are risky, even dangerous:

A wheel has two basic components, rim and center.  The rim holds the tire and the center attaches the wheel to the vehicle.  The center is designed to insure the wheel mounts to the vehicle properly and can carry the load of the vehicle.  The rim design is based on compatibility with the tire and can also carry the load of the vehicle.  The position of the center in the rim determines the position of the wheel and tire on the vehicle. When a wheel is widened, the offset and backspacing (see TECH Stuff #1) are increased.  Offset is a factor used in the criteria for determining the performance test loads in the initial design validation.  Increasing the offset, boosts the test load requirement.  Increasing the width and the offset puts more stress on the center and can cause excessive or early fatigue.It is common practice to widen wheels by cutting the center out of an old used steel wheel and welding it in a new wider rim.  Something to consider is the condition of the old used wheel.  It could have fatigue cracks from years of use.  The lug nut seats may have been damaged by over tightening or improper lug nuts.  The old used wheel may not have been designed to carry the load of the vehicle you are putting the widened wheels on.Widening aluminum wheels by cutting the rim and welding in a ring is not a good idea.  There is not enough space in this article to discuss the complications and effects of that practice.  I’ll just leave it at not a good idea. 
Changing bolt pattern

 It is pretty tough changing the bolt pattern in a steel wheel.  I think it would be easier to change the brake drums or rotors/axles.  Aluminum wheels can be modified fairly easy.  Caution is advised when considering drilling a new set of lug holes in aluminum wheels.  It is done frequently and there are machines that are built especially for this purpose.  If you choose this type of modification, make sure you use someone who knows what they are doing and has had experience.  One thing that is absolutely not recommended, is putting a truck bolt pattern in a passenger car wheel.  Trucks have a much higher load requirement than passenger cars. 

Straightening and refinishing

There are shops with special equipment to straighten bent wheels.  Steel and formed or forged aluminum are the easiest and least risky.  Steel can be bent and straightened without much fear of fatigue or cracks.  Cast aluminum however is another story.  Most cast aluminum wheels are made from heat treatable alloys.  Some European wheels are made from high silicon alloys that don’t require heat treatment.  The high silicon alloys have more elasticity and can be bent back into their original shape with less chance of fractures or cracks.  Heat treated alloys are not so pliable and can easily crack when not properly done.  Again, knowledge and experience are the keys to success. Refinishing is not much of a problem.  Steel and aluminum painted wheels can be stripped and repainted with no problems.  Steel chrome wheels have to be taken apart and rechromed separately (rim and center).  Chrome plated aluminum wheels are easier than steel because they are already one piece.  Stripping the chrome requires some knowledge because the chrome is stripped chemically, and if not done properly, can damage the aluminum casting.    The big no-no in refinishing aluminum wheels is re-machining the face of a wheel to clean it up and take out nicks and scratches.  Machining the face of the wheel removes metal from the wheel.  This changes the thicknesses of the original design and therefore changes the structural integrity of the wheel.  Enough said. I am not a fan of any type of modification other than refinishing.  Buy them new the way you want them.  If you can’t do that, make sure you do it right and make them safe. 



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