Rolling down the street in your SUV with 22 inch rims can be
something that makes you feel like you are king of the road. Oversized rims are
all the rage on all sorts of vehicles and nothing adds bling to your ride like
wheels that are huge and loaded with chrome.
While you might think it makes your ride look good, and I’m
not saying it doesn’t, there are a few problems that you have when you put
big custom rims at each corner of your ride. The biggest problem with this
type of customization has to do with what we call unsprung weight.
Anything on the vehicle or in the vehicle that exerts the
force of its weight on the springs of the suspension system is sprung weight. This
would be most of the vehicle, such as the body, frame, engine and transmission,
or anything that is placed inside the vehicle like passengers and cargo. This
is sprung weight because it is all supported by the springs, and suspension
system action can control the force of this weight.
Anything that exerts the force of its weight on the tires only,
and not on the springs, is unsprung weight. This is because the weight is below
the springs. Things like rims and tires, steering knuckles, brake assemblies,
and drive axles fall into this category. These are all items that spring action
and suspension articulation cannot control.
Generally speaking the more unsprung weight a vehicle
carries, the harsher the ride is. Pickup trucks and many SUV’s that are built
for heavy-duty applications tend to have more unsprung weight and therefore
have a ride that is not so smooth. Higher unsprung weight can also lead to
handling characteristics that are undesirable. All that weight causes the
wheels to bounce around more and lead to more situations where they are not
firmly planted. Wheels that are not firmly planted cause poor ride quality and
poor directional stability.
Oversized rims are very heavy and add a tremendous amount of
unsprung weight to the vehicle. Even if the rims are made of aluminum they can
still add hundreds of extra pounds, especially if you add bigger tires with the
bigger rims. Many times the tires are not much bigger in diameter than the
stock tires, but the section height, or the height of the sidewall, is narrower
to accommodate the larger rims. This low profile tire adds to the modern, sporty
look of the large rims but it further decreases ride quality.
Another common mistake when having custom rims installed
relates to the overall fit of the rim and tire assembly. Obviously the tire and
rim assembly must fit within the wheel arch and not be so big that it rubs on
any of the body or suspension parts. In order to get some wheels to fit
properly, or to provide the look that the owner of the vehicle wants, wheel
spacers are added to the hub of the wheel and then the tire and rim assemblies
are bolted to the spacers.
Wheel spacers can cause big problems and are actually
illegal in some states because they can make the vehicle handle dangerously,
and they are easy to install improperly which may cause the wheels to fall off
while driving. Like the over-sized rims, they can cause excessive wear and tear
on the steering and suspension components as well because suspension geometry
is changed.
None of this means that you can’t customize your wheels but
it just means that you need to be careful. Just because a wheel assembly bolts
on doesn’t mean that it will work just fine. With so many different types of
custom rims available for nearly every vehicle on the road there is no reason
not to find something that will fit just right, and give you the look that you
want.
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