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AutoAmenity Chrome Wheelskins Hubcaps Home > FAQ > Wheel and Tire Terminology

Wheel and Tire Terms & Diagrams to help you understand

what they are talking about:

1. Diagram with technical terms describing parts of wheels:

               Note "Safety Humps" in diagram and picture below

The Safety Hump (AKA Bead Bump) is required by DOT to help hold the bead of the tire against the flange in case of blowout air pressure loss, while the vehicle is decelerating, to decrease the possibility of tire shredding and complete loss of control.

Hubcap and Trim Ring mounting clips are designed to seat into the groove formed by the Safety Hump, marked in red in the pictures below, for increased hold on the wheel. 

If the Safety Hump groove is not present, as in some off-road, ATV, riding lawnmower, or cheap wheels imported from India, Brazil, and other sources, hubcaps or trim rings may not hold the wheel as would normally be expected.

Wheel and Tire Terminology


2.  "Safety Hump" Marked in Red in the pictures below

Toyota Truck  Steel Wheel with red mark in the "Safety Hump"Mod Steel Wheel with red mark in the "Safety Hump"



3.  Another Wheel Diagram:

Wheel and Tire Terminology



4.  Aspect Ratio:

Wheel and Tire Terminology



5. Wheel Offset: 

Wheel and Tire Terminology



   Standard Steel Wheel    Eight-Spoke Steel Wheel         Mini-Mod Steel Wheel

       Standard Steel Wheel, black        Eight Spoke Steel Wheel       Mini-Mod Steel Wheel



This picture shows a Cut-away Hubcap mounted on a wheel, intended to show how hubcaps are designed to bridge over the space occupied by wheel weights, so that most wheel weights are no problem with most hubcaps.

However, as of 2013, all states will require conversion to Non-Lead Wheel weights, which are made of lighter metals like iron or zinc,

and some of these may be thicker than those shown.

Hubcap cut-away on Standard Steel Wheel