In order to get a better understanding of why they are there, it helps to know when they actually came to be in the wonderful world of automobiles. The earliest form of were created to cover up the center portion of the wheel where the steel spokes met what is known as the hub. This was what was used up until about 1932 which is when snap on center hub covers or caps came about which were a bit more decorative than what was previously used. These caps were equipped with a special snap feature that allowed them to be pushed and locked into place for a secure fit. This very system is the foundation of what is still used on hubcaps and wheel covers today.
After the 1930's things started to get a little more fancy as hubcaps were now turning into wheel covers, which are made to cover the entire rim of the wheel except for a tiny portion of the rim closest to the rubber tire. We first started to see the more decorative style hubcaps and wheelcovers being introduced in the 1940's, which was about the time when more and more were being made with stainless steel or chrome plated material. If you really wanted to go all out, you purchased a set of wheel covers that had an extra chrome ring on the outer edge in addition to the chrome center hubcaps. These were quite expensive during those times and were typically only purchased by those who could afford them.
So now after reading this it is more clear as to the difference right? Hubcaps were originally just the small piece covering the hub section or portion of the wheel while a Wheel Cover as it was rightfully named covers the whole wheel. Nowadays these are commonly spoke of the same part as most center portion covers are only those that are now called center caps. The days of Hub Caps are more or less gone with the era of centers and trim rings and have evolved into center caps which are usually the center portions of alloy and custom wheels.
Hubcaps Unlimited specializes in both Hubcaps and Wheel Covers and has done so for 30 years.