Some wheels are lug-centric (the lugnuts center the wheel on the hub) and some are hub-centric - (the wheel is centered on the hub by a plastic ring) - this plastic ring is placed on the wheel hub before the rim or placed in the hub hole in the center of the wheel. If the new wheel didn't come with them, they are probably not needed since your wheel is lug-centric. And if it did come with hub-centric rings you will have a vibration if they aren't used since the wheel won't be centered on the hub. If you bought the wheels used, then you will just have to trust the person selling them I guess if he/she says the wheels never had them new. Your best bet it to call the wheel company or the vendor that sells the brand of wheel to be sure.