Those are oval-style caps, the softest of which is still very hard. When "caps" were used in roadcourse/On-Road racing, they were generally more like and sometimes quite literally, "capping" a standard foam tire with a bicycle innertube, usually not even wrapping the rubber over the sidewall to give a very soft tire. It was popular technique for F1-rubber classes some two decades ago but I'm pretty certain they've closed that loophole in their rules by now.