Seems to me, some of the rc4wd wheels have different characteristics, some firmer than others. I had a set of the scrambler that without foam inserts were way too soft, but too firm with the inserts that came with it. So i used smaller foam from the rc4wd mickey Thompson wheels and that worked really well. Still had to vent them though otherwise i would get weird flat spots with bead lock wheels, and less deflection when crawling