The Thundertiger wheels uses the same bead as the white 40series wheels above. The Thundertiger wheels are the exact same diameter as the traxxas geode wheels which the Masher 3.8´s is supposed to be mounted on but uses the "old school" bead. You should be able to mount the 3.8 mashers on the Thundertiger wheels mate.
I´m planning to do exactly that for this summer season.