I just got 2 new Radrunner 2 bikes and both have what I would describe as oversteer. When I start to turn they tend to have a life of their own and want to steer more aggressively. Is this common and if so, can tire pressure reduce the tendency?
Sounds like it could be low tire pressure. Did you top them off after assembly?
There is also a chance the fork is backwards which would lead to heavy steering and over correction etc. Make sure the disc rotor and the fork mounted caliper are on the same side as the rear wheel. (Left side)