N-Gauge model railway in loft - Graham Farish Virgin HST & Mainline Class 60

Looking at the quadruple main-line section, a Class 60 with oil tankers (that are so light they always jump off the tracks!!) is overtaken by a Virgin HST set at speed. Both these loco's are after Bachmann took over G.F. and luckily the Class 60 can run at very low speeds thus the train manages to stay on the tracks - especially at points. Do other people have the same issues with these tanker wagons??