Hi Ben, I've also done the tire-exchange in the past. And also out of Telekom's by now... :-) My best Trick: just add more power on the track. I've exchanged the Lego-transformer for a standard 6-dollar-one (with 2 outlets!): 2 times ~11,5V / 1,25A (...) (22 years ago, 10-Oct-02, to lugnet.trains)
(...) At LEGOWorld, Intertoys will probably have these in their megashop there. And current Intertoys price is 99 Eurocents :D (22 years ago, 10-Oct-02, to lugnet.trains)