My late uncle was a keen model railway enthusiast back in the 1960s, he was a member of the Clydeside Model Railway Club who are still active https://www.clydesidemrc.com/

One of the things I remember him doing was making a mould of the inside of the locomotive and then casting a lump of lead in the mould to increase the weight of the loco and then putting on little rubber tyres on the driving wheels of the loco to also help adhesion so the loco could pull a lot more weight, they had competitions to see whose loco could pull the most.