@TechConnectify Depends if you count gearing cogs (at least in the UK). The longest trains here are about 22 freight cars with 4 axles + 6 axles for the locomotive (188 rail contacting wheels) though most trains are passenger trains, the longest being 11 cars of 8 wheels (88 rail touching wheels total).
The ones I drive tend to be from 1 to 6 cars (of 8 wheels per car) which brings that average right down.