There’s a rail shortcut at the beginning of each lap that you can access by either shrooming through the tyres, letting other players break the tyres for you, or doing a well timed charge jump against the sign to jump over the tyres.
Arriving from Crown City, Whistlestop Summit, DK Spaceport, Desert Hills, Wario Stadium, Choco Mountain, or Toad's Factory
You can take an off-road shortcut right after the start line but be careful you don’t stick to the unwanted rail at the end. You can also take the usual rail shortcut (now at the end of the lap) in reverse, although it’s not possible to do it itemless.
Shortly after the start of section 2, there is a helicopter up for grabs to the left and a truck behind the building to the right. If you are in 1st, go for the truck because it’s faster. If you’re slightly further back and someone else is going for the truck, go for the helicopter, which isn’t as fast as the truck, but it better than not getting anything at all.