Transmissions do.
Ever seen the YouTube video of the 1955 Le Mans crash?
It helps if you don’t make the entire car out of a very flammable magnesium alloy. Specifically, the same magnesium alloy that was used to make incendiary bombs in WW1 and WW2. Once ignited, it is impossible to extinguish and burns so hot that it can melt its way through battleship plate and tank hulls.
But Mercedes had to have the lightest thing around, so they constructed the entire car out of this ‘Elektron’ magnesium alloy. What could possibly go wrong?