The platinum-to-palladium ratio compares these two platinum group metals (PGMs). Both are used in catalytic converters, but gasoline vehicles primarily use palladium while diesel vehicles traditionally use platinum.
Why is this ratio important?
Palladium became more expensive than platinum around 2017 due to surging gasoline vehicle demand and supply constraints. Some automakers are now substituting platinum for palladium in catalytic converters due to price differences.