Question: SMP F4 Championship is a racing series based on what type of car?

Context paragraphs:
Formula 4: FIA Formula 4, also called FIA F4, is an open-wheel racing car category intended for junior drivers.  There is no global championship, but rather individual nations or regions can host their own championships in compliance with a universal set of rules and specifications.

Jarno Opmeer: Jarno Opmeer (born 4 November 2000) is a Dutch racing driver.  He currently competes in SMP F4 Championship, where he finished vice-champion.

2015 SMP F4 Championship: The 2015 SMP F4 Championship season was the inaugural season of the SMP F4 Championship, a motor racing series for the North European Zone (NEZ) regulated according to FIA Formula 4 regulations, held in Estonia, Finland and Russia.  The 2015 season began on 16 May at Ahvenisto in Finland and finished on 3 October at the auto24ring in Estonia, after seven triple header rounds.

2016 SMP F4 Championship: The 2016 SMP F4 Championship season is the second season of the SMP F4 Championship.  It began on 29 April at Sochi and will finish on 10 September at Ahvenisto after 20 races held across seven rounds.

2017 SMP F4 Championship: The 2017 SMP F4 Championship is the third season of the SMP F4 Championship.  The series is also known as FIA North-European Zone (NEZ) championship.

Danny Kroes: Danny Kroes (born 5 November 1999) is a Dutch racing driver currently competing in the TCR International Series and TCR Benelux Touring Car Championship.  Having previously competed in the SMP F4 Championship and F4 Spanish Championship amongst others.

Niko Kari: Niko Kari (born 6 October 1999) is a Finnish racing driver.  He won his first single-seater championship in his debut year in SMP F4 Championship.  He is currently competing in GP3 Series.

Koiranen GP: Koiranen GP, also known as Koiranen bros.  Motorsport, is a Finnish auto racing team based in Barcelona, Spain.  The team currently competes as a promoter of the SMP F4 Championship and Spanish Formula 4 Championship.

China Formula 4 Championship: China F4 Championship () is a racing series regulated according to FIA Formula 4.  The inaugural season is the 2015–16 China F4 Championship.

SMP F4 Championship: The SMP F4 Championship (also known as the F4 NEZ Championship by SMP Racing) is a racing series regulated according to FIA Formula 4 regulations.  It is based in the FIA's North European Zone and the Netherlands, and is only open to drivers from these countries.  The inaugural season will be the 2015 SMP F4 Championship.

Supporting paragraphs: SMP F4 Championship Formula 4
Answer: open-wheel