In the 2021season Rahal Letterman Lanigan Racing again expanded to three cars, with Graham Rahal and Takuma Sato driving two full-time entries while several drivers would drive a third car on a part-time basis. Graham Rahal drove #15 backed traditionally by United Rentals, American equipment rental company. Rahal’s best finish was 3rd at Texas Motor Speedway, but his consistent top-5 and top-10 placements put him to 7th position in the final series standings.
|Graham Rahal||15||Rahal Letterman Lanigan Racing|
|Dallara DW12 (IR18)||Honda||United Rentals / Fifth Third Bank|