In a Championship, go to the 'BOX' (car upgrades) and max all five upgrades. Takes 45 tokens in total. Earn tokens by completing races in Championship mode (4 for 1st-5th, 3 for 6th-10th, 2 for 11th-15th, 1 for 16th-20th).
Once you have all five are maxed the achievement will unlock, no need to start a race another race.
*Edited for more detail from comment feedback*