Board Thread:Game Discussion/@comment-31295789-20170506001114/@comment-122.172.71.165-20170508174919

If you have all 3 cars with around 48 or 49 PR, you can upgrade one car to PR 55. I chose the Renault: 635355 for 193 GC after 50% discount. With a PR 53 or greater you can complete Formula E: Showcase for 30 GC (100% completion reward). After spending around 175 GC for badges in Formala E: Experience, you get 300 GC reward.

A: PR > 55 upgrades: 193 GC

B: Buy badges for non-upgraded cars in Formula E: Experience: 175 GC

C: 100% completion reward for Formula E: Showcase: 30 GC (requires a PR 53 car)

D: Reward for getting all 21 badges in Formula E: Experience: 300 GC

Total = D + C - B - A = 300 + 30 - 175 - 193 = -38 GC

So you pay 38 GC to get a nearly fully upgraded Formula E car.