Always complete the daily challenges. They reward "Scraps," which are used to level up Tuning Parts. Level 3 Tuning Parts are infinitely better than Level 1.
Players collect coins and gems to unlock and upgrade over 30 different vehicles, ranging from basic jeeps to advanced supercars. Key Game Modes Hill Climb Racing 2
If you are looking to "create" specific performance parts for your car, you can use the Unlock Requirement : You must reach the rank to unlock the Scrapper. tab in your garage. Always complete the daily challenges
This is the biggest downside. Progression slows drastically at higher levels. Upgrading vehicles costs a huge amount of coins and gems. While not strictly "pay-to-win," paying players will advance much faster. Hill Climb Racing 2