Check the upgrade description
Open the current upgrade menu and note the displayed cost and effect before purchasing. The listing confirms performance upgrades but does not publish upgrade tiers, stat caps, or exact gains. If a stat is not shown, treat the effect as unconfirmed. Do not infer a speed percentage from a thumbnail or an old community post.
Test one change at a time
Use the same open stretch and camera to compare how the scooter responds before and after one upgrade. Focus on the behavior the menu says it affects, and keep the test short and repeatable. Avoid testing at the same time as a new scooter or multiple tuning changes; otherwise you cannot tell which change mattered.
Re-check after updates
Scooter Empire is labeled early beta, with frequent updates and possible balance changes. Re-read the in-game description after a major update before relying on old costs or conclusions. There is no verified best upgrade order in the public listing. Choose based on your current goal and the information the game shows.