Does the Stance Tuning options improve the performance of the vehicle?

Solution 1:

Sorry, no Camber and Height do not affect you car's handling, they are purely cosmetic.

NFS Payback's customization options are not consistent on whether or not they affect your vehicle's performance. For instance, modifications like your car's spoiler or canards will affect downforce strength and improve agility at high speeds but other changes like brake discs don't have any effect.

I'd advise you to look through Payback's wikia page to get a better idea of what modifications affect performance and what modifications don't.