What upgrades affect car performance?

Solution 1:

According to the IGN Wiki, the following upgrades have an effect on the car's performance:

• Armour (+20-100% defence)
• Brakes (increase breaking)
• Engine (increases acceleration)
• Transmission (increases acceleration)
• Turbo (greatly increases acceleration)

The following have no effect on the car's performance:

• Bumper
• Chassis
• Exhaust
• Fender
• Grille
• Hood
• Horn
• Lights
• Plate
• Roll Cage
• Roof
• Side Step
• Skirts
• Spoiler
• Suspension
• Tailgate
• Wheels
• Window

The following are online-only upgrades:

• Explosives
• Tracker GPS Tracker in your car
• Full Coverage Insures your vehicle if destroyed

Solution 2:

After doing some testing, I have noticed a difference between off-road tires and high-end tires, both on the street and off-road. I can tell a difference in cornering (as well as traction over bumpy terrain) when I alter the car's suspension.

Therefore I'm quite sure that it is wrong to say that wheels or suspension have no effect on car performance.

However, I don't know to what extent the other changes, if any, have upon car performance.