Wanna know what you'll gain for investing in the four upgrade areas!? Here is the list. Keep in mind that the prices get exponentially more expensive as you level your way through the upgrades.
Engine - Spend your hard earned money at this upgrade to give your vehicle an overall speed boost.
"Improved engine parts result in power increase. Higher horsepower helps you climb hills and make longer jumps and tricks for more bonuses."
Suspension - Tumbling out of control after a particularly big leap!? Well upgrade your suspension.
"Lower weight point and improved shock absorption improves stability at high speeds and makes the car more stable on bumps."
Tires - If you are struggling with both speed and traction tires upgrade might help.
"Improved tires result in better traction and better power delivery to the ground."
4WD - Simpli put it boosts your overall performance.
"Improving all wheel drive system will result in better traction and better handling of the vehicle."