• Vehicles were controlled by the server making them latent and not fun to play on the Internet
• Predicting the vehicles on the client failed as the client and server simulate the physics differently, causing the vehicles to get rapidly out of sync
• Correcting the predicted vehicles position made the game feel unresponsive and caused the vehicle to travel unexpected paths
• Valve themselves said that it was currently impossible to predict and therefore network vphysics objects accurately (think of the barrels in  CS).
• The SDK does not allow for direct modification of physics
• Could not implement manual transmission due to SDK limitations
• RPM calculations were erratic and more often than not incorrect
• RPM values could not be recalculated accurately

Via HLRally