Garry's Mod Vehicle system ?

If you are looking for a vehicle replacement I would personally recommend a free workshop addon called [Simfphys]
Workshop id: 771487490
This addon adds GLua based vehicles that do not use the normal vehicles mechanics that the Source engine uses, but the addon creates a new system that is entirely made using GLua to create a more customization in many ways.
It adds some helpful features such as a speedometer on your HUD to show your speed, a working fuel system that can be customized to be pretty realistic or you can disable if you just want to ride free. It also adds vehicle damage that actually affects the performance and appearance, for example if you were to shoot one of the tires the wheel will deflate, or if you were to damage the car enough it will catch fire and explode.
The addon also allows you to create/modify cars very easily and has a wiki to help you through the process.

Hope this helps!