Synchronizing multiplayer car game

Hello!
I also posted this question in the forums, but I’m getting a little frustrated over this…
I have a multiplayer driving game (not a race, just driving). I’m not using the Unity built-in Network framework, but something my company has developed - basically every command given to a specific Unity player can also be broadcasted to all other Unity players which are connected to the server.
So far so good - but when the cars move (I’m moving them using WheelCollider.motorTorque), they run out of sync pretty fast.
I understand that interpolation might be the way to do this (we’ve tried a very wide variety of other solutions…), and I’d really appreciate it if anyone could point me in the right direction - how and where should I start?

Thanks!

I would suggest having a look at this if you are not using the built in unity networking:

http://developer.valvesoftware.com/wiki/Source_Multiplayer_Networking