Unity car rigging trouble

G'day,

First time poster, long time stalker. Just to start, I've read the Support FAQ and I'm still not sure if this is the correct sub-forum to post help about Unity problems other than bugs? I'm just having a bit of trouble rigging up some wheels on a truck model.
Please move this to the correct sub-forum if I've posted it in the wrong place.

So I've had a go at the car rigging demo on Unitys web page, was great to have a play with that and all seemed to go well, now I'm trying to start from scratch using a Youtube tutorial by the label of "Creating a driveable vehicle in Unity 3D - YouTube" with two scripts called
PlayerCar_Script.js WheelAlignment_Script.js given to download from the Youtube video description.

So anyway I've lined up my Wheel Colliders nice and centre to all the wheels, followed the tutorial step by step (a few times over), so in the editor it looks something like this -



Got my Chassis setup with the scripts attached and pointing to the correct wheel colliders -



Yet when I press play, this is what I get -



The wheels do spin (kinda) but on a massive rotation, which I can't seem to find any way to make smaller?
I've tried tweaking the settings with the Wheel Colliders and any others I can mess around with, but nothing seems to bring that
massive rotation down for the wheels.

I would attach the Project but because of the truck model it's around 170megs, not sure if that would be allowed in the upload system?
Anyway I'll upload the script files that might give some more insite on things. (which I think I have done right).

Any advice would be great! Thank you very much

 

Oh I seemed to have fixed that problem by creating a empty object and connecting the colliders up to that instead of the prefab model.
So the wheels are spinning good, except now when the front wheels touch the ground it flys the vehicle off!
I've set a rigid body with a large mass and toned down the engine but it still shoots off really fast once the front wheels touch the ground