# Help with Suspension Distance

Hi All,

I’m trying to understand the Suspension Distance within wheel collider. say I have a car model and I add wheel collider to each wheel model (and of course adjust the wheel collider’s radius and center for each wheel). I want to make my car with semi munster track suspension but when I increase the the suspension distance and the increase the spring coefficient the car start to oscillate as I want but the wheels (the model wheel and also wheel colider )are in the air and never tuches the ground - only the suspension distance in the scence view tuch the ground).
Please help me I’m so cunfused I’ve been tryig to understand it for couple of hours now

It’s incredibly hard to get this right !!

One tip:

Note that the wheel colliders should actually sit AT THE TOP OF the travel of your wheels. That is - imagine the main model or just painting of your car or truck. The wheels will be at a certain position right? In fact, the wheel colliders should sit QUITE A BIT ABOUVE THAT POSITION … in fact at the very top of the travel of the real suspension (so let’s say, as if touching the inside of the wheel arch.

it is really a shame that Unity don’t mention this in their manual, it’s a critical tip regarding wheel colliders.

Also – ensure all your models are imported at exactly 1:1. Nothing will work otherwise. If this is not the case, have your art department redo everything. It’s the only way. Also: ensure everything is Z-forward. Nothing will work otherwise.

Also - ensure your vehicle has typical real weight and so on (say 2000 kg).

ALSO - there are a number of car systems for sale in the assets store. Buy one, and your job is finished. It’s a great asset store!

#FURTHER EXPLANATION…!

#On a REAL CAR, think of the FOLLOWING THREE REAL POINTS:

1. Push the wheel UPWARDS as far as possible (“all the springs are totally compressed”)

2. Where the wheel sits WHEN THE CAR IS PARKED

3. Imagine a giant lifting the car up in the air – the wheels fall downwards. Imagine the FURTHEST down point the wheels can fall down to (“all the springs fully compressed”)

#It is essential to see in your head these three three positions, on a real car!

Now surprisingly…

POINT 1 is where you MUST POSITION YOUR “UNITY WHEEL COLLIDER”

Point 3 is exactly what you set THE “LENGTH” of the collider.

Now you ask - how the HELL do you set point 2?

#There is only one way to set point 2 – literally adjust the mass of the vehicle!!! That’s how you do it. Strange but true!

Adjust the mass of the vehicle, while the scene is ACTUALLY RUNNING…

until the height (2) of the car matches what your designer has drawn for the car sitting there. That’s how you do it!

You must set the wheel collider to these values:

Spring about 8000. Damper about 800. Target position must be ZERO. Mass is largely irrelevant - but try “1”.

(PS don’t forget it’s absolutely essential that all four wheels (and indeed every single component of the vehicle) faces correctly Z-forwards. A common mistake is to quickly “flip around” the two left wheels to make the two right wheels! You can’t do it.)

Hope it helps!