The customs can do this
1) Fine you to the max of 10X the tax value
2) Charge you for smuggling, which means your car will be impounded
3) Jail but that would have to be in court, if it goes that far.
A sign of tip off is that they will ask you very nicely if you have anything to declare, they would even ignore the tyres. Walks around your car maybe look into your boot and innocently ask again if you have anything to declare. You say no, and he walks to your tires and says these look new, can you proof that these were bought in Malaysia? Of course you have to stick to your story and say that the receipts are in KL. Then he'll say leave your car here, it is impounded. You are suspected of smuggling because he asked you twice and you said no, nothing to declare. He will let you go home (without your car) to get your proof or have someone bring it down.