every time i go over 250mph my wheels seem to swell up and explode, is there any way i can stop/prevent this from happening?
Most (if not all) economy road tyres (like the ones that are fitted to BeamNG's vehicles) are not strong enough to remain stable at such speeds. To solve this, you will need to alter the tyre jbeam settings to make the tyres stronger.
250MPH is 402KMH. A standard tire isn't meant for such speeds, and in real life it would probably end up heating and exploding at some point.