D&D 5E (2024) Building A Contemporary Fantasy Setting For 5.5E

[Remathilis]

How fast is the pickup? How much damage does it do if I ram it into the dragon?

Vehicle rules exist already. You just need to create stats for modern vehicles.

Bare in mind, I'm not saying you wouldn't need some new things. You would need to stat new gear, probably add new subclasses, feats and backgrounds. But you don't need to rewrite base classes or combat rules or redo the magic system. You don't need a wholesale rewrite of the PHB, any more than Dark Sun or Theros needed wholesale rewrites of the PHB.

 

[AlViking]

How fast is the pickup? How much damage does it do if I ram it into the dragon?

As long as the characters don't have access to military technology, I don't see why D&D wouldn't work. Yes you have to assume action movie logic for guns (running crouched with one hand raised to cover the side of their head obviously makes them bulletproof), but that's largely because we've never seen someone take a direct hit from a sword.

As far as how much damage a pickup does if it hits a red dragon - who cares? Make it up. Just like if you were piloting a sailing ship and rammed the dragon, or dropped your Daern's Instant Fortress on it's head and activated it as it fell. There are all sorts of things we have to just kind of guess at.