There are rules for chases in Rulebook, but they don't say anything about actual combat during chases. Did you have any ideas on how should it work? Here's what I'm thinking:

Such fights consist o two phases.

- far chase

- close chase

Far chase is described in a rulebook: vehicles are far away from each other, and their drivers test their operate skill in each round with bonus equal to their advantage in cruising speed over the opponent. For each degree of success the gap between them gets shorter by 10m. When the chasing vehicle gets closer than the tactical speed of the faster one (or 30m if you will), we're going into phase two:

Close chase , in which we assume that vehicles move with the same average speed. They can make all the manouvers described in the rulebook for vehicles, but with a penalty equal to -40. This penalty is smaller for vehicles that drive under their full power: for every 10kph that they're not using they can lower that penalty by 10.

Here's an example of a situation:

Ork Battle Wagon drives with speed of 45kph - that's its full speed. Then Dark Eldar appear: Reaver Jetbikes are on it's tail! Their cruising speed is 130kph. That means they can match Battle Wagon's speed and they still can accelerate 85kph. That means that their penalty to manouvering is nullified.

If the Ork driver wants to make for example evasive manouver, but would like to increase his chances, he may slow down (ork? really?) to gain better control over the vehicle. For example to 25kph that'd change the penalty to -20 (but it will be risky if there's something slow and dangerous chasing him in the back)...

Shooting out and into vehicles in a chase

Far chase

For simplicity's sake all vehicles are treated as they moved with Floor It! maonuver. Therefore penalty for shooting out from or into those vehicles equals (-20 for cruising speed -20 for Floor It!) + (-20-20)=(-80). One of the chasing vehicles may choose to stop to reduce that penalty to only (-40) or match the other vehicle's speed to reduce it to 0 (of course in this case it has to score higher than the other vehicle in operate test described in the Far chase rules above; you can't match other vehicle's speed if you're slower than it)

Close chase

Here all the penalties for shooting depend on which manouvers from the rulebook we use. Average speed that the vehicles are moving with is of course ignored for the purpose of determining speed with which the vehicle moved this turn.

Ramming

Ramming is still possible. More than that: you can also ram with your side or even back! Since you and other vehicles are actually speeding it's totally possible for you to slow down and make your enemy crash into your rear. The same goes for enemies trying to flank your vehicle while driving on the cliffside - you can try to push them off the road. It works the same as in rulebook.

Boarding

Yes, this feature would be nothing without possibility to board bigger vehicles and fight hand to hand with their passengers... I think it should be possible only in Close chase phase, obviously for all the characters equipped with jetpacks and things like that. There should be a penalty to Operate skill while testing for jump equal to the penalty for BS. Characters using some kind of devices to board other vehicles - ropes from above, swinging poles like those from Mad Max should test with the same penalty.

I'm curious what you're thinking about it.