How do you run a chase scene in your games? Does each side roll basic effort and whoever is highest pulls ahead? Do you contest CON or DEX? Something else?
I’m prepping an encounter, and I think that it might reasonably conclude with a chase: after a fight, the bad guys cheese it with some MacGuffin that the PCs need/want. The PCs don’t have to give chase, but they might; and I want to be prepared!
Set difficulty, say 1-3 hearts of effort
Set a target - adjust based on stay/loot
Base damage based on what the players do
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Profit?
Maybe make it a group challenge and make it a few hearts. Or, make it an individual challenge and failure = capture/death.
Flesh this bad boy out and I’d gladly try my brain at it. I’ve done a ‘running away’ before but not a ‘chasing them down’ and some details would help. Will your players have horses? A chariot? A hot air balloon? Or will they be on foot? Are you planning to have it in a city or on an open road? I’m guessing fantasy. You can clarify that part.
You might not have these figured out yet but maybe by asking, it gets your gears turning. Give the story a little more meat and I’ll toss some darts at your board 
This is how I do it:
The lead starts with 1 heart. Each round (or turn, depending on the situation) a player rolls against the target and if he succeeds, adds basic effort to the lead if they are escaping or deducts it from the lead if they are pursuing. When the lead reaches 0, escapees are caught. When the lead reaches 2 hearts, escapees escape. Also the chase can have a max round limit, and when it expires the escapees automatically escape.
Post-apocalyptic. Physical mutations only; no magic or psionics or similar. Mostly humans with mutations, though there are a few awakened animals (one of the PCs is such: an intelligent raccoon) and anthropomorphized animal-like creatures. Relatively low tech at the moment. The part of the world in which this takes place is mostly provincial farmlands with a couple of small hamlets dotting The Road between the two major cities: one in the south, and one in the north.
Our characters are on the outskirts of the big city in the north, a place called Sto. They have made the acquaintance of a group of archivists and tinkerers called The Junkers, who collect tech from The Ancients and figure out how to make it work. They have a squat little building that doubles as home and workshop, and a large yard (The Junker’s Yard) that people today would rightly call a junkyard.
Taking a cue from the old Gamma World games, there is a festering animosity between a small group of bio-form bigots who think pure humans are the proper inheritors of the world, and all mutations are an abomination. There’s a similar, though much smaller, group of mutants who feel the opposite. Most day-to-day life isn’t effected by either group too much, but things are about the change.
The human speciests are going to raid the Junker’s Yard to collect some of the tech they have there. They don’t entirely know what they’re looking for, aside from an ancient suit of powered battle armor. The human antagonists don’t know how it works, but figure that if a bunch of mangy animals can work this stuff then surely a real human can, too.
I envision three “rooms”.
Room 1 The Junker’s workshop. Target 11. The PCs will be in here, having just completed a light RP session the last time talking to the Junkers. They have some info about a possible point of interest, and the names of a few people they might seek out. At the start of the next session, the humans will begin their raid. I am undecided at this time if they are going to barge in guns blazing (or even if they ram a truck into the building, or something similarly dramatic); or if a couple dudes go in to distract the Junkers while a different group breaks into the Yard.
Room 2 The Junker’s Yard. Target 12. This will be a fight in a junk yard. There are rows and piles and mounds of junk. The unnatural terrain will provide some fun opportunities for the players. I expect the human adversaries to be pretty pedestrian, and unlikely to use the terrain or any of the junk therein to their advantage. These are not real soldiers, just a bunch of close-minded jackasses looking for a technical advantage so they can prosecute their campaign of bio-form bullying.
Room 3 The chase. The bad guys will retreat. They may get the power armor, or they may snatch something else. Something that can be a game changer to a militia, but also something that could easily and safely be stashed in a junk yard. I am assuming that the leader of this human strike force will high tail it away, and not fight to the death. The party may give chase.
The Junker’s Yard is maybe a mile or two away from the main elements of the city of Sto. I have a rough map, and the party has been through Sto briefly before, but they would be at a severe disadvantage in any kind of pursuit through the streets and alleys.
I kind of want the humans to make off with something useful, so that future interactions have some built-in threat. I don’t want to just narrate the get-away; and I really don’t want to cheat the dice, so the chase may be a bit of a risk on my part. Maybe there are multiple people fleeing the Yard in different directions: the party needs to choose one to pursue, knowing that they can’t catch them all (this isn’t Pokeman, after all! 
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I’d love suggestions or feedback from this group! Thank you!
You could make 3 items – > power cell, blue prints, and the actual armor. The “humans” bolt in three different directions with each item. The players have to decide which one they want to pursue. Bikers go one way (fast, agile, and sneaky), a war truck goes another way (big, heavy, and well defended), and hot rods go a third way (aggressive, road spikes, and passengers).
Then stick to CHUNKS in the core rules with a TIMER – > players have until the TIMER expires to stop the escaping thieves before they run out of gas! Either put them all in the same vehicle or split them up. Ignore the idea of movement and let them play like they are in fast moving vehicles. If they manage to hinder the enemy – like destroying a CHUNK – don’t tick down the TIMER on your turn and tell them they bought themselves some time.
Yes! Earlier this evening I finished sketching out the junkyard, and placed inside it power armor, an ancient artillery weapon, and a weapons rack (and found the corresponding art cards to place on the actual battle map). Three groups of pairs (each pair has one melee, one ranged combatant) will run in to each snatch something. I like the power cells a lot, though: that’s something the players know about and want for their own weapons, so it would be something they’d feel a little more personally than just “a rack of rusty melee weapons”.
I had written down that the timer is “in 6 turns, the baddies make their retreat”. Depending on who the PCs engage in the junkyard, someone will likely get away with some of the loot. My players are super crafty, though, so I wouldn’t be surprised at all if they manage to foil two of the groups.
I haven’t done a lot with vehicles in this game world, but now might be a good time to surprise the party with an adversary that has better tech than they do. I might have a burned out power sledge in the yard that the players can fire up to give chase. I had glossed over the CHUNK bits in Speed Kills because I hadn’t expected to need it: reading up now!
Thank you!