Ability Scores
Cars have ability scores just like characters and they are generated just like characters. The Ability Scores for cars are Hard, Rev, Drive, and Smarts
Hard as in how hard is the chassis. Cars with high Hard can take more hits and probably have steel plating or a similar padding.
Rev as in rev that engine. Cars with high Rev can travel farther and don't use up as much fuel. This is the main stat for determining how many hexes your car can travel before suffering mechanical failure.
Drive as in how she drives. Cars with high Drive can turn on a dime.
Smarts as in computer smarts. Not all cars are analog. Some are equipped with computer technology. This technology can vary from an advanced AI, like Knight Rider, or automatic parallel parking. Cars from the analog age don't have this ability score.
Damage
In order to even dent a car a source has to deal 10+ damage to it. Yes this means most conventional weaponry is useless against cars. You'd need something heavier, like a machine gun or rocket launcher to really do some damage.
When a car takes damage she makes a Hard save with a -1 penalty per 2 points of damage over 10.
For example if Mercedes the Mercedes took 16 damage from a Glory Rider's Hexsaw Buzzomatic Launcher, she would make her Hard save at -3.If she makes the save, nothing happens; she's A-OK. But if she fails, her driver rolls 2d6 and references the Table of Vehicular Calamities (see below.)
Travel
A car can travel a number of hexes per day equal to her Rev score. So a car with a 16 Rev can travel 16 hexes in a 16 hour period. If her driver wishes to push her farther after this limit, she must make a Rev save. Failure means a permanent -1 to her Rev score due to the strain. As soon as the engine gets 4 hours of rest, she's good to go for another drive.
Fuel
All cars require fuel. A car's tank is represented by her Fuel Die, which starts at a d12. After traveling through a hex, the driver rolls the car's fuel die. If the result come up 1, the Fuel die decreases a level. If this happens when the Fuel Die is on a d4, the car is out of gas.
For Example if Mercedes' driver drove her 8 hexes that day, starting with a full tank, he would roll a d12 8 times after exiting each hex and if any of them come up 1, her fuel die goes down each time.Most fuel is carried in Fuel Canisters, which take up two slots of inventory per canister. Characters can empty canisters to increase their car's fuel die by one level.
For example if Mercedes was on d6 and her driver filled her up with one fuel canister, her fuel die would now be a d8.Storage
A car has 20 slots of inventory with which to store stuff...That's it....
Repairs/Upgrades
All cars need upkeep and maintenance. The cost of these is determined by a sliding, but consistent scale.
Upgrades/Repairs have 5 grades. They are Minor, Normal, Major, Severe, and Totaled. These grades are arbitrarily given by the DM (but in this DMs opinion this is not an issue and the DM will probably not use his gift of omnipresence to fuck you over.)
The cost of the repair or upgrade is equal to the grade's die (d4, d6, d8, d10, and d12 respectively) times 100gp.
So if Baby-Baby Jenkins wanted to get some cool new rims for his mustang, he would roll a d4(minor)*100gp. Turns out he rolls a 3 so those new rims are going to cost him 300gp. But fuck will he look cool!---
The Table of Vehicular Calamities
2: BOOOM!! She goes up in a flaming ball of glory. Your car is completely destroyed instantly and her passengers take 4d6 damage from the explosion (save for half.)
3: Blowout! A wheel is shot. Your char is immobilized and requires repairs to get running again.
4: Fuel Leak! The tank is fucked. At the end of each round/turn/hex, roll your car's fuel die. Now it goes down on a 1—4.
5: Barrel Roll! Make a Drive save with penalty. If you fail your car flips over, causing 2d6 damage to everyone inside, and needs to be flipped right-side-up before she can move again.
6—8: -d6 points from a random ability score. If an ability score reaches zero, the car is disabled and needs repairs.
9: Road bump! Lose a random item located in your car's storage. Passengers take d4 damage from bumping their heads.
10: Surprise! A secret compartment you were unaware of up until this point opens and reveals...something...to be determined by the player. The only stipulation is that it isn't anything good.
11—12: Why nothing at all!