I like the idea of using distance driven too. I'm pressed for time so these numbers will be in miles.
A Semi Truck like my Pete can go 100k miles before needing a new set of tires (this is usually an annual expense). It can go 500K miles before needing an "in frame" rebuild of the rear end, top of the motor (head gasket) and throwout bearing in the tranny (at about 5 years of service). It will be worn out at 1 Million miles (about 8 to 10 years of daily driving/service).
A typical passenger car can go about 100k or 7 years (whichever comes first) before major component failure begins to occur. A medium-duty truck (5-Ton delivery style) can hit 250K miles or 10 years of daily use.
I think rating the Suspension (tires), Motor, Body, and any custom Electronics, Weapons, or Sensors would be appropriate. You simply DIVIDE the maximum Miles/Kilometers the vehicle can go by 10 to determine WHEN to check for a Wear Value Increase. For Electronics, I'd use HOURS OPERATED and a "ROUND COUNT" for cannon or missile launchers.
Getting a successful roll AGAINST a Wear Value Increase would reflect the vehicle getting the needed maintenance which can greatly increase service life. As we already discussed in the thread on suspension/track life, the tires and tracks are the "weak link" on vehicles (pun intended).
