Continuing from the original post here, based on the Juhlin.com forum thread here. I realized I’d never recorded my follow-up thoughts on the blog. Let’s rectify that.
Twilight: 2000 in all its editions is much more post-apoc adventure survival fantasy than excruciatingly-accurate simulation (Apotheosis Saga, anyone?). So treads and lube aren’t usually tracked to the level of tank extinction. But let’s talk about the mechanics of mechanical issues for our hypothetical T-72 owners.
Maintenance
v2
A T-72 requires 14 hours of maintenance per week. Potential breakdowns occur every 8 hours of movement or combat, rolled against the vehicle’s Wear value (10% for like-new, to 100% if it’s on its last legs). If there’s potential for a breakdown, the mechanic who did the last maintenance rolls a Difficult Mechanic check to see if his work prevented the breakdown.
Assuming a well-optimized but not maxed mechanic PC (Strength 8, Mechanic 8), a Difficult Mechanic check has an 80% chance of success.
v4
Every vehicle requires the same amount of maintenance: 6 hours per week in which it was driven at least one hex on the overland map. Maintenance requires a successful Tech roll. Failure reduces Reliability by 1 (with most vehicles maxing out at Reliability 5, so you have some margin for error).
Assuming a well-optimized but not maxed Mechanic PC (Intelligence d10, Tech d10), a Tech roll has a 75% chance of success.
Parts and Repair
v2
A well-buried rule indicates that parts need to come from a vehicle identical to the one being repaired. Furthermore, there’s some text indicating that parts are also component-specific (engine, main gun, radio, etc.). There are no explicit rules for scrounging or buying parts.
No roll is required to cannibalize a donor vehicle’s component for parts. However, if the component is damaged, there’s a 30% chance that the part is useless.
A character who’s a capable machinist (or gunsmith, for ordnance repair) may also fabricate mechanical parts with a successful skill check andaccess to a machine shop.
Most repairs require 1d10 parts (1d5 for minor breakdowns).
Damage is tracked by vehicle component, with most components having two states: OK or inoperable/destroyed. A few have an intermediate damaged-but-still-partially-functional state.
v4
“Vehicle parts” are generic – when needed, a bolt, brake cable, or turbocharger materializes out of the quantum foam of your mechanic’s spares box.
A successful Tech roll when scavenging a vehicle yields one part per success rolled, -1 for a destroyed vehicle. Parts are considered to be “common,” which means a 67% chance of availability in a typical settlement.
Only one part is needed to repair a destroyed item, though each repair only restores 1 Reliability per success, so thorough work will likely consume more than one part. Restoring reduced Reliability on an item that wasn’t fully destroyed doesn’t consume any parts.
A vehicle’s Reliability score covers its overall structural integrity, its transmission, and its engine. Weapons, radios, and other subsystems either have their own Reliability tracks or have OK/inoperable states.
Ammunition
v2
2nd edition provides varying availability levels for different ammo types.
125mm HE is common (80% chance of being available in cities, 70% in towns, 30% in villages).
125mm HEAT is scarce (60% in cities, 40% in towns, 20% in villages).
125mm sabot is rare (20% in cities, 10% in towns).
12.7mm and 7.62x54mm for the MGs are both common.
v4
As a broad category, all non-guided heavy weapon ammo is scarce (33% chance of availability in any settlement).
All small arms ammo is common (67% chance of availability in any settlement).
In both cases, chance of availability is for the broad category of item. The referee decides whether a specific sought-after model/type/caliber from that category is available. The West Possum Trot Trading Post may be fresh out of 125mm HEAT, but surely 122mm howitzer mustard agent shells are close enough for government work, right?
(Really, that last paragraph captures it. Ammo availability, perhaps more than any other resource, will be subject to referee judgement and fiat, even with strict adherence to the framework of the rules.)
To close it out, here’s a price comparison for main gun ammo: