I have recently been playing around with the vehicle size and weight rules on Machinas, looking to streamline them and make the penalties and advantages consistent and easier to remember. Off the back of it I also ended up changing the way vehicles take damage from Shooting, removing an oddity where faster vehicles were harder to destroy and adding in the chance of knocking out weapons and defences on opposing vehicles. I am still testing them, but I think that the basics are good to go, so am posting them here for comment and criticism.
Vehicles have a size from 1-6:
1 - Bikes
2 - Buggies, Sports Cars, Subcompacts
3 - Sedans or similar. This is the size I use for standard games.
4 - Large pickups, Vans
5 - Bus or Camper Van
6 - Trucks
A vehicle can carry weight equal to twice its size. The penalties for exceeding this are as given in Machinas
You'll notice a column for Hits. I felt that Shooting causing Speed loss and Speed therefore equating to a vehicles capacity to take damage didn't really work for me. So now Shooting no longer causes direct Speed loss. Instead 2+ Successes on the Shooting table cause a loss of Hits.
The more Successes you score, the more Hits you score - if you score more Successes than the target you score Hits equal to the difference -1. So +2 Successes scores 1 Hit, +3 Successes scores 2 Hits and so on.
When a vehicle has lost at least half of its Hits then it is damaged and automatically suffers a -1 Success on all Passing attempts. Then roll 1D6 for each 'system' on the vehicle - on a 1-3 that system is considered lost for the rest of the game. 'Systems' are any Car Feature, Weapon or Defence which has a positive cost. In addition all vehicles have an Engine system; on a 1-3 that system is damaged and the vehicle suffers and additional -1 Success on all Passing attempts.
Example: A van can take 5 Hits and has a Grenade Launcher and Sloped Armour. It takes fire and the attacker scores +2 Successes on the Shooting table, so the van suffers 1 Hit. It has 4 remaining, so isn't considered damaged. A second shot scored +3 Successes on the Shooting table, however, so the van suffers 2 more hits. It has now taken 3 of its 5 hits, so is considered damaged. It now automatically suffers -1 Success on any passing attempt. In addition it rolls a D6 for the Grenade Launcher and Sloped Armour, losing each on a 1-3. Finally it rolls an additional D6, and receives a second -1 on all passing attempts if the score is 1-3.
When a vehicle reaches zero Hits it crashes as described on the Shooting Table.
You'll notice that sports cars and subcompact cars operate the same, unlike how they work in Machinas. To this end I have added a new Car Feature:
Underpowered: Vehicle gets -1D6 in all passing attempts - Cost -1
So a sports car is considered the 'default' Size 2 vehicle, whereas a sub-compact is the underpowered version; only as good at passing as a sedan, but more vulnerable to bashing. The trait, however, can be applied anywhere on the scale rather than just having a special rule to cover subcompact cars; I have it earmarked for a large vehicle I'm currently working on, for example.
Comments: There's less granularity in the sizes of vehicles than those described in Machinas, but more consistency and logic in how things are applied. I did try and come up with a means by which smaller vehicles couldn't exceed weight capacity as readily as larger ones, but couldn't get it to work, so abandoned it. You'l notice that I have dropped the Control Roll modifiers for vehicle size. This is basically because it didn't make sense to me that a bike was more able to survive the Box of Nails attack than a truck - if anything it would be other other way around. I have assumed that the ability of smaller vehicles to avoid things which cause loss of control is offset by the ability of larger vehicles to just plough through those things, so the roll is always made at the same odds, regardless of size. Small vehicles are now vulnerable to shooting as well as bashing, although it is, of course, generally harder to line up shots on them because of their passing bonus. Conversely getting a shot on a big vehicle is easy, but it takes several hits before the vehicle will notice.