Cars, cycles and trikes have two different limitations on the weight they can carry - the power factors of the plant, and the strength of the chassis. The variant below will allow loads to exceed the strength of the chassis for short periods of time. The power plant limit of three times the power factors in weight pulled is still in effect.
Overloading is usually done only in an emergency situation. For example:
Two escort vehicles, a station wagon and a luxury, are returning from a mission. Along the way, the luxury is disabled, but the driver and the gunner are unharmed. The station wagon has the capacity in spaces to carry the two unfortunates, as well as the excess power factors in his plant, but except for a couple of machine gun bursts, his vehicle is at its maximum weight. Our wagon driver, being a merciful sort, allows his buddies to get on, anyway. At this point, the extra weight the vehicle is carrying is calculated and the following rules apply.
Tire damage: For every mile travelled, roll 1d6. On a 6, each tire takes one (1) point of damage for every 100 pounds or fraction that the vehicle is overloaded. This damage is produced by the tires scraping against the fender wells, debris, etc.
Chassis damage: For each mile travelled, roll a second d6. On a 6, the vehicle suffers chassis damage. The vehicle permanently loses 1 to 3 points of handling, determined by die roll (divide result by 2, round up). This is permanent damage, which may only be repaired at an expense at least equal to the replacement cost of the car itself. (It is a Very Hard job for a mechanic, when attempted.) Each time a car takes chassis damage, add a +1 modifier to all subsequent overload checks (tires, chasses, and suspension). This damage is produced by structural stress.
Suspension damage: For each mile travelled, roll a third d6. On a 6, the vehicle takes suspension damage. Additionally, if an overloaded vehicle hits debris or an obstacle, it also takes suspension damage on a failed control roll. Each time suspension damage is indicated, the vehicle loses one point of handling until repairs can be made. This loss is cumulative with possible chassis damage. These repairs are much cheaper than chassis repairs would be, as suspension damage consists of bent shocks or stressed springs or some other easy-to-replace item (an Easy job for a mechanic). Suspension damage may be avoided if speed is reduced to 15 mph or less.
If a vehicle has Active Suspension, a roll of 6 when checking for chassis and suspension damage may not actually cause damage. Instead, roll again. Only if the second die roll is a 5 or a 6 is the chasses or suspension damage counted. Active Suspension is no help with tire damage.