Let me be the first to say that I love GURPS Vehicles 2nd Ed. I was an avid fan of 1st edition, and the 2nd edition seems to improve upon it in nearly every way. The major change from 1st to 2nd edition is the general design strategy. In 2nd edition, you work from the inside out: choosing components first, then wrapping a body around it. This is an excellent strategy when all you need is to design a functional vehicle. Unfortunately, if you are trying to reproduce a "real world" vehicle, it is often more convenient to chose a body size first and then install components. I've cludged together the following formulas to help create vehicle with specific design parameters. Estimating Vehicle Mass First, decide on an the estimated body volume (EBV). From this, compute the estimated surface area (ESA), using either the chart or formula on VE18. Then, decide on the vehicle's frame strength and determine the Frame Strength Modifer (FSM): Super-light FSM = 1/10 Extra-light FSM = 1/4 Light FSM = 1/2 Medium FSM = 1 Heavy FSM = 2 Extra-heavy FSM = 4 Note that the FSM is the same modifier Frame Strength gives to the Hit Points of the body. Next, decide on the vehicle's structural Health (HT), usually 10. If HT is 10, then the Maximum Load is Maximum Load = 60 * FSM * ESA Otherwise, Maximum Load = 300 * FSM * ESA / (HT - 5) For calculations involving top speed, estimate the Loaded Weight in tons by dividing the Maximum Load by 2000. Estimating Vehicle Volume To estimate volume from mass, determine Frame Strength and Health as above. If HT is 10, then the estimated volume is Volume = [ square root of (Weight / FSM / 60) ] cubed Otherwise, Volume = [ square root of (Weight * (HT - 5) / FSM / 60) ] cubed The above calculations assume that the vehicle is designed weigh almost as much as its Maximum Load. Internal Volume Estimated body volume (EBV) gives the volume of the exterior of the vehicle. Streamlining and other factors decrease the interior volume. To find the interior body volume, take estimate volume and divide (rather than multiply) by all the factors given in the Body Volume section on VE16. This will give the volume available for interior components. Also note the estimated body volume does not include any subassemblies like turrets or wheels. Estimated Ground Propulsion Power Using the estimated Loaded Weight in tons, you can go on to estimate how much power will be needed to move your vehicle at a certain speed. To estimate ground speed, first find the Speed Factor (Sf) from the table on VE128 (remember to add any bonus for improved suspension). Then find the Streamlining Mod (SLM): No Streamlining SLM = 1 Fair Streamlining SLM = 1.05 (Min Speed 52.5 mph) Good+ Streamlining SLM = 1.1 (Min Speed 55 mph) Settle on an estimated top speed. The estimated Kilowatts of power (Kw) needed will be Kw = [ Speed / (SLM * Sf) ] squared * Loaded Weight Choose a drivetrain and power plant with the required power. If sails, airscrews, jets rockets or reactionless thrusters are being used to move the vehicle, multiply the necessary power by 4. Estimated Water Propulsion Power First compute the estimated Hydrodynamic Drag of the ship, using the formula on VE130 or VE132 (for submerged vehicles) and the estimated Loaded Weight in tons. Choose an estimated top speed. The pounds of thrust needed will be Thrust = [ Speed ] cubed * Drag / 216 Estimated Aerial Propulsion Power First of all, estimate how many exterior substructures the vehicle is likely to have. If none, use the Estimated Surface Area (ESA) of the vehicle. If the vehicle is using wings or rotors, compute the surface area of those subassemblies, using the Estimated Body Volume (EBV) and the rules on VE17. Estimate any additional surface area from turrets, sails, etc, but not for any retractable components. Use this estimate to compute the Aerodynamic Drag for the vehicle using the formula on VE134. Then, settle on a top speed. The pounds of thrust needed to achieve that speed will be Thrust = [ Speed ] squared * Drag / 7500 Estimated Stall Speed If the vehicle has some form of static lift, such as helicopter rotors, gas or contragravity, figure that now. Estimate the vehicle's Lift Area as per the rules on VE133, generally 10% of the body area and 100% of all wing area. Also find the Streamlining Index (SI) as per VE133, and finally, use the formula on VE133 to estimate Stall Speed. Use the rules on VE128 and whatever engine you've installed to estimate the vehicle's ground speed. If the top ground speed is less than the vehicle's Stall Speed, the vehicle cannot get off the ground, and should either have more thrust or more lift (bigger wings). Vehicle Frames If you plan on designing a lot of vehicles, it behooves you to design a number of Vehicle Frames; empty bodies with of various sizes. Here are a few frames for cars: Size Volume Wheels SA Max Load Weight Cost Light Cycle 12 0.6 35 1900 280 350 Medium Cycle 15 0.75 40 2200 320 400 Heavy Cycle 18 0.9 45 2400 360 450 Subcompact 100 10 160 7800 1280 1600 Compact 140 14 200 9600 1600 2000 Midsized 180 18 235 11400 1880 2350 Sedan 220 22 270 13200 2160 2700 Luxury 260 26 300 14700 2400 3000 Van 300 30 330 16200 2640 3300 The above chart assumes that (a) the vehicles are TL6, (b) medium frame strength and (c) no worse than HT 10. The surface area (SA), weight and cost includes the car's wheel assemblies. The frame's weight does count towards the maximum load, so that (for example) a midsized car has only 9520 lbs of available weight left. Changing Frame Strength: Multiply the Max Load by the Frame Strength Modifier (FSM) from above, and the weight and cost by the appropriate modifiers on the Vehicle Structure Table on VE19. Actually, most cars and cycles have light frame strength, which will half Max Load, Weight and Cost. Changing TL: Multiply Cost x5 for all TL7+ cars. Multiply Weight x0.75 for TL 7, x0.5 for TL8, x0.375 for TL9, x0.25 for TL10, 0.1875 for TL11 and x0.125 for TL12+. Other Changes: Cheaper or more expensive materials, streamlining, etc modify Weight and Cost as on the Vehicle Structure Table on VE19. Most cars are often made from cheap materials, halving Cost and multiplying Weight x1.5. The above table readjusted for TL 7 vehicles made from light, cheap materials is Size Volume Wheels SA Max Load Weight Cost Light Cycle 12 0.6 35 950 157 420 Medium Cycle 15 0.75 40 1100 180 480 Heavy Cycle 18 0.9 45 1200 202 560 Subcompact 100 10 160 3900 720 1920 Compact 140 14 200 4800 900 2400 Midsized 180 18 235 5700 1057 2820 Sedan 220 22 270 6600 1215 3240 Luxury 260 26 300 7350 1350 3600 Van 300 30 330 8100 1485 3960 Example Suppose I want to make a sporty midsized car. I estimate the car will be 180 cf in size and have light frame strength. Using the formula on VE18, its surface area will be: Surface Area = [cube root of 180] squared * 6 = 190 Since the car has a light frame, the Frame Strength Modifier (SFM) will be 1/2. If the Vehicle HT is to be 10, the Maximum Load will be Maximum Load = 60 * 190 * 1/2 = 5700 lbs The vehicle will therefore weigh at most 2.85 tons. Suppose we want the car's top speed to be 100 mph. By the chart on VE128, the Speed Factor (Sf) for wheels is 16. If we give the car good streamlining, the SFM is 1.1. This is allowed because our top speed (100 mph) is higher than the minimum (55 mph). The kilowatts of output that our drivetrain needs is Kw = [ 100 / (16 * 1.1) ] squared * 2.85 = 92 kw Thus, to get the performance we want, we will need to install a 92 kw Wheel Drivetrain, and an engine powerful enough topower it. Odds are, in the final calculations, speed will be a bit better than our initial estimate, because the car is unlikely to weigh as much as its maximum possible load. Also note that Good Streamlining normally multiplies the volume of the vehicle x1.2. Thus, we only have 180 / 1.2 = 150 cf of interior space to install components in the car.