Hi, I'm making a car simulation game not just a simple one, one that closely matches the kinds of Gran Turismo, therefore, it has to be extremely precise and realistic and use real life physics. I have been searching around for information regarding this subject and was able to get some info here and there about parts, about maths but it's hard to put it all together correctly and that's where you guys could help me out. The first thing i'm trying to establish and confirm is the following question: Speed of an object such as a car is directly related to the rotationnal speed of the tires right? If a tire is 15in radius, thus he is grossly 94.25in circumference and if i roll the wheel once, the car should then move by 94.25 inches right? If this is true, then i can assume that a car's engine turning at 3000 RPM or 50 Main shaft revolutions by second, will spin the wheel by 50 turns each seconds. In between that comes the transmission which may drastically lower this ratio to make the car pickup inertia more easily. So if i have a transmission that has a coeficient of 4.00 in the first gear, the calculation should be the following if i am not wrong: (These numbers are grossly calculated to remove the numerous decimals but will be kept in the final calculations.) Engine Revs / s = 50 Gear 1 ratio = 4.00 Wheel Revs / s = (50 / 4) = 12.5 Distance covered / s = (94.25 * 12.5) = 1178 inches (or 98 feet) Speed = 66 mph If i put that in miles per hour it makes the car roll at 66 miles per hour.... This makes no sense right? I mean, a car in the fifth gear could do that speed around 3k RPM, not at gear 1. Same thing again, with gear 5 having a ratio of 0.98: Engine Revs / s = 50 Gear 1 ratio = 0.98 Wheel Revs / s = (50 / 0.98) = 51 Distance covered / s = (94.25 * 51) = 4806 inches (or 400 feet) Speed = 272 mph What am i not grasping correctly in your opinion?