Physics related to cars

by Aaron_Mason
Tags: cars, physics
 P: n/a Hey, I'm trying to make a racing game that will run completely within a browser. It will be similar to BATracer, except that rather than using carsets - a model employed by games such as TOCA, NASCAR and V8 Supercars - I will follow the model employed by Gran Turismo, where you buy a car, improve it, race it and get glory. While I know that > realism = < fun, but I'd like for a true play-by-play of races, like BATracer already is. To do that, I'd like to understand how cars work so I can truly simulate the cars. I've got the gearbox worked out, what I need to know is how various "variables" such as bore and stroke, the weight of the car and the weight of the engine can make an impact on how much engine rotation is sent to the gearbox. Hope I haven't left anything out, and thanks in advance.
 Emeritus Sci Advisor PF Gold P: 10,426 Cars are very complex machines. Some variables like total vehicle weight can be used in simple equations to determine changes in vehicle performance. Other variables, like bore and stroke, intake manifold shape, valve timing, etc. are virtually impossible to model with simple equations. Car manufacturers and tuners typically use a dynamometer to empirically measure changes in a car's performance. - Warren
 P: n/a Hi, It doesn't have to be simple. As long as I can implement it in logic for a computer program. I can understand how much speed a car will go at if 3000RPM is thrown into the gearbox in first gear... what I need to understand is how (and if) I can work out how quickly the car gets to 3000RPM. Sorry if I sound like a complete n00b, there's a lot of things I don't quite understand and that I wish I could remember from high school physics.
Emeritus
PF Gold
P: 10,426

Physics related to cars

It's not high-school physics. Vehicle dynamics is typically an upper-division course in university mechanical engineering curricula. There are textbooks on the topic.

- Warren
 P: n/a Hey Danger, That helps a lot for logic. I'd still like to know how weight affects this, though. At least offer a slightly higher sense of reality for the hard core racers.
 PF Gold P: 8,963 Right. Weight, generally, is a detriment. The only exceptions to that are when a vehicle becomes so light that it can't maintain traction, or lacks the structural strength to stay in one piece. The solutions to that are to use aerodynamic features such as inverted wings and spoilers to create a downforce that supplements the gravitational attraction to the ground, and to use composite materials for strength. In any circumstance, you have only to adjust your performance level upward as your power-to-weight ratio increases.
 P: 6 Aaron, What you've discribed sounds a lot like Forza Racing [for xbox]. First you need a game plan such how many variables you'd like to include. In Forza you alter just about everything which is interesting to a wrench-head like me. However the level of complexity may limit how many will actually play the game. Weight is a key performance variable. In regard to the engine it depends on the material that's used, [aluminum head and block vs. cast iron]. I wouldn't put too much emphasis on bore & stroke - it depends on how it's built, [N/A vs. turbo vs. supercharged]. Power [torque] is determined [as mentioned] using a dyno. Typically there's a 15-20% loss through the driveline. Of course other variables are the tire size and gear ratio of the differential. I'd suggest checking out one of the many sites deadicated to automotive science & math.
 PF Gold P: 8,963 Hi, C12. Maybe it's just because of my age, but I still say that there's no substitute for cubic inches. I'll take my 440 over anything from Mitsubishi any day. (And a 6-71 Roots over a turbo, but that's just personal preference.) Good advice about the gearing (including tire size). A couple of points about NOS that I neglected to mention. One is that it should never be used for more than 10 seconds or so at a time, and only at full throttle. Elsewise there's a good probability of blowing the motor. The second is that its effectiveness is inversely proportional to the efficiency of the engine. An off-the-showroom car could see a 50% increase in hp from it; a perfectly tuned race motor will barely notice it.
 P: 6 Hi Dan, I wasn't really endorsing any particular configuration, but rather referring to the physics... One reason the muscle cars have such big cube engine is becasue they're heavy, most around 3700lbs. Ironically my muscle car has a better power to weight ratio, 10.5:1 vs. my sports car which is 12.8:1. The Z06 Vette is ~ 5.5:1 [woohoo - fun!], in contrast is the average car which is ~19:1.