What is This Simulator You Speak Of?
CarTest is quite simply the best piece of software I've ever come across when it comes to simulating how your car performs. Best of all, it's free! It comes in 2 flavors, the DOS version and a Java version. They are both essentially the same and the Java version has a more up-to-date repository of pre-configured cars spanning several decades but I actually prefer the DOS version because it's easier to use and I make my own car file anyway.
In a nutshell, you open the program up, load up a preloaded car or make your own and then run it through a series of tests and analyses to see how it performs. You can take it to the drag strip and see what it does every millisecond, you can obtain power and torque curves, you can calculate best launch RPMs, compare your car head to head with others and even put it through one of several racing circuits around the world to see what sort of lap time it would get. All of this is very very accurate and based on tons of parameters that you have to meticulously dial in so that the virtual car is as close as possible to the real one. Rest assured if you've done that right, the simulations will match very closely with real life and you can save yourself a ton of grief by seeing how certain mods will affect the car before you install them. You can also get an idea how which changes are going to net you the most by trying them all out virtually and seeing how they affect your acceleration, top speed, quarter mile times, etc. Let's go over some of the key features of this program so that it's clear how CarTest can be your best friend!
Pick/Add/Configure Your Car
The Primary Car Configurator
I'm going to work with the DOS version but the Java version is very similar so you should have no problem using this review if you downloaded that one.
After running the program you can either edit an existing car from a massive list or you can "add" a new car. You can also copy an existing one and tweak it if you don't want to start from scratch. Either way, once you pick a car or make a new one you'll be sent to the main configuration screen. Here you can set all the most important car-specific parameters that will most heavily influence the car's dynamic behavior. You'll enter the engine displacement, engine location and type, brake horsepower and torque along with their respective RPM values, the redline, compression ratio, clutch type and starting RPM of your choosing (which can be tuned in later). Then it's on to the transmission and driveline where you enter all your tranny's gear ratios and the final drive as well as whether the car is FWD, RWD or AWD. Finally the section on the right concerns itself with the shape and size of the car for things like aerodynamics, traction and stability. Most, if not all of these parameters can be found by looking up the specs of your car or by direct measurement. You might have a bit of trouble with the drag coefficient and frontal area but if you look hard you can find these too. The more accurate you are here, the better the results will be. Fill everything in and hit F1 to save.
Notice I Can Configure Any Car I Want, New Or Old
Advanced Car Settings
If you hit F4 at this point you'll go to another screen that has a huge list of advanced settings. Some of them concern themselves with the environmental conditions on the day you want to drive your car. Weather affects performance so this is key. Other parameters deal with driveline efficiency, human reaction time, computer reaction time (for things like transmission shifting), friction coefficients, tire pressure, the list goes on. You can even take a real dyno curve of your car (brake dyno) and enter data points one at a time and CarTest will interpolate a polynomial equation to fit all the points! If you don't do this it's ok but the program will take your main table maximum HP/Torque values and just fit a generic curve to it. You can also enter specific shift points here and then tell the program to use them rather than what it decides is best. I usually let the program decide because of a test it performs that I'll tell you about later. Anyway, fell in this section to your heart's content and save with F1.
This is One of the Main Simulators
...and the Real Thing
Analysis and Simulation
Now hit F3 from the main configuration screen and the program will take you to all of the test suites that are available. The most useful tests are "Standing Start Acceleration", "Optimize Launch Method", "Power Loss Curves", "Drive Power in Gears" and "Skidpad and Slalom". The other tests are good too but you'll find you use them more for reference and sanity checks.
Standing Start Acceleration is really cool and basically simulates a drag race from a standstill. You can change your starting RPM and it reports back several times each second what your 0-X speed and distance times are, you've got tach and speedo gauges in real time, an acceleration and speed graph as well as a message telling you what the car's doing at any given point in time (for example "Clutch Slipping", "Accelerating", "Shifting", etc.). The graph is awesome because it shows you if the car is wasting too much time in a given gear or switches gears too early and may prompt you to run a follow-up test called "Drive Power In Gears".
Drive Power in Gears is really excellent because it tells you the force from the tires on the road throughout each and every gear. What this idoes is tell you what your shift points should be. Any time the force in gear 1 drops below the force that would be applied in gear 2, you know you should shift. So all you have to do is look at the graph and see where all the lines cross each other. This is a very clear way to tell what the shift points should be without having to do all the math. The program does it for you. No guessing by looking at dyno curves!
Optimize Launch Method is an optimization algorithm that uses clutch slipping and clutch dumping and iterates through all possible start RPMs until it finds the RPM that gives you the best time. You tell it what distance you're racing to or what speed you're trying to hit and it will test over and over with every start RPM possible and report back the RPM that resulted in the best time. Then you feed that back into the Start Acceleration test from earlier and see how your time improves.
Power Loss Curves does 2 things. First, it identifies all sources of power loss for you so you know how many HP you're losing from drag or from the tranny or what have you. Second, it lets you know when the losses are equal to the power of the engine, which essentially limits the car's maximum speed. You get an idea of the relative proportions of each contributor and this helps you determine which parts of the car to address so that you can reach a higher top speed and attain lower times.
Skidpad and Slalom is super basic and just tells you how many lateral gees the car can pull and what your fastest slalom speed is. It's based on tire traction calculations so make sure you've filled in the advanced options really well if you're to trust these numbers but they can be very useful for determining the limits of the car when negotiating curves at speed!
This is the Drag Race Comparison Test... Very Cool!
Other Very Useful Simulations
Remember the very first screen where you picked or added your car? Well if you go way back to that screen there are 2 options at the bottom called "Comparison Tests" and "Track Tests".
Track tests lets you pick any track in the database, of which there are many and you can then virtually drive your car on that track. The computer simulates real world conditions and drives the car as hard as it can be driven without spinning out and losing control and then tells you what lap time you can achieve. The whole thing is in real-time and you can even see the acceleration vector of the car due to curves, braking and accelerating. It's very cool and very useful!
Comparison Tests opens up another menu with several sub-tests. These tests all evaluate several vehicles at once so you have to select from the database which cars to compare before running the test. You can run all of them to see what they do but the most important one is the Drag Racing test. This puts your cars head to head on a drag strip with little icons representing each car, which move accurately across the screen in slow motion as the clock ticks in real-time (well, slowed real-time). You can see the speed, distance and operating status of each vehicle and times are reported at critical distance markers so you know at what point a certain car really pulls ahead or lags behind.
Take Your Car Around Any Track in the World!
CarTest Summary and Review
This is an absolutely superb program. Even for a free, low-res DOS program, it's really exciting to run the simulations. They even threw in some cheap engine sounds, which make running the tests feel more intense and exciting. The wealth of data you can collect from these simulations can't be overstressed. I highly recommend this program to any performance enthusiast. The only bad thing I can say about it is that the age of the program means the list of cars is out of date but who cares! You can create your own car in the configurator anyway so if you're using this program in the first place, chances are you're smart enough to make a new entry with enough detail to run the simulations accurately. Check this program out!!!