Disclaimer

This article does not tell you what RPM to hold at before launch.
This article does not guarantee a certain 60 foot time.
I am not a race engineer.
I am not a driving instructor.
I am not a professional driver.

I am just your everyday car enthusiast who wants to help out the community by explaining some of the basic laws of physics behind the complex science of tire mechanics and launch techniques. The model used here is overly simplified, and is not entirely accurate, but for the purpose of our discussion it should be good enough. So, I hope you will enjoy the article and perhaps learn a few things.

Introduction

I choose to write about launching because it is, quite often, the determining factor of whether you win or lose in a race. We have seen how launches have affected Team Ferrari in Formula One racing, due to poor launch control programming as well as tire choice. Launching is of even greater importance when it comes to drag racing as can make or break a run for you.

The Problem

Our problem at hand is actually rather simple: power vs traction. The objective of the game is to have maximum acceleration and if you remember your Physics 101, you should remember the following two equations:

F = ma (Force = Mass X Acceleration)
f = umg (Friction Force = Friction Coefficient X Mass X Gravity)

Since our mass is not going to change, you want to maximize force to achieve greatest acceleration. That force comes from our tires! The second equation is the equation to determine friction force (read: available traction) and if you remember correctly, static friction coefficient is greater than kinetic friction coefficient. What that means is that you do not want wheel spin during a launch. An ideal launch is achieved when you apply maximum force without wheel spin.

And that means you'll have to worry about tire compound, footprint, tire pressure, tire temperature, pavement conditions, engine RPM, throttle position, boost level, flywheel mass, gearing, wheel size, tire weight, clutch slip, and wheel spin.

And all of a sudden, our simple problem is not so simple anymore!

Traction

In order to maximize traction, you would want to run a soft compound tire with a large footprint. (At this point some of you guys might wonder why the size of contact patch matters since it's not part of the equation mentioned above. Right now, I can only tell you that it does, and bigger is better.) Chances are though, you are not going to change your tires just for launching purposes, we will have to maximize traction with other available means. The easiest way of doing so is to lower your tire pressure to increase the size of contact patch. It is also important to understand the type of tires you are running because different tires have different optimal running temperatures. If the tires are too cold or too hot it could seriously affect traction. Finally, pay attention to track temperature, a cold track provides much less grip than a warm one.

Power

We all know that our engines produce most power during wide open throttle, high RPM, high boost condition. The question is: how are we going to do that while staging? It is easiest with an automatic because all you have to do is hold your brakes as hard as you can, and step on the gas to a point where the car is just about to start moving. With a manual transmission, it becomes very tricky. While it's easy to reach high RPM before launch, it is hard to get a high power output because we cannot hold a wide open throttle position without the engine bouncing off the rev limiter. Furthermore, it is difficult to develope any kind of boost since the engine is not under load.

While in theory, we can do the same trick as automatic guys and hold the brake and step on the gas while partially engaging the clutch, in practice it is extremely difficult to achieve any kind of repeatable results. By doing this you can cook your clutch in a very short time and your clutch will catch differently when it's too hot. If somehow you can manage to launch this way successfully, repeatedly, more power to you!

Another option is to stay off of the throttle until the last second, and go full throttle just before the light turns green. However, timing has to be precise because if you're too early, you'll bounce off the rev limited; if you're too late, you won't have enough time to bring the RPM as high as you'd hope for. Once this technique is mastered, however, you will be launching at high RPM at full throttle and have engine partially under load to develope boost. Again, this technique is only repeatable if you know how fast your engine revs, and how quickly the light/tree changes.

The Balancing Act

For the purpose of this discussion, clutch life is not considered a factor because that's the nature of racing. If you are going to worry about wear and tear, stay out of the sport. We are, however, going to worry about breaking parts because it's expensive and it stops us from racing. So rule number one: do not dump your clutch because it leads to broken parts and expensive towing bills.

What we know right now is that we want our engines to produce maximum amount of power in order to get a great launch, and that we don't like wheel spin. Well, thank God for AWD! Since traction has never quite been a problem for you guys, I would recommend running at normal tire pressure in order to minimize roll resistance. However, since we have so much traction available, it becomes very easy to bog a launch.

Here are a couple of things to keep in mind. First, you want to launch at as high an RPM as you possibly can because your flywheel has more rotational inertia and it can help during a launch. Secondly, you want to control your clutch so your RPM doesn't drop off too quickly as it will hurt your launch. But also, don't let out of your clutch too slowly as that will only cause excessive wear and tear on the clutch and it won't transfer the power to the wheels!

Now that you know all that you need to know about launching, what it all comes down to is just practice, practice, and more practice.