(By Dave Nutting) – (Editor’s Note: As we get ready to unveil our newest project car later this week, which is going to burn corners and the strip, we are going to be bringing you more tech centered around making your junk do more than just haul ass in a straight line. Here’s the first piece by Dave Nutting.) It’s a story everyone can relate to. You’re at a stoplight in your muscle car next to “One of those guys”, typically some teenager in a hand-me-down import with a 5″ melon shooter exhaust tip or Bob from middle management with his German sports car. Engines rev, one hand tightening on the steering wheel, the other on the shifter, and you’re both off the line with tires blazing at the green light.
All is going well for you and your thunderous V8 engine until the inevitable happens: A corner looms up ahead, along with the knowledge that you’re going to have to slow down to avoid making friends with the nearest immovable object while your opponent in the other lane deftly corners with ease at speed. Cursing the car gods, you go home, defeated, with dreams of laser straight roads and a quarter mile between stoplights…
All dramatizations aside, handling is unfortunately one of the shortcomings of classic iron as it was delivered from the factory. The formula for the stereotypical muscle car, big engine in a small car, worked great in a straight line, but the underlying chassis was still designed for a safe and predictable driving experience for all levels of drivers: Soft springs and shocks for a smooth ride, small sway bars (If any at all), tires with tall sidewalls, and small brakes (By today’s standards) translated into under steer, body roll, and a lack of driver confidence when it came time to turn a wheel in anger. What’s a guy or gal with performance in mind to do?
Luckily, there is hope: The Pro-Touring movement is huge, and here at Bangshift.com we fully support the idea of old school bruisers beating late model sports cars at their own game.
Now, we fully understand that like anything else in our hobby, suspension tuning is “quick to learn, a lifetime to master”, so we’re starting off slow with the basics.
Let’s call it “Pro-touring 101″, with our first lesson being the definition of traction.
Everyone is familiar with traction: It’s the result of the friction between your car’s tires and the road that allows the car to accelerate, turn, and brake. Losing traction can be fun for a big smoky burnout or a drift around a turn, but it can also result in some serious pucker factor if that loss of traction occurs when braking to avoid an accident.
Suffice to say that there’s a whole lot of math involved to figure out exactly how much traction is available at any given moment, and the real-world factors involved are too numerous to count, so today we’ll work at a high level and dig in deeper in later installments.
To discuss traction, we’ll first need to understand a concept known as “The circle of traction”. This concept simplifies to the idea that only so much traction is available at any moment for a tire, and this must be split between cornering and braking/acceleration. You can have both acceleration/braking and turning at the same time, but the two added together cannot be more than the total available traction. Increase one of the forces (Cornering or braking/acceleration) and you’ll decrease the amount of available traction for the other.
Notice that North and South represent acceleration and braking respectively, with East being a right-hand turn and West a left-hand turn.
Using more traction for braking will result in less traction for cornering, with hard braking (Think “At the limits of locking up the tires”) resulting in virtually no ability to turn the car simultaneously. The same applies for acceleration. Remember this the next time you’re doing a rolling burnout in a parking lot and there’s a pole up ahead…
This leads us to an ever-popular metric for performance: Skid pad numbers
Quite simply, skid pad testing consists of driving a vehicle as quickly as possible around the perimeter of a circle, typically 200 feet in diameter, without the vehicle leaving the perimeter. The time taken to do so is recorded and the g-force that the car can corner at is calculated from there. The higher the g-force, the better the car can stick to the road while cornering at speed. To put it in perspective, a 2011 ZR1 Corvette can pull over 1 G, while your average modern mid-sized Japanese “appliance on wheels” is around .75 or so at best. We weren’t able to find any definitive numbers for classic muscle, but our best guess is that the numbers are probably a little worse than the next-door neighbor’s minivan…
For your math nerds out there, below is a quick simplified formula which can be used to calculate an estimate of G-force. For everyone else, feel free to sit at the back of the class and throw spitballs.
G is the G force generated
R is the radius of the skid pad
T is the time in seconds for a full lap
Using the Corvette mentioned earlier, let’s say that exactly 1G was generated on a skid pad with a 200 ft diameter (100 ft radius). Working backwards using the formula, we can calculate that the car was able to lap the skid pad in a hair over 11 seconds. Putting on the thick black-rimmed glasses with tape holding them together, we can calculate the circumference of the skid pad (Roughly 628 feet) and estimate that the Corvette was cornering at roughly 39 MPH to generate that number. That may sounds slow give straight-line speeds but grabbing some chalk, drawing a 200 foot diameter circle, and attempt to drive your stock muscle car around it at close to 40 MPH will demonstrate just how fast 39 MPH really can be.
Touting your skid pad numbers to your buddies at the next Garage Night may result in some blank stares and awkward silence, but trust us when we say that higher numbers are better, and increasing the “number of Gees” that your car is capable of will produce real-world results that will impress your friends more than the 10 HP they gained from a cold air intake.
Boiling it all down, traction really amounts to maximizing the friction between the tire and the road, which can done through tire compound choices, tire contact patch (Amount of the tire in contact with the road), and vertical load, AKA weight, on the tire.
Over the next few installments, we’ll dive into ways to increase this friction, starting with the tires themselves and the technology behind them.