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Good Performance Car Building Plan For Manufacturers- Slip Angle

The No-Brainer Guide To Building A Better Compact Sports Car

Aug 1, 2008
0108_sccp_01_z+editor+full_shot Photo 1/1   |   Good Performance Car Building Plan For Manufacturers- Slip Angle

What you're about to read is completely arbitrary. It came from a car guy's dream world and was developed on a whim. Sure, there's some reasoning behind it all, but it mostly follows the "subjective rants" theme that this column is known for.

Occasionally at Sport Compact Car, we have the honor of meeting with manufacturers and talking about their upcoming products. Often manufacturers are interested in our opinions about dynamics, weight, power and other factors which influence a car's performance. Naturally, we take every opportunity to share our thoughts in an effort to make tomorrow's cars perform as well as possible.

Recently, after one of these meetings, it hit me that there's got to be some common ground from which we draw our conclusions on which cars we like and which cars we don't. Maybe there are certain traits which all these cars share that make them truly impressive. Maybe they all lack certain downfalls that keep them high on our list. Maybe there's a simpler way to find out just what makes us really fall in love with a performance car. A formula, perhaps.

That's the basis for this month's "Slip Angle"-a formula for all manufacturers. A bare minimum for making a real performance car. A simple plan for building a car that works right.

First, I'll divide into two categories appropriate for SCC fans. Of course, we'll begin with the performance coupe because it is, after all, the car most fans of this magazine are interested in or perhaps even drive themselves. Next up will be the roadster. While roadsters may not be as popular as coupes (Miatas certainly aren't as prevalent as Integras), they have different driving dynamics and therefore different needs.

Both, however, must have certain fundamentals. Things like four-wheel independent suspension must be present on both coupes and roadsters. No solid axles here please. And, both must have four-wheel disc brakes with a minimum of two-piston sliding calipers in the front.

The Bare Minimum CoupeRather than rambling about what kind of engine will meet my arbitrary performance requirements, I'll simply handle the output equation with an old favorite-power-to-weight ratio. I'll set the minimum based on what we know already works-an established and proven number which, with the right hardware, can be easily improved. Fourteen pounds per horsepower seems like a fair starting point. The current Acura Integra Type R comes in slightly better at 13.3:1 and the late second-generation Mitsubishi Eclipse-a quick car-was still respectable at 15:1.

The power-to-weight minimum leaves manufacturers breathing room on both ends. They don't have build a low-production, lightweight car like the Type R and they're not stuck into the complexity of a heavyweight Eclipse. Very reasonable.

Drive wheels will remain open. It's been established now that real performance cars can drive the front, rear or all four wheels with reasonable success on a racetrack and their roadgoing counterparts are often quite potent performers in the first place.

OK, with the power and drive wheel problems solved, let's move on to putting that power to the ground. Here's my rule: If the car is only driving the front or rear wheels it must have a limited-slip differential. However, with four-wheel drive and the power-to-weight ratio described above, there seems little point in mandating the expense and complexity of limited-slip differentials anywhere but the rear on these cars. This will help maintain rear-biased handling on any surface with less-than-perfect grip and should provide better overall balance in high-grip situations.

Steering is perhaps the most important and most often overlooked driver interface on any performance car and we regularly notice the way it changes a car's personality. For a coupe, lock-to-lock steering inputs should take no more than three turns. Quicker is better and more than three is simply too slow.

The Bare Minimum RoadsterBecause the fundamental driving character of a roadster requires it to be fun and tossable, I will set a weight limit. My arbitrary numbers are simple. Roadsters can't weigh more than 2,200 lbs. That's the weight of the MR2 Spyder-a whopping 187 lbs less than the current Miata, but still several hundred pounds heavier than say a Lotus Elise.

With this weight minimum comes a horsepower requirement. Manufacturers traditionally use lightweight and tossability as excuses to give roadster enthusiasts miniscule horsepower numbers. Roadsters need power. Ever driven a 2,200-lb car with 280 hp? Lots of fun. Of course, mass production requires that I be more realistic with my expectations. I'll say that a 2,200-lb roadster needs at least 155 hp. This output will give both my coupe and roadster similar, respectable power-to-weight ratios.

Roadsters are rear-wheel drive. It's as simple as that. They always have been and they always will be. Front-drive roadsters just don't make sense. Remember the Mercury Capri and reintroduced Lotus Elan of the early '90s? Call me traditional, call me biased. That's just how it is. Not only that, but with 155 hp, they must have a limited-slip differential.

Steering in a roadster must be quick. In fact, the roadster's agile nature requires significantly quicker steering that the coupe. Let's say 2.7 turns lock-to-lock.

As I see it, that's all it takes. The right power, the right weight and the right combination of drive wheels, steering and brakes. This isn't hard-at least in my little world.

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