First thing is to look at what’s wrong with a lot of cars, especially those made in the last ten years:
Too much electronic interference
Too much grip
Too much stiffness in the suspension
Most of these things are consequences; manufacturers stuff cars full of electrickery, which makes them heavy, which makes them need firm suspension and lots of grip.
For my purposes, a sports car should weigh no more than 1200kg at the absolute limit. Ideally less than a tonne. It should have mechanical simplicity when it comes to the driving experience; no adaptive cruise control, no multiple gearbox settings, no electronic interference stopping you having a good time. All controls should be mechanical, with no drive-by wire interfaces putting barriers between the driver and the road. A lightweight car is naturally easy to handle, so electronic aids are unnecessary – no traction control, no ESP, no ABS, and so on. In order to give a good feeling of control, the chassis should be pliant. The body itself should have a rigid frame built into the monocoque, yet sit on supple suspension with a good amount of travel. Polyurethane bushings, while increasing a little NVH, will ensure the control is precise and predictable. To add a little more pliancy, chunky sidewall tyres (compared to modern vehicles which have horrific rubber bands stretched over their wheels) should be used, though with a naturally stiff construction to minimise sidewall flex without compromising ride.
For a road car, the best layout by far is the front/mid engine position (engine in the front, yet sitting behind the front wheels) driving the rear wheels. Unsprung and partially unsprung weight should be kept to the minimum, so titanium wishbones, cnc machined billet hubs, lightweight billet wheels, and ceramic brakes will help keep things steady, albeit at the expense of increasing the cost of the car. Centre of gravity should be kept low, with no weighty overhangs fore or aft of the wheels – a wheel at each corner, and nothing of any appreciable weight higher than the top of the tyres. Steering should be mildly power assisted, keeping as much feel as possible, with a quick rack. No more than two turns lock to lock. Fairly rigidly mounted steering rack to preserve feel. Good steering lock for parking and countersteering. Brakes should have a lot of stopping power but not be over-assisted; you should have to put a fair bit of force through the pedal to get the maximum braking force.
Cockpit should be sparse but trimmed to a high quality using lightweight composite materials. No computer displays, and as few dials and switches as possible. Tacho, trip counter, speedo, fuel gauge, water temp, oil temp, oil pressure. All high quality analogue gauges. All switchgear should be reachable while wearing a secure five point harness. Shell style fixed back bucket seats in Kevlar. No rear seats. Manual gearbox, very short throw shifter with open gate in brushed titanium. Flat shifting enabled. No visible carbon fibre in the interior – it’s tacky. Driver should be sat around midway between the front and rear wheels, so the sensation when cornering is of the car turning around them.
Engine should have a good level of low down torque, but building in a linear fashion through the rev range. Emphasis on response rather than outright power. Probably no more than 250bhp would be necessary. Despite the mechanical simplicity of the chassis, the engine should be modern and high-tech. It should be fuel efficient, most likely a small capacity turbocharged engine, with all the associated gubbins to manipulate the engine power based on how you’re driving it. No ERS though, it’s just unnecessary weight. Should be capable of 50mpg driven sensibly. Engine should be able to rev out to 8k if the mood takes you. Four short gears for accelerating, a medium length fifth, and a very tall sixth for motorway cruising.
Nothing too crazy on the body style. Classic coupe shape, something along the lines of the E Type Jaguar, just simple curves, with rounded haunches and a pulled in waist.