I came cross the comments and figures below on understeer ratios, which I find interesting. Whatever the measurement method in use, I found interesting to see 997 and Cayman with the same ratios, and M5/6 much higher. Given the complexity and sophistication in today's cars, does the weight distribution dhave such a direct impact after all?


Understeer values

How much a car understeers can be measured in the number of degrees more the steering wheel have to be turned per G of lateral acceleration. Note that cars have different steering ratios—one with a higher ratio will require more rotation of the steering wheel to get a given change in front wheel angle. Most road cars have fairly similar ratios, typically around 14–15:1, but some may be substantially higher or lower. Here are the measured linear range values for some cars.[2] The higher the number the more the car understeers.
Car model Understeer value
Nissan 350Z 19
Mazda MX-5 21
Nissan 350Z Roadster 21
Ford Mustang GT 22
Renault Megane Sport 22
Maserati Gran Sport 23
Mini Cooper S 23
BMW 330i 25
Alfa Romeo 147 GTA 27
Corvette C6 27
Corvette Z06 28
Lotus Elise 111R 28
Porsche 997 Carrera S 28
Saab 9-3 Aero combi 28
Škoda Octavia RS 28
Porsche 997 Carrera 29
Porsche Cayman S 29
VW Golf GTI 29
Porsche 987 Boxster S 31
BMW M6 32
Range Rover Sport Supertech 32
Ford Focus ST 33
Mitsubishi Lancer EVO8 34
Porsche 968CS 34
Audi RS4 35
BMW M5 35
BMW Z4 Roadster M 35
BMW M3 Comp Package 36
Opel Astra OPC 36
BMW Z4 3.0i 37
Subaru Impreza WRX STi 37
Subaru Legacy 3.0 aut 38
Volvo V70 T5 39
Audi A4 2.0 T Q 41
Mercedes E55 AMG 42
Audi A4 V6 3.2 Q Avant 43
Porsche Cayenne Turbo 45
Smart ForFour Brabus 45
Mercedes SLK 350 47
TVR Tuscan 49
Alfa Romeo 159 2.2 JTS 51
Morgan Roadster V6 71

 

I remember seeing lots of values such as those in MotorTrend tests of late. They are interesting, nut not of much value. A car that may have nearly linear response (no under or oversteer) at .5G, may plow like a pig at .65G. The most interesting way to place a value to understeer is to do an 'area under the curve' type calculation that plots ateering angle Vs Gs across the entire grip curve. I believe that motortrends first test of best handling cars from 3 years ago did this very scenario and it seemed well matched to the subjectives on the car

 

Also, keep in mind most cars have a lot of understeer dialed in from the factory. Usually as a result of the wheel and tire choices. For example, BMW puts staggered wheel and tires setups on all the M models. A nice square setup on a BMW is going to give you very neutral handling. But thats a front engined car with nearly perfect 50-50 weight distribution.

Jason

Jason