In Reply to: Mpower, Thanks for being honest and more on tires posted by JonM on September 27, 1999 at 16:58:41:
c&d claims the tests are averages of two complete laps in each direction. there are plenty of variables. surface type (do they test in the same location?), surface condition (temperature, humidity, dust, amount of rubber from prior testing), tire temperatures and pressures, etc. for example, when most M's leave the dealer, tire pressures are set to 35f/38r, which makes it understeer significantly (for safety?).
also, skidpad testing only measures steady-state lateral grip on a flat surface, not transient behavior. slalom times are a much better indication of real-world handling - although all the variables are still there, and driver skill is a significant factor too. autoweek reports slalom times, but i could not find a summary for comparison...
as for braking, c&d states that their test starts the moment the driver touches the brake pedal, so brake system response time is included in the result. therefore speed of brake application, pedal free travel, leverage ratio and amount and speed of power assist all come into the equation. in the c&d test, the Z3 coupe outbraked such cars as NSX Zanardi edition, esprit V8, ALL porsches and ferraris, etc. (and 'outcornered' most of them).
believe what you wish, but to me this says that on the day they tested the Z3 coupe the variables were all in its favor.
: I wonder if tires could make 0.03g difference. There is no doubt the Michelin Pilot is a better tire than the 'Lop-sideds. I also wonder what the natural variation is in measurements on the C&D skidpad test. Do they test several times and average them? Who knows.
: Jon Maddux