ryoung

When comparing the braking performance of cars, I'd find it much easier to relate to deceleration "g's" rather than the stopping distances reported in the various car magazine tests. It doesn't help that they report stopping distances from 60-0 mph, 70-0 mph, 80-0 mph, or 100-0 km/hr, etc., making comparisons almost impossible.

This simple formula converts stopping distance to g's, where the initial speed V is in fps and stopping distance SD is in feet.

g = V²/(64.4 x SD)

And the results from a not so random sample of car tests,

Ferrari Enzo ......................1.14
Chevrolet Corvette Z06 ..... 1.13
Suburu WRX STI ............... 1.11
Mitsubishi Evolution ........... 1.10
Lamborghini Gallardo .......... 1.10
BMW M3 ......................... 1.09
Audi RS6 ......................... 1.06
Porsche Boxster S ............ 1.06
BMW M5 ......................... 1.05
Honda S2000 ................... 1.03
Porsche 911 Turbo ............ 1.03
Porsche GT2 .................... 1.02
Audi TT .......................... 1.01
Lamborghini Murceilago ...... 1.00
Audi D3 A8L ..................... 1.00
Audi S4 ........................... 0.99
Audi S8 ........................... 0.99
MB S55 AMG .................... 0.99
Mini Cooper S ................... 0.99
Audi A6 ........................... 0.96
Ford SVT Mustang Cobra .... 0.96
Toyoto Camry .................. 0.96
Audi D2 A8 ...................... 0.95
Land Rover Range Rover ..... 0.90
Audi A4 3.0 ...................... 0.87

Obviously the tests are done on different days, on different tracks, with different tires, etc; but I find this interesting. When someone reported the stopping distance from two different speeds (R&T uses 60-0 and 80-0), I used the higher speed.

And if you want another car added to the list, just give me it's stopping distance and starting speed.

Morgan Conrad

cause they have fantastic brakes. Or maybe this is the first car on the list with no ABS and they are too incompetent to modulate?

ryoung

the 282 ft stopping distance from 80 mph stood out as suspicious, compared for example, to the 213 ft stopping distance for the A8L. Even from 60 mph, the Miata's 150 ft stopping distance results in only 0.80 g.

The Miata data came from the June '00 Road & Track. Was it available with ABS then?

Mark Dalen

Of course grip can change from day to day - even lap to lap on a track so it is really hard to have different tests compare to each other.

Another big factor is the 60-0 vs 80-0. Wind drag helps a lot more at 80 than at 60 so the average g's should be higher from 80. At ~150 mph, many race cars generate 1g of braking without ever using the brakes. That part can not be overlooked.

ryoung

almost every time I checked the car at two speeds, I got higher g's at the lower speed. They usually differed by 0.02 g or less, and the 0.04 g difference for the Miata was the worst case.

Of those I checked, the Enzo was the the only car with lower braking g's at 60 mph. Are the Enzo's venturi tunnels generating enough useful downforce at 80 mph to improve braking performance? Are the Enzo's pads coming up to optimum temp with higher speed stops?

At 60 mph, the Mitsubishi Evo was #1. Actually, the EVO had the shortest stopping distance from 60 mph of any street car in the entire R&T data base. So much for the theory of poor braking performance from front engine nose-heavy cars.

I can think of three other things that might explain different g's when braking from different speeds with most street cars.

1. A heavy forward brake bias is not optimum until the car reaches maximum g's of deceleration. Up to that point, the rears are doing less work than they could be doing. From the higher speed stops, the car spends a higher percent of the time at max g's, improving the average g over the entire stop.

2. At higher speed, are we starting to see the effect of rear end aero lift?

3. At higher speed, are we starting to see the first hint of fade?

KevinC SJ,CA

Great brakes prevent fade. Great tires grab the road and haul the car to a stop. Even wimpy brakes can lock up the wheels.

ryoung

Do the WRX and Ivo use better tires than any Porsche and BMW? To top it off, the WRX and Ivo have the same poor nose-heavy weight distribution as Audi's. The Porsches have a rear weight bias, which is prefered for braking performance.

In any case, the WRX and Ivo have great braking in spite of tire and weight distribution handicaps.

Morgan Conrad

I'm amazed at how many car comparisons don't put the same tires on all. This month's Grassroots Motorsports has a perfect example. They buy a used TT, M3, and Boxster. They put decent new tires on the M3 but are too cheap and run crappo worn tires on the TT and Boxster.

Guess which one wins?

Potomac-Greg

My A6 womps a Mustang SVT!?! Interesting numbers.