Should our Boxster have better braking performance?

[CharlesGordon]

This is a question I can’t believe I’m asking, as the brakes in my 2.7 feel great and are extremely effective. My memory of some reviews places the 60-0 stopping distance somewhere around 120 feet, a laudable performance.

But what confuses me is that in reading a recent review of the monstrous BMW 745i, it apparently can drag its 4,376 lbs from 60-0 in 123 feet! What is going on here?

I assume the 120 ft (986) and 123 ft (745i) numbers are from using stock wheels/tires. Perhaps the 245/50-18 Bridgestone Turanza EL42 tires on the BMW are somehow much stickier than our stock tires? (How on earth so?). And these are dry tests—would rain show the Boxster’s mettle?

With no physics behind me, my gut feeling is that our 1,500+ lb lighter Boxster ought to stop at least 10-15 feet shorter than the 745i (and I’m trying to be conservative).

Anyone?

[Dave R in El Cerrito]

Braking distance depends mostly on tire traction in a straight line, except for the inital period including reaction time of the driver and braking system. The Turanza tires used by BMW are very grippy (my BMW Turanza'a had a 140 tread wear rating, while my Boxster's Conti's have a 280 wear rating). To actually compare braking of the CAR rather than the tires, one should use the same compound on each car.

All tires are compromises between many factors, including straight line and lateral traction and transient response, wet and dry, etc.