Dan GSR

Having only driven front engined cars before. I know that most cars do 90% of braking with the fronts. Therefore most of the time you use a less aggressive compound in the rear to avoid lock up.

How do the 997 compare? Will there be significantly more rear grip due to engine layout and big rear tires? Do you guys normally run same compound front and rear?

Frank 993 C4S

You can change brake bias by running different compounds front/back but you need to be careful not to freak out your ABS.

ProCoach

Data indicates that the rear engine platform is one of the most effective and efficient braking platforms, potentially far better than front engined cars. Try equal compounds before experimenting...

Krokodil

After doing the math on Porsche brake systems, they get it near perfect on matching wheel torque (braking force) to dynamic weight distribution (under braking), with a slight bias to the front axel (makes sense for safety). This applies to both the street and race cars.

Given this, we find that equal compounds work best, however a slightly higher CoF pad in the rear seems to aid in trail brake rotation.

As a refresher, wheel torque is a function of brake line pressure, caliper piston size, and rotor diameter (at the centerline of the pistons).

Cheers,

Bill Verburg

Porsche has been using a very front biased brake set for years on most of their street cars, Compare their late water cooled bias which is in the 1.8 to 2.2 range to their older aircooled bias in the 1.5 area. The higher the # the more front bias is present. I believe these #s come more from the lawyers than from the engineers.
Crock is correct as the factors that cause this
1) hydraulic bias from the # of pistons and their sizes
2) rotor bias from the effective radius of the installed rotor, ie the distance from the axle center line to the caliper piston center line.
3) bias introduced at higher line pressures by the p/v on the rear

many of the water cooled guys use higher Mu rear pads to compensate

Here are some #s
911 thru '83 1.491 no p/v
964 1.734 3.21 above 55bar
964Cup 1.713 no p/v
993 1.604 2.640 above 55 bar
993 RS/Cup 1.426 2.640 above 40 bar when used
996 & Boxster S 1.811 below 55 bar 3.353 above
early GT3 w/ 4 piston fronts 2.084 p/v induced bias not calculated because I don't have the data fro the p/v

2002 GT3R w/ twin m/c 1.302 - 1.938 1.666 neutral no p/v
2007 GT3 w/ 6 piston front 2.084 p/v induced bias not calculated because I don't have the data fro the p/v
2007 GT3R w/ twin m/c 1.26 - 1.920 1.613 neutral no p/v
2007 GT3 RSR w/ twin m/c 1.26 - 1.875 1.613 neutral no p/v

mark kibort

yep, compared to most front engine cars, the 911 platform can have 15% less braking forces in front and 100% more rear braking forces to help with front brake fade and over heat and overall rear end braking stability, just by the fact that the weight distribution at rest is 40 -60 vs 54/46 of a common front engine racer.

But, wheel torque is mostly a function of mechanical grip (or weight transfer) of the tire under different deceleration rates and it depends on the slip% of the tire, the decel rate, and the height of the CG and wheel base length.