I have 20 days of track use (i.e. one year) on my 993's big red rotors, and I'm wondering if I'm due for replacement. What kind of rotor life are you guys seeing? I know the rule that if the stress cracks are 7mm long, then they should be replaced. By that measure, I'm probably overdue. I'll measure the crack lengths and rotor thickness tonight to see if they're in spec. But I'm still curious to know what life others are getting.

 

I get 2-3 years.

Then again my car is only 2450lbs and has only 134 rwhp. You don't use much brakes in a car like that.

 

Eric, I got roughly 30 track days on my big reds on my 96 C4S. As usual cracks were the problem. The rule (according to the Porsche tech manual) is if cracks join 3 or more holes or, any crack goes to the edge of the rotor you replace them.

Best,

 

Bob, I like that rule better than the 7mm rule. I'm going with that one.

 

OEM Porsche rotors can be pretty durable. I put 930 rotors on my 1973 911 in 2000, and totaled the car a couple of years later. They got moved to my new 1972 tub, and are going fine (by either the 7mm or 3-hole rule) in their sixth year. This is with three week-long Open Track Challenges (finally won the class and division), at least two track days a month, and a complete season of wheel to wheel with the ARC (won my class). I also drive it about 8000 miles a year on the street.

The car is heavy, for its year, at 2500 pounds with a full tank of gas and no driver, and the horsepower (250-ish) is nothing to write home about in the world of track cars.

78-9 front 930 rotors are over $400 a pair, though, so I'm glad they're lasting.

But a lot depends on the tracks you drive. I spend most of my time at Willow Springs, which is too fast to do much damage to brakes.

 

I've got 993 TT rotors on the front of my 930 that I bolted on in January. They are on their last leg.
In fact, I'm trying to locate some before my Mid Ohio event 2 weekends from now...

 

The biggest factor is weight. On my 2000lbs 914/6, my 930 rotors would last 2 years. On my 3000lb 964 Turbo, the rotors last 12-15days.

 

Colin has the secret. The more mass you are stopping, the more likely that rotors will suffer.
My car races at 3370# with driver. One set of stock [undrilled] rotors might make it through a full season if I'm lucky. The last set had some serious cracks when I replaced them. Massive cooling ducts and fully ducted rotor housing, so the rotors run as cool as they can.

 

Cooling has a big effect too. 996 GT3 rotors are good for about 15-20 track days only. Maybe the cup car cooling kit will help, I'm going to try it.

 

I am up to 19 track days and this weekend I pulled out the digital caliper, down to 27.1 mm so I think I am up for a change. I have few cracks but nothing longer that 3mm.

I run Padgid Yellow with cooling.

 

eric used his 993 Big red rotors until you could put your fingernail into some of the cracks (probably a little too far gone because they prematurely wore out his pads that way too)...

..and the thickness was too low as well but no warping problems so why not keep going?

 

Do brake cooling ducts really increase the life of rotors on a mild, street driven track car?

 

i got a whole season on a set last year...using Pagid Black pads...2450 lbs. brake "scoops", no ducting. just replaced them with non-cross drilled, but slotted factory rotors. they were cryo treated...we will see how long they last...

 

yup.. he has them.. as do I ... as did eric on his former 993

 

Yes. Maybe more important, decent cooling can double the life of brake pads. Keep 'em cool and they last much longer. My 85 Carrera was a true dual-use car. Drove it to and from the track for three seasons. Bought pads from Pete Tremper, who knows more about Porsche brakes than most people. Pete suggested ducted cooling to extend pad life, and he was absolutely right!