Hey men,

Does anyone have any experience with upgrading 996 Turbo brakes to 997 Turbo Rotors using AP brackets and longer bolts as in the kit Vivid Sells obviously keeping the standard 996 turbo calipers.

My main concern is affecting the BIAS.

Looking forward to your feedback.

Cheers,

 

Cm on someone must know something about this

 

I know there are several running Girodisc 350mm rotors with stock calipers. All the feedback on this setup has been very positive (you can search), I can't imagine the 997 turbo rotors would be much different, especially on the street, however on the track, the 997 rotors would be subject to cracking like any other cross drilled rotor.

 

Bias will not be effected because you're not changing anything in the hydraulic system(calipers, master cylinder). The 350mm rotor has a larger area, which allows it to conduct heat away from the pads and cool better, but as JSBear said, you are still going to experience the cracking issues with the drilled rotors. Are you tracking your car? If the answer is no, then I don't see any benefit over the stock rotors. If you are tracking the car, I would use a slotted rotor over the drilled. Many people are using the Girodisc with good results, but they are about 2400 a set of four. A much cheaper alternative is slotted Sebro rotors that run 800 for four. I know of several vendors that carry them and I've heard that they last a long time. I plan on switching to cup ducts for better cooling and running the Sebro slotted rotors on my car.

 

do a search there is a lot of threads on this but going to bigger rotors doesn't help with braking power, only helps with brake cooling like Bret said.

 

There is some wrong information here.

Larger diameter rotors give the caliper a longer lever, allowing it to apply more brake torque to stop the wheels.

A larger diameter front rotor will absolutely affect the brake bias if a corresponding larger diameter rear rotor is not used,

Later, Steve

 

Sorry guys, but you're all a bit confused:

The bias is determined by looking at the total piston area at a corner and the effective radius between the centroid of that area and the hub centerline. The ratio between the product of these two parameters for the front and rear axles is essentially what determines bias.

So - If you pop in a 350mm rotor without moving the caliper, the bias doesn't change because the piston area and the effective radius stay the same. You'll simply have a larger heat sink at that corner.

BUT - if you space the caliper out, you WILL change the bias.

As it pertains to this discussion, if someone drops in the AP spacers with 350mm rotors, this will likely shift the bias. I don't know the dimensions of the spacers, so I can't tell you how much it changes. But if someone can measure them, I can calculate it very quickly.

 

Brake Bias is expressed as a final value in many different ways.

Rotational values bring in a whole different ball of wax.
Final bias percentages represent the rotor torque expressed as final bias as measured as -> Applied tire torque at the ground.

Even things like changing tire weight and diameter have an overall effect on bias.

And changing rotor sizes by equal amounts both front to back does not keep the ratio equal either because each wheels rotational forces are expressed as a ratio of rotational diameters and weights. Oh another complex issue but should we keep it simple.

 

For sure. I was assuming everything else on the car would stay the same, and we're talking about steady state. With seal drag and DLR changes etc, it gets messy quick (which is why car companies used to pay me to worry about it!).

 

With a larger diameter rotor, the caliper will have to be relocated further from the center.

 

Depends on the setup. My 996 GT3 front calipers have the same total piston area and effective radius as a stock 996 turbo caliper, but use a 350mm rotor instead of the stock 330mm rotor.

 

OK men, what is the outcome ?

Is this upgrade offered by vivid worth it or not ?

I don't want to **** about with the bias so if that's the general consensus I'll stay with 330mm rotors.

Appreciate ur feed back thus far.

Cheers,

Tim

 

Interesting, in that case, it wouldn't change the balance.

Later, Steve

 

I was in a similar situation last month and wanted to swap out rotors and pads to something that will hold up better for track. I was running stock drilled rotors and CoolCarbon pads along with high-temp fluid and Gt3 ducts. Great for street and 7/10ths track days. It's when you start pushing these cars you need to step it up.

I went with slotted Sebro rotors and PFC pads. Haven't had a chance to excercise them but certainly looking forward to it.

 

What do you want to do with your car? Why do you feel a need to upgrade your brakes?

FYI - factory brake setups are laughably unsuited to performance driving due to safety/liability concerns. In other words, your car can handle a LOT more rear bias than it came with from the factory. So don't fret about changing bias, it's OK to do, as long as you do it right.