Latest brake options for 15" and 1.25" rotors?

[Cory M]

Sounds like you know what you're looking for. For what it's worth we have used a couple of the stoptech kits and they are nice. I've only experienced them on the street so not really abused, but I know the same calipers are used on track with several other makes (Honda, Miata, etc).

[kent olsen]

Of course the other question not addressed is weight. That's what the brakes do, slow the vehicle down and that means the weight of the vehicle.

My old 72T, now with a 3.0L 245hp engine, only weighs 2200 lbs. I've run it, track days, in Florida, Georgia, Alabama, Calif, Oregon and Washington. All I've done is replace the front calipers with ones from an SC, about 20% more surface area, and then replaced all four disc's with drilled and slotted disc's. I run racing pads on the track days. I considered some kind of ducting to get more air to the brakes but on any track with a long straight they cool right down.

[Bill Verburg]

Originally Posted by kent olsen

Of course the other question not addressed is weight. That's what the brakes do, slow the vehicle down and that means the weight of the vehicle.

My old 72T, now with a 3.0L 245hp engine, only weighs 2200 lbs. I've run it, track days, in Florida, Georgia, Alabama, Calif, Oregon and Washington. All I've done is replace the front calipers with ones from an SC, about 20% more surface area, and then replaced all four disc's with drilled and slotted disc's. I run racing pads on the track days. I considered some kind of ducting to get more air to the brakes but on any track with a long straight they cool right down.

The difference in hp required between a front 930 rotor and a front SC rotor is ~.1hp

for all 4 it's< ~.4hp

in terms of torque it's ~2.6lb-ft for all 4

[Bravoaloha]

I discovered the Elephant solution the other day and got excited as I have been looking for a brake upgrade solution for a while now.

Everyone knows the 930 setup is the holy grail. The Elephant solution seemed great to me until I saw the price. At that cost, why not spend a bit more and go full 930 with brand new calipers?

When I win the lottery I am going straight here- 930 Brake Upgrade 911 - Carrera - 914 - 914/6

[kent olsen]

Bill

I guess the point I was trying to make is, before you go the route of upgrading to expense brakes, removing some weight will give you more braking as well as a better power/weight performance.

For instance I replaced my stock muffler with one from M&K, nearly 20 years ago, a 10lb muffler vs a 30lb stock one. And were is it located, at the extreme rear. Weight reduction from the rear, good idea.

[VFR750]

Just a thought: R compound tires generate far more traction than a1980 P7.

If you really use that traction during braking, then you will brake later.

Later normally means a little faster as most tracks are too short for our cars to reach terminal velocity.

Faster means more kinetic energy.

Better grip means much higher deceleration rates. And more weight transfer to the fronts. Which Means even more traction.

So you can brake later, faster, harder.

And consequently higher transient heat load on the brakes.

Higher heat load will fade the fronts quicker. And as the laps go on, more front fade and a greater percentage of the rear brakes having to make up for it.

At the end of the day, bigger brakes can tolerate higher heat load rates without overheating the pads and fluid.

Lime Rock is one 125-65 mph brake event every 63-68 seconds for me. Starting between the 400’ and 300’ markers. Followed by trailing the brakes with throttle to create rotation in the second half of turn 1.

It’s nice to finally have brakes that feel good at the end of a 200+ mile track day.

[winders]

Originally Posted by VFR750

Better grip means much higher deceleration rates. And more weight transfer to the fronts. Which Means even more traction.

Hold on. Taking load from the rear and adding it the front while braking does not mean you have more braking traction. Assume for a moment that the tires are same front and rear, the car will have its best braking traction if all four tires were equally loaded. If load the front tires more than the rear tires, the traction at the front does increase. But, the traction gain is not linear so you have less overall braking traction. Add in factors like thermal issues, tire size, and camber, and the loss of overall traction gets worse, not better.

[VFR750]

It means you have more load, which means more adhesive traction. Up to the point of rubber overload and transition from static (adhesion) to dynamic (sliding, melting, shearing).

I say adhesion, because the tires generate more than 1.0 coefficient of “friction”.

So yes, it is harder to lock up your tires when more weight is on them.

[winders]

You aren't getting it. Moving load from the rear axle to the front axle under braking results in more traction at the front and less at the rear. That also means the overall traction is reduced because moving 30% of the load from the rear to the front does not increase the front traction by that same 30%. Again, the traction gain at the front is not linear.

There is a reason that, generally, cars that transfer a lower percentage of the load to the front brake better than cars that transfer more of the load to the front. It's one of the reasons that race cars often have bias adjusters: to keep the rear tires doing as much of the braking as is reasonable.

It's the same reason that you make the front of the car more roll stiff compared to the rear to reduce oversteer.

[VFR750]

Weight transfer, in a 911 is normal. It isn’t something we can easily change.

And under heavy braking I’m guessing the static 40/60 weight bias may approach 50/50. With a 225/50 front and 245/45 rear, the ideal weight bias is probably around 48/52.

By observation there are significantly larger front brakes on all cars, including new porsche 992, weight transfer and high heat load is very significant. And may be even more like 55/45? 60/40?

But spring rate will set weight transfer too. Softer springs is more transfer.

Traction is not a constant. Downforce increases cornering speed by increasing the apparent weight in the tires.

Why isn’t this true for weight transfer under braking? Meaning the fronts will generate a higher percentage of the braking, and brakes that are more capable of withstanding the heat input, will be able to generate the same higher force, with less fade.

If the tires can stick, and the front brakes are not fading, higher deceleration rates will continue to be available.

Tire temperature also affects grip. My experience was I’d wear out the fronts in two sets of rears. So I also have more available grip late in a session.

At the end of many track days I was on the edge of locking up the rears, because the front brakes were no longer able to take as much heat, as they were heat soaked.

Now, I don’t. And the front tires are still capable.

Btw, another benefit of bigger brakes is wheel bearing and hub temps. Overheating the grease and having it dribble out, before. Now, now not as much, and NEO racing grease solved that.

[winders]

Please read:

https://en.wikipedia.org/wiki/Tire_load_sensitivity

[VFR750]

Traction and the brakes ability to stop are two different but related things.

My point is focused on heat absorption and dissipation as it affects the creation of a stable, repeatable deceleration force.

It’s not about the first stop (lap) of the day.

It’s about the 15th, 20th, 25th lap, on a 95F day, and the ability to generate the same braking because the rotors can dissipate the heat and the pads are big enough to distribute the heat load over a larger surface area.

Getting to a thermal cycle that has the energy “in” equal to the energy “out”.

My experience has been the stoptech level 2 upgrade made a big difference. And I can brake later and harder. Lap after lap.

[winders]

I was pointing out that more load transfer to the front does not mean "even more traction". That's it. My point is that with any given braking system, more load transfer to the front means less over all braking traction.

I was not taking about "heat absorption and dissipation as it affects the creation of a stable, repeatable deceleration force."

[VFR750]

Total traction did not go up, I agree.

[VFR750]

Brake fade induced reduction of the capability to maximize available traction is the problem.

Front traction goes up with weight transfer.

Rear traction goes way down.

[3literpwr]

Waiting on a quote from Belgium for the AP setup. Got the engine and Tuthill wire harness installed.

[Cory M]

Looking great! Would you recommend the Tuthill wiring harness? It looks like an awesome solution, but you're the first person I know that's actually installed one. You went with the full wiring harness including the dash panel? I have purchased AP parts through Essex here in the US, I assume you've spoken to them already. This car is killer, deserving of its own thread.

[3literpwr]

Tuthill harness is high quality and very simple. Install was easy, but it did not include a wire diagram and i'm still waiting on info for gauge wiring. The dash panel was part of the install, and i don't know if they do any other versions.

[chrismorse]

Echoing what VFR759 said, it is comforting to get to the end of a session and still have a firm pedal and linear braking. Additionally, I have found that a brake upgrade substantially extends the time between brake maintenance. I have heard of some avid trackers only getting a few track days out of a set of discs and pads.

Bill, Do you have any graphical data on Temps and Wear??
chris