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Carbotech Brake compound thoughts

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Here's what Carbotech says about the gas film that's built up from heat:


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Carbotech Performance Brakes: Frequently Asked Questions

6. What is brake fade?

Fade, or brake fade is the reduction in stopping power caused by a buildup of heat in the braking surfaces (and in the case of drum brakes the arc of the brake shoe don’t match the arc of the drum in response to heat). Brake fade can also be caused by the brake fluid boiling. Compounds are held together by resins, these resins can revert to gas when high temperatures are reached. When this happens the brake pads can “aquaplane” on a film of gas created by the over heated resins. Many low quality pads suffer continuous fade at very low temperatures.
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So in the case of slotted and drilled that gas film has some place to go and less area for the pad to be "aquaplaning" across the film layer that's created. It makes sense to me but the true test is comparing each rotor, drilled, slotted, and flat on a brake test that is rather consistent.

But the issue I'm having when wet is as if there's a film running between the rotor / pad. So still trying to figure out what it is.

1) Slime from the brake dust collected and now weeping out slowing from the drilled hose of the rotor?
2) The rain is creating a film between the pad/rotor and needs more pressure to actually apply an appropriate force to the pad so it can actually bite the rotor. Hence a dual piston / possibly larger rotor up front.
3) Or the brake pad can't heat up enough with water cooling down the rotor to allow it to work.

Augie's suggestion sounds like a way to troubleshoot it with the stock rotors for #1. Before the next big storm I'll try to pull off each wheel, remove the rotor, thoroughly wash the rotor reaming out all the holes so there's a lower chance of slime running across the rotor when it rains.
 
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So after researching the issue of loss of braking performance in the rain, it does appear to be a common problem with other cars as well. Some cars show the issue more than others and there's some owners who drive the same car with no issue but others who experience it. With that I believe that difference has to do with what type of brake compound you're running as well as the condition of your rotor. If its glazed it'll show the issue more. All this in combination with a wet rotor, the key is how fast you can wipe or dry off the rotor to get back your braking "bite".

What appears to happen is that the rain layers the rotor, the pad also is wet. With that two things happen. The pad temp and rotor temp drop. Brake pads work best when heated up some, they also want a dry surface in order to achieve a "bite" with the steel rotor surface. If there's water on the surface of the rotor, typically the brake pad has to wipe the rotor and dry the contact surface before it will actually begin to stop the car. Some people will hold the brake down to try drying it before they stop and that works for them.

With the Roadster, it has drilled rotors which are to be better than your typically flat rotors in the rain. The holes are a place where the water can escape and then push out through the inner cooling vane. However the drilled holes are too small to be effective for that they fill up with brake dust. I then believe when they're wet the dust acts like a sponge. It no longer allows the water to escape, but now its absorbing and it just pools in the pockets. When it comes out and drips on the braking surface of the rotor, the dust now acts like a lubricant and braking becomes even more compromised in the rain. Lastly when the rotor has a layer of water on it, the pad aquaplanes on top of the water which again lowers your braking ability.

Slotted rotors also work great and better than a solid rotor for that the water now has a place to go. The pad wipes the water, the water falls into the groove, and then its expelled on its exit rotation. The flat portion of the rotor allows friction to build up and help dry the pad to achieve its bite. Best part is that the brake dust has no where to go, its only option is to blow off when the car is being used dry. In the rain, the slots are not deep enough for the dust to lay stagnate, the centrifugal force with the rain slings the dust out and away. Slots won't be a hellacious hangout den like the drilled rotors. There should be a significant performance improvement in both the wet and dry conditions with the floating slotted rotors.

We're looking to get a custom set of floating rotors made that are heat treated in a corrosive resistant process similar to what the Chevy Volt uses. There has been some discussion that this corrosive resistant process also improves braking when its raining. So there's going to be an extra safety and performance factor added with these. If anyone is interested in ordering a set of custom floating slotted rotors with aluminum hats, feel free to reply your interest in the following thread or send me a PM:
Custom Aluminum Rotors - A possibility
 
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Hi guys,

I had a weird braking issue the other day. The windshield was so dirty from the mag chloride that I could hardly see. I pulled into a parking lot and for a second it was as if I had no power assist for the brakes. I almost went through the spot I was hoping for, and into the next spot. I haven't been able to reproduce it, but it has made me VERY wary of needing to use the brakes. The previous owner ran into a tow hitch on the bumper of a truck in front on him when parking. He said he just pulled in too far. But now I wonder if he experienced the same issue. Any thoughts on what to check?

Either way, I'm ordering the Carbotech AX6s. But if there is some random failure, it's not going to help much in that case.
 
Hi guys,

I had a weird braking issue the other day. The windshield was so dirty from the mag chloride that I could hardly see. I pulled into a parking lot and for a second it was as if I had no power assist for the brakes. I almost went through the spot I was hoping for, and into the next spot. I haven't been able to reproduce it, but it has made me VERY wary of needing to use the brakes. The previous owner ran into a tow hitch on the bumper of a truck in front on him when parking. He said he just pulled in too far. But now I wonder if he experienced the same issue. Any thoughts on what to check?

Either way, I'm ordering the Carbotech AX6s. But if there is some random failure, it's not going to help much in that case.

Was the parking lot bumpy? If the Traction Control detected a change in tire rotation between the front / back wheels it'll shut regen off completely and you're solely relying on the brake pads to stop you. If I'm driving in a spirited manner though twists and turns I turn TC off so it won't cut regen off unexpectedly. If regen is cut as you're entering a turn pretty fast and getting ready to brake into a turn at the last possible moment you'll definitely overshoot your line and possibly miss the turn if you're not expecting this.

And yes, if you're on the stock pads they're junk, so that's a very smart move upgrading.
 
Thanks guys! It very well could have been the regen. I haven't noticed it off, yet, but that could have been the first case. It was very cold, and I was paying attention to the window being so dirty. I could have missed the light on the dash.