Hello guys.

I never post in this section but I though it would interest some people to see the progress on the brake upgrade I have been working on for the last few weeks.

Two criteria I kept in mind for this build are, low costs while maintaining safety and improved braking (less fade).

This is for my personal car, not for sale, I just feel that with around 500whp its about time to work on the reigns for the horses.

I didn't want to take the plunge on aftermarket discs right away because I want to test out the system and ensure that it works before I go spend all kinds of money on two piece discs. For this reason I decided to go with stock sized Crossdrilled rotors (I don't do autocross and I don't want slots eating away at my pads). I feel that the rx-8 has adequate rotor diameter for its weight and if I were to change to anything it would be to a thicker stock diameter two piece disc with directional vanes.

I concentrated on having more sweep area and a more distributed pressure more rigid caliper. I went with billet 6 piston calipers. These are identical in mounting and function as Willwood Outlaw/SL6 calipers. The calipers can work with .81"-1.25" thick discs The brackets are CNC machined out of 6061-T6 alum.

The caliper uses about 107% of the total piston area the stock caliper has. I doubt the 7% will affect my bias by anything noticeable. It maximizes the use of this piston area by using a longer pad that doesn't go as far into the disk as the stocker but covering more area near the outside of the disc where it matters most since its the point of longest "arm". This causes a small section of the disc brake area, about 3/8", towards the center of the disc to remain untouched by the pads exposing one row of crossdrilling. I have seen many companies sell kits like this and when you use it....you can tell the caliper doesn't match the disc and its horrible in my opinion. To deal with this visual effect, I decided to use a little of creativity. I masked the sweep area fo the new pads and painted everything else in VHT, semigloss, brake paint which can withstand 900deg (I have had great experience with this as opposed to duplicolor brake paint). I then took aluminum rivets and put a rivet in each of the exposed cross holes that are not in the pads sweep area. The result can be seen below in the before and after photos :D.

I know its almost "ricer" but I felt it was for a good cause since it would be even more ricer in my opinion to have a half exposed disc which would be obvious. Besides, I don't do many "ricer" things, nothing I do is for looks, all of it is functional...so maybe a little rice in this instance wont hurt anything .

Please excuse the messy pics...my camera isn't working right now so these were with a cell phone. Also, I will post pics of the brackets and the hardware sometime in the next few days.


Opinions?

Best regards,

Chris

 

look's pretty. waiting for someone to say something about adding unsprung weight with those rivets lol

 

Yeah, I know...you know some one eventually will...to which I will answer;

on the stock rotor, those holes are filled with steel, the aluminum rivets weight about 20% of what the filled hole would weigh...lol...haha

Chris

 

What is the point of the rivets? Give it a 2 piece look? Gotta say it does look ricey...

 

The point of the rivets is to not have a row of exposed cross holes that never get touched by the pads. I figured the rivets would at least give it a two piece look...which is better than an incomplete rotor look.

Remember, I am going with proper two piece rotors once I prove the system works...



Chris

 

How about finding a set of calipers that cover the whole rotor surface

You know someone was going to say that as well

 

i think it looks pretty good for a homemade project

 

That makes sense to me. Seems like kinda waste to not use the entire braking surface.

 

^+1

 

I like it.

 

I say they look cool. Keep posting

 

Agreed. Now you have less swept area than stock; that seems like a brake downgrade.

 

Lion, is it actually less swept area? Or did he just put rivets on that surface of the rotor where the pad doesn't actually sweep? I agree, it looks like less swept area, but maybe it's just kind of an optical illusion?

 

Yes it is less swept area. The shiny surface of the rotor in picture 2 is the normal stock swept area as he's using a stock sized rotor. He has painted his own application and some of that shiny surface has been painted over, so it's very obvious this is less swept area.

 

The amount of people I get going on about swept area (not just on here, I do brake parts for other cars that seem to upset some people for the same reason ) - larger swept area doesn't improve braking performance as such, it just reduces the pad surface temperatures and reduces wear, brake pads are fairly insensitive to surface pressures - they have to be, or they'd be very inconsistant during different braking situations.

Using just the outside of the rotor as Chris is doing actually improves the leverage of the braking system, as the mean torque application point is further from the the wheel centre, much the same as using a larger disc, although, obviously, the pad interface temperatures will be higher.

 

So he's going to have rotors and pads that will be warmer, making it more likely to fade. And in addition his effective leverage in front is higher, but his rear is unchanged, and his brake bias is not adjusted for this. So his fronts are just going to lock sooner delivering less than optimal braking distances.

 

Not necessarily, more braking effort/better tyres needs more front bias anyway due to the additional weight transfer.
In addition to that, the new calipers will be stiffer, give a better pressure distribution across the pad (which will reduce the peak temperatures slightly, and reduce pad wear), and also dissapate heat faster than the standard calipers, and looking at it, the pad is quite a bit longer than the OEM pads, which reduces the pad temperatures still further (although the disc peak will still be higher).

You've got to consider everything as a system when it comes to brakes.

 

I am considering everything. Whatever extra weight transfer he can gain from a higher front leverage is going to be more than offset by the extra bias from the leverage change. Not to mention with his power amounts, he's going to use his brakes more and for longer than a typical RX-8, so he needs his brakes to cool down quicker. The smaller swept area doesn't help and I don't think his pads will be cooler as rotors and pads have a tendency to want to equalize in temperature because they're in conduction so often. Therefore, his hotter rotor is going to lead a hotter pad.

 

Chris is a smart guy--better rest assured he has thought of all the above.
i like the creativity of what he did and it will keep the set up looking good and neat after it has been used some.
The cross drilled rotor (not my favorite- especially on front) will also help to reduce the temps some.
I do wonder about cracking--but i dont know about these rotors, these may do fine. like the posche and bmw ones.

The weakest part of the oem braking system( which is a dang good one by the way) is the calipers. It would be a good guess that a lot of people dont realize how much caliper flex we get. After ours get a little wear and tear of them they are more likely (on track) too flex than not. Talk to the race teams.
Some of our members that track with us have very obvious wear areas on the rotors from this flexing.
Hope he has GOOD spring rates and driveline bracing---between 500hp acceleration and the "whoa" he is going for ---better have a strong neck!:
olddragger

 

The surface temperatures do but the mean temperature gradient across a disc and a pad are both very, very different.


Edit, slight thread hijack Chris, sorry, but I'm going to confuse some people here in the name of education, here's some of mine....



Now, they must be terrible right?

 

Philip, i love those brakes. I had them on my husqvarna supermotard and really loved them

 

Not to be argumentative, but wouldn't you say confusing people is the opposite of promoting education?

Maybe explaining why those are NOT terrible is better than just posting them and declaring so much.

As the OP states, he doesn't do autocross (and I see no mention of track time for the car either), so I guess I don't fully understand why the brakes need upgraded in the first place. I would love to see some actual performance numbers comparing this new setup to the stock setup - especially considering that since there is no autocross/track time, fade really shouldn't be much of an issue. I don't mean to sound dismissive, I'm just curious why this upgrade is needed and what the actual gains will be.

 

No, making people think about why someone would do that tends to let them get their heads around it much better, then you help with the explanations

 

You realize his car is nearing 3x the stock power level, right?

 

Yes. But since he doesn't track or autocross his car, I don't see why the stock brakes aren't adequate. Unless you're constantly on and off the brakes, and maybe he is, the stock brakes are perfectly capable. A single stop from 80 mph in a 500 hp car is virtually identical to a single stop from 80 mph in a 180 hp car, all other things being equal. Having 3x the power means absolutely nothing when it comes to average braking. And I really doubt that the stock brakes are so poor that they can't handle average daily driving.

In the end, it's the driving habits that will determine whether or not there is any true benefit to a brake upgrade. The blanket statement that you need more brakes just because you have more power is a bit misleading.