Here comes the age old debate between bigger rotors and bigger calipers and which one actually dissipates more heat during track days. The obvious answer is that bigger rotors COMBINED with bigger calipers would manage heat the best. Sometimes both options are not possible together so let me explain the two reasons I am asking.

One, I am vaguely considering upgrading my front calipers to the Brembo 6 piston front calipers and know the feel of the brake pedal and stopping distance will probably improve, but will the larger caliper also help deal with heat better? Two and more likely, my next car is probably going to be a Cadillac ATS-V or a BMW M3 or M2 Competition. The ATS-V has slightly larger front rotors than our G37S cars with Akebono brakes and slightly smaller rear rotors, but much larger front 6 piston front calipers and 4 piston rear calipers. The M2 has calipers similar to our cars, but much larger rotors than both the Akebonos and the ATS-V. The M2 Competition is the ideal solution with bigger calipers and rotors than any cars I mentioned already.

Let's pretend for a second that the ATS-V and M2 weigh the same, have the same tires, the same blank 1 piece rotors, and the same suspension so weight transfer is identical when braking. Which set of brakes manages heat better and why?

The large 6 piston front calipers on the ATS-V


The large front rotors on the M3/M4 with moderately sized 4 piston front calipers.


The enormous front rotors and 6 piston front calipers on the M2 Competition. Sweet!

 

Rotors deal with the most heat.

Brakes on the ATS-V are marketing. Look at what race teams use, especially something as heavy as the GT-R.

 

4DRZ, don't your 2-piece rotors have directional vanes? Doesn't that help?

IIRC, didn't you install cooling duct work for your brakes, too? I can only image those things, and a set of track-day pads, are about as far as you can go with that car.

 

I always thought the rotors did the majority of the cooling, but I realize that larger calipers also help dissipate heat a bit. So do you think the larger rotors on the M3 with the smaller calipers would hold up better than the ATS-V brakes at a track day?

What do you mean when you say, "the ATS-V brakes are marketing?" They look pretty serious to me for stock brakes. I can always go to a true race BBK like the AP Racing set up I had on one of my cars. Those were great, but I would much rather get a car that comes stock with brakes that can withstand the abuse of a track day.

Yes, all of those things definitely help with cooling, but my brakes do still get a bit warm at Road America with the speeds I carry at the end of the long straights. I could always upgrade to a serious race BBK for the G37, but I think my money is better spent on a newer car with better handling, chassis, brakes, power, etc. at that point.

 

I just discovered something interesting about the front 6 piston calipers on the M2 Competition. Because they came off of another BMW never intended for track days (probably some suv) they have a non-removable stiffening brace that goes right over the top of the brake pads. This means that you have to remove the entire caliper just to swap brake pads at a track day. Bummer.

 

Larger rotors have more area, therefore have more area (mass) to absorb the generated heat, so each unit part doesn't get as hot, and more area to dissipate the heat. The calipers themselves have little to do with it. In fact, the pads are insulators, keeping the heat out of the caliper and therefore the fluid.

Under extreme braking, it's usually the tires that are your braking force limitation. IF you can still lock up the brakes, not that you want to, the brakes still have more braking power available. Yes, we can get into a discussion of brake caliper and rotor stability and feel, which absolutely makes a difference in how well the driver can modulate the brakes which determine how quickly you can shed speed. IF you are using ABS, then it won't matter as much. Have you already upgraded to the bigger Akebono from the sport or an even further upgrade to something else? And still haven't installed cooling? IMHO, that is absolutely your next step. The goal is to stay within the heat range of the pad you are using. There are paints available to mark rotors, at the edge, to see your peak temps. It is entirely possible to over-cool pads. Which is why race pads aren't used on the street. On the track, definitely use race pads.

The other thing to consider is diminishing returns, a slight increase in size isn't going to make a big difference.

Edit.: So to answer your question, Larger brakes handle heat better than smaller brakes. However, there is a limit to the benefit, AND there are compromises. Larger brakes handle more heat, but weigh more, more rotating mass and unsprung weight = negative effect on handling and acceleration. Not something to be arbitrarily dismissed. Larger brakes also need more room under the wheel. If you need new wheels, costs go way up. And you still have to deal with the negatives on performance. If we could start from scratch, we would chose a fixed caliper (that we have) floating rotor, with the smallest rotor for the pad chosen, that keeps it within it's heat range, and didn't boil the fluid. Also didn't have excessive rotor wear. Not really a concern for a race car. But for street/track cars it is.

I'm new to this board, but not to cars or racing. I don't know what you are trying to accomplish, if you're racing or for track days. Or for that matter your experience. The above is just my humble opinion. Nice to meet you. I also love Road America. It's my 2nd favorite track.

 

I just read your thread started from a few years back, starting with your first day at the track. I see that you did install brake ducting. My advice is to make sure it's getting enough flow, maybe a scoop at the intake and make sure you exit the duct as close to the center of the rotor as possible. But you haven't boiled your fluid. So, as it stands, you're doing the right things and probably don't need to change anything.

What kind's of times are you getting now that you've been doing it for a few years? I had to look it up, but the last time I was there was in 2003, running my SM and turning 2:50.3's, bear in mind we had to run crappy Hankook tires and about 120 RWHP. So don't hold it against me! They're a lot faster now.

 

RBF600 is supposed to not boil until 600°F. A rotor can see 1,000°F. That tells me which part gets hotter.

 

I agree with all the stuff you said earlier. I do have the Stillen/Z1 brake ducts with the brackets that mount directly to the hub to send air right into the center of my Z1 2pc. front rotors. When I first got the car I was running Hawk DTC60/70 pads, but now I run carbotech XP10/12 pads. The carbotechs seem to provide very similar bite with a lot better wear. (This was not my experience with Carbotech about 15 years ago on a different car.) The only time I wore my carbotechs unusually fast and cooked my RBF600 fluid was when I was royally overdriving the car to try to catch a Camaro ZL1 that I had no business catching. I was putting down 2:46 laps in my car which should really be in the 2:50's unless you drive a good deal beyond the limit, even considering all the other mods on the car and sticky tires. It is just too heavy with not enough power to be much faster. I also run stainless braided lines on my brakes.

I was considering the Brembo 6 pots for a bit better bite and a touch more head absorption. I know they will absorb some heat as I had a car that I used titanium shims on the track that were supposed to save your fluid, but I was amazed just how much heat stayed in the pads and made the pads so hot that they started to chunk apart. I know the rotors do absorb more heat, but like you said earlier, there is a point where the additional weight requires a 2 pc. rotor with an aluminum hat.

No doubt the rotors get hotter, but it is still easier to crack decent rotors than boil good fluid. When looking at brake fluid the wet boiling point is a lot more important than the dry boiling point because the fluid will start absorbing moisture as soon as you open the bottle. On RBF 600 the wet boiling point is 399 which is definitely the highest number for the price amongst brake fluid. That fluid has suited me well for the better part of 20 years of track days. I only cooked it once and that was this year when I was braking super late. I have cracked rotors way more often.

 

I have never experienced a cracked rotor. Granted, I have only twenty-three track events under my belt over the last twenty years but no one in the Sentra SE-R, Miata, or G communities have mentioned this problem that I can recall. I've heard that cross-drilled rotors are notorious for cracking and are not recommended on a street car but have no direct experience.

 

That's a good thing that you have not experienced cracked rotors yet. Fortunately SE-R's and Miatas are pretty light and not very fast so they are a lot easier on their brakes. Not too many people are hitting 140+ mph on track in their G cars either, but at least we have some pretty decently sized brakes for those of us crazy enough to drive fast regularly.

You are right about cross drilled rotors. Those suck for track days. It seems like every Porsche, Mercedes, BMW, or Corvette with factory cross drilled rotors that I see at a track day has cracks forming from the holes drilled. Solid or slotted rotors are a lot more durable.

The worst set I ever cracked was at Road America in a heavily modified WRX on coilover race suspension and slicks. They were upgraded calipers, rotors, pads, etc, but the rotors were the factory size and just getting overworked by all the extra grip and speed that they were not designed for (ie. heat). On the last run we were really flying. I came off the track and was driving around to try to cool off the brakes when I heard a loud "PING." I thought it was the coilovers making noise, but the driver's side front rotor had cracked all the way through to the hub. I was showing some of my friends in the paddock when I heard the same loud "PING" on the passenger side causing that front rotor to crack in half as well. Of course I did not have a spare set of rotors that day. I always bring a set now, but fortunately have never needed them. The worst I have seen since that day have just been some small surface cracks starting to form.

Remarkably the WRX rotors stayed pretty round, but I downshifted and used the e-brake all the way home just in case an edge of the rotor decided to eat my brake pads. This led to an interesting moment when a cop pulled up right behind me and I had to just touch the brake pedal at the stop sign so he would think my brake lights worked even though I was not using the brakes to stop.

 

I didn't know what they looked like, now I do, the Stillen brake ducts look perfect. A little sticker shock, but the business end at the rotor is perfect. The other end should have some sort of scoop, like this, if you have room for it. That's just a pic grabbed off of google as an example. Cooling is not a cure all, especially at long straightaway tracks like RA, because the rotors will go through a very wide range during it's heat cycle, the thermal shock will reduce rotor life, cracks. If you're not experiencing that, then you're fine. Regardless, you're not boiling fluid, but the cars are HEAVY, 3800lbs. You might want to try a more aggressive pad if you have increased wear at higher speeds.

IMO, you're not going to gain anything with larger brakes. You might need larger wheels and lower profile tires, cost and increased risk of wheel damage. I'm new to FM platform cars, there must be someone somewhere that has raced them competitively. After some searching... we have 12.6inch rotors. The kit I saw was 14in, 6 piston. That is a significant increase in size. Fitment etc. applies. HOWEVER, the price tag!!! $3000! I bought my whole car for $6500. And $3000 is probably what I spent during a whole season of SM racing. Ever thought of racing? Nothing like it in the world. Yes I'm an addict and a pusher.

Braided lines are all about pedal feel. Some racers don't like them because it's harder to modulate. Do you disable the ABS at the track? I'm a big proponent of no ABS on the track.

 

We hit 140 indicated on the downhill straight at Road America in our Spec Miata's. Granted we were in a 4 car bump draft, and would push each other 3 times over the length of the straight. That qualifying session was the most memorable I've ever had.. The reason I liked RA so much. The other RA, Road Atlanta, is my favorite track. The reason is simple, it's the highest adrenaline track I've driven. Read: there's 3 places you can easily destroy a car.

FWIW, some cars are light and have oversized brakes. Like Miata's. The brakes last forever. Other cars aren't as fortunate. I used to race 1st gen Rx-7's. Those rotors would last 3 weekends before they cracked.

 

I should mention that four of my DEs were actually 24 Hours of LeMons races in a Sentra SE-R. We used slightly bigger brakes than stock so never had fade or rotor failure. We raced at MSR Houston, which is flat and only 2.4 miles long.

 

I made a number of homemade brake duct kits on cars past, but they always get shredded in the winters here. This Stillen kit is not cheap, but it is durable. I removed the fog lights and use the chrome rings as my air inlets. Sort of a sleeper brake duct kit. It seems to work well. I am very familiar with heat cycles and heavy cars. I have a G37S that has 14" rotors up front and 13.8" in the back. I love the feel of the brake pedal with braided lines, but I know that is a personal preference. I ended up doing about 1/2 a track day with no ABS because our rear ABS sensors are mounted on the rear differential. Bad design for track days as the stock differential and fluid get so hot that they can actually melt the plastic ABS sensors mounted to them.

That is moving, even for a group of Miatas. Those are definitely momentum cars at Road America with the long straights. Road Atlanta sounds fun. The guys at Z1 Motorsports in Georgia always talk up Road Atlanta. (I get most of my parts from them.)

How fun is the 24 Hours of LeMons? That race sounds awesome!