chknhwk HalfDork
May 2, 2012 11:38 a.m.

So I'm looking at a GRM-priced brake upgrade and I've been focusing on a package deal, like upgrading to S60/V70R or XJR calipers and rotors but I'm finding it difficult with regards to finding an off the shelf solution for both rotors and calipers so I got to thinking, what if I just change out the rotors? My problem is heat sink and brake fade after about 15 minutes on a technical track like NHMS where they incorporate both the infield and outfield. I've been looking at the RX330 rotors as compared to the X-Type:
OD - thickness - CB - height (RX330 vs. X-Type):
320mm 28mm 62mm 49.3mm
300mm 25mm 63.5mm 47mm
The RX would only need to be bored out and a new bolt pattern done - Racingbrake or Coleman would probably be able to make two piece rotors for me pretty easily and even take into consideration the 2.3mm height difference making replacement rotors cheaper on the long term. I really think the extra 20 mm OD and 3mm in thickness would make a difference in heatsinkability ().
My question is, how important is it to change the calipers to compensate for swept area? What things do I want to look for in calipers when looking to upgrade besides pad availability? I would lik to keep the stock calipers because I know I can get SS brake lines with the proper fittings and I wouldn't have to worry about creating adapters thus keeping my costs down even more. I'm probably going to stick with Carbotech because they already offer everything I need if I stick with my stock calipers.

chknhwk HalfDork
May 2, 2012 11:39 a.m.

I should note the figures given are for the front rotors only, contemplating taking my stock front rotors and moving them to the rear thus negating any cost benefits from the front.

Stealthtercel
Stealthtercel HalfDork
May 2, 2012 12:14 p.m.

Watching this thread with interest, since I know there are people out there who can talk helpfully about rotor thickness as a metric of brake performance. I understand how rotor diameter helps, through the magic of pi & math, but thickness isn't quite so obvious (at least to me) on a practical level. Yes, you have more mass to use as a heat sink, but does it really help THAT much?

BTW, what kind of car are we talking about here?

dculberson Dork
May 2, 2012 12:18 p.m.

Are you using a race pad? That can help a lot with fade.

chknhwk HalfDork
May 2, 2012 12:18 p.m.

In reply to Stealthtercel:

Jaguar X-Type, 04 with auto trans and 3L engine. Only upgrades have been sway bars (and broken end links, lol), SS brake lines, race pads for the track, ATE super blue, and a wheel tire combo that allows for 245/40-17" Toyo T1R's. Basically I only focused on lean, stick and stopping and I'm already having a problem with heat soak. Plans also include brake ducts but that's going to be involved because I do not want to lose my fog lights. (Lasik surgery, night vision SUCKS, I get nervous driving at night in the rain, fogs are a must.)

chknhwk HalfDork
May 2, 2012 12:19 p.m.

In reply to dculberson:

Carbotech XP10's.

AngryCorvair PowerDork
May 2, 2012 12:23 p.m.

you don't change the calipers because of the swept area, you change the calipers because (1) the caliper with new pads will be 3mm too narrow across the bridge to fit over the rotor, and (2) even if you shaved the pads to make the caliper slip over the rotor, you won't be able to bold the calipers onto the knuckles because the OD of the rotor will hit the inside of the caliper bridge.

oh, and the 2.3mm difference in height will possibly put the inboard braking surface of the rotor into the knuckle

Stealthtercel
Stealthtercel HalfDork
May 2, 2012 12:37 p.m.

"Grace, space & pace" FTW. And hey, on lots of vehicles you actually have to pay extra to get sway bars that disconnect.

Gearheadotaku SuperDork
May 2, 2012 12:47 p.m.

I'd focus on pads, fluid, and ducting before rotor / caliper upgrade. If you have good braking before heat soak, the brake size seems like it should be ok. How long are your sessions? I you just need a few more laps, ducts and pads my fix it.

yamaha Reader
May 2, 2012 1:11 p.m.

is the jag 5x108.....if so, some crafty taurus people can probably help you with cobra PBR setups on 13x1.x rotors....

dculberson Dork
May 2, 2012 2:33 p.m.

Sorry, I forgot to ask - what brake fluid are you running?

You can sometimes just swap the rotors but stick to the factory calipers by using (usually DIY made) a caliper relocation bracket. The thickness of the rotor is important - if it's too thick, as AngryCorvair said, you can't put the old caliper over it as it won't retract the pads far enough. You won't have as much swept area (versus using larger pads intended for the larger rotor) but you'll have the additional mass and cooling ability.

chknhwk HalfDork
May 2, 2012 10:08 p.m.
Gearheadotaku wrote: I'd focus on pads, fluid, and ducting before rotor / caliper upgrade. If you have good braking before heat soak, the brake size seems like it should be ok. How long are your sessions? I you just need a few more laps, ducts and pads my fix it.

I'm already running ATE Super blue and full race pads, Carbotech XP10. Only thing I don't have is the ducting. Yet. Sessions are anywhere from 15-30 minutes long. At the 15 minute point is where I'm usually running into issues, depending upon ambient temp.

chknhwk HalfDork
May 2, 2012 10:11 p.m.
dculberson wrote: Sorry, I forgot to ask - what brake fluid are you running? You can sometimes just swap the rotors but stick to the factory calipers by using (usually DIY made) a caliper relocation bracket. The thickness of the rotor is important - if it's too thick, as AngryCorvair said, you can't put the old caliper over it as it won't retract the pads far enough. You won't have as much swept area (versus using larger pads intended for the larger rotor) but you'll have the additional mass and cooling ability.

ATE Super blue and I always do a full flush before every event with fresh fluid so I should have the highest boiling point available for the fluid.

I'm hoping to do just that, rotors + stock caliper + relocation bracket. Just wondering if there's any reason I shouldn't, I'll deal with any reasons I can't (i.e. physical interference) in the process of fitting.

DWNSHFT Reader
May 3, 2012 12:09 a.m.

I vote for brake ducting. That is how you improve the rate of heat dissipation, which is how you solve the problem. Bigger rotors just masks the problem, at the expense of unsprung rotating mass. Also, all those big metal pieces are expensive. Also, it is my understanding that the cooler temperatures from ducting yields better pad feel as well as longer rotor and pad life.

I've seen brake duct kits that just mount a small intake on the lower control arm. Less effective than mounting a big hose in the air dam but it would allow you to keep your fog lights.

David

dculberson Dork
May 3, 2012 9:23 a.m.

Larger rotors don't just mask the problem if the brake system was under-specced to begin with. Jags have good brakes but they're stopping a relatively heavy car that's not really intended for track use, so I think an upgrade isn't out of the question. But you could add some ducting, try it out, and if its not enough work on the rotor upgrade.

One note, I did see that Carbotech says the XP10s aren't recommended for cars over 2900 pounds. (found here: http://www.ctbrakes.com/brake-compounds.asp ) Take that into consideration when looking at what to upgrade.

wbjones UltraDork
May 3, 2012 4:21 p.m.
Stealthtercel wrote: but thickness isn't quite so obvious (at least to me) on a practical level. Yes, you have more mass to use as a heat sink, but does it really help THAT much?

as I understand it ... the heat sink thing is it ... angry corvair could probably help here

chknhwk HalfDork
May 5, 2012 4:40 a.m.
dculberson wrote: Larger rotors don't just mask the problem if the brake system was under-specced to begin with. Jags have good brakes but they're stopping a relatively heavy car that's not really intended for track use, so I think an upgrade isn't out of the question. But you could add some ducting, try it out, and if its not enough work on the rotor upgrade. One note, I did see that Carbotech says the XP10s aren't recommended for cars over 2900 pounds. (found here: http://www.ctbrakes.com/brake-compounds.asp ) Take that into consideration when looking at what to upgrade.

Personally my opinion is the brakes are simply too small from the factory, I just can't see front rotors at 300mmx25mm and solid (non-vented) rear rotors slowing down a 3400+ pound car at speed repeatedly.

That's interesting! I would SWEAR that wasn't on the website when I purchased them two years ago. I went on a CT sales person's recommendation as well as reading the descriptions.

clownkiller Reader
May 5, 2012 1:19 p.m.

Duct the brakes, it will make a huge difference.

chknhwk HalfDork
May 5, 2012 3:25 p.m.
clownkiller wrote: Duct the brakes, it will make a huge difference.

That seems to be the resounding recommendation here so I've been churning gears in my head. Anybody know where I can get some some teardrop shaped naca ducts? I'm thinking of mounting them in the outer edges of the lower mouth of the front bumper.

My feeling is the ducts should be somewhat straight to the center of the rotors and I'll attempt to fab up something like the Roush or Agent 47 brake cooling plates. Thiefed from their websites respectively:


I think this would work although I still know I'll need bigger brakes in the future.

Max_Archer Reader
May 5, 2012 3:36 p.m.

I bet you could put the intakes for the brake ducts under the bumper instead of in front of it. They could either just be holes that the air goes up into, or a long narrow rectangular intake facing forward and at the bottom.

Looking at the car, though, I don't know if you'd even need any sort of special intake, I think you could just run the duct hose to right behind the lower grill and attach it there.

chknhwk HalfDork
May 5, 2012 5:00 p.m.

That might work, plan is to find some place I can get it up on the lift so I can take a look at the sway bars again and pull the front bumper to gauge clearance for the ducts. I need to find a damn garage I can use. It sucks not having any family and few friends in an area you don't know.

Max_Archer Reader
May 5, 2012 5:55 p.m.
chknhwk wrote: That might work, plan is to find some place I can get it up on the lift so I can take a look at the sway bars again and pull the front bumper to gauge clearance for the ducts. I need to find a damn garage I can use. It sucks not having any family and few friends in an area you don't know.

Yeah I know all about that, I moved to where I am three years ago 'cause of my GF's school and knew nobody here. Even now the only real friends I have in the area are still like 2 hours away from here.

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