Larger Rear Brake Rotors?

Discussion in 'Brakes, Wheels and Tires' started by VoodooBoss, Dec 1, 2013.

  1. VoodooBoss

    VoodooBoss Rick Moderator

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    If you maintain 14" front rotors are there any issues with increasing the rear rotors to 13" or 14"? I've been told by a couple of people that it's not a good idea to install 14" rear rotors with 14" front rotors. Why? Regardless if there is a possible imbalance in the system wouldn't ABS compensate for that? Anyway I'm looking at the three kits below. I'm leaning towards the Steeda 13" kit but I'm not looking forward to installing it. I'll probably have someone install the kit for me. Thoughts?

    BTW the reason I'm considering this is I'm going to upgrade my front rotors and calipers to increase heat dissipation and want to do something similar for the rear. Plus the stock rotors look so small. ;)

    Steeda 13" Rear Rotors: advantage is replacement rotors are inexpensive.

    http://www.cjponyparts.com/steeda-rear-disc-brake-upgrade-kit-13-inch-2005-2013/p/DBR22/

    [​IMG]

    Baer 14" Rear Rotors: advantage is installation is easier. I've been told you can order slotted only rotors.

    http://www.cjponyparts.com/baer-rear-brake-rotor-upgrade-kit-eradispeed-plus-two-14-inch-2005-2013/p/BR37/

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    Ford 14" Rear Rotors: advantage Ford parts and replacement rotors are the most affordable.

    http://rehagenracingproducts.com/Shelby-GT500-350mm-Brembo-Rear-Brake-Upgrade-2005-2014-MUSTANG-RR-2300-TRA.htm

    [​IMG]
     
  2. 2012Boss302

    2012Boss302 TMO Addict

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    What is the factory rear size, 11 inch IIRC ? I assume you are going with a 15 inch front? Are you going with a six piston front caliper?

    I ask because I think a larger rotor with a stock single piston caliper is going to give you better heat management correct? With that it seems that unless the rear caliper is upgraded as well it would be best to go with the Ford piece.
     
  3. VoodooBoss

    VoodooBoss Rick Moderator

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    The stock rears are 11.x and the idea is to improve the heat dissipation. Up front I'm going with a 14" four piston Stoptech Trophy kit. The rotor is wider at 35mm so 355x35 which increases the mass compared to our stock 355x32. This kit can be ordered with seals in the caliper and anti-rattle hardware for the rotor. The Stoptech 380x32mm kit will fit my Enkei 18" wheels but it's a tight fit and I've decided to go this route.

    http://www.cortexracing.com/shop/stoptech-str40-355x35mm-s197-spec-mustang/
     
  4. Eric

    Eric TMO Advanced

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    Rick,

    I have the Baer 14" 2-piece/slotted (not drilled) rotors installed...no issues with ABS. The install was very straight forward and was able to keep my Stop Tech SS lines.

    r
    Eric

    Couple of pics

    [​IMG]


    [​IMG]
     
  5. KBBOSS1086

    KBBOSS1086 TMO Addict

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    Rick: FWIW I went with Ford GT500 setup (purchased individual parts through Tousely Ford for under $340 shipped). I had my car at the dealer for warranty replacement of the rear calipers so I had them put the brackets and rotors on too. The labor was aproximately $180. If I had it to do over again I would probably buy the Baer kit as long as it's available in slotted vs slotted & drilled. The price for the Baer kit isn't much more than the cost of the Ford parts plus the labor as long as you installed it yourself. You don't have to pull the axles like with the ford brackets so the install should be very easy. Plus you will get a much nicer, two piece slotted rotor vs an OEM ford rotor.

    Sean
     
  6. VoodooBoss

    VoodooBoss Rick Moderator

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    Where did you order the kit with just slotted rotors?

    Sean, I'm back and fourth on this but I like the idea of either OEM pieces or the easier installation of the Baer kit. But I also like the 13" rotors of the Steeda kit. Hmmm
     
  7. Eric

    Eric TMO Advanced

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    Rick,

    I ordered the Baer kit through Chicane23 (www.chicane23.com); ask for John. I also installed the Baer front 2-piece/slotted rotors at the same time. They were both shipped direct from Baer.

    You can also get them from Kenny Brown.

    http://store.kennybrown.com/product/brake-rotors/baer-eradispeed2-rear-rotors-2005-2014-mustang-boss-302-and-shelby-gt500

    r
    Eric
     
  8. sadil

    sadil TMO Race

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    I dont think changing the rear discs will have any effects at all because the caliper and braking force remains same. If you were to change the caliper ie braking force at the rear, then you would throw the bias off and could have problems unless you compensate upfront. The larger rotor should just give you better heat dissipation resulting in better response from your brakes during longer stints.
     
  9. wwilde001

    wwilde001 TMO Addict

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    +1. The 302S comes with a full race 14" Brembo front setup with a stock rear setup. I'm thinking Ford probably did some testing and found out that they didn't need anymore on the rear. If I was (and I did) to invest any money, it would be on the front setup.
     
  10. 2012YellowBoss

    2012YellowBoss TMO Addict

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    Rick, the calibration of the ABS will not change or compensate for changes to the car. As far as I know it is set for the way the car came and any changes made to the setup would require an update to the module.

    As you know I have the Shelby parts sitting in the shop collecting dust for the upgrade of my factory rear 11.8 discs. However the race shop would not install them even with my 14 inch Brembo front race setup no matter how much I wanted to. They were not the only knowledgeable people who told me not to do this.

    I know some have made the change while still running the 355MM setup up front. Maybe it works on the street but I am not going to chance it on track. Best thing that can be done is leave the rear rotor alone and get a more aggressive rear pad. I am going with an 06 PFC rear now since Racers Edge had some for sale, I was using the 97's with PFC01 in front.
     
    Gt500jerry likes this.
  11. VoodooBoss

    VoodooBoss Rick Moderator

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    I've been told the same thing but why?

    There are many people running the larger rear rotors that track their cars with no issues. Has anyone had an issue using the larger rotors?

    Bill read post #3. ;) BTW I've accidently left my TC on and come back in from a track session with the rear brakes smoking.
     
  12. 2012YellowBoss

    2012YellowBoss TMO Addict

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    Basically because it will change the bias and the ABS is not programed for it.

    While I am guessing here it may be fine up to a certain point but when you need it most I don't want something to go wrong. Lets say a car spins or blows in front of you at high speed and you get on the brakes hard, full ABS event. I would not want one or both of the rear catching harder at speed, again just a guess. As I have learned to drive a little better I find myself on occasion getting to a brake zone at a much higher speed then I was use to. This has caused me to get into the ABS until I learn a new brake point, before I rarely had an ABS event on track. When this has happened I was glad the system was working as it was suppose to and setup correctly for my car. At the TUDOR testing last month I saw a set of tires taken off of a GTD car that had issues with the ABS programming. They were just short of blowing out since they locked up, you could see each layer of rubber all the way down and into the cords. It was an eye opener of what could happen without the proper ABS programming, wish I had taken a picture of those tires, it was way worse then a flat spot from a spin..

    The guys that help me out are very knowledgeable and at times question my over use of tires, rotors etc. They would not do the same and have gotten use to these things and understand why I do but not adding the bigger rear rotors to my setup was one of those things they were adamant about.
     
  13. ArizonaBOSS

    ArizonaBOSS Because racecar. Moderator

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    I'm with Scott on this one. The stock rears are fine for use with a 14" front rotor setup, and you can then use the BOSSR/S ABS module with the correct bias setup.

    Spend that rear rotor "upgrade" money elsewhere!
     
  14. KBBOSS1086

    KBBOSS1086 TMO Addict

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    Playing devils advocate...if it's advised to not upset the braking bias then why is it routinely recommended to use a less aggressive pad in the rear when upgrading to track pads on a stock setup? Isn't the front and rear stock pad compound the same? If the logic of keeping everything in line holds true then wouldn't we want to run identical track compounds in the front and rear (with stock caliper/rotor setup)?

    I realize that too much braking force in the rear is not good, but if the goal is to reduce the temperature in the rear it seems like going with a larger rotor paired with a less aggressive pad (vs the front) would balance things out.

    I've been running carbotech xp20's on stock fronts and XP12's on the GT500 rotors for the past year and have not had any problems under extreme braking. This topic has got me wondering so I wanted to think this through out loud to see if I'm making any sense. It seems logical but then again, I wasn't too kind to my brain cells during my youth :eek:
     
  15. VoodooBoss

    VoodooBoss Rick Moderator

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    Good points Sean. I'd like to know why installing a larger rear rotor throws off the balance and the ABS can't compensate for it? The GT500 brake kit states that it works on our cars the the difference between the F&R rotors compared to our stock kit is much smaller. I can't find anything that states it throws off the braking balance. So maybe the right move here, if there is a concern about braking balance, is to use 13" rear rotors with the 14" fronts. Of course it does say off road use only. Thoughts?

    http://www.fordracingparts.com/parts/part_details.asp?PartKeyField=22422

    Original equipment on 2013-2014 Shelby GT500
    Fits 2005-2014 Mustang GT Coupe
    Fits 2012-2013 Boss 302
    Front features: 15-inch Brembo® vented brake rotors and 6-piston Brembo® aluminum calipers (gloss black finish)
    Rear features: 13.8-inch Brembo® vented brake rotors, single-piston calipers and rear axle caliper brackets.
    Includes production front brake hoses, front and rear brake pads, front tie-rod heat shields and installation hardware
    Off-road use only!
     
  16. Fat Boss

    Fat Boss TMO Addict

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    I don't see how a larger rotor can change the bias enough to affect the ABS when more aggressive pads won't.
     
  17. Grant 302

    Grant 302 OPM Spent: $587,402 Moderator

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    I think some are confusing two separate issues.

    Regardless of having ABS working or not, I wouldn't want the brake bias to rearward enough to cause the rear to step out first under any braking situation. Even if the goal is just to have more mass for cooling, a larger diameter rotor with the same caliper and pad will also apply more brake torque and rear brake bias. If you're running staggered tires, then you probably have a little more leeway to go with the larger diameter rotors. The only way to really know would be to test the car at the limits under braking. And if it's an issue, a less aggressive/lower torque pad could be used to compensate...or you could just start with the less aggressive pad.

    ABS can't compensate for too much rear bias safely IMO. There's no calibration that would make it safe. Even if it 'works', as I suggest above, you don't want the rear stepping out first under any braking.

    If you wanted the Steeda kit, yesterday was the day to get it 15% off directly from Steeda. Personally, I think I'd go for the GT500 kit for the OEM style bracket and hardware. And I'd definitely stay away from significantly different rear brakes like 4/6 pots plus a larger diameter...asking for issues/trouble IMO, without going larger on the fronts.
     
  18. further

    further TMO Race

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    I'm running square tires, Hawk DTC 60s all around, and stock rotors. The ride is very neutral. With R comps, I still have trouble engaging ABS. I have Hawk plus for the street. The race and street pads both bite hard, but I don't get fade with the race pads. I think that is the main benefit between pads, rather than degree of bite.

    Get good high temp track pads all around and go with higher grip tires (r comp) for more grip.
     
  19. ls110

    ls110 John

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    This last season I ran with the GT500 13.8" rears and 14" Frozen Rotors front. My pads were Hawks then Pagids mid season, with more aggressive front pads in both cases. Staggered set-up with 285s and 305s. I did not have any problems with the rear stepping out on me, and most of my track time was at BIR with lots of very aggressive braking.
     
  20. 2012YellowBoss

    2012YellowBoss TMO Addict

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    Good post Grant, and yes the bias and ABS are two separate things. When I was told not to do this I asked why and got the simple answer posted above. Normally I ask a ton of questions but again they were absolutely against doing this so I did not go into details. I would think the problems with the ABS are less dangerous then that of bias. ABS should work by individual wheels so I think the biggest problem could be it engaging before it is needed.

    Another guess on my part would be what Grant said about the rear stepping out or lets say the front swerving. If a car only had rear brakes it would stop the car in time, at slow speeds it should stop somewhat normally. Now think about only having rear brakes and stopping at high speeds and braking limits. I would think the front of the car would be out of control, swerving back and forth or just heading off in one direction or the back end just coming around. This is what I was talking about above, when you are on track at high speed you want everything working as it should be because even a little instability in a brake zone is too much. I know the feeling since I ran a few weeks ago on very low front and rear pads at the same time. The car did not stay straight in the brake zone and it is not a good feeling. This and the other issues like the heal/toe taught me not to do this ever again.

    I also don't think (guess) the pad compound is going to effect the bias enough to cause a problem. If someone was to put bigger rears on with the 355MM fronts and use a less aggressive pad because of this, I would think the whole project who be counter productive. Even so a less aggressive pad is not going to make up for the added lever effect of the bigger brakes.

    What I would do is pose these question directly to Carbotech, PFC or another brake maker for more answers. As for me my parts will continue to collect dust until I upgrade to the 380MM fronts. I said it 100 times I am lucky to have access to people with extreme knowledge about these cars and can only pass on what I was told. Just like you guys continuing to push the issue I also did the same, I brought the parts up to the shop on two different occasions thinking I could talk them into installing them. I wish I had more technical answers for you but I just trusted their word. If I get the chance I will ask about it next time, maybe it is less of a safety issue and more about how bias effects the perfect braking every zone, every lap but that is not how they made it sound to me.
     

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