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Suspension | Chassis | Brakes -- Sponsored by 949 Racing Relating to suspension, chassis, and brakes. Sponsored by 949 Racing.


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Old 10-10-2013, 02:28 PM   #15
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Quote:
Originally Posted by ZDan View Post
Horsepower absolutely DOES heat up brakes! Braking from 80mph to 40mph requires 21.5% more energy than braking from 75mph to 40mph. BIG difference! More power requires more capacity to dissipate heat energy from the brakes, it's a fact.
You may be able to get up to speed quicker with more horsepower, but unless you're on the throttle while braking, stopping from 80mph with 1000 horsepower is the same as 80mph with 100 horsepower. Obviously with more power you'll likely have higher peak speeds (on a track), which could translate to needing more braking power.
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Old 10-10-2013, 02:31 PM   #16
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Originally Posted by Firestorm_86 View Post
You may be able to get up to speed quicker with more horsepower, but unless you're on the throttle while braking, 80mph with 1000 horsepower is the same as 80mph with 100 horsepower.
What Dan is saying is:

On a given track, with specific parameters, you'll get to a faster top/entry speed with more HP, so you need more heat dissipation on hand for the brakes, where BBKs come in handy.

-alex

Edit: you edited right when I quoted you...
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Old 10-10-2013, 06:57 PM   #17
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Once you've determined you are ready for a brake upgrade there are some good options out there. Like @Dave-ROR said, be careful when selecting an "upgrade" as it is easy to mess up performance. My personal track choice has always been AP Racing but there are plenty of other good bbk's out there that will work and help with your track days.

Remember what Dave said,
Quote:
Originally Posted by Dave-ROR View Post
bigger isn't always better...
Adding too much rotational mass can actually hurt your braking (and accelerating) performance.
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Old 10-11-2013, 12:54 AM   #18
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Originally Posted by ft_sjo View Post
Larger discs are not just about heat capacity. It increases the effective lever-arm of the brake system to give you a different pedal feel. I'm putting 330's on mine purely for this.
Yes, you will have more brake torque with a larger rotor. You will also have more unsprung rotating mass farther from the axle centerline. It can also screw up your brake bias and increase stopping distances, but rock on I never noticed any real change in pedal feel just from larger rotors, but calipers.. yes. It may be there but I'm not good enough to notice it, by feel I'm assuming we are talking about tactile feedback and not what the body of the car is doing, etc.

These are all reasons why brake upgrades should be properly designed. I think a lot of us have went through the "I'm going to run XXXmm front brakes with 4 pots..." only to use the same brake marker on track and end that braking zone with a "oh shiiiiiiiit" due to improperly thought out changes. Not saying that you haven't taken these things into account.
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Old 10-11-2013, 12:56 AM   #19
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Quote:
Originally Posted by wparsons View Post
Doesn't matter how much heat the rotors can absorb unless they can keep the pad temps in a range the pads are happy with, and I can't imagine there's a rotor big enough to do that with stock pads

If you're overheating race pads with stock diameter rotors and aren't driving wrong, then sure there's a case for bigger rotors, but for 90% of the people out there they just need better pads and fluid.
Sorry I didn't realize we were limiting that conversation to stock pads. I agree with you generally, but there are other benefits to brake upgrades. My pads are cheaper than OEM size for one. My pads and rotors also last longer. They are also lighter than OEM parts. Better brake feel too.

Just sayin...

Speaking of brakes, I really should install those SS lines that have been sitting around for a year. There's absolutely zero need to do so but I'm kinda sick of looking at them taking up shelf space in my garage. :shrug:
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Old 10-11-2013, 01:32 AM   #20
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Quote:
Originally Posted by Dave-ROR View Post
Yes, you will have more brake torque with a larger rotor. You will also have more unsprung rotating mass farther from the axle centerline. It can also screw up your brake bias and increase stopping distances, but rock on I never noticed any real change in pedal feel just from larger rotors, but calipers.. yes. It may be there but I'm not good enough to notice it, by feel I'm assuming we are talking about tactile feedback and not what the body of the car is doing, etc.
Drive a stock 2002-2005 WRX then drive a 2002-2005 WRX with "H6" rear rotors. The difference isn't in the pedal, it's in how the car stops and how much the front end dives.

Quote:
Originally Posted by pierce88 View Post
Why the interest in the WRX 4-Pots? I know on the 05-09 Legacy GT they were actually a downgrade despite "looking" better. Might want to make sure they are even marginally better than stock...

-Pierce
Legacy GT had 316mm front rotors, so moving to a 290mm-ish rotor wasn't the smartest move. On this car, the rotors are identical up front so the 4 pot isn't a "BBK" as much as it simply an opposed-piston fixed caliper that feels better.
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Old 10-11-2013, 03:31 AM   #21
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Quote:
Originally Posted by Dave-ROR View Post
Yes, you will have more brake torque with a larger rotor. You will also have more unsprung rotating mass farther from the axle centerline. It can also screw up your brake bias and increase stopping distances, but rock on I never noticed any real change in pedal feel just from larger rotors, but calipers.. yes. It may be there but I'm not good enough to notice it, by feel I'm assuming we are talking about tactile feedback and not what the body of the car is doing, etc.

These are all reasons why brake upgrades should be properly designed. I think a lot of us have went through the "I'm going to run XXXmm front brakes with 4 pots..." only to use the same brake marker on track and end that braking zone with a "oh shiiiiiiiit" due to improperly thought out changes. Not saying that you haven't taken these things into account.
I think you've assumed i'm not also changing calipers. I can assure you that is not the case.

I appreciate what you're trying to say about rotating mass - I have found that it doesn't really become an issue (gyroscope effect) until you get to ~380mm or larger.
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Old 10-11-2013, 01:36 PM   #22
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Originally Posted by ft_sjo View Post
I think you've assumed i'm not also changing calipers. I can assure you that is not the case.

I appreciate what you're trying to say about rotating mass - I have found that it doesn't really become an issue (gyroscope effect) until you get to ~380mm or larger.
I assumed that you would switch calipers too. My point was just that larger rotors increasing feel is something I haven't experienced. Other parts often involved in that will, but you can increase rotor size without replacing calipers, etc (custom brackets, different brackets, etc).

I tend to follow this path:
1. If I beat on the car on track for extended periods of time, does it fail?
2. If yes, what's the best way to resolve it without increasing mass?
3. Does that change require a rear brake change to resolve any bias issues? If so, are more agressive pads (up to a point) enough?

That's simplified a bit, but... basically I want AS SMALL of brakes as I can get away with. If I can make them lighter and cheaper overall than stock that's a great bonus. I never want more thermal mass than I *need* because it's not as ideal as having "just enough". I currently run ~more or less OEM diameter rotors, they are just a lot thicker with a lot better cooling. They hold up to abuse and have help up to boosted track cars without issue so I just will never see the *need* for huge brakes on these.
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Old 10-11-2013, 01:57 PM   #23
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I am curious on opinions (backed up or not) on Cross Drilled and/or Slotted Rotors as and upgrade for stock braking systems.
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Old 10-11-2013, 02:02 PM   #24
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I am curious on opinions (backed up or not) on Cross Drilled and/or Slotted Rotors as and upgrade for stock braking systems.
Do we really have to go there again? lol

I'll grant slotted rotors can have a purpose but I honestly don't feel that either are an upgrade for a stock brake system. Both remove mass (less in slotted) and introduce stress risers (again less in slotted). Neither are additional features I want in a brake system that is, IMO, borderline for extended track use already. They add some noise as well but my car sounds like a dump truck mixed with a frieght train under braking so I don't care about that.

Of course I barely track the BRZ anymore so.. oh well. My dedicated track car and the race car have even smaller brakes.. with sliding calipers.. oh the horror.. err. :shrug:
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Old 10-11-2013, 02:07 PM   #25
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Quote:
Originally Posted by Dave-ROR View Post
Of course I barely track the BRZ anymore so.. oh well. My dedicated track car and the race car have even smaller brakes.. with sliding calipers.. oh the horror.. err. :shrug:
So does mine, and having slots or espeically cross drilled holes are just places for cracks to start in my $15 rotors made proudly in China.
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Old 10-11-2013, 02:10 PM   #26
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So does mine, and having slots or espeically cross drilled holes are just places for cracks to start in my $15 rotors made proudly in China.
Speaking of that, I need to go pickup some more mini cooper rotors for the GS-R.. they are ~$30 each :~(
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Old 10-11-2013, 02:11 PM   #27
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I personally like the application of slotted helping keep the rotor and pad surface clean. I agree with Dave in that removing a lot of mass from the rotor just hurts thermal capacity. I do love the look of cross drilled rotors but as far as being applicable for performance I stray away from them. Seems to be more of a gimmick than anything (not in reference to Carbon Ceramic Brake which I don't know much about).
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