Cobra vs. Bullit vs. Stock GT brakes, are they worth it? lets find out. - Page 3 - Mustang Boards


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  #61  
Old 07-27-2009, 07:51 AM
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Damn. When I'm at top speed my rotors are rotating at nearly three-hundred miles an hour... holy ****. No wonder the new GT-R has, I believe, 19-inch rotors!
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  #62  
Old 07-27-2009, 07:57 AM
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wrong. You're rotors are rotating at exactly the same RPM as your tires. The linear distance traveled by your brake pads over the rotor is DRAMATICALLY lower than the distance your tires have covered.
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  #63  
Old 07-27-2009, 08:01 AM
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This is exactly why I should have paid attention in Physics 103.
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  #64  
Old 07-27-2009, 08:52 AM
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or geometry more accurately heheheh
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  #65  
Old 07-27-2009, 10:33 AM
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Originally Posted by r3dn3ck View Post
You're partially incorrect: it's actually a higher rotor speed if you're measuring linear velocity. If you're measuring angular velocity it's exactly the same.

The larger surface area and higher linear velocity of the larger diameter rotor creates greater friction across a friction pad of similar area using a caliper of similar clamping force capacity by exposing a greater surface area to the friction pad in the same amount of time at a given wheel speed than a 10.8" GT brake setup. In short, bigger rotor is better pretty much regardless. And I 100% do not agree with them as a race item. There are 4 and 6 pot calipers for 14" rotors for real racing. The cobra brake kit is what I'd call a minimum for reliable stopping of as powerful a machine as ford puts into the hands of total motards.

Pads and rotors are slightly more expensive but stopping that extra 30ft sooner sometimes is important. It's like carrying a pistol or a pocket knife or a hanky, you're better to have it and not need it than to need it and not have it.

I was using linear velocity to prove that larger disc brakes require less work to stop/slow down. Like if you use UDP as a point of reference, the bigger the gear is the lower your rpm's will be and less power will get to the rear.. get a smaller pulley gear for it and you will get higher rpm's faster. the point I'm trying to make here is that the bigger the disc the slower it will be moving at it's edge where the caliper is and the easier it will be to stop.

if you want to test this buy 2x different size rotors and pop your wheels off, get a scientific strobe light and rev it up. I guarantee the smaller ones will have a faster rpm (make sure they are drilled or slotted so you can actually tell what rpms with the strobe)

maybe I'm muddling up my math somehow I don't know, it's been awhile since I've been in any math class and I have never really needed that sh** until I read this thread lol oh well

but yeah, 14" with 4piston calipers FTW (unless you drive like old granny, then you might want the honda civic downgrade.. stop too fast and you might give yourself an anuerism)
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  #66  
Old 07-27-2009, 03:35 PM
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Originally Posted by Kyanbi View Post
Damn. When I'm at top speed my rotors are rotating at nearly three-hundred miles an hour... holy ****. No wonder the new GT-R has, I believe, 19-inch rotors!
The GTR does not have 19" rotors.
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  #67  
Old 07-28-2009, 07:17 AM
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19" rotors would be retardedly heavy and BAD for handling. It has 19" wheels for sure as, IIRC, the GTR has a 15" 2-piece rotor and a set of cast Brembo monoblock 6 pot calipers in front. It's a nice track day brake setup but not for true racing, and don't get me started on cross drilled rotors from the factory... even they do stupid **** sometimes.

I have no idea how they can justify a 15" brake kit for a street car though. All it does is drive the cost of ownership through the damned roof. Imagine the cost of 2 piece 15" rotors, my 13" Baer thick cheek eradispeeds were almost 300 each, so pricey that I don't use them outside of a track environment anymore.
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  #68  
Old 07-28-2009, 06:41 PM
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Originally Posted by r3dn3ck View Post
19" rotors would be retardedly heavy and BAD for handling. It has 19" wheels for sure as, IIRC, the GTR has a 15" 2-piece rotor and a set of cast Brembo monoblock 6 pot calipers in front. It's a nice track day brake setup but not for true racing, and don't get me started on cross drilled rotors from the factory... even they do stupid **** sometimes.

I have no idea how they can justify a 15" brake kit for a street car though. All it does is drive the cost of ownership through the damned roof. Imagine the cost of 2 piece 15" rotors, my 13" Baer thick cheek eradispeeds were almost 300 each, so pricey that I don't use them outside of a track environment anymore.
I saw the price for just rotors for the ZR1, they were about $1700 a piece. I think all together with rotors, pads, and calipers, the whole kit was like $7000. And the rotors don't last very long.
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  #69  
Old 07-28-2009, 07:10 PM
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God damn I don't know where I pulled all of that horrible knowledge from... excuse my ignorance at the moment but somehow I got the wheel size and the rotor size mixed up. Must have been a bad day
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  #70  
Old 07-29-2009, 07:12 AM
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Originally Posted by Kyanbi View Post
God damn I don't know where I pulled all of that horrible knowledge from... excuse my ignorance at the moment but somehow I got the wheel size and the rotor size mixed up. Must have been a bad day
It happens. Just don't let it happen again. haha
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  #71  
Old 07-30-2009, 12:49 AM
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19" rotors would require 24" rims or larger right? lol

bet you could turn a lot of heads with 19" rotors
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  #72  
Old 08-05-2009, 08:08 AM
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Yes you would assume so since you are likely what 300lbs lighter or more? Not sure what the 02 GT's weigh; plus you have alot less weight on the nose of your car than I do on my 03 cobra.
Just to jump to the top for a moment, I don't think that this little tidbit can be overstated enough. I'm autocrossing a v-6 mustang right now simply because the horsepower is less limiting than having front end weight (on a short course). When I put the Kenne Bell on the 99 GT the handling totally went down the dumper (adding about 75 lbs) adding the IRS improved things (about 80 libs to the rear) and helping to balance the car but I still needed the most massive front (over 1 inch) front sway bar that I could find to prevent oversteering, stopping was never an issue for the courses we run, but it would most certainly jump out at you on a longer course with less down time or on a road course.
Let's face it, it's a fun car for the highway, but you generally don't make a competitive race car by adding weight, hence the V6. Smaller engine, less weight up front. smaller brakes (less weight), stick axle, manual trans, etc.
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  #73  
Old 08-05-2009, 08:58 AM
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You don't nomally correct oversteer (loose) by adding cornering stiffness to the front, you do it by putting on a weaker sway bar (or springs in extreme cases) in the rear. If you're trying to decrease understeer or plow in the front (push) then you can put in a little more negative camber, positive caster and add front sway strength (you can also put a little toe-out in the front end to make it turn snappier). If you're trying to make the car looser you can add spring to the back.

GT brakes are perfect for most street driven v6's but GT's are seriously under-equipped with stock brakes. With the right pads they're good for autox. Longer events would be hard on rotors.
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  #74  
Old 01-12-2010, 09:09 PM
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I do open track events and nothing is scarier than looking at a 25 mph 90 degree left hand corner and feeling the brake pedal just sink all the way to the floor while the speedo slowly oozes south of 80mph. Downshifting into 2nd and awesome tires saved the day, but bigger brakes have been near the top of my list of things to do for a long time. Good post
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  #75  
Old 01-14-2010, 03:46 AM
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I don't even think the Cobra, bullitt, Mach1 setup is good enough for track events. But for a budget upgrade for the cheap price its defiantly a better step up from stock.
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  #76  
Old 07-22-2010, 04:42 PM
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edit: I posted that in the wrong thread due to aimless clicking.

Oh well, I need to pick up cobra brakes for my car at some point. There, on topic

Last edited by 330ciJarryd; 07-22-2010 at 06:24 PM.
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