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Old 11-29-2010, 05:10 PM   #121
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Originally Posted by ZX-Tex View Post
That will do it. Energy goes up with the square of the velocity. E=1/2mv^2.
This is true but I think not always but many times you can find if you put two drivers in the same performance level of car the faster more consistent driver will be the one who is less hard on the brakes.

Having said that I will also say there is getting to be a larger number of really fast miatas that simply can't be driven near there potential with brakes that would work fine on a spec miata due to the difference in speed at the end of straights.

Bob
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Old 11-29-2010, 05:15 PM   #122
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I notice a lot of people run lesser pads in the rear (XP12/10, XP10/8, etc). Is there a specific reason for this? I see NA chassis lock up the fronts all the time, so it seems counter-intuitive to do so. I have an issue w/ mine under braking so I am trying to figure it out.
I wonder why this is as well. If you look at the torque curves it seems like this just makes the front lock up even worse. My brakes always feel the best running the same compound on all 4 corners.

Bob
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Old 11-29-2010, 09:49 PM   #123
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I wonder why this is as well. If you look at the torque curves it seems like this just makes the front lock up even worse. My brakes always feel the best running the same compound on all 4 corners.

Bob
Sorry if you already mentioned this but, what compound are you running.
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Old 11-29-2010, 10:01 PM   #124
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Sorry if you already mentioned this but, what compound are you running.
9 posts ago, he even mentioned it while replying to one of your questions.
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Old 11-29-2010, 10:10 PM   #125
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This is true but I think not always but many times you can find if you put two drivers in the same performance level of car the faster more consistent driver will be the one who is less hard on the brakes.
True. There are many variables but I was trying to keep it simple. But, all else being equal, for the sake of illustration, if someone approached a corner twice as fast, and slows to the same entry speed, the brakes will need to absorb four times as much energy. Point being, small changes in the delta-v result in large increases in thermal load.

Brakes have to deal with a lot of power, or put another way the energy conversion rate of kinetic to thermal energy. For example earlier this year I calculated the average power an F1 car dumps into the brakes when braking at the end of the back straight for a hairpin at a particular track. I forget the exact numbers, but Hamilton's car slowed from ~195 mph to ~60 mph in less than 3 seconds. Mindblowing. The average power output of the brakes was some ridiculous number that I cannot remember for certain so I won't post it. It was on the order of tens of thousands of horsepower.

Last edited by ZX-Tex; 01-04-2011 at 06:33 PM.
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Old 11-30-2010, 12:04 AM   #126
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For an example using numbers attainable by us mere mortals... a stock NA with full interior and street tires will trap in the ballpark of 100 mph at the end of the front straight at VIR. An FM-II'ed 1.6 I know pretty well is trapping about 130 (indicated) on a "paltry" 210 whp, so after I strap on the Absurdflow I don't think it's unrealistic to assume a ballpark of 135-140 mph. Going from 100 to 140 is darn close to twice as much energy dumped into the brakes (1.96x). I know I'm mostly preaching to the choir in this thread, but impressionable noobs are reading too.
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Old 11-30-2010, 11:25 AM   #127
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9 posts ago, he even mentioned it while replying to one of your questions.
Ooops, its easy to miss a post or two with my blackberry. Thanks
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Old 11-30-2010, 03:47 PM   #128
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FWIW I have been getting like 5 or 6 full track days out of a set of Cobalt Friction XR2's....I am using uses pads that are 15.2mm thick as appose to 12.4mm like most of the Miata Dynalitght kits....Iím almost certain you will get more life out of the cobaltís
Bob, what are you paying for XR2s? Retail on the DTC70s is like ~$80 and I am getting ~3 track days out of a set (depending on where I drive). I'm fine with a pad that lasts 70% as long provided it's 50% of the cost.
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Old 11-30-2010, 05:50 PM   #129
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Bob, what are you paying for XR2s? Retail on the DTC70s is like ~$80 and I am getting ~3 track days out of a set (depending on where I drive). I'm fine with a pad that lasts 70% as long provided it's 50% of the cost.
I'm getting them from Adrenaline racing. Seems like they were a little over $100. I can’t remember now. I did 5 track days on the set I have now but not all of them were full track days where I did all the sessions. They lasted all season and still have half the life in them. They were new for the two days at Laguna and that hardly put any wear on them.

Also keep in mind that the Dynapro pads I’m using for the Mini Kit are a total of .6” thick where the Dyna lights or the DP6 are .49” thick. By the time you back out the backing plate thickness and a minimum wear thickness it is a little over 25% more life just due to usable pad thickness avalible to wear down.

Bob
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Old 11-30-2010, 06:32 PM   #130
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XR2s for Dynalites go for $119. The dimensions of the Forged Dynalites call for the 12.5mm pad thickness, which would be part number CRB.XR2.RC6-12.5MM for cotter-pin calipers like the 120-6806. Interestingly, the XR2s do also come in 16mm for the same price, but it looks like those thicker pads only work for certain Dynalites such as the radial-mount Dynalites or the Forged "Narrow" Dynalites. Looking at the sketch for 120-6806, based on subtracting half of the disc width from the mount offset it might actually accommodate a hair thicker than 12.5mm, like maybe 14mm, but I'm not sure those diagrams show every relevant clearance point for the pads so somebody would probably have to have parts in hand to determine that for sure. In any case they don't appear to make an off-the-shelf pad between 12.5mm and 16mm.

Clearly I am thinking out loud and rambling a bit, but I just find it interesting that Cobalt doesn't appear to charge any more $$$ for additional pad thickness, and that appeals to my inner cheap bastard.
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Old 11-30-2010, 06:43 PM   #131
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XR2s for Dynalites go for $119. The dimensions of the Forged Dynalites call for the 12.5mm pad thickness, which would be part number CRB.XR2.RC6-12.5MM for cotter-pin calipers like the 120-6806. Interestingly, the XR2s do also come in 16mm for the same price, but it looks like those thicker pads only work for certain Dynalites such as the radial-mount Dynalites or the Forged "Narrow" Dynalites. Looking at the sketch for 120-6806, based on subtracting half of the disc width from the mount offset it might actually accommodate a hair thicker than 12.5mm, like maybe 14mm, but I'm not sure those diagrams show every relevant clearance point for the pads so somebody would probably have to have parts in hand to determine that for sure. In any case they don't appear to make an off-the-shelf pad between 12.5mm and 16mm.

Clearly I am thinking out loud and rambling a bit, but I just find it interesting that Cobalt doesn't appear to charge any more $$$ for additional pad thickness, and that appeals to my inner cheap bastard.

The thicker pad material wont fit unless the caliper was designed for it in conjunction with a given rotor thickness such as the radial mount Dyna-Pro found in the Mini-Cooper kit I am using on my miata.

Bob
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Old 11-30-2010, 07:57 PM   #132
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Also keep in mind that the Dynapro pads Iím using for the Mini Kit are a total of .6Ē thick where the Dyna lights or the DP6 are .49Ē thick. By the time you back out the backing plate thickness and a minimum wear thickness it is a little over 25% more life just due to usable pad thickness avalible to wear down.
The closest caliper to the 120-6806 that would accommodate 16mm pads is probably the 120-11575 Forged Narrow Dynalite. Same 1.38" piston size, same .81" rotor thickness, same outer radius, still lug mount, but uses 3.5" centered mounts instead of 5.25" so would require a different bracket. It's also 0.44" wider overall; clearly, they use "Narrow" in reference to the mount points and not the caliper body. That caliper uses the same exact (thicker) pads as your radial-mount Dynapros and retails for only $5 more than the -6806, though I could envision the additional width posing problems with wheel clearance. In any case, Sav and his existing customers might accept 20% more frequent pad changes than you require in order to keep the Dynalites they already own. I have only thought this out because I am not yet constrained by owning any fancy brake parts, and also because I am temporarily bored.
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Old 11-30-2010, 08:49 PM   #133
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I wonder why this is as well. If you look at the torque curves it seems like this just makes the front lock up even worse. My brakes always feel the best running the same compound on all 4 corners.

Bob
I ran Hawk HP+ and after a few sessions, a very slight tap of the brakes and slight turn in at the same time makes the rear want to come out, whether it be on a steeply downhill into an off camber turn or not... Does it sound like I'm missing driver skill/not being used to oversteering with the Miata or a setup issue? (this is my first track day w/ sticky street tires on the Miata, RE-11s, and I've only had all-season Falken ZE912s prior to the RE-11s so I am getting into faster speeds now obviously... I'm used to an oversteer prone FWD on the same tracks and didn't have this much of an issue)
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Old 12-01-2010, 12:05 PM   #134
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Originally Posted by Savington View Post
Bob, what are you paying for XR2s? Retail on the DTC70s is like ~$80 and I am getting ~3 track days out of a set (depending on where I drive). I'm fine with a pad that lasts 70% as long provided it's 50% of the cost.
Sav,

I'd recommend the XR1 for you. All of our SCCA cars run on XR1s, from a T3 S2000 to a SSB Civic Si. I don't think the XR2 will be aggressive enough for you.

In my experience Cobalt >> Carbotech. The owner of Carbotech has been trying to give us pads for years but we've been buying Cobalts instead because they have been that much better for us. I can't comment on how they compare to Hawks DTC compounds, I don't have any experience with them.
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Old 12-01-2010, 06:04 PM   #135
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I ran Hawk HP+ and after a few sessions, a very slight tap of the brakes and slight turn in at the same time makes the rear want to come out, whether it be on a steeply downhill into an off camber turn or not... Does it sound like I'm missing driver skill/not being used to oversteering with the Miata or a setup issue? (this is my first track day w/ sticky street tires on the Miata, RE-11s, and I've only had all-season Falken ZE912s prior to the RE-11s so I am getting into faster speeds now obviously... I'm used to an oversteer prone FWD on the same tracks and didn't have this much of an issue)
Hawk HP+ will be a complete failure on a car like Sav's or mine. pretty easy to get them above their comfortable temp range and the fronts will get there first leading to too much rear bias.

This brings up a good point. Perhaps the reason for running worse pads in the rear is people are not using good enough pads in the front.

This is not a problem if you are running good track pads on the track or good street pads anywhere else. Cobalt pads will work on glowing red hot rotors without much degradation in feel at all.

Bob
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Old 01-04-2011, 06:28 PM   #136
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FYI I just ordered a set of Cobalt XR2 pads and a new set of Corrado rotors for the front. I'll be trying them out at the next trip to the track. This is one last try to get the offset stock calipers and Corrado rotors to work before I spend the big money on the BBK.

That or I could just get some huge Hoosiers so I do not need to brake at all
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Old 11-24-2011, 11:52 AM   #137
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Looking for an update as I want to buy a set of pads that are only used for the track.

What are the opinions now almost a year later. Cobalt vs Hawk DTC60/70

For me, the cobalts sound appealing since I can swap back and forth from street pad to track pad without swapping rotors. I haven't researched enough to see if the hawks are the same.

So, have any Hawk guys converted to cobalt or vise versa???
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Old 11-24-2011, 01:45 PM   #138
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I wouldn't mind trying a set of cobalts, but I still love the DTCs. I switched the rental from XP12s last month and just slapped the pads on without swapping rotors- it went fine and the modulation/bite is perfect.
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Old 11-24-2011, 02:17 PM   #139
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I wouldn't mind trying a set of cobalts, but I still love the DTCs. I switched the rental from XP12s last month and just slapped the pads on without swapping rotors- it went fine and the modulation/bite is perfect.

Good to know.I just picked up a set of used XR4 pads for the rear and I plan on running the XR2 on the front. I'm not fast enough to need the XR2 in the rear. I can just turn my bias valve more towards the rear. I plan on getting a set of the XR2 for the front.

DTCs are cheaper though, and it's nice to here that you could just slap them on and go.
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Old 03-06-2012, 03:09 AM   #140
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I know it's an older thread, but had a question regarding the Cobalts. How far do you run them down to? I ask because I thought I had plenty of life left in a set, but when I took them out to inspect them you can see the "rivets" that hold the pad material to the backing plate. There doesn't seem to be any grooves in the rotor, but I've just never seen rivets in a brake pad. All of the brake pads I've used on my old Evo I could run almost to the backing plates and never noticed any rivet things.
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