Hawk HPS vs Carbotech 1521

[The WidowMaker]

im looking for new pads for my c6 z06 calipers. id like a pad thats pretty quiet on the street but works very well on an autocross as well. i talked to carbotech and they said that their ax6 (autox) pad would squeal like hell on the street. ive also read that the hawk hp+ will do the same. both the 1521 and the hps are semi quiet pads. any reviews on either compound?

im also debating the newer 8 full pads vs the 20 padlets. i know the larger pads have about 20% more friction surface, but most claim that this doesnt equate to more braking ability. they might help the brakes run a little cooler since they can dissipate more heat. any thoughts on this? it seems to me that although the amount of force as a whole isnt changed, the pad is making more contact at a lighter pressure (per sq in) and may be more effective.

im also wondering if the extra pedal pressure required to stop my car may limit the squealing. i have about 800lbs on the car these brakes were initially designed for.

the four choices i have are;

hawk hps padlets, 200
hawk hps full pad, 300
carbotech padlets, 400
carbotech full pad 500

its a pretty big swing between the hawk padlets and a carbotech full pad. any suggestions?

[6spdcamaro]

I have used the hawk HP+ compound, and the noise isn't as bad as I had expected. It only squeaks at low speeds under light pressure, approaching a stop sign or light. But they are very dusty, so if you plan on doing a majority of street driving I wouldn't recommend them.

Pad surface area has no effect on braking force. The 1 piece pads should be a little larger, and therefore may be able to absorb more heat, but I'm not sure how much of a difference they make. I'm not sure how the z06 calipers are constructed, and how a pad change is done, but the 1 piece pad might make it more difficult to change? Also not sure, but something worth looking into.

I believe the reason the z06 calipers use padlets instead of 1 piece pads like most calipers, is to minimize tapered pad wear. This is why most high quality aftermarket calipers have different piston sizes across the caliper, as it helps the leading edge of the pad from wearing more quickly than the trailing. GM tried to accomplish the same thing by using the same size pistons and individual pads, most likely for cost reasons. If you scroll down the stoptech page explains (better than I could) tapered wear on a more detailed level.
http://www.stoptech.com/tech_info/wp_brakesystems_upgradeselections.shtml

Depending on the kind of driving you are doing, I would probably use the Hawk hps padlets to save some money and possibly get more pad life by wearing more evenly.

I'm curious as to what other people on here think about the padlet vs 1 piece pads. It seems to be a debate that, at least on corvette forums, doesn't have a definite answer. Have you talked to tobin in relation to that?

[The WidowMaker]

Pad surface area has no effect on braking force.

i understand the physics, but this means that each in^2 of the pad is applying less pressure. my thought would be less pressure for a given pad may allow it to squeal a little more. case in point, the bobcats on the mitsubishi evos. carbotech claimed that the evos brakes were too efficent and therefore required very little pressure to brake the car. they said that this, coupled with a thin rotor, was causing excessive squealing on their application. their solution was to brake later and harder.


I'm not sure how the z06 calipers are constructed, and how a pad change is done, but the 1 piece pad might make it more difficult to change? Also not sure, but something worth looking into.



they are. with the padlets you can remove the torx bolts and change pads without removing the caliper. all the single pads require the caliper to be removed.


Have you talked to tobin in relation to that?

i havent. i hope he chimes in though.

[68sixspeed]

for the money if you can find a set of GM z06 pads (take-offs, check corvetteforum.com) they are a bit less aggressive than the HP+ and are quiet. The HPS are actually a bit softer than the stock GM pad. HP+ will squeek at low speeds, you can get around it for a little while by gooping the backs of the pads with the anti-squeel compound. That being said on just put the z06 calipers on the 68 and I put my HP+ pads from tracking the z06 last year on the rear, fresh 1pc hp+ pads on the front. -Dan

[The WidowMaker]

for the money if you can find a set of GM z06 pads

im actually ditching the stock pads. i bought the calipers loaded, but have read way too many negative reviews on the stock pads. maybe it makes guys feel better to think that the aftermarket pads are better, but ive read mostly about less dusting, less fade and increased stopping power.

if i buy the closest thing to the stock pads, im only out 15 bucks. but ive actually been thinking about dropping the money on the carbotechs and picking up a set of the xp8s to run during events that contain the short road course. if i did it this way i wouldnt have to prep the rotors between pad swaps and id most likely leave the 1521s in the rear.

[68sixspeed]

I'm with you, I never tracked my z06 with the stock pads or w/o adding full cooling ducts etc. But then one of my instructor friends took a bone stock z06 and ran the tar out of it for many events on the stock pads, sometimes running two drivers per day so that's a couple hundred track miles. They are a pretty capable pad that doesn't squeek. The GM pad does make more dust than the HPS, but less than the HP+ as well. I have a friend who likes a XP10 front XP8 rear combo for track days w/slicks but the 8's or 10's might be a bit much with street tires (lots of lockup), more of an issue without abs! -Dan

[Payton King]

I run AX6's all the way around on my car for street and autocross. They are a little dusty, about like a stock BMW but mine do not squeak at all. For track, days I change the fronts to XP10's and I am running street tires. Ran them at Gingerman last year and they were fantastic. My car is a solid axle rear and not a corvette IRS, why the big drop between front and rear pad compound to keep the rear from hopping. I have not tried the Hawks. Happy with the Carbotechs.

[sik68]

If you are doing purely autox, you might want to try out the stock pads (padlets) you have already. Autocross braking does not introduce nearly the heat that road courses do.

[The WidowMaker]

I run AX6's all the way around on my car for street and autocross.

i read that during a search and was going to send you a pm. im really surprised that they dont make noise based on other reviews. what is the rest of your braking system? power or manual brakes? how much do you autox them?


If you are doing purely autox, you might want to try out the stock pads (padlets) you have already. Autocross braking does not introduce nearly the heat that road courses do.

they are actually already sold and being shipped out today.

Thanks for the replies though. if i can get a few more guys that run the hp+ or ax6 i could be convinced.

[Apogee]

The pad area and volume of the C6 Z06 front calipers is very close to that of the FMSI D731 spec pad used in the 2-piston C5/C6 calipers. This means that while your calipers are much larger and slightly more rigid, your pad contact pressures are very similar assuming the same hydraulic system driving it. The downside relative to a more conventional monoblock caliper (Brembo, AP, Alcon, etc) is shorter pad life, something that the 1-piece Carbotech's tend to improve upon...plus, they make good pads, period. Since I never change the pads using the GM prescribed method of removing the pad guide pins, that's not an issue for me. I'd rather pull two bolts versus 6 or 8 pins any day. If you don't pull the caliper off the rotor, retracting the pistons is more of a chore as is fighting the anti-rattle springs when installing the pads in my experience.

We initially had issues with the C6 Z06 pads not wearing consistently from pad to pad, which when combined with their cost, pushed us to run the HPS pads for street/auto-x applications most of the time. While the HP+ are dusty, they are still a solid choice for those looking for a pad that can be run on the track just as easily as the street. Noise seems to vary from car to car, but my personal experience has been that they typically only squeal at light pressures, especially when cold. If/when you get to the point of running dedicated track tires, that's when you should consider swapping pads/rotors as well. You won't beat dedicated track pads in a track environment.

Tobin
KORE3

[Payton King]

Wilwood 6 piston front on slotted 2 piece 13 inch rotors front and 4 piston rears. Twin master cylinder with balance bar, obviously manual. I got the AX6's becasue I wanted a pad that was high bite cold since I have manual brakes. I found other pads (BP10's from Wilwood) to not stop 1/2 as good cold. My personal feeling is the BP10's are great for a power brake car, but they did not give me the performance I was looking for. Most of the autocross that I have done, I do not feel I generated that much heat in the 30-50 seconds it takes to make a run that I would need more than a street pad. I have not tried the 1541 (bobcats) but I plan on putting those on the wife's M3 which is strictly a street car.

I can tell you that you can get too much pad. While I was trying to find a pad that I liked, I tried a set of Wilwood race pads "B" compound. Where I could not get the BP10's to lock at 40 mph, I could get the "B" to lock at 80 mph. Way too much for a street tire, but would work well with race rubber. They were also very hard on the rotors from the short drive I did.

come to think of it, the only time I can get the AX6's to make any noise is when they are hot and I am stopping with the lightest possible pressure...as in rolling through the neighborhood at 20 mph slowing for a stop sign.

[The WidowMaker]

thanks for the responses guys.

payton, im also running manual brakes with dual masters and a balance bar. have you ever had any regrets with the ax6 on the back, or do you feel it compliments the fronts? im almost worried that the bite might be too agressive and i worry about locking the rears up before the fronts. do you think they make noise equally under those light stops, or do you think its coming from one end more than the other?

[Payton King]

Comes from the front for sure. When you have dual set-up, you will size the masters according to your caliper piston area, pedal ratio and desired caliper line pressure and leg pressure. They most likely will be differnent sizes for the front and rear. My Wilwood stuff is almost the exact size as the stock C5 calipers. Car is probably 3500 lbs with me in it and I ended up with .70 (7/10)front and .75 (3/4) rear using tilton mc with a pedal ratio of 6:1. With a little over 100 lbs of pedal pressure I can generate 1200 psi front and 950 rear with the balance bar in the center. may take a little trial and effort to get the MC size dialed in, but very easy to tune from a front rear balance with the balance bar after that. No problem what-so-ever with rear locking first...tuned that out. Only reason to go to 2 different compounds is with a solid axle car on the big track you may get a little wheel hop in the rear because so much of the braking is done at the front. Not too many places on the street you will be hammering your brakes at 120 mph trying to slow down for a corner. Actually I did not need to change my brake bias going from AX6's all around to the XP10's front and AX6's rear.

Kind of told you how to build a watch when you asked me what time it was. I would do AX6 all around especially given you car is manual brakes and the weight for street and autocross, unless you do not like brake dust.

[Flash68]

Is a balance bar the same thing as a proportioning valve?

[Ron.in.SoCal]

Tobin will probably correct me on this: Technically, no. It does the same thing, but is not the same thing. Accomplishes the same result of metering fluid pressure to the front or rear brakes. Balance bars are seen more in race set ups and are more frequently making their way into PT type builds.

[The WidowMaker]

Is a balance bar the same thing as a proportioning valve?


i once called tobin and asked him and the explanation went WAY over my head. maybe someone can put it into words or has a good link.


Kind of told you how to build a watch when you asked me what time it was. I would do AX6 all around especially given you car is manual brakes and the weight for street and autocross, unless you do not like brake dust.

thanks for the help. i dont like dust, but i'll take it if necessary. i really want to stay away from the squealing though. it kind of goes back to when i first met my wife. big cam 350 with delta 40s. she thought my car was broken.

i think im now trying to decide whether to run the 1521 on the street and get some xp8's for the track or just give the ax6s a try all around. if they were 200 a set i would give it a shot. 500 is another story for me. im with you on the manual brakes though. the extra bite would be really nice.

[Flash68]

Tobin will probably correct me on this: Technically, no. It does the same thing, but is not the same thing. Accomplishes the same result of metering fluid pressure to the front or rear brakes. Balance bars are seen more in race set ups and are more frequently making their way into PT type builds.


i once called tobin and asked him and the explanation went WAY over my head. maybe someone can put it into words or has a good link.


Thanks guys..... Tim, if it was over your head, I'd hate to think what it would sound like to me. LOL

[Payton King]

A balance bar is basically a bearing with a threaded shaft running through it. There is a sleave on the brake pedal that this assembly goes in. The push rod of the master goes on each side of the threaded shaft with the bearing and brake pedal in between the 2 masters. As you turn the adjustment shaft (threaded rod) the fulcrum point moves to the left or right. If it is in the center and pressure is applied, there will be equal force on both MC's. If you move the bearing closer to one master cylinder you will increase the force to that master cylinder while lessening the force on the other. Think using a pry bar moving an object.

Proportioning valve as you tighten reduces/resticts pressure....similar to above but different

If you were closer, I would let you drive my car and see for yourself. By the way, when I was at Motor State I was too lazy to switch pads from track to street. Ran all weekend on XP10's and AX6's in rear and got very little noise with that set-up on the street.

[Apogee]

I'll see if I can come up with some pictures/graphs since I know a picture can be worth more than a thousand words, but as has already been stated above, a balance beam and proportioning valve are not the same thing. That said, they do both serve basically the same function which is to adjust front to rear brake bias such that the fronts lock just before the rears in a typical installation.

A balance beam is a simple, mechanical device that can be used to increase or decrease front or rear caliper pressures relative to one another when using a dual master cylinder configuration. Once the bores sizes of the MC's are set and the balance beam is adjusted, this front to rear ratio is constant, regardless of the pressures and/or deceleration rates. Because cars transfer weight differently based on the deceleration rate, with more weight being transferred at higher deceleration rates, you would normally tune your balance beam for maximum the deceleration rate that your tires can handle. This means that your brakes are optimized for maximum deceleration, exactly what you want in a track environment. When doing anything less than maximum braking, you will however be underutilizing your rear brakes/tires.

A proportioning valve works differently in that it allows full pressure to the rear brakes until you reach a set point. This means that you maximize your rear brake use at low deceleration rates commonly found in street driving as well as with various loading, weights, etc which comes with hauling multiple passengers and cargo. Most OE units are fairly conservative as you would expect. The pressure set point in these valves is typically fixed at a certain pressure in an OE style proportioning valve, but can be moved up or down in an adjustable unit. How much pressure decrease occurs depends on the geometry of the armature inside the valve, however the aftermarket industry standard seems to be such that you can achieve a maximum pressure reduction of 57% line pressure, assuming you move the set point to zero pressure so that it is immediately in effect. The adjustable prop valves are not meant to fix huge component mismatches and using them as such typically does not yield the best results.

Sorry it's not the best explanation, but this topic definitely deserves some FAQ attention or something along those lines.

Tobin
KORE3

[Ron.in.SoCal]

^ And there you have it. It's what he does...!

[Flash68]

Yes thanks very much for the explanation.

Sorry for the little detour there. Back to some pad comparisons!

Once I am ready to upgrade from the Wilwood pads that came with my brakes (I thought they did pretty well at RTTC actually) I am leaning toward the HP+ on the recommendation of Dave Pozzi.

[The WidowMaker]

Because cars transfer weight differently based on the deceleration rate, with more weight being transferred at higher deceleration rates, you would normally tune your balance beam for maximum the deceleration rate that your tires can handle. This means that your brakes are optimized for maximum deceleration, exactly what you want in a track environment. When doing anything less than maximum braking, you will however be underutilizing your rear brakes/tires.



this is the part i was having trouble understanding. that clears it up again.

[The WidowMaker]

i ended up getting the ax6 full pads and they got here today. im still waiting to see if im keeping them since there was a slight error on the part of the company i ordered them from. i am supposed to hear back tomorrow.

its going to be a little while before i actually use them, but im thinking that squealing will be minimized with the manual brakes and increased pressures required to slow my car down. i have a few pounds on the z06 they were designed for.