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New review of AP Racing BBK from Urge Designs

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Old 03-09-2015, 10:39 PM
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Default New review of AP Racing BBK from Urge Designs

I purchased the AP Racing BBK from Urge Designs over a year ago. Since then, I have participated in 22 HPDE days at CMP, VIR, RdAtl, BMP, and AMP. I have only used one pad in that time, and it is the same pad I used on my OEM brakes, Ferodo DS1.11, therefore, I can eliminate the variable of different pads from contaminating my results. My driving skills have gone from novice to advanced in that same time, so there is something to consider with this. My ability to truly understand the difference between OEM and BBK was based on novice skills at the time I made the change (and now that I am an advanced driver, I’m not going to put the OEM kit back on to compare them again). Therefore, this review is perhaps better suited for novice drivers looking to improve their braking system and stopping ability.

The AP Racing BBK differs from the OEM in two major ways, consistency and durability.

My first point is a fact you can find in any high school physics book. Though it is difficult to believe, the size of the brake pad has nothing to do with stopping force. Stopping force = coefficient of friction (Mu) x applied force. Surface area is not in this equation. Therefore, if you want to increase your stopping power, you should ultimately change your pads. But don’t run off to read the pad reviews just yet. Novice track drivers need to be more concerned with consistency than stopping power – consistency throughout each stop and consistency from lap to lap. Here, calipers, rotors, and pad size make a huge difference because the coefficient of friction of the pad material changes drastically depending on its temperature. Small OEM calipers hold small OEM pads with tiny thermal mass, and the small OEM rotors with small thermal mass and small vents that dissipate less heat. While braking, momentum is converted to heat energy, and less thermal mass means small brake pads get much hotter per unit of mass and their coefficient of friction (Mu) changes dramatically as does stopping force. So your high school physics book was technically right; surface area is not directly related to stopping power, but in real applications, it is indirectly related as heat impacts Mu. The other variable is the applied force (in this case pedal pressure transferred hydraulically) and excessive heat can boil the brake fluid causing the applied force to drop (this is an ugly can of worms I don’t want to open, but suffice it to say, better heat management = more consistent stopping all around.)

Sorry for the physics lesson, but this is extremely important. The fact is, my OEM system stopped just as hard as my BBK …on the first stop of my session. As I added laps, heat built up, and I started experiencing brake fade, so I had to increase my brake zone throughout the session. This is exactly the opposite of what a novice driver should be doing. As a novice driver, I needed to focus on my threshold braking skills and shortening my braking zones. I needed to gradually shorten the brake zone with each lap based on the previous lap’s stopping distance. For this exercise, I clearly needed to have consistent braking. (Only change one variable at a time, in this case, driver skill – not Mu.) All too often, I read about people trying to solve brake fade by changing the pad material, but changing pad material changes every variable except heat management (the one that matters the most). Mu, heat generation, and consistency all change when you change pad material causing a setback in the learning process. Now I have much shorter stopping distances than most other cars I encounter on track. Physically, this is a function of the pad material - and that has not changed since I had OEM brakes. Mentally, this comes from confidence, and confidence comes from knowing my car will stop precisely as hard this lap as it did the last. Now that I am a fairly consistent driver and have consistent heat management, I can change a new variable – different pad material. Actually, I reached this level long ago thanks to the consistency of the AP Racing BBK, but I’m just now using up my first set of pads ...which brings us to durability.

Durability is directly related to heat management too. In general, pads wear out faster when they are overheated. Small OEM pads overheat more quickly and thus wear out faster (decreasing their thermal mass) therefore getting even hotter faster ...see where this is leading? Obviously, BBK pads are much larger to begin with, so there is more material to wear; less obvious is that the BBK system keeps the heat down, so the pads literally wear slower. (Note, this is why even BBK race pads start to wear quickly as they get thin – under 3/16” check them after every session)

For comparison, I went through a set of OEM-size Ferodo 2500 in two days at CMP, and Ferodo DS1.11 only lasted 2 days at CMP plus 2 days at VIR (~1/8” remaining when I changed to BBK). After changing to the BBK, I did 20 days on the Ferodo DS1.11 (one pad was down to the backing plate and the others were close). The rotor is starting to show wear toward the center but the full J-hook is still fully visible – no cracks. I have not done the math, but I expect am close to paying for the kit in wear-part savings.

Other points: The kit is designed extremely well, but you can read all the technical details on other reviews. Several highly advanced drivers have written very detailed reviews of the technical aspects, and I encourage you to read them even if they are too technical at this point. One member did a detailed cost analysis, with projected ROI. The Urge and AP Racing webpages also have a lot of good information. In particular, watch the AP Racing video on bedding brake pads - http://www.essexparts.com/learning-c...ds/post/Bed-in (you’ll never run track pads on the street after learning the difference between abrasive and adherent properties.)

Drawbacks: A minor drawback is that the pistons are harder to compress when you need to change pads. There is no fancy tool to push them in like with the OEM, but this is probably the case with any opposing-piston system. Wheel fitment can also be a disadvantage depending on your objective. The ever-popular Enkie PF01 8” fits with ~2.5mm to spare (I ran this setup for 20 track days). However, when I started looking for wide square wheels and keep the wheels inside the OEM fenders (to meet Honda Challenge HC1 guidelines,) my options got very limited. I ended up getting the CWW wheels from Urge, and I am very happy with them too.

In summary, I have consistent braking after 40 minutes on track, it helped me to make huge improvements as a student, and the quality is top-notch. AP Racing BBK increased my pad life by ~5x. If you are just starting to track your car, I highly recommend this setup. It will help you improve your skills, and over time it pays for itself. I recommend them to every S2000 owner I meet at the track, and now that I am allowed to carry passengers they are welcome to experience them from the right seat (brown pants recommended). Discuss your skill level and tracks with Patrick - he can help you select a good pad material.
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Old 03-10-2015, 05:47 AM
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Likely, a tool like this will help during pad changes.

To further expand upon the wheel fitment, you will be hard-pressed to find a 9" wheel to fit around the calipers. I believe a 20-25mm spacer is necessary on a 17x9+63 CE28N or a 17x9+63 6ULR, based upon the caliper template. While some people will run lower offsets, or wider wheels, the risk of putting the tire into the fender is increased.
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Old 03-10-2015, 06:32 AM
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The Weds TC105N 17x9 +49 barely clears the kit. I normally use the handle end of my ratchet and the rotor as leverage to easily push in the pistons on multi piston calipers like these.
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Old 03-10-2015, 09:43 AM
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How did it affect brake bias? I really like the design of the kit, but I want increased front brake bias and I'm concerned that without increasing rotor diameter (and getting the resulting increase in leverage/torque), brake bias won't be affected much on the Essex kit.
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Old 03-10-2015, 10:56 AM
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I have same material front and rear, and this setup is very well-balanced with OEM rear brakes. I have not introduced other variables yet. At some point I want to play with unbalanced Mu front/rear. Again, heat management is paramount here. If I increase the front bias, I need to get rid of more heat in the front for Mu to remain constant lap after lap. This is what the AP Racing BBK does best.

One advantage of smaller rotors is less angular momentum to accelerate/decelerate (wasted energy). With low-HP cars, this can be noticeable. Check out this entertaining explanation by a NASA Propulsion Lab engineer as he explains how angular momentum robs a classic momentum car of speed. http://youtu.be/-RjJtO51ykY
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Old 03-10-2015, 11:58 AM
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Originally Posted by will010100 View Post
Drawbacks: A minor drawback is that the pistons are harder to compress when you need to change pads. There is no fancy tool to push them in like with the OEM, but this is probably the case with any opposing-piston system.
Remove one old pad. Flip it 90 degrees and stick back in center. The width of the backing plate will hit both pistons. Then just apply pressure to the end sticking out and it will retract both pistons.

99SH (user on here) bought an actual tool to do it which is pretty slick, but iirc it was $$$.
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Old 03-10-2015, 01:04 PM
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I was thinking of running these under 17x9 +49 Weds TC105N, would a 1-2mm spacer be recommended? I know I can get off the shelf 3mm spacers but I am already so close on fender clearance I was thinking of having some super slim ones made.
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Old 03-10-2015, 03:07 PM
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Originally Posted by will010100 View Post
One advantage of smaller rotors is less angular momentum to accelerate/decelerate (wasted energy). With low-HP cars, this can be noticeable. Check out this entertaining explanation by a NASA Propulsion Lab engineer as he explains how angular momentum robs a classic momentum car of speed. http://youtu.be/-RjJtO51ykY
Right, that's exactly why I like the Essex/Urge design: Reduced rotational inertia. But I already have a BBK on the rear that increased rear bias (stock caliper on much larger rotor) so I want to balance that out. I suppose I could run staggered mu pads.
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Old 03-11-2015, 12:17 PM
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Originally Posted by carrnut21
I was thinking of running these under 17x9 +49 Weds TC105N, would a 1-2mm spacer be recommended? I know I can get off the shelf 3mm spacers but I am already so close on fender clearance I was thinking of having some super slim ones made.
I've read that wheel works without spacers, but I have never tested it, so I cannot say for sure. Be careful that you don't create a fender problem as you solve a caliper problem.

What I can say for certain is Patrick has a list of wheels that work and is very knowledgable. Perhaps he can comment or you can reach out to him.
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Old 03-11-2015, 12:23 PM
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Originally Posted by will010100 View Post
One advantage of smaller rotors is less angular momentum to accelerate/decelerate (wasted energy). With low-HP cars, this can be noticeable. Check out this entertaining explanation by a NASA Propulsion Lab engineer as he explains how angular momentum robs a classic momentum car of speed. http://youtu.be/-RjJtO51ykY
Couldn't the inverse be true as well... takes less effort to slow the assembly down since it's further away from the center? Less effort, less friction, less heat, etc, etc?
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