IceY2K1

iTrader: (3)

Anyone catch the Car&Driver "Boost"..."Small Cars--Fast Parts" Premiere Issue Spring 2004 currently on news stands about BBKs?

I don't have time now to regurgitate the whole article, I will try later, but they brought up some VERY interesting points especially considering the NEGATIVE impact of dramatically increasing FRONT braking force only without changing the rear braking force or at least bias.

Basically, they used an EXAMPLE that if you have a 50/50 static front-to-rear weight distribution, 100in wheelbase, 24in center of gravity, that with 1.00g of braking you'll end up with a 74/26 dynamic front-to-rear weight distribution. Also, that in this scenario there must be 2500lbs of braking force acting on the car to hit 1.00g. So, using the 74/26 dynamic-weight distribution split that translates into 1850lbs for FRONT and 650lbs for REAR.

Now, with a sample BBK, it generates 62.7% more FRONT braking force then stock, which drives the front tires to lock up at much lower brake-line pressures compared to stock. They then ASSumed that if the stock brakes originally reached lockup at brake pressures of say 1500psi, that the new BBK would reach the lockup point at only 922psi. The FRONTs must still generate 1850lbs of braking force at the contact patch, but now the REARs aren't doing much besides just "going along for the ride".

Then the proportioning valve comes up and they say REAR brakes typically never see brake pressures as high as the FRONTs, however they're still important. Using a typical proportioning valve as an example, they calculate that if the FRONT brakes are at 1500psi, the REAR will be at 875psi for STOCK, but now for the BBK, FRONTs are at 922psi and the REAR will be at only 586psi. This means that instead of generating 650lbs of braking force when the FRONTs lock up, the REARs will only be generating 435lbs of braking force. Adding it all together the TOTAL overall braking force for the vehicle went from the STOCK 2500lbs(1850front/650rear) to the BBKs 2285lbs(1850front/435rear) for a maximum deceleration from STOCK 1.00g down to only 0.91g or a 9% decrease. They also say that although it may be surprising that a 62.7% increase in FRONT brake output only generates a 9% increase in stopping distance, however you must consider the rear brakes only contribute 26% of the vehicles total deceleration. A 9% increase in stopping distance for a 70-0mph for STOCK at 164ft, means 180ft for the BBK.

They also explain why people get so giddy about BBKs and that really what they're noticing is reduced pedal force, which makes the brakes seem more responsive, ie a little pedal effort quickly changes braking force and that *FEELS* like they're really slowing down fast, when actually they've LOST peak deceleration.

Last, they state that a properly designed BBK will take advantage of the increased torque effects of the larger rotor and be offset with caliper pistons of SMALLER cross-sectional area OR it will also include new REAR brake components to preserve force balance. If done properly, they say it *MIGHT* knock a couple feel off a stock stopping distance, but this level of performance REQUIRES testing-and-measuring equipment that FEW COMPANIES POSSESS.

Now, this whole article is assuming no ABS. However, with ABS, you take the BBKs lower 922psi lock up pressure on the FRONTs as when the ABS kicks in. So, now you must consider how stopping distance will be affected when ABS starts applying/releasing brake pressure to prevent skidding. In slippery conditions, ABS will stop shorter. On MOST vehicles ABS will stop shorter on dry pavement, however ABS is designed assuming stock wheels/tires and DEFINITELY stock braking force biasing. Of course, they build in some tolerance to account for different grip tires and varied road conditions, however increasing the front braking force 60+% and reducing the rear, I'd say probably not. I've read about how complicated it is to design ABS systems, how many variables they must take into account, and how much testing is involved for SPECIFIC biasing to prevent dangerous situations. So, I'm concerned about if it's possible that ABS systems can become "confused" or miscalculate due to BBKs, lighter rims, bigger tires, etc., causing stopping distances to further increase or just not work at all.

According to Jons' comments here, http://forums.maxima.org/showthread.php?t=309117, it sounds like ABS activation is definitely sooner which agrees with the 922psi vs. 1500psi lock up pressure theory. He also states that he's learning how to modulate the brakes better to stop shorter withOUT activating the ABS. However, I'm a panicky type of driver that *SLAMS* my brakes in emergency situations and attempts to steer clear, so I doubt I'd be able to keep it out of ABS. Yes, for normal driving this isn't a concern, but if you drive like myself and have had ABS save your azz a few times, you don't want to mess with a safety system even if it's just for "emergency use".

So, my questions are....are BBKs for ONLY the fronts worth the risk? Also, couldn't an adjustable rear brake bias valve be added to adjust more braking pressure to the rear to PRESERVE front/rear brake force balance? Would eliminating the ABS by "pulling a fuse" or something more drastic be of benefit? Wouldn't the non-300Z caliper BlehmCo BBK be a better idea, since you'd be offsetting the increased torque effects of the larger rotors as suggested in the mag article?

Finally, I'm not looking to "bash" BBKs and definitely not Matts', so keep the debate technical and the flames for other threads please.

Colonel

Wow...an interesting read there. Might have to scour the racks to go read the whole article.

Hopefully it will be raining good this weekend as I am trying to get testing done on the ABS part of the system. Doubt there is anyway I can test for "confusion", but I can test "activations and duration". Wish I had thought about this with the stock brakes on But oh well. Havea to throw it through some turns as well to see what the ABS does.

As for ABS, I understand and might be oversimplifying it, but does it really only measure the rotation (tick marks or gear) and go through an algorithm? Wow, when the sensor is on the axle itself, can bigger rims/tires make a difference. I can see how clamping force changing with a different caliper set might mess with the calc's.....

And yes, before all you doubters show up, I dont have scientific equipment.

Larrio

iTrader: (10)

interesting article and sad at the same time since I wanted to get a bbk.

I feel that disabling ABS with a maxima in this case running a bbk is not recommended IMO. My sponsor TET tuning runs a 95 maxima with the stillen two piece 13.1 inch rotor kit and he locks up his tires too easily without abs.

braking bias has always been a concern of mine, especially since I want to have track days in the future. I do wish the article would have covered vehicles that had bbk's up front and upgrade lines/pads/rotors in the rear to see if it made any difference. Not too many members only upgrade the front without doing something to the rear

also, I know for a fact that stillen has a brake testing analysis machine in their facility. They test alot of empirical evidence and collect data before selling their kits.

IceY2K1

iTrader: (3)

I don't claim to know much about ABS systems anymore. Every time I read something a new improved version comes out or you find somebody does it different.

Anyways, IIRC the ABS uses the toothed ring to know when the wheels are slipping only, however it uses MANY programmed variables such as wheel mass/diameter to calculate how to control braking force front/rear even left/right to minimize wheel slip.

I can post more on typical ABS system designs/control later once I have my SAE handbook.

Jeff92se

iTrader: (82)

I know I like mine. My bbk also greatly aid fade resistance along with the shorter dist. I'm glad I didn't pay $1,500-$2,500 for mine

Plus I'll be running larger Z31 rotors on stock calipers for the rear soon again.

MAXimumHP

iTrader: (7)

Everything they are saying make sense to me. One point that I feel is often misunderstood is that a BBK should really be purchased with the intent that it will help in multiple high speed stops. Fade resistance should be your number one reason for buying a big brake kit. Nearly all the time, Tires are the limiting factor to how fast a vehicle can stop. I do agree with most of the article and always thought this to be somewhat of a downfall to BBK's

I just want one so my rotor doesn't look so puny behind the 18's

IceY2K1

iTrader: (3)

Yeah, heat capacity and looks were the biggest benefits they said.

I just can't believe more companies aren't selling 4-wheel kits with these kinds of limitations.

Colonel

I would HAVE to think that there is some kind of table/learning necessary here for ABS to work correctly. Given the input (wheel locked) reduce XXX ft/lb pressure. As the wheel starts to move again...apply more ft/lb pressure. I would think that it should be able to bounce very quickly through tables in an effort to modulate the best way and decelerate the car while keeping it in control.

I believe the old style (single channel) ABS might have been a more "fixed" type of operation. Hence why many people disliked it so much. But now a days, with multi-channel ABS...I dunno...I should hope we have progressed leaps and bounds.

I WONT ever disable the ABS. Just wont happen. Its STILL a safety feature. To many people think ABS is supposed to slow you down faster. Its not...its to keep you in control and ABS application will INCREASE stopping distance.

Since we have not really had a good rainy day since I have been able to mash the brakes...I cannot really comment on ABS kickin....I can only comment on dry weather application.

IceY2K1

iTrader: (3)

Jeff,

You'd better wear you seat belt or you'll throw yourself out the windshield.

IceY2K1

iTrader: (3)

Let's just say an ABS engineer I've talked with said it takes MANY many months of testing just to account for a wheel diameter plus changes. He said BMW is the ONLY company he knows of that designs their ABS to accomodate 1-2 plus size larger wheels, since they know MOST owners will go larger.

It's not fixed per say. It's just that any change to the inputs will cause it to compensate and a drastic change like wheel weight/diameter, braking force/biasing, even center of gravity *cough*lowering*cough* will cause the ABS computer to work harder to control skidding. It's a feedback system. The ABS controls valves that increase or decrease brake pressure and then via the toothed sensor knows whether or not to increase/decrease pressure more.

The purpose of ABS is NOT to shorten stopping distance, but to keep the vehicle under control and allow steering to still be possible in low grip or emergency braking situations. All of which may or may not increase/decrease stopping distance, since that's not it's PRIMARY design concern...control is.

MAXimumHP

iTrader: (7)

I can't even fathom the complexity involved with designing brake systems anymore. Since the new Z and G35 as well as others are now implementing the Electronic Brake Force Distribution system and stuff, I wonder what kind of impact adding a BBK to one of those is...

Colonel

Hmmm, interesting point on the larger diameter wheels. I would be curious if people that have gone to 18, 19, or even 20's have even noticed anything at all. I am very close to purchasing a set of 18's for summer wheels...SO maybe I would be the one to notice the most off top for now?

I think it would be cool/interesting to see the testing process/code for ABS systems.

Luquire

I think my head is going to explode. i am afraind to jack with my breaks now. I think that matt blehm and i need to talk about brake kits. (2004 maxima rotors)

IceY2K1

iTrader: (3)

You seen the $3K+ price tags on them bad boys, THAT'S why~!

Colonel

I would not let it worry you. BUT, I would do more research if there are nagging questions in the back of your mind. To ME (Me, myself and I), it was a matter of relearning the braking process a little. I would ALMOST attach it to a process similiar to jumping into a foreign (not driven by you on a daily basis) car.

I tend to take the analytical side of things. I took my car, once brokin in, to a parking lot and did all kinds of "emergency" stops. Wheels turned, straight...even tried to spin it out. This kind of "information" allows ME (me, myself and I) as a person to learn and adapt to a car. And by doing my controversial test, I was able to learn how to really drop the stopping distance using the new brakes.

I dont want you to think I am downplaying your worries, I think the best bet is for you to gather more and more information. Alex's article puts things into black and white and does not leave much interpretation. Does that mean its super evil....ooga booga bad? Dunno. To ME (me myself and I) I took the risk and as of this moment cannot see these black and white disadvantages...yet.

And look at it this way, on the first good snow of the season...how many people go to a vacant lot to "relearn" how their car reacts in the snow? I do. I relish it every season. Driving should be instinct/reaction....not thinking...if you gotta think...pffft, to late.

spirilis

iTrader: (2)

Cool, I think I hear what they're talking about. I think I am still justified in buying the BlehmCo BBK with stock calipers, because the chief goal was to eliminate the chronic warping problems, which I have not proven as of yet, but time is required to tell.

Colonel

You mean $30K+ tag on the car or is the option 3K+

irish44j

iTrader: (38)

...makes me happy to have gotten the BlehmCo BBK with the OEM calipers. I've had them on for a couple thousand miles now, including some hard braking in heavy rain, and I have yet to feel that the ABS was kicking in any differently.

By all this discussion, though, one could assume that changing ANYTHING could disrupt the braking balance. This could include using different pads front/rear, different rims, etc.

That said, don't know how much diff rims could make considering the same brakes are on maximas with both the 16" and 17" OEM wheels....

Well, Matt said he's working on a rear BBK kit as well, so maybe that will balance out any possible downside to the front BBK.

That said, I also use diff pads front and rear....front I use pads that resist heat and fade better, since the front ones tend to heat up faster. My back pads I use a more basic pad. I feel like the balance is very good....

One thing I DID notice with OEM pads on all 4 brakes is that the REAR ones wore down faster. This seemed odd to me, since on all other cars I've owned, the front pads wore 2x as fast as the rear...

just some more food for thought.

Matt93SE

iTrader: (44)

A couple of issues I'd like to address here, along with some other links to companies that actually do the testing (i.e. Stop Tech)

This is a MAJOR concern of mine in designing my brake kits as well, which is partly why I made the kit to fit the OE calipers up front- it only changes the brake bias by a couple of percent, yet you get the improvements in braking by the larger diameter rotor and increased heat capacity up there.

for the 300ZX kits and most of the other brake kits out there, it DOES throw brake bias way off, and I'm currently designing a rear brake kit to compliment my front set.

When you go to most BBL websites that attempt to address this issue, they play it off. "The larger brakes up front are creating more braking force, thus more weight on the front wheels during hard braking, so you need 90% of the brakes up front." COMPLETE BULLSH**!!

that would ONLY be the case if you had race slicks on and were able to stop much much faster than before because the tires are sticking to the ground better.

In 99.99% of cases, the car's braking ability is limited by the TIRE's ability to keep from slipping against the concrete, NOT the caliper/pad/rotor's ability to create enough braking force to stop the car.

A quick illustration.. you're cuising along at 60mph on ice and decide you want to stop. you barely touch the brakes and the front wheels lock. you're obviously limited by traction between the tires and the road surface (ice). now, you've barely put ANY pressure on the brake system, yet you're sliding. stuff your foot even farther into the brake pedal and what are you doing? you're still sliding!
It's the exact same thing on the street as well. when you mash your brake pedal to the floor, the ABS kicks in (for those so equipped), and the stopping of the car is limited by the tire's grip on the road. The ABS system modulates (lowers) brake line pressure to keep the wheel from locking up!

Sooooo, how the heck will a BBK enable the car to stop faster, when it's not even the weak link in the chain?! 90% front brake needed my ****.
(this is of course throwing heat, race slicks, and brake fade issues out the window- all factors that should be addressed as well, which this article fails to do.).

The solution? If you bolt big brakes up front, you need to size the pistons to cooperate with the rear brakes and retain the factory bias (or do your own testing-$$$), or you need to upgrade the rear brakes to cooperate with the massive front brakes and keep said bias.

The only company I know of that does this already is Stop Tech. You can see an article on their kits for the 350Z here: http://www.zeckhausen.com/testing_brakes.htm

Since I don't have the equipment, testing facilities, or money that Stop Tech does, the only way I can get close is to keep as close as possible to the factory bias.

Now, let's look at some hard numbers on a Maxima. (5th gen, since that's the one I've built the kit on).
The factory dual proportioning valve creates a pressure bias of 1067:770 approximately- which comes out to 71.9% front bias- and that's just the hydraulic pressure on the lines.

Now, look at the caliper piston sizes and rotor size.
the 2000 Maxima has 11" rotors up front. diameter is 5.5" the pads are roughly 2" tall, so the center of the force is in the middle of that- 1" from the edge of the rotor.
that gives a torque arm length of 4.5"
the factory caliper piston diameter is 2.25", which gives you an area of 3.976in^2.
Let's just assume that all brake pads have a friction coefficient of 0.50u (a good number for race pads, but usually around 0.35u for street pads. 0.5u is good estimate though, since we're keeping the front and rear the same.)

Now for the rear numbers:
rotor dia: 10.94"
pad height: 1.75"
piston dia: 1.337"
piston area: 1.404in^2


Soooo, what that means is that if you put 1500psi of pressure into the FRONT brake system, it's going to produce
1500lb/in^2 * 3.976in^2 * 4.5in * 1ft/12in * 0.5u = 1118ft-lb of braking torque.

for the rears, that number comes to 290ft.lb.
that gives you a STOCK front/rear bias of 79% front.

That gives you a good ballpark to shoot for when building a brake kit to match the car.

Now we can start doing some numbers on aftermarket bias calculations..
using the 12.6" 2004 rotor and factory caliper up front, stock rear brakes, you wind up with 84% front. not too far off the previous numbers- only 5%.

Let's throw a big 4 piston Wilwood Forged Superlite caliper in there using 13" rotors:
Depending on the piston size in the Wilwood calipers (they offer them in 1.12”, 1.25”, 1.38”, and 1.75”) the brake bias can go anywhere from 82% front to 92% front- So it obviously depends on which piston size the designers choose.

Now we can look at my 300ZX kit.. using the front kit only, the bias goes to 87% front..
BUT, when you throw in the rear kit I’m developing (shooting for completion within a month), the bias goes to 76% front.. Just a hair more rear bias than the factory bias- which is generally set intentionally forward to prevent the back end from coming around too easy during trail braking maneuvers. Given that the people buying this kit are going to be track junkies- they’re going to want a hair more rear bias in order to help get the car to rotate at Auto X and on the track..

So that’s pretty much how I’ve developed everything. I was never intending the kit to be used as a front setup only- I just haven’t had time to finish developing the rear kit.. BUT, the parts are done and I’m waiting on the fab shop to machine me a prototype set and you’ll see some pictures very soon.

Matt93SE

iTrader: (44)

anyone done reading all that drivel yet?

As for the abs/wheel issue....

the ABS sensors monitor wheel speeds relative to each other, looking for any particular wheel to be different under braking (i.e. when a wheel locks up, it slows down while the other three wheels are still going the same speed). it doesn't matter whether you're using 12" 130spoke Daytons, 17" track wheels, or 22" chromies. as long as they're all the same size and the tires are the same size, you're going to be okay with most of the ABS issues.

Yes, there's of course more things involved, such as caliper piston size (back to the hydraulics and brake bias stuff), wheel weights, car's center of gravity, etc... but in general you will be okay as long as you don't put different size tires/wheels on different ends of the car.

irish44j

iTrader: (38)

Matt,
Also would mention that as you probably have noticed, there is maybe 3-5% of the pad (when using the 2k4 rotors and OEM calipers) that does not actually touch the rotor surface.

So by your calculations you are changing the bias for 79% to 84%, but in actuality, it is probably more like 80-81% due to the small amount of pad that is not making contact.

!Which is even better!

NewLoveI30

Yeah... I noticed the same thing. My rear wheels seem to collect more dust than the fronts. It has been the opposite on every other car I have ever driven.

Im confused.

Matt93SE

iTrader: (44)

It's not a pad contact issue, it's a hydraulic piston force issue.
that tiny amount of the pad material that's not contacting the rotor doesn't change anything.. there's still the same friction coefficient (based on the pad and rotor material and temperature) and the same hydraulic pressure on the piston behind it.
the pad area only serves to spread out the force to a larger surface on the rotor- it helps distribute heat. The larger the pad area you have, the cooler the pads operate, and the longer they last.

irish44j

iTrader: (38)

good point...not sure what I was thinking. It's been a long time since physics class

CCx

iTrader: (2)

In the last 25 minutes I've learned more about brakes than I've learned about anything in the past month. This site is incredible....

IceY2K1

iTrader: (3)

Baaaastards~! Good article until the end when they stopped on the 4-wheel kit.

Makes more sense now. Also, the original article doesn't ignore the heat capacity and fade resistance improvements of BBKs:

irish44j

iTrader: (38)

ha you Cali boys have it good....nice, dry roads. No worries about frequent heavy rain, snow, and ice.....

point in question about why any car mods you do need to be suited to not only your driving style, but also the weather where you live....

Jer

iTrader: (2)

What's funny is that I've managed to swing out my back end while braking reasonably harder than average on a ramp - I felt the tail flash out because of simple laws of physics - I was going down a slope, steering right, and the front end got so much more grip than the back that the butt end fell out and sent me into bad oversteer. As a result I'm looking for a pad that will bite into the rotor as well as my front HP+'s (I'm thinking HPS's).

Matt93SE

iTrader: (44)

Ummm, your car will do that no matter what brake setup you have. it's called trail braking. Any car will do that.

Jer

iTrader: (2)

Let me Ummm, correct you No. You'd never see it on my crummy stock pads or on the Metalmasters w/stock rotors, not like this.

If you like, I'll switch the fronts on your car, and do a demonstration - just hope you have good rubber or I may take it into the ditch with your "trail braking"

spirilis

iTrader: (2)

The most important piece of information in this thread for me is Matt's hard numbers on the actual effects of the BlehmCo BBK... that is good stuff

Chinkzilla

Great thread.

I'd like to add that I doubt having more pistons and a bigger caliper in the front is going to help your pedal feel any. Most ppl do feel an improvement in pedal feel, but I believe this is vastly due to the stainless lines eliminating expansion and flex in the system. What do I base this on? I saw a show on the history of hydraulics and braking on the history channel last night

Also the reason for me to get a BBK primarily would be for the fade resistance. Stock brakes simply get scary after a few hot laps.

I've been concerned about the brake bias differential for some time now, it would not be good to lock up and plow or even just understeer a bit while trail braking. There are a few options I've been considering, including an adjustable proportioning valve, or running a much more aggressive pad in the rear... say race pads maybe? It wouldn't matter too much that they didn't stop you very well since you have your front brakes till they warm up.

Matt93SE

iTrader: (44)

Let me rephrase that... Trailbraking WILL get you in trouble if you've got aggressive pads in the back- no matter what you have up front, ABS or not.
It's simple physics, and you can't fight it... or it'll bite you sooner or later.

I've got porterfield R4S pads in the back and 13" Wilwoods running track compound up front, and I still spun it out trail braking into a corner.. slammed into a dirt embankment going sideways at about 60 and FUBAR'd my rear suspension because of it. fun stuff. (yes, at the track. I don't drive like a moron on the street)

you can only put so many Gs into a tire. you can do it with braking, turning, or accelerating- but go past that limit and it WILL slide. brake while you're cornering at 100% and the back end will come out.

Chinkzilla

i don't see how that can be, if you lock up the front before the rears, the only thing that is going to happen is your going to understeer badly and the rears will just be along for the ride. Unless you have some CRAZY rear biased braking system.. it's all a balance i guess between front and rear braking torque, tire grip/width, pad material, rotor size... lots of factors to balance

Matt93SE

iTrader: (44)

If you're going downhill, into a corner, and your foot is still on the brake, you have very VERY little weight on the rear wheels. it takes almost nothing for them to start sliding.

go back to the part where I said the tire can only take so much before it starts sliding. If you're already going into a corner too fast, the tire is doing everything it can to keep from sliding (i.e. back end coming around), then you throw braking forces on top of it-- the back tires will start to slide. thus oversteer.

I've found the worst trailbraking problems on my car are when I'm on the track-- I run very aggressive pads up front and leave the rears alone (always run porterfield R4S in back, Wilwood C, D, or E compound up front, depending on the track and weather).. when I'm going into a corner- especially a downhill one, I'm on the brakes HARD, and even M3s with StopTechs are having a hard time not running me over.. Anyway, I've got most of the weight of the car up front- more than usual since I'm doing 100+, the brakes are digging in HARD, and I've got good traction--so it takes less for the back end to come around when I'm on the track than when I'm on the street.

At auto X, I have a hard time actually getting the car to rotate because I've got my suspension set up for roadcourses with long sweepers-- so I keep my foot on the gas through corners and stick my left foot into the brake. voila! turning!

irish44j

iTrader: (38)

This is a great thread and alot of the newbies (and oldies) can learn alot from it (and would never find it buried 8 months back!), so I figured it deserves a free bump to the top.

Jeff92se

iTrader: (82)

Does he still feel this way?

Larrio

iTrader: (10)

dunno. He has a 95 with abs now and a staggered rear setup

doublea

iTrader: (7)

Hey Matt, you just sold me your kit with your comments, I'm really concern about my next brake set-up, which will be due early spring. I was lurking toward a kit like Brembo or AP or SS Corporation, but what concern me now is the fact they have nothing to offer us to keep the bias balance and my though is puttin BBK in front and keeping the stock brake rear doesn't make sense to me.

So I will hopefully order a complete front-rear Z kit from you for my maxima.

Thanks again Matt for the very usefull informations.

I also want to thank ICEY2K1 for his dedications to this forum. I'll be visiting my sister in Tucson around april, I'd really like to meet with you and perhaps pay the lunch and beer.

Cheers

AA

theMax

SOOOO.. What about using coilovers to adjust the wheel loading? Would this help balance the increased force on the fronts?