brake bias for cadillac caliper swap and other BBKs

[Lynxis]

Originally Posted by finch1750

does anyone actually have the piston size from the RR kit or is it still just taking their word for it?

They use the standard Wilwood caliper piston sizing.
6 pot, 1.38 inches first piston, 1.12 inches 2nd and 3rd pistons.
4 pot, 1.25 inches on the 4 pot sport kit.

Rotor sizing is published on their website but it's just a standard STI rotor.

Originally Posted by churchx

RR IS reasonably priced. And their bias seems no that bad off as some of retrofits. BUT - if even vendor says that for proper use one needs to use different pads front-rear, i translate it "we didn't care about getting right bias, so use this hack to workaround" putting big red sign against considering them. I get if such hack is used for retrofits, i get it if used for non-standard aero / staggered wheel & tire setup .. but NOT if for standard set marketed for most cars, without clearly stating if it's for some specific setups.

There is some context to this statement which I think is important. RR Racing seems to be of the opinion that our cars benefit from additional rear brake bias even when stock. They have recommended people with stock cars to have more aggressive pads in the rear. That is part of the reason why their rear kits send the bias so far backwards. While I don't think having additional rear bias will hurt, I don't really agree with the statement due to the overwhelming body of information and experience that says the OEM bias is pretty much optimal and honestly, I think it was just a marketing grab to get people to buy the rear kits.

Regarding the price point, it's clear to me that using standardised parts is how they achieved the price point they have. Unfortunately, this does mean that things aren't perfect and their front kits DO have a small forward bias shift when used with OEM rears. @JRitt ran the numbers in another thread that I can't be bothered to find right now where he saw around 3% bias shift forward on the 6 pot kits and 5% bias shift forward on the 4 pot kit. He was of the opinion that it was a bit too far forward for their customers who track at the highest levels of HPDE and motorsport but I think it would be perfectly adequate for the remaining 9/10 customers.

[bhmax]

Originally Posted by Bobster

I hear the WRX 4 pots move the BIAS to the rear as wheel, does that make them a better option?

I mistakenly read this as the Wilwood 4 pot kit for the WRX which was discussed earlier. Haven't checked on the OEM Subaru 4 pots. Previous post from me refers to Wilwood.

[Racecomp Engineering]

One note, and something I've not seen mentioned on this forum (though it's mentioned in the Stoptech white paper linked in the OP's article)....

If you run very high grip tires, then you can potentially generate more forward weight transfer than on OEM tires. Essentially this means that the "ideal" brake bias for a car on hoosiers is not the same as it is for a car on OEM tires (or in the rain).

This is not to say that you should increase your front brake bias from OEM when moving to sticky tires. The OEM brake bias has other design considerations beyond just achieving the shortest stopping distance possible and the ABS system complicates things.

But a massive shift rearward can suck just as much as a big frontward shift. Small changes in bias can shorten stopping distances slightly and help a driver feel more comfortable with the car, but it's important to think about the complete picture.

A rearward shift can also be helpful if you're running aero that's actually effective.

- Andrew

[sickmint79]

i'm actually confused on the RR. on the one hand they provided that excel bar chart, and noted the friction was the same front and rear. i don't know how any inputs to it were made or measured at all though.

on the other, i got the piston sizes in an e-mail - and it's the standard wilwood 6-piston front - which using the calculator appears to push it almost as forward (12.88 wilwood rotor vs. 12.8 RR) - even if i try to make a better effort at comparing something like effective rotor diameters, the shift forward still ends up being a 4% increase vs. oem instead of 5% just using outer diameter.

so it is hard for me to conclude the bar chart is valid and the net change vs. stock is zero. thoughts?

[sickmint79]

Originally Posted by Lynxis

They use the standard Wilwood caliper piston sizing.
6 pot, 1.38 inches first piston, 1.12 inches 2nd and 3rd pistons.

1.62 1.12 1.12

and indeed the same caliper.

dark's experience http://www.ft86club.com/forums/showp...97&postcount=6 would seem to jive with it actually moving the bias forward as well. i am having a tough time accepting the bar chart now.

There is some context to this statement which I think is important. RR Racing seems to be of the opinion that our cars benefit from additional rear brake bias even when stock. They have recommended people with stock cars to have more aggressive pads in the rear. That is part of the reason why their rear kits send the bias so far backwards. While I don't think having additional rear bias will hurt, I don't really agree with the statement due to the overwhelming body of information and experience that says the OEM bias is pretty much optimal and honestly, I think it was just a marketing grab to get people to buy the rear kits.

stoptech pushes it back a little, the sprint more... i'm under the impression when you go as far back as wilwood or RR front and rear together that you may/should have a fair amount of aero on the car?

Regarding the price point, it's clear to me that using standardised parts is how they achieved the price point they have. Unfortunately, this does mean that things aren't perfect and their front kits DO have a small forward bias shift when used with OEM rears. @JRitt ran the numbers in another thread that I can't be bothered to find right now where he saw around 3% bias shift forward on the 6 pot kits and 5% bias shift forward on the 4 pot kit. He was of the opinion that it was a bit too far forward for their customers who track at the highest levels of HPDE and motorsport but I think it would be perfectly adequate for the remaining 9/10 customers.

a problem with my article/knowledge is that i don't really know where things are truly problematic... i do know that between 1000 and longer braking distances and 1500 and oem or shorter, that i'll happily spend the extra 500, even though i'm not doing anything on the track that would impress anyone. at least my car is more capable of it!

[86ft.lb]

These calculations are sound and necessary for sanity check. However, a few % difference should not be a major factor to evaluate a kit. The actual bias will never be the same.

- front / rear pad and rotor temperature difference, thus friction difference, throughout a session or even one braking zone.
- RPM and gear dependent engine brake on rear.

These two factors alone can easily shift over 10%. Moreover, it is hard to say one bias is better than other. Optimum bias changes throughout braking phases. In the initial phase, I want very strong front bias as rear unloads (Wf >>> Wr). In the middle phase, I want mild front bias as rear settles(Wf > Wr). Towards the end phase, I want strong front bias (Wf >> Wr).

[Bobster]

Originally Posted by bhmax

I mistakenly read this as the Wilwood 4 pot kit for the WRX which was discussed earlier. Haven't checked on the OEM Subaru 4 pots. Previous post from me refers to Wilwood.

Thanks I worked out the maths WRX 4 pot will move the BIAS a little towards the rear, might actually be a very good combination with stock rears

[finch1750]

Originally Posted by bhmax

I mistakenly read this as the Wilwood 4 pot kit for the WRX which was discussed earlier. Haven't checked on the OEM Subaru 4 pots. Previous post from me refers to Wilwood.

Originally Posted by Bobster

Thanks I worked out the maths WRX 4 pot will move the BIAS a little towards the rear, might actually be a very good combination with stock rears

correct. OEM WRX 4 pots are the same caliper as the Z32

[JRitt]

w I thought the article raised a lot of good questions. I don't have the bandwidth to go through all of the numbers again, but it's great to see people thinking these issues through! Slapping the cheapest kit available on the car always appears to be a reasonable option in the short-term, particularly to someone who is working with incomplete information (which frankly, is most people since we can't all be experts on everything). Since you're going to own your car for a number of years however, it makes a whole lot of sense to carefully choose where you'll invest a couple grand of your hard-earned money.

One of the OP's quote in the article really made me think about the idea that someone may not know what they're really getting until they have it:

I recently supervised/held my beer while a buddy replaced friction rings on his Wilwood 6R. I have quite a few more track days than him, so I’m not sure why his needed to be done already.

We (Essex/AP Racing) stand by our choices/options for FT86 brake applications. We did the math. We did our testing. We found that unless you have some fairly drastic modifications on your car (huge rear downforce), any significant bias shift either frontwards OR rearwards is inappropriate and will hurt your overall brake performance. That could come in the form of longer stopping distances, shorter pad and disc life on one or both ends of the car, or pad or fluid fade. Unfortunately some of those effects are hard to recognize if you have no baseline for comparison. That means you may be leaving a lot on the table and not even knowing it.

Our Essex Sprint and Endurance Kits are now running on many hundreds of BRZ's, FRS's, and GT86's all over the globe. Our incidence of problems or issues is incredibly low. Most of our customers tell us that our brake kit was the single best modification they've done for track use, and that it has saved them tremendously on their lap times, consumable costs, and wrenching time. Many of those customers have also had their kits on their car for four years now, and are still on the first set of discs! Finally, keep in mind that ALL of those customers are running OEM rear brakes with upgraded pads and lines...NOT a complete rear brake kit.

So was it worth a few hundred bucks more initially to get the best front brake system available? We think so, unless you're just looking for those extra 'hard parking points' mentioned in the article which come with a rear BBK. I saw a great quote the other day that I think is extremely applicable to the brake kit market. "Buy the best and you'll only cry once."

[JRitt]

Originally Posted by sickmint79

i'm actually confused on the RR. on the one hand they provided that excel bar chart, and noted the friction was the same front and rear. i don't know how any inputs to it were made or measured at all though.

on the other, i got the piston sizes in an e-mail - and it's the standard wilwood 6-piston front - which using the calculator appears to push it almost as forward (12.88 wilwood rotor vs. 12.8 RR) - even if i try to make a better effort at comparing something like effective rotor diameters, the shift forward still ends up being a 4% increase vs. oem instead of 5% just using outer diameter.

so it is hard for me to conclude the bar chart is valid and the net change vs. stock is zero. thoughts?

I also questioned that bar chart and asked RR to publish all of the relevant numbers on their components for calculating bias somewhere fairly early on in their big thread about their brake kits. I was subsequently crucified for posting in their thread, told I had poor forum etiquette, told to go look up the information myself, etc. We subsequently ran the calculations using the standard Wilwood components, and determined that the bias numbers we found are definitely not optimized for the majority of our customers (mildly modified cars attending autoX, track days, HPDE, time trials, etc.).

[Cartman]

Originally Posted by sickmint79

1.62 1.12 1.12

and indeed the same caliper.

dark's experience http://www.ft86club.com/forums/showp...97&postcount=6 would seem to jive with it actually moving the bias forward as well. i am having a tough time accepting the bar chart now.



stoptech pushes it back a little, the sprint more... i'm under the impression when you go as far back as wilwood or RR front and rear together that you may/should have a fair amount of aero on the car?



a problem with my article/knowledge is that i don't really know where things are truly problematic... i do know that between 1000 and longer braking distances and 1500 and oem or shorter, that i'll happily spend the extra 500, even though i'm not doing anything on the track that would impress anyone. at least my car is more capable of it!

I have the RR kit, I will post what happens to the car once I install matching set of pads front and rear... BP20 + Ferodo DS2500 felt ok, but the BP20 have 0 bite and I was used to running Raybestos ST43 on the OEM calipers... granted, I did have major Front bias on my car running ST43 front and DS2500 rears, and got used to running the car that way.

BP 20 + ST45 rear would cause the rear to lock up under braking, so not a good combination either, (had bought the pads to go with the ST43 in the OEM setup, but bought the kit shortly after and never bought ST45 for the RR kit)

I just ordered Ferodo 2500 for the kit to match my rear (and stop the excessive squeling from the BP20s) And will report after I try the setup at the track day.

[infinity21]

Originally Posted by Cartman

I have the RR kit, I will post what happens to the car once I install matching set of pads front and rear... BP20 + Ferodo DS2500 felt ok, but the BP20 have 0 bite and I was used to running Raybestos ST43 on the OEM calipers... granted, I did have major Front bias on my car running ST43 front and DS2500 rears, and got used to running the car that way.

BP 20 + ST45 rear would cause the rear to lock up under braking, so not a good combination either, (had bought the pads to go with the ST43 in the OEM setup, but bought the kit shortly after and never bought ST45 for the RR kit)

I just ordered Ferodo 2500 for the kit to match my rear (and stop the excessive squeling from the BP20s) And will report after I try the setup at the track day.

What tire spec are you running? Would be interested to hear back on the results.

[Cartman]

Originally Posted by infinity21

What tire spec are you running? Would be interested to hear back on the results.

215-45-17 Hankook RS-3 on OEM wheels.

[Lynxis]

I have the RR 4pot Sport kit and I'm running it with BP10 in front and EBC Yellowstuff in OEM rears right now and I have been very impressed with this combination for daily and intermediate track use. Knowing what I know about the bias of the SP kit now, this makes sense because the BP10s have ~.45 peak friction coefficient and the yellows have ~.55 which I'd guess sets my bias close to OEM.

I do have a set of Yellows for the front kit which I had trouble fitting when I first got them. It could have just been because I was tired at the time but I think they may need a tiny bit of grinding to fit. At this point, I'm just keeping them around as spares for when the BP10s wear out.