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Thread: Adjusting brake bias without murdering tires?

  1. #1
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    Adjusting brake bias without murdering tires?

    Title pretty much says it alló AFAIK the only way to properly test proper front/rear brake bias is to see which tires lock up first? Doesnít that put flat spots in the tires? If you keep it slow, maybe itís not really that noticeable? Maybe Iím just being overly babying on my 200 TW tires, but damned if they werenít the most expensive tires I ever bought 😀 Any other tips/tricks or processes people use for proper adjustment that are easier on the tires?

    P.S. not that I plan to go easy on them for longó just feels wrong to start off on a bad note
    Last edited by Alphamacaroon; 10-17-2019 at 10:11 PM.

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    You might consider a smooth grass surface to see where you are on bias.
    A wet parking lot, would be easy on the tires.
    I do not know where you can find it, but polished concrete, wet or dry would be nice.
    I will be watching this for tips.
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    EFI Rules and Carbs Drool Arrowhead's Avatar
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    You could use an infrared thermometer on the rotors to check temperature. Not sure if that is a proper way to do it, but it will at least tell you which end is working harder.
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    Quote Originally Posted by Railroad View Post

    You might consider a smooth grass surface to see where you are on bias.
    A wet parking lot, would be easy on the tires.
    I do not know where you can find it, but polished concrete, wet or dry would be nice.

    I think lower traction surfaces are a bad idea for setting this up.


    A key aspect is that the operator's approach to the brake pedal is critical.

    There's a big difference between coasting down a hill in neutral and jumping on the brake, versus running up to redline in 2nd gear and jumping off the throttle and onto the brake - The second example is likely to take years of practice to become reasonably safe + proficient, and it's going to allow a lot less rear bias - due to engine braking.

    The better you get at "tossing" the car around, the less rear bias you'll be able to tolerate - because as you get better with the brake pedal, you're going to transfer more weight off the rear of the car during braking.


    If the rears tend to lock first - sooner or later you're going for a ride you're not going to like - very unstable situation, which will very suddenly turn you into a passenger going round + round + round.


    Tire traction and road surfaces are also critical - less "grip" is going to directly cause less weight transfer and therefore allow more rear brake bias. Do not fool yourself and apply more rear bias in these conditions - you're setting yourself up for trouble when you actually do have grip - more weight will transfer in a panic stop, the rears will lock, and you go round + round uncontrollably (at the worst possible moment).


    I set mine up by coasting in neutral down a hill and dragging the brakes - aiming to get all 4 rotors approximately the same temperature.

    Reasonably gentle - no need to get the rotors so hot you need a heat gun - I used the back of my hand to judge temps (approach with caution).

    You should be able to work this up (with great care), and then drive the car with care - understanding that you are only safe because you're lighter, with stickier tires, more braking, and can easily stop better than most anything else on the road - make it a point not to get cornered into a situation where you need a "panic stop".


    Then I relied on autocross for further development (+ self training) - anytime I detected a rear locking early I'd take a full turn off the adjuster (reducing rear brake bias).

    Again - the better I got with the car the less rear bias I could stand.


    In general, I try to stay two full turns on the adjuster away from losing traction on the rear during my "best autocross panic braking" (= the most weight transfer off the rear axle).


    I use a lot less rear bias than I started with, but there are countless variables in hardware / grip / operator / etc.


    I have also noticed considerable variables as the brake pads seat / bed to the rotors - my rear rotors actually tend to run hotter than my fronts now, despite the fact that I have substantially reduced rear bias over the years (lower relative hydraulic pressure going to the rear calipers).

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    Senior Member Avalanche325's Avatar
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    As Mike stated, there are endless variables when driving a car. You can only set up for the "average" scenario. After that it is driver skill.

    You can get reasonably close on a sandy road or slightly wet surface for a starting point without frying your tires. You don't need to panic stop from 100 mph. 40 mph will do. Also you don't lay on them until you stop. The second you get a lockup, GET OFF. You are just making sure you are not rear heavy so you don't do a brake induced spin. I did pretty much like Mike. Went until the rears were just locking and backed off a couple turns. Then made sure that I could panic lock the fronts WITHOUT any rear lockup.

    In an ideal world, for a street car, the rears NEVER lock up. Some people shoot for all 4 locking at the same time, which sounds good until you realize that a car with all 4 locked up is now a totally out of control hockey puck. They think they are setting up for maximum braking, but they are really setting up for a trip to the ditch or opposing lane. You always want the rears acting like rudders. Which means that they have to be rolling. Even if the fronts are billowing smoke. (<<< driver skill upgrade needed - see next paragraph :-))

    Then the best place to fine tune your car and especially yourself is autocross. As I learned more, I did a few clicks on my remote adjuster. But really not many. I added in a few clicks of rear. I haven't touched it for a long time. Always err to the front heavy side if you don't have good butt feel. I really learned a lot about brake modulation, which I *thought* I was already pretty good at. There is a lot of "thought you were pretty good" driving skills that autocross will prove you wrong at. That is why I always recommend it for Cobra owners.

    I am not sure about using rotor temp for initial setup. The front and rear do different amounts of work. They are not the same size. The cooling is not the same. No matter what you do, the proper amount of work done will be around the 70 / 30 split. So equal temperatures don't mean anything. I guess after you are set up, you could use temps as a base line. Most race cars use line pressure for baseline and adjustments. Or just the driver.
    Last edited by Avalanche325; 10-18-2019 at 01:30 PM.

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    Quote Originally Posted by Avalanche325 View Post

    I am not sure about using rotor temp for initial setup. The front and rear do different amounts of work. They are not the same size. The cooling is not the same.
    All agreed - I used (equal) rotor temp as an indication that I had (in fact) all four corners working - and if one end of the car (rotors) is hot while the other end is cold, something's probably too far out of kilter to proceed.


    Further thoughts - incremental "baby steps":

    1- Make sure all four corners are working.

    2- Start dialing out "too much" from one end or the other with the balance bar.

    3- Something I'd forgotten - This is an excellent time to be working on your ride height and cross weights.


    Added discussion for unasked questions - think of a 4 legged stool - what happens if one leg is longer than the rest? - Two diagonally opposed legs are going to carry all the weight (typically).



    As you start getting the front dialed in to lock up first, you're almost certain to find that one of the front wheels locks before the other.

    This is almost always best addressed with cross weight adjustments.

    You don't really need scales - you just need to know which front wheel locks first - it needs to be carrying more weight (the other front wheel is carrying too much weight).

    So first, get your ride height where you want it by adjusting the coilovers (all four corners).

    Know which corners are "slightly" low + high (it's never going to be absolutely "perfect").


    If the right front locks up first you need to add 1/2 a turn to the coilover on the right front or the left rear - or take 1/2 a turn off the left front or right rear - back to a four legged stool - have you got a leg that's too long, or is a leg too short?

    By the time you get "happy" with your brake bias front to rear - your cross weights will be "near perfect" - if you are also paying attention to which front is locking up first while you are adjusting your front to back brake bias (and know what to do about it).


    Get it?

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    Senior Member CraigS's Avatar
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    I disagree w/ temps and surfaces. The only guide is whether the tires lock up or not. That's it. Rotor temp means little. Think like this. Say you had a perfectly biased system and decided to put larger rotors/calipers on one end. Those larger rotors will run at lower temps for a given amount of braking. So the temps are different but the braking is the same. Testing on different surfaces also doesn't work. Say you have the bias perfect on standard macadam. Then go to a surface w/ less grip. Now the car won't stop as hard, so there is less weight transfer to the front. So you would need to adjust for less front brake to keep the bias correct. Normally we don't change the bias on the street because it would take too much testing for every change of conditions. But this is also one benefit of having correct bias in normal driving. As the conditions deteriorate, we end up w/ a car that locks the fronts first in these worse conditions. This is what we would want because front locking is stable. Brake distance may be longer this way but it's a LOT better than ending w/ too much rear brake which would pretty much guarantee a spin.
    FFR MkII, 408W, Tremec TKO 500, 2015 IRS, DA QA1s, Forte front bar, APE hardtop.

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    Here’s my two cents. First brake bias is to a large extent is driver preference. Which depending on driving style and driving skill level will determine how you like it. For novice drivers learning a high performance driving I would suggest reducing the rear brake bias. The reason being is that when a newer driver goes into a curve and has a “cone to Jesus” moment and slams on the brakes the rear is the last thing you want to lock up while turning. Same applies to track driving and trail braking. Sure straight line braking you can add more bias rearward to an extent to improve it. But once again this is a balancing act. More seasoned and trained track / race guys usually prefer less bias in general. However the over all balance is changed depending on the track. Some times more works some times not. This is the reason for brake bias adjusters. Rotor temps I completely agree is not to be looked at when setting up bias. You look at rotor temps or more importantly caliper temps to make sure your system is sized correctly so that you don’t boil your brake fluid and chew up pads like candy. Low traction environments are also usually not recommended due to the coefficient of friction change due to heat with high load stops. This will also play into what the correct setting for you is. My suggestion to you is simple, first start front biased with straight line stops. Stop as repeatabily as possible with quick progressive brake pressure from say 60mph. Note what wheels lock first (should be fronts) The goal here is to just cross the line to make the tires lock. One this is done feed in the rear bias 1 turn at a time till the rears lock first. Then back of 1-2 turns. This should be a good starting point. After that find a HPDE on a real track with real instructors (AutoX does not count). Register, buy track insurance and lean how to brake and turn. From there you’ll know if the rear steps out while trail braking reduce the rear bias more if not feed it back in. As I stated before this isn’t a black art it’s more driver preference. I personally never raced with much rear bias because trail braking and mid corner speed is part of where races are won. Lots of rear bias means you would have to do lots of late braking and late apex turns to get the most from the set up. Otherwise over steer due to overly aggressive brakes will occur. This is great for blocking and late breaking moves bad for lap times, mid mid-corner speed and overal brake control. Almost forgot don’t worry about flat spotting tires as that is not any realistic worry. In fact, your more likely to flat spot tires by leaving a car setting on them over the winter.
    Last edited by GFX2043mtu; 11-05-2019 at 11:04 PM.
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    Thanks for the help everyone! Gives me confidence to do this right as I'm nearing the gokart stage.

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    Senior Member jkrueger's Avatar
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    What GFX said about starting with less rear bias and exactly for the reasons he stated. Having the rears lock up in a panic stop is the quickest way to end up backwards in these cars.

    When I set mine up I used brake pressure gauges to get the initial set up close. Then I went out on the road in a safe place and did hard stops to see how it felt. Then to the track to really get a feel. If the back end locks up first, take bias out until it doesn't. Under hard braking at the track I can tell if I have to much rear bias by how the rear end feels under braking. If it squirms around under braking I take bias out until in tracks straight under hard braking.

    JC

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    Speaking of brake bias, I do have one other question: my coupe was ordered with standard front brakes and 13" IRS rear brakes (I don't recall FFR giving me much choice other than the upgrade to wilwood, and figured I could always upgrade later). I never saw the size of the front brakes until I put both sets on and noticed the rear rotors are quite a bit larger than the front— seems really strange and backwards to me.

    Is this a normal configuration with stock brakes, or did I order a bit of a frankenstein?

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    Senior Member CraigS's Avatar
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    That is the way it is. I did a 2015 IRS upgrade and used the brakes that came w/ the salvage yard rear suspension. The rotors are definitely larger than my Fox Mustang front brakes. They work great. This is actually a nice side benefit. When we use all older Mustang front and rear we end up w/ parts set up for a front heavy Mustang. But our FFR is rear heavy so, w/ all older Mustang brakes, we don't have enough rear brake. The 2015 IRS rear brakes take care of that problem.
    FFR MkII, 408W, Tremec TKO 500, 2015 IRS, DA QA1s, Forte front bar, APE hardtop.

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    Dumb Question. I have only go carted the car, but I am about ready to get it on the road for real so I need to set up the bias. How exactly do you tell which lock up first? Is this something you just feel in the car, or it is something you need to see? I presume I need to bed in the brakes before setting up the bias.
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    Quote Originally Posted by rychi1 View Post
    Dumb Question. I have only go carted the car, but I am about ready to get it on the road for real so I need to set up the bias. How exactly do you tell which lock up first? Is this something you just feel in the car, or it is something you need to see? I presume I need to bed in the brakes before setting up the bias.
    I think itís a great question. Iíve been wondering the same. I guess maybe if the rears lock first maybe youíll hear it before you see it? I thought of maybe having a spotter on the side with slo mo video on my iPhone. But maybe Iím overthinking it.

    Another more dangerous option would be to lock them up in a turnó keep adding front bias until you donít end up backwards 😀

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    Senior Member edwardb's Avatar
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    Been watching this thread, and a lot of good information. But also some overthinking and unnecessary hand-wringing IMO. Everyone's setup is likely different. But you don't have to kill the car or the tires. Especially not at first when getting to know the car, checking it out, etc. Following is based on my experience with Roadster #8674. Standard Wilwood pedal box, no power assist, and the upgraded big Wilwood IRS brakes. My Coupe build has the exact setup. First up, build it with the balance bar centered as the instructions state. Once you've driven the car a bit and are confident with it, do the Wilwood bedding procedure. Follow it exactly. It's necessary before doing anything else to get the pads and rotors working together. It's a pretty aggressive procedure, so make sure you have the right place to do it. You're going to find out real fast if the bias is way off. You may find, like I have, that with the balance bar centered and everything else being equal, the bias is quite close. For my street driving, with the bedding process and more miles, I've done enough hard stops to validate, at least for me, that the bias is good. I can feel the slight front bias, and have never felt the rear move unexpectedly when braking hard. I also closely watch my brake pads, rotors, dust, etc. and can see that all four corners are working about the same. Some have described taking it further and pushing to the point of lock-up. No problem, I just haven't felt the need to do that. Although I might have if initial driving and the bedding process didn't work out the way it did. No question more important for a track car where there are many more variables. Even to the point of changing bias while on the track. For a street car, just haven't found that additional complexity is required. The hardcore guys are probably going to flame this less aggressive approach. But I guess my main point is you don't have to kill the car to see where you're at. Which was the original question.

    On a side note (not to go too far off topic...) both of my builds with the above setup (Roadster #8674 and Gen 3 Coupe) are of the vintage where Factory Five was recommending and providing different size MC's for the front and rear. Mine have .75 MC's in the front, and .625 MC's in the rear. For the last year or so, seems they have gone back to .75's for both front and rear. I've not heard an explanation for why this change was made. The .75 rear MC is going to provide slightly less pressure than the .625's like I have and previously used. Obviously that would change the bias somewhat, so something to watch for. But still wouldn't change my personal approach. At least at first.
    Last edited by edwardb; 11-08-2019 at 12:04 PM.
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    Thanks for a great perspective edwardb.

    Specifically to the MC sizes, mine is indeed a newer one where they are both equally sized, but the instructions don't appear to coincide with this. Also, the fact that the standard brakes appear to have very different rotor sizes (the wilwoods seem closer matched), makes me think there are enough differences between your setup and mine that it may not work to center the bar.

    Regardless, it seems like throughout this discussion the one common thread is that there is no single formula— you just have to drive the car and adjust based on preference and feel.

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    Senior Member CraigS's Avatar
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    For many years I had the old Mustang Cobra rear calipers w/ the 5/8 MC. When I went to the 2015 IRS and used the brakes that came w/ the suspension they are a significantly larger piston. Larger enough that the 5/8 MC didn't have enough volume to operate them. I ended up w/ a 3/4 MC for the rear and the front.
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    Steve >> aka: GoDadGo
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    Install The Wilwood Pedal Adjuster Shown Below:

    https://www.speedwaymotors.com/Wilwo...able,1388.html

    Then do.. "Dad's Top 10"..brake adjustment method:

    .1. Stop, Adjust, Then Go!
    .2. Stop, Adjust, Then Go!
    .3. Stop, Adjust, Then Go!
    .4. Repeat As Necessary Until Happy With Results!
    .5. Stop, Adjust, Then Go!
    .6. Stop, Adjust, Then Go!
    .7. Stop, Adjust, Then Go!
    .8. Stop If Tires Are Flat Spotted & Ruined!
    .9. Order New Tires If Step #8 Occurs.
    10. Stop If You Are Being Arrested For Reckless Operation Of A Motor Vehicle!

    Just Some Southern Stopping Humor From The Dad Side!

    Steve
    Last edited by GoDadGo; 11-13-2019 at 10:31 AM.

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    Sounds about right GoDadGo!

    Regarding the Wilwood Pedal Adjuster, I have considered that route, but can't for the life of me figure out how you would get it to fit/attach in the pedal box without the 90 degree adapter. Does anyone have any good pictures of one installed in a Gen III?

    This one actually looks like it might be easier to install, https://www.speedwaymotors.com/QTM-B...er,138445.html because you can side mount it instead of having to drill through a panel. Anyone have experience with the QTM?
    Last edited by Alphamacaroon; 11-13-2019 at 11:54 AM.

  23. #20
    Senior Member CraigS's Avatar
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    There was a thread on that recently. Search here and the other forum.
    FFR MkII, 408W, Tremec TKO 500, 2015 IRS, DA QA1s, Forte front bar, APE hardtop.

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