F Bobcat + R XP8 pads = heavy rear bias

[BlackHole]

Since I didn't like the stock brake bias (too front biased), I figured I'd try a front set of Bobcat pads w/ XP8s in the rear. Well, the XP8's coefficient of friction is so much higher than the Bobcats the car became quite rear biased, to the point that I wasn't using much of the front brakes and reducing (perceived) overall braking power. So I just replaced the XP8s w/ Bobcats in the rear and I'll live with the front bias until I can upgrade the rear brakes.

 

Sometimes experiments don't turn out quite the way you'd hope.

[PhilT]

Go with XP10's on the front, you will be impressed !

[BoxerGT2.5]

I had Bobcats, I pulled them off the car and wiped my ass with them....POS loud mofo's.

[Xenonk]

Since I didn't like the stock brake bias (too front biased), I figured I'd try a front set of Bobcat pads w/ XP8s in the rear. Well, the XP8's coefficient of friction is so much higher than the Bobcats the car became quite rear biased, to the point that I wasn't using much of the front brakes and reducing (perceived) overall braking power. So I just replaced the XP8s w/ Bobcats in the rear and I'll live with the front bias until I can upgrade the rear brakes.

 

Sometimes experiments don't turn out quite the way you'd hope.

 

what?

[Xenonk]

I had Bobcats, I pulled them off the car and wiped my ass with them....POS loud mofo's.

 

again, what??

[PhilT]

again, what??

 

try this

 

http://www.joe-ks.com/archives_dec2004/MegaHearingAid.jpg

[TRS]

I had Bobcats, I pulled them off the car and wiped my ass with them....POS loud mofo's.

Must be either a makeshift anti-squeal treatment or a bedding-in procedure I've never heard of.

[Xenonk]

in all honesty, i've mis-matched front rear brakes of all sorts, even stock pads up front with XP10s in the rear and I had no issues of the brakes being too biased in the rear, and this is track time we are talking about. There's is really nothing wrong with doing trail-braking oversteer, it's one way to get around a corner. I don't understand how you are thinking your rear is doing more work than the fronts.. If anything, if you are not locking up the rears, then you're not braking hard enough to take advantage of the car's ability. The higher coeff. of friction should lock up the rears quicker (and it should considering that weight transfer is towards the front of the car, which lifts the rear making it easier to lock them up). Perhaps you need to change your suspension to make use of your bobcats/xp8 setup by changing to a stiffer spring and shock combination (coilovers would be the easier answer to all of this, but if you adjustable shocks like Ohlins, that would another way to go). If you are still on stock suspension, then that could explain the feeling of rear brake bias, but it's not to the point where it felt like you just yanked up the e-brake. Most people would enjoy power-oversteer, but many don't understand or know how to deal with trail-braking oversteer (or brake drift techniques for the modern day genre/masses).

 

As for the noise on the Bobcats, that's very minimal compared to a dedicated track pad.. Bobcats rarely squeal.. maybe a tiny bit when they are cold, but nothing to the point where it's LOUD. Bobcats are still afterall, and upgraded set of street performance pads.. anything higher and you'll need to venture into the realm of track entry pads.

[BlackHole]

If you are still on stock suspension, then that could explain the feeling of rear brake bias, but it's not to the point where it felt like you just yanked up the e-brake.

 

Bingo, stock suspension. And yes, it does feel like the rear e-brake is on with the XP8s. The bias was so bad with the rear XP8s that I couldn't break-in the front pads even after following the Carbotech bedding procedure multiple times and 2500 miles towing a 1700# trailer. I've bled and rebled the brake system and can't get rid of the "rear e-brake" feeling nor get the front pads to bed (all rotors were resurfaced before pad install).

 

I'm open to any suggestions on what I may be missing here and why I'm having these problems. Don't get me wrong, I really like the XP8s and Bobcats, just not in this configuration.

 

As for the noise on the Bobcats, that's very minimal

 

No complaints here. The Bobcats are quieter than the XP8s and I found the XP8s acceptable on a DD as long as they get washed / de-dusted regularly.

[BoxerGT2.5]

try this

 

http://www.joe-ks.com/archives_dec2004/MegaHearingAid.jpg

 

 

That's awesome!

[Xenonk]

Bingo, stock suspension. And yes, it does feel like the rear e-brake is on with the XP8s. The bias was so bad with the rear XP8s that I couldn't break-in the front pads even after following the Carbotech bedding procedure multiple times and 2500 miles towing a 1700# trailer. I've bled and rebled the brake system and can't get rid of the "rear e-brake" feeling nor get the front pads to bed (all rotors were resurfaced before pad install).

 

I'm open to any suggestions on what I may be missing here and why I'm having these problems. Don't get me wrong, I really like the XP8s and Bobcats, just not in this configuration.

 

 

It shouldnt be that dramatic of a feeling (because I've tracked on a set of Stock Pads with XP10s in the rear and I had my rear shocks and rear sway adjusted to full stiff to get the car to really drift under trail-braking, and it does).

 

You should be able to bed the pads just fine.. how are your tire pressures? With that kind of setup using stock suspension, your next (and only adjustment) would be to change the tire pressures a little bit more up front possibly. Maybe a change of 2 to 4 psi from your norm. Ultimately, you may look into better shocks to stiffen the front end of the car's dampening (and spring work if neccessary) to get the front end from diving so hard (although that IS a good sign that the front brakes are working if you get that kind of weight transfer to the front of the car).

 

You really shouldnt have lesser braking performance.. the situation you are going through about not needing to press the pedal or not needing to input as much braking is the first sign of better braking response. My personal concern is that you're not used to having the car to be trail-braking oversteer. By choosing that pad combination, you are purposely forcing this very notion.

 

The real matter is understanding what you want the car to do under the situations you plan to put them in as well as understanding how you may also change your driving style to maximize the performance of your new setup. I personally think that the driver has much more room for improvement and learn to adopt and maximize the car. From a motorsports standpoint, if two cars are identical in setup, but one car is that much slower in lap times, it's very obvious that the slower driver doesn't know what else to do to make the car faster. I've been around performance driving long enough to see that some cars are far advanced than the owners of the cars, it's very common (I was one of those people when I had a WRX).. granted that the cars people own are indeed fast (from Porsches, Corvettes, down to Honda Civics, BMW 3 series), riding and instructing these people is the key to making sure the driver knows how to use their car to a higher level.

 

Try driving the setup again and practice with it. I'd suggest that if you are around any autocross events, try those out and have an instructor drive your car with you in the passenger seat, you may get a different opinion on how good your brakes are (or bad, depending on what kind of instructor they are and their knowledge). I've had other drivers drive my GT at many other autocross events and I had plenty of mixed reviews, most of the common ones are:

 

FWD drivers = "this car is really tail happy under braking"

RWD drivers = "this car doesnt turn at all"

AWD drivers = "wow, you got rid of most of the understeer"

MR-RWD drivers = "it's hard for me to find the balance point of this car"

 

You'll be suprised that if you know or understand why other drivers say that, then you'll know how they are driving the car to make such remarks.

[BlackHole]

You should be able to bed the pads just fine.. how are your tire pressures?

 

I agree that I should be able to bed the pads, but it hasn't happened. I've even gone as far as repeated hard 60-0 stops trying to keep the ABS from kicking in, but no improvement as the front rotors are not even 25% bedded yet. Tire pressures are 32psi F, 35R.

 

Ultimately, you may look into better shocks to stiffen the front end of the car's dampening (and spring work if neccessary) to get the front end from diving so hard (although that IS a good sign that the front brakes are working if you get that kind of weight transfer to the front of the car).

 

There is plenty of front end dive and a whole lot of weight transfer. As soon as finances allow a set of coilovers will find their way onto the car.

 

You really shouldnt have lesser braking performance.. the situation you are going through about not needing to press the pedal or not needing to input as much braking is the first sign of better braking response. My personal concern is that you're not used to having the car to be trail-braking oversteer. By choosing that pad combination, you are purposely forcing this very notion.

 

I don't use significantly less brake pedal with the Bobcat/XP8 combo than stock, which leads me to suspect that I still have air in the system somewhere, but I can't seem to find any when I bleed the brakes using the factory procedure.

 

As for trail-braking, I don't know enough to comment but I do prefer neutral-to-oversteering handling characteristics. With this pad choice I was trying to get to closer to even brake lockup F/R and reduce the front end dive a little, but it hasn't worked out quite the way I hoped. Eh, you live and learn.

 

The real matter is understanding what you want the car to do under the situations you plan to put them in as well as understanding how you may also change your driving style to maximize the performance of your new setup.

 

Yup, I know I need a lot more practice. Thanks for the input, it is appreciated.

[magnetic1]

Must be either a makeshift anti-squeal treatment or a bedding-in procedure I've never heard of.

 

Agreed. They shouldnt be making THAT much noise if any. Some people have Zero noise, some people have little, but rarely so I hear of "loud" noise.

 

Make sure the metal "clips" arent making contact with the rotor....

[Xenonk]

I agree that I should be able to bed the pads, but it hasn't happened. I've even gone as far as repeated hard 60-0 stops trying to keep the ABS from kicking in, but no improvement as the front rotors are not even 25% bedded yet. Tire pressures are 32psi F, 35R.

 

There is plenty of front end dive and a whole lot of weight transfer. As soon as finances allow a set of coilovers will find their way onto the car.

 

I don't use significantly less brake pedal with the Bobcat/XP8 combo than stock, which leads me to suspect that I still have air in the system somewhere, but I can't seem to find any when I bleed the brakes using the factory procedure.

 

As for trail-braking, I don't know enough to comment but I do prefer neutral-to-oversteering handling characteristics. With this pad choice I was trying to get to closer to even brake lockup F/R and reduce the front end dive a little, but it hasn't worked out quite the way I hoped. Eh, you live and learn.

 

Yup, I know I need a lot more practice. Thanks for the input, it is appreciated.

 

 

Ah, that's not the correct pressures you should be using with your car to begin with. In fact, that's too low in the front anyways which you are going to understeer the moment you are going to get hard on your brakes.

 

If you have air in your system, changing just the brake pads back to Bobcats all around or matching pads around isnt going to fix the mushy brake input.

 

If you dont know enough about trail-braking, you may want to consider changing your driving style or learn more about it to provoke oversteering using the brakes. If you are relying on just having "even braking forces", that wont be enough for you to get the car to oversteer.. you still have a lot to do as a driver to know how to pitch a car. If you dont have front end grip, you wont oversteer.. it's the other way to look at it. You are already lessening rear grip, which is giving you the false impression of your car's performance already. You're taking away the car's performance by over-doing the rear mods of the car without focusing on how to increase the front end grip.

 

There's two ways to oversteer setups:

Increase the front end grip

Lessen the rear end grip

 

You did the later.

[BlackHole]

Thanks for the input, seriously. You are waaaay beyond me - I wish I had a clue what the heck you were talking about in a fundamental sense.

[Xenonk]

Thanks for the input, seriously. You are waaaay beyond me - I wish I had a clue what the heck you were talking about in a fundamental sense.

 

Let's put it this way: How would you drive the car IF your car handles as if you pulled the e-brake every time you hit the brakes to make a turn? The rear end will lock up and drag around. Focus on getting on the brakes harder so that you can lock up the front first to maximize your braking, don't worry about the rear.. if you can pivot the front end of the car, then you use the rear to steer your car around.. this eliminates the need to turn the steering wheel because your rear end is already swinging around for you. It's no different than you pivot your own foot by applying pressure to the ball or toes (front) of your feet and letting your heel come off the ground (rear of the car) to spin around. Once you want to stop the spin, you put your rear heel down to get grip (so for a car, you add throttle to rock the car back down on the ground, most people understand this as acceleration squatting).

 

Adjust your driving first, worry about the mods later.. You should be able to make the car rotate and oversteer if you put enough pressure down on the front of the car through hard braking, which should cause the car to tilt down and lift the rear off the ground. Here's me driving my buddy's STi at the Subaru Challenge autocross this weekend:

 

http://www.toddlampone.com/pictures/subaru/subaru_challenge_2007/DSC_1539_crop.jpg

 

You have to use your brakes to pivot the front of the car down, and if you are not locking up your front brakes, it means you're not braking hard enough. Don't worry if the rear end gets loose, it only means that you need to brake in a straight line more so so that the rear end stays behind you, not swinging around in front of you to the point where you end up spinning the car out.

 

FYI: Most production cars brake bias are set to as much as 90% front, 10% rear.. very seldom that even race cars (except for Porsches or any other car that has the motor on top of the rear axle or behind the rear axle) dont even have brake bias to no more than 60% front 40% rear, that would make a car REALLY scary to drive at high speeds.. you would have to stop in a straight line every single time because if you tried to brake and turn the steering wheel even the slightest, you'll spin the car out.

 

FYI part 2: In high performance driving events, whenever you see yourself about to lose control and spin the car out, I teach all my students to "learn to put two feet in if you're about to spin". In other words, you push in the clutch and brakes hard so that you lock up your wheels and disengage the engine from producing power to the wheels, This locks up the brakes (making ABS work less actually because there's no power to force the tires to roll forward) and your car will spin in a straight line rather than the car trying to spin wheels to grab a direction and shoot you out in some other direction of travel. It's safer to know where the car is going off rather than trying to guess when you're going to get grip back or lose grip while you're out of control. It's already bad enough that you're in a spin.

[BlackHole]

How would you drive the car IF your car handles as if you pulled the e-brake every time you hit the brakes to make a turn?

 

I'd have a huge grin that would mean I'm cornering in the snow with a FWD car or I'm really flying on the motorcycle, sliding the rear. But more seriously, I've never figured out how to do that well in an AWD since when I do lock up the rear brakes it feels like the center diff transfers torque to the front, changing the car from RWD-biased to FWD-biased handling and increases understeer.

 

Once you want to stop the spin, you put your rear heel down to get grip (so for a car, you add throttle to rock the car back down on the ground, most people understand this as acceleration squatting).

This I understand, thanks. This makes the rear vs. front grip comments make a lot more sense.

 

Adjust your driving first, worry about the mods later.

Yeah, I'm hoping to adjust the nut behind the wheel next year and take a couple of driving classes, 'cause I know I'm a pretty lousy driver. Nice STi pic.

 

You have to use your brakes to pivot the front of the car down, and if you are not locking up your front brakes, it means you're not braking hard enough.

I can lock the fronts but I'll play with getting the rear end loose.

 

Thanks for all of your input!

[Xenonk]

I'd have a huge grin that would mean I'm cornering in the snow with a FWD car or I'm really flying on the motorcycle, sliding the rear. But more seriously, I've never figured out how to do that well in an AWD since when I do lock up the rear brakes it feels like the center diff transfers torque to the front, changing the car from RWD-biased to FWD-biased handling and increases understeer.

 

I can lock the fronts but I'll play with getting the rear end loose.

 

Thanks for all of your input!

 

 

that's exactly what it does, when you lock up the rear, the center diff isnt going to like you by not allowing a place for the power to go anywhere, so it'll just transfer the power to the front.. this also happens the same way when you spin the tires too much (viscous LSDs shine here) when you spin up the fluid and transfer the power to the wheel that isnt spinning as fast. In the case for the braking situation, the differential oil is spinning/swirling around still, so when you lock up the rears, the fluid in the center diff will want to spin the front (it has to go somewhere). And for an open front diff, it will spin the wheel with the least resistance (normally the inside wheel up front, which will end up being more understeer).

 

if you can do it in the snow and on a motorcycle, you should be able to know when the rear locks up and that's when you can nudge the steering wheel to get the rear end to come around.

 

if you can lock up the front still, then i dont see what the problem is, you are just fine as it is.

[botbs]

Quick question for you experts,

 

Did you guys have ABS problem or any other problem with two different coefficient brake pads? (ie: did the abs light turn on?)

 

I am planning to use XP12 Front and XP8 rear as I have plenty of XP8 left from last year.

 

Thanks,

 

Sam

[magnetic1]

Quick question for you experts,

 

Did you guys have ABS problem or any other problem with two different coefficient brake pads? (ie: did the abs light turn on?)

 

I am planning to use XP12 Front and XP8 rear as I have plenty of XP8 left from last year.

 

Thanks,

 

Sam

 

Sam, that wont cause any issues.