Potentially Dangerous Rear Brake Bias Problem... - The Saab Link Forums

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Performance Modifications for the NG900 / Old 9-3 This forum contains PERFORMANCE related Q&A's for the NG900 and 9-3. This may also include suspension.

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Old 04-12-2012, 02:39 PM   #1
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Potentially Dangerous Rear Brake Bias Problem...

Upgraded to the 308 fronts with EBC yellow stuffs. Now, it stops so hard the back end keeps trying to swing around; when I'm on the brakes on the highway or trail-braking, it gets wicked hairy. Got it sideways the otherday on a sweeper and essentially shit myself.So 1) will better rear brakes make the back even more squirrely ? 2) Would I benefit from better pads (stock, currently) or bigger rear rotors and better pads? I ask because I've been told big rear rotors are not necessary because the car isn't heavy enough to heat 'em up. What say you? I've seen some threads before on this, but it was more from a "feel" standpoint and less safety.
ideas?
-Cm
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Old 04-12-2012, 02:56 PM   #2
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did you upgrade the arb as well? my 9-3 would kick the rear out after switching to viggen springs, bilstein sports and a 25mm arb
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Old 04-12-2012, 04:30 PM   #3
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Rear ARB is the 22mm one I believe....or whatever the non "race" GS upgrade is, 19?
-Cm
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Old 04-12-2012, 04:49 PM   #4
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Old 04-12-2012, 05:39 PM   #5
 
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Upgraded to the 308 fronts with EBC yellow stuffs. Now, it stops so hard the back end keeps trying to swing around; when I'm on the brakes on the highway or trail-braking, it gets wicked hairy. Got it sideways the otherday on a sweeper and essentially shit myself.So 1) will better rear brakes make the back even more squirrely ? 2) Would I benefit from better pads (stock, currently) or bigger rear rotors and better pads? I ask because I've been told big rear rotors are not necessary because the car isn't heavy enough to heat 'em up. What say you? I've seen some threads before on this, but it was more from a "feel" standpoint and less safety.
ideas?
-Cm
Adding more stopping power in the rear will definitely help. I used the 300mm 9-5 Aero rears and a good set of ceramic pads to balance out 316mm fronts
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Old 04-12-2012, 08:31 PM   #6
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What is the cost to benefit ratio for the upgraded Aero rears? If adding decent pads to the back end will do 80% of what the full upgrade will do, then obviously this is my choice for now.
The viggen brake upgrade was pricey-the rotors were mucho denero and the carriers were 100 bucks. Worth it I'd say, but, not sure I want to incur that all over for the rear.
-Cm
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Old 04-12-2012, 08:43 PM   #7
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I'm no expert, but if the back end keeps coming around, I'd say you have too much rear brake, not too little. I think the 300 mm rears will make things worse. I haven't used the Yellowstuffs, but if they are a race pad with poor cold bite, you might be doing all your cold stopping with your rear brakes, which would cause the instability you are seeing.
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Old 04-12-2012, 09:37 PM   #8
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You need to stiffen up the front (springs/struts). The more you nose dive the higher the rear end is going to ride up and the more likely its going to try to come around. On the flip side, that's why GS sells those stiffer rear springs to keep the ass end from squatting down on acceleration to keep the nose from jumping up and loosing traction.
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Old 04-13-2012, 12:40 AM   #9
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I'm no expert, but if the back end keeps coming around, I'd say you have too much rear brake, not too little. I think the 300 mm rears will make things worse. I haven't used the Yellowstuffs, but if they are a race pad with poor cold bite, you might be doing all your cold stopping with your rear brakes, which would cause the instability you are seeing.
I was going to say that as well.
Yellow's are race pads. they take a while to warm up.

How are they warm?

Things also might just need a bit of time to "bed in"
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Old 04-13-2012, 04:59 AM   #10
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what are you riding on for suspension? i agree that if you are braking hard enough to nose dip and that's throwing the weight off balance then a suspension upgrade is due. also upgrading the rear to the 300mm aeros will even the braking out and reduce nose diving believe it or not.
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Old 04-13-2012, 05:15 AM   #11
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If the rear is locking up early I would swap the front pads out for something that's just a street pad. Looks like yellowstuff is a street/track pad, could be more on the side of track which can be difficult to heat up on the street. I used Hawk HP + on my viggen a few years ago, probably similar to the yellow stuff being a track pad which can squeek by on the street. It would take me over a lap to get the pads up to heat with my stock viggen brakes at that time... but once heated the car wouldn't skip sideways when hitting the binders hard.

If $$ is tight... try a more street friendly pad up front. If you take your car to a track swap the pads for the track day. You could even buy a 2nd set of rotors just for that.
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Old 04-13-2012, 06:05 AM   #12
 
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The issue really isn't lock-up, but uneven braking force. I've always heard you want to keep the front/rear bias pretty equal to the weight distribution of the car.

Putting big stoppers on the front and leaving the rears alone tends to make the rear end light and swingy because of the weight shift upon braking. When I upgraded just the fronts, I used 9-3SS Aero front rotors on with 4-pot Brembos and Hawk HPS pads. Front end would dive, weight would come off the rear and I could induce oversteer with just a tap on the brakes. It was fun, but REALLY scary when it happened unexpectedly.

It lessened considerably when I switched to the 300mm 9-5 Aero rears. There was only about a week's gap between the two but it was night and day. They're not enough to overpower the fronts, but big enough to bring the balance back in line...
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Old 04-13-2012, 07:08 AM   #13
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Mike, given that stock brakes can easily trigger ABS lockup, at least for one stop, how can big front brakes cause even more forward weight shift? It seems the grip of the tires would be the limiting factor on forward weight shift, not the size of the brakes.

I'm also confused because if I'm reading it right, the OP essentially now has a stock Viggen brake system. Nothing unstable about that.

I'm not trying to argue what you experienced, I'm just trying to figure out why it's happening. I know Nick has warned against going to a 25 mm rear ARB with the Aero 300 mm rear brake upgrade, and I always assumed that was because now the rear brakes are just that little bit closer to lock up....
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Old 04-13-2012, 07:17 AM   #14
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I'm no expert, but if the back end keeps coming around, I'd say you have too much rear brake, not too little.
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Old 04-13-2012, 07:31 AM   #15
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Correct with ABS it's not really locking them up.... but unsettling the car etc...

On my old SPG which had a gutted interior I went with AP Racing 335mm 4 pot brakes up front & rear was totally stock the car stopped 100x's better this way vs stock. The back would not step out under braking (track or street) which would happen sometimes with stock brakes. There were a few turns at Putnam Park that I would lock up the back upon braking, going larger rear brakes on that car I think would of just made it worse.

When I went with the 300mm aero on the rear of my viggen the back would lock up & be unsettled quicker then the front. That was with Hawk HPS pads in the front.... a street pad. Stock suspension plus the largeer rear ARB. I then swapped AP's from my SPG to Viggen & it finally stops how it should....

But like mentioned if the back steps out I think there is either two much rear brake &/or the suspension isn't up to the task.
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Old 04-13-2012, 08:11 AM   #16
 
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Mike, given that stock brakes can easily trigger ABS lockup, at least for one stop, how can big front brakes cause even more forward weight shift? It seems the grip of the tires would be the limiting factor on forward weight shift, not the size of the brakes.
What I found was the onset of the weight shift happened much quicker, prompting the nose dive and lighter rear...even during straight line braking. Tires were fairly new BFG KDW2s on dry pavement. I'd still have plenty of traction in the front, but the car would feel tail-happy.

Quote:
I'm also confused because if I'm reading it right, the OP essentially now has a stock Viggen brake system. Nothing unstable about that.

I'm not trying to argue what you experienced, I'm just trying to figure out why it's happening. I know Nick has warned against going to a 25 mm rear ARB with the Aero 300 mm rear brake upgrade, and I always assumed that was because now the rear brakes are just that little bit closer to lock up....
You're right....that's basically a stock Viggen setup, so he might be able to just try a different compound and call it a day.

Nick's recommendation is because the 25mm bar reduces understeer to the point where it can induce trail-brake oversteer with that size rotor. You don't even have to lock up the brakes to feel the difference in weight shift. I kept the 22mm bar for this reason...
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Old 04-13-2012, 08:13 AM   #17
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I have no idea where you guys are getting this front pad not heated theory. I have no idea where people get the idea that the EBC's have crappy cold performance. It brakes 90% of stock cold and when they are hot...holy shit! The problem is nose dive, I guess. Kinda hard to tell while my eyeballs are popping out of my head. It stands on its toes when I get on the brakes hard.
It's fine on the straights, really, but when it comes to turns I get that sphincter-shrinker feeling of the back end getting light.
-Cm
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Old 04-13-2012, 08:16 AM   #18
 
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Correct with ABS it's not really locking them up.... but unsettling the car etc...

On my old SPG which had a gutted interior I went with AP Racing 335mm 4 pot brakes up front & rear was totally stock the car stopped 100x's better this way vs stock. The back would not step out under braking (track or street) which would happen sometimes with stock brakes. There were a few turns at Putnam Park that I would lock up the back upon braking, going larger rear brakes on that car I think would of just made it worse.

When I went with the 300mm aero on the rear of my viggen the back would lock up & be unsettled quicker then the front. That was with Hawk HPS pads in the front.... a street pad. Stock suspension plus the largeer rear ARB. I then swapped AP's from my SPG to Viggen & it finally stops how it should....

But like mentioned if the back steps out I think there is either two much rear brake &/or the suspension isn't up to the task.
I think I might have been unbalanced, and with the added handicap of a platform not known for its handling.

But I totally agree: The combo of the 4-pots in front and the 300mm rears made all the difference in the world...
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Old 04-13-2012, 08:18 AM   #19
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Also, the car is beautifully neutral in turns; driving at the limit yields an even 4 wheel slide, no plowing. Hell, I've broken the tires loose mid-turn and it's still behaved.
-Cm
Ps Hawk Pads blow. Their popularity remains a mystery to me. They glazed badly and were noisy as hell. I've had the EBC's smokin and 'stankin and they've held true...knock on wood!
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Last edited by Cm452; 04-13-2012 at 08:21 AM.
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Old 04-13-2012, 09:55 AM   #20
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I had the opposite experiece with pads.... tried two different sets of EBC's & thought they sucked. By far the best pads I used on my viggen brakes were Hawk pads. The HPS didn't dust & performed quite well at a few track weekends.... not nearly as good as the HP+ which did dust, made lots of noises & ate my rotors up really quick. But the braking power after the pads got HOT was quite impressive..... I will never go EBC's... been there.... tried & hated that

It's not that EBC's have poor cold weather performance, it's if you use a track oriented pad on the street it cannot build up enough heat to work. A track/street pad blurs that line.... & will sacrifice track performance for cold bite when used on the street, like driving to/from a track. OTher pads which are for street use do not need any warming up to work 100% but will not make it through a track day.

From what I read the yellow stuff pad is a track/street pad, probably similar to the HP+ I used from Hawk?? The HP+ I used had excellent bite when HOT but I wouldn't suggest using it on the street in the winter.... I tried that... didn't like it....

If you want to car to oversteer a bit just add a few PSI to the rear tires..... I always preferred a little oversteer vs neurtal or understeer.

Not known for handling is a understatement
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