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Old 01-07-2014, 06:55 AM   #1
vicious_fishes
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Default How much grip before knockback/knockback on stock brakes?

Basically i've got a stoptech BBK but i'm concerned that once i slap it on, i'm going to get epic knockback with my 5x100 bearings/hubs.

I was also intending on buying some wider wheels/stickier rubber but, same problem. I could however sell the BBK, and buy some two piece rotors (dba5000)/nice shiny brake ducts if I get the fat rubber. But that's pointless if I get knockback even with the stock 4pots.


Input/thoughts?
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Last edited by vicious_fishes; 01-07-2014 at 07:08 AM.
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Old 01-07-2014, 07:50 AM   #2
rjrutzky
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stop tech, 5x100, pfc11, hoosier a6 = never had knockback
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Old 01-07-2014, 01:35 PM   #3
Mike.J
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knockback is a new term for me. Can you explain in simple/short words?
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Old 01-07-2014, 01:41 PM   #4
lemming
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It's basically rotor motion due to cornering loads. The hub/spindle either flex or experience other relative motion (due to worn wheel bearings, for example). If you are using a fixed caliper, the motion of the rotor will slightly compress the pistons. Thus, a longer pedal stroke (and possibly even "pumping" the brakes) will be required for the next stop.

http://stoptech.com/technical-suppor.../pad-knockback
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Old 01-07-2014, 05:33 PM   #5
JDwhiteWRX
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How big is the diameter on the rotors with the Stoptech kit? if its same as standard sti Brembo then bolt it on and see how you go.

Either way I don't see why you should worry about things that "might" happen because it happened to someone else. For all the problems you hear people complaining about on forums like this there are a thousands of people running the same setup with zero issues.
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Old 01-07-2014, 05:40 PM   #6
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The majority of pad knockback issues happen when there is side loading combined with a vibration of some sort, such as curbs or dropping wheels off track. I've driven enough cars that have enough brake issues where I've gotten in the habit of "pumping" the brakes before major brake zones. By pumping the brakes, you only need enough pedal pressure to set the pads against the rotor, and you do not want enough pressure to slow the car down. If you're comfortable pumping the brakes with your left foot, that is also a plus.
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Old 01-07-2014, 06:00 PM   #7
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Quote:
Originally Posted by kfoote View Post
The majority of pad knockback issues happen when there is side loading combined with a vibration of some sort, such as curbs or dropping wheels off track. I've driven enough cars that have enough brake issues where I've gotten in the habit of "pumping" the brakes before major brake zones. By pumping the brakes, you only need enough pedal pressure to set the pads against the rotor, and you do not want enough pressure to slow the car down. If you're comfortable pumping the brakes with your left foot, that is also a plus.
definitely a good habit to have. plus, sometimes your competitor will think you are braking and check up early
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Old 01-07-2014, 09:20 PM   #8
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Quote:
Originally Posted by rjrutzky View Post
definitely a good habit to have. plus, sometimes your competitor will think you are braking and check up early
i've heard about systems being put in place that automatically keep the brake lights on for a couple of seconds after you take your foot off the pedal too
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Old 01-07-2014, 11:46 PM   #9
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Quote:
Originally Posted by kfoote View Post
The majority of pad knockback issues happen when there is side loading combined with a vibration of some sort, such as curbs or dropping wheels off track. I've driven enough cars that have enough brake issues where I've gotten in the habit of "pumping" the brakes before major brake zones. By pumping the brakes, you only need enough pedal pressure to set the pads against the rotor, and you do not want enough pressure to slow the car down. If you're comfortable pumping the brakes with your left foot, that is also a plus.

This is second nature before I enter any hard braking zone's..all I do is a quick tap with my left foot right before the brake zone, which is just enough to re-seat the pads and take up any "slack" before getting on the brakes hard. They do make anti-knock back springs which are fitted inside the caliper pistons that always keep the pads pressed against the rotor but have heard these springs increase pad wear noticeably.
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Old 01-08-2014, 10:35 AM   #10
kfoote
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Quote:
Originally Posted by vicious_fishes View Post
i've heard about systems being put in place that automatically keep the brake lights on for a couple of seconds after you take your foot off the pedal too
There is also the opposite that has been used in the past as well, with a delay before the brake lights come on. This is especially useful when people try to brake in a spec series as late as you are braking.

The up side of the anti-knockback springs is that they do indeed eliminate the knockback. The other downside in addition to the extra pad wear and brake heat, is that it does create drag on the rotors, reducing acceleration.
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Old 01-09-2014, 06:19 AM   #11
vicious_fishes
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Quote:
Originally Posted by kfoote View Post
There is also the opposite that has been used in the past as well, with a delay before the brake lights come on. This is especially useful when people try to brake in a spec series as late as you are braking.

The up side of the anti-knockback springs is that they do indeed eliminate the knockback. The other downside in addition to the extra pad wear and brake heat, is that it does create drag on the rotors, reducing acceleration.
that would definitely not be legal

but we're off topic.
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Old 01-09-2014, 10:11 AM   #12
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I've experienced knockback even with 5x114.3 hubs (Hoosier R6's and Stoptech 355mm kit). I just learned to tap the pedal with my left foot before entering major braking zones and it became a habit, I don't even have to think about it anymore. One thing you can do that would help is to remove the anti-rattle hardware from your 2-piece rotors. Obviously this will cause some noise on the street, but it allows more float between the hat and ring. Also replacing your wheel bearings fairly often would help.
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Old 01-09-2014, 02:23 PM   #13
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I got knock back several times on my car (06 with stock) 4-pots running Goodyear F1GSD3 215's on a windey mountain road, particularly on the hairpin uphill turns (angle + cornering load).

The goodyears were summer tires, but far from being the sticky that's out there now (even non-rcomps). You're gonna have knock back, I doubt you can avoid it. Pump the pedal is the non-modified solution.
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