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Have you ever watched a video of a top sedan racer racing an older car where they had to use all the peddles all the time? Its amazing watching them left foot set pads before braking zone prior to beginning threshold braking with right foot.
I've done a lot of this.
The problem is flex in the upright/hub assembly causing the rotors to push against the pads and subsequently push the pistons back in to the calipers. Typically worst in high-G back and forth complex sections. Floating rotors eliminate the knock-back. It's a reactionary solution, I'd prefer to eliminate the flex that is the root cause, but at least at this point in the development of fast Miatas, we don't have that solution yet. Floating rotors are a solution. Regarding floating rotors, how much float you need depends on lateral grip and specific track. Stoptech has a Street and Race version of the floating hardware. The Street has solved 99% of the knockback in my car for all of the SoCal tracks I frequent. At VIR I had substantial knock-back, first time since changing to floating rotors. Possibly because that track has way more complexes with lots of load than most, including the "esses" which I was doing 135mph through. On my dry laps I was pre-loading the pistons with my left foot before every braking zone, and elsewhere just to reassure myself they were still there. Looks like I need the race version at that track.
As a result of my testing, we sell the floating version of the ST kit because that's what works. Street floating version by default, Race by request.
I haven't tested the Ken Auto brace, but I'm skeptical.
I too have been chasing pad knock back ever since I installed my TSE dynapro kit. Glad to hear its not just me. Anyone else having issues with slightly funky pad wear? I think the calipers need the bridge bolt that FM sells. https://www.flyinmiata.com/dynapro-bridge-bolt.html
Its not that bad. Only slightly tapered but enough for me to care. FM says 10% increase in stiffness which should be enough to take care of most of the problem I think. Its only $30 for the kit so whatever. The flip side is with how much im tracking the car, im thinking of doing superlites on custom full float rotors. Or an AP racing caliper of some sort. This will allow more pad without the knocked issue. We are working on a potential kit now.
I haven't worn out a set of pads with my setup working properly, but the set that ate **** in quick fashion were tapered/uneven as well. Hopefully i'll get enough driving in this year to wear the PFCs to see if they're tapering or not. I just added bridge bolts and went to the HD rotors in my car.
With a good driver in a fast car, you can only expect to get 3 days or so from a set of 12mm pads. Maybe 4-5 days from 16mm pads. 6-7 days from 20mm Superlite pads is the norm.
I just saw a discussion about that valve on another forum yesterday. Apparently it's frequently used by honda road racers who have problems with knockback caused by flex from weak hubs and knuckles. Supposedly works pretty well. Should have basically the same effect as the knockback springs that AP Racing and some of the other high end calipers have built in. I'm trying to get my friend to try it on his V8 car.
When is the last time the calipers were rebuilt? I fought knock back for a while on a different car and it went away when i rebuilt the calipers with new seals and pistons. Sticky pistons on old seals make the problem worse. I also added anti knock back springs behind the pistons.The springs are made by Brembo and I got them from Hoerr Racing Products.
The problem is flex in the upright/hub assembly causing the rotors to push against the pads and subsequently push the pistons back in to the calipers. Typically worst in high-G back and forth complex sections. Floating rotors eliminate the knock-back. It's a reactionary solution, I'd prefer to eliminate the flex that is the root cause, but at least at this point in the development of fast Miatas, we don't have that solution yet. Floating rotors are a solution. Regarding floating rotors, how much float you need depends on lateral grip and specific track. Stoptech has a Street and Race version of the floating hardware. The Street has solved 99% of the knockback in my car for all of the SoCal tracks I frequent. At VIR I had substantial knock-back, first time since changing to floating rotors. Possibly because that track has way more complexes with lots of load than most, including the "esses" which I was doing 135mph through. On my dry laps I was pre-loading the pistons with my left foot before every braking zone, and elsewhere just to reassure myself they were still there. Looks like I need the race version at that track.
Update - back on Rivals at WSIR and therefore less lateral load (about the same as most non-aero cars on A7s), only a very minor hint of knockback after T2. This is still with the "street" floating hardware.
Thanks to all for the great feedback and insight. Having a better understanding of the problem I now understand why it shows up when it does. I am able to drive around it for the most part but a solid pedal would help me with that last few seconds left on the table.
I am tempted to try the 11” stop floaters but I’ll likely wait for V8R to release their upcoming 11.75 floater kit. I got a lot of rear bias now and going to 11” kit won’t help that. I am also tickled pink with pad life on the 11.75/Cobalt/Stoptech setup so I’d hate to go backwards there. I think shimming pads pads as they wear will help as it keeps the pistons in the bore. I may even try the knockback springs. I would love to know how much drag they have though. The hydraulic solution looks intriguing too.
Thanks to all for the great feedback and insight. Having a better understanding of the problem I now understand why it shows up when it does. I am able to drive around it for the most part but a solid pedal would help me with that last few seconds left on the table.
I am tempted to try the 11” stop floaters but I’ll likely wait for V8R to release their upcoming 11.75 floater kit. I got a lot of rear bias now and going to 11” kit won’t help that. I am also tickled pink with pad life on the 11.75/Cobalt/Stoptech setup so I’d hate to go backwards there. I think shimming pads pads as they wear will help as it keeps the pistons in the bore. I may even try the knockback springs. I would love to know how much drag they have though. The hydraulic solution looks intriguing too.
We made some big changes to our brake system recently with (amongst other changes) going to the Trackspeed 11.75" SUperlight kit and suddenly have to pump the pedal 2-4 times to get the brake pedal up to full position.
We never had this proble EVER with the 11.75" Dynalite kit.
Would you (and others with this issue) mind posting the following?
We are trying to figure out where our problem is coming from.....im being a bit vague on purpose to start with. Will explain more after a few responses.
- M/C size?
- Booster or not?
- Caliper
- Rotor size
- Pedal system / leverage factory or modded?
One pump is knockback. 3-4 pumps is a major hydraulic system issue. The Superlite calipers we use are 3.00" piston area, same as the Dynalites they replaced, so hydraulically they are identical. If you changed nothing else, it's either a caliper issue (not specific to the Superlite) or a bleed issue.
One pump is knockback. 3-4 pumps is a major hydraulic system issue. The Superlite calipers we use are 3.00" piston area, same as the Dynalites they replaced, so hydraulically they are identical. If you changed nothing else, it's either a caliper issue (not specific to the Superlite) or a bleed issue.
Thank you. I appreciate all that. We think we have something else going on we can't quite resolve. Please note, in no way do we believe it is the Trackspeed Superlight kit at fault.
We can get it to happen in first gear in the car park just turning around. Without turning a corner the brakes work 100% and stay that way so we don't believe it is a hydraulic issue (of course we stand to be corrected). Although we have tried repeated bleeds with no sign of air resulting.
It ONLY Happens after cornering, using the brakes on the highway on straight roads in normal traffic leaves pedal perfect.
I would blame flex in spindle or hub (as mentioned in this thread) but it happens in first gear at sub 20 km/h as well, to me this rules that out so intersted to hear if this happens to any of you guys also?
We have made some changes to the system (things most of you haven't) so if any of you could provide the following I would appreciate it.
- M/C size?
- Booster or not?
- Caliper
- Rotor size
- Pedal to MC pickup point factory or modded?
@MX5-kiwi, Your knockback sounds severe. I would look at the hubs etc. Knockback was an early symptom of a failing hub.
I had similar knockback with my V8R 11.75 Dynalite kit. I swapped to the Stoptech kit hoping to solve it. It has remained consistent through both 15/16” & 1” master cylinders. It has gotten worse as my speeds have improved. I vaguely recall it being there on the 11” wilwood kit too. It’s the worst after bouncing curbs through a series of esses.
I have improved the problem by keeping the hubs fresh. New pads have less knockbad than older ones. This tells me the further the pistons bores come out the worse the problem. With the superlites you got a lot of piston coming out of the bore as pads near end of life. Shimming pads as they age will help this.
1” stock style master
stock pedal ratio
boosted (sport )
Stoptech 38/36 calipers with V8R brackets.
11.75 V8R rotors
05-21-2018, 06:41 PM
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