ACR-X Brakes

Longdaddy said:

3. They are truly "floating" rotors (unlike stoptech). Once they go through the first few real heat cycles, they are "track only" rotors, low speed noise/vibration are too much for street driving, especially with worn pads. Also they create more wear on the pads, I think J shaped grooves are the main reason. I like to drive the car to the track, and that experience is a lot less nice with these rotors.

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Wondering if others with these rotors are experiencing this? I definitely just started to experience it in the sense felt like I was getting a rattle or something loose every time I hit a bump. I also get some vibration above 70mph. I then realized if I applied the brake over bumps, all noise gone.

So, Longdaddy, is that what you are referring to? Funny part is I was parked next to your car for about 10min sat morning in Kirkland and notices the different rotors.

As a note, after a lap or two on the track, all vibration/rattle goes away I guess do to the expansion from the heat. Glad to see this info as was concerned something was wrong.

there is now a version that fits as well as Brembo motorsports ring! Details here: http://forums.viperclub.org/threads...-style-quot-rotor-experience-street-and-track

yep the post above describes my experience with Brembo "J groove" rings exactly^

Getting a bigger rotor with less bite makes no sense to me...why not just stick with the Stoptechs? Maybe I'm missing something...but I do time trials not racing. FWIW, I have not had the issues that Logndaddy is reporting, and I have a full season on the Brembos (including a track record). However, I don't drive my car on the street. I use Performance Friction pads front (#1) and rear (#3). The biggest difference I notice is that I am not getting into the ABS all the time like with the Stoptechs. I used the same pad compound with the Stoptechs.

Initial bite is more gradual/"softer" with RB rings compared to Brembo. Either one has more pronounced bite compared to ST/D968 combination.

As far as "why not just use ST":
Constant torque is likely similar or higher. Maximum braking force/deceleration is, of course, unaffected, as that will be determined by tires and downforce (unless your pads overheat). The main advantage is distributing the friction/heat over larger surfaces (and mass) for both pads and rotors, so that maximum force brake applications can be made consistently for many laps - which is why I like the ACR-X "wide annulus" configuration.

In any case, I avoid any StopTech rotor/ring for track work. They turn out to be incredibly expensive over time, as they warp after 15 heat cycles, and become unusable after about 20-25. I even warped the ones in the rear! When I tried ST rotors a while back on a corvette, I had a similar experience as well.

I doubt that getting/not getting into ABS has much to do with rotors, it sounds like you may be able to go with more aggressive front pads for the tire and downforce configuration you are using.

Congratulations on your Time Trial track record.

P.S. The issues with noise/vibration have been reported by several people (incl. this thread). While they are most noticeable when driving with unloaded suspension (i.e. street), they do produce "Did I lose my wheel weights?" vibration at triple digit speeds on the track eventually. I am attaching the picture that explains why it gets worse with time. This is after about 25-30 hard cycles with Pilot Sport Cups and maybe a dozen or so rain cycles with a combination of PS Cups (NOT a good rain tire) and NT05 tires.

Boxer12 said:

Getting a bigger rotor with less bite makes no sense to me...why not just stick with the Stoptechs? Maybe I'm missing something...but I do time trials not racing. FWIW, I have not had the issues that Logndaddy is reporting, and I have a full season on the Brembos (including a track record). However, I don't drive my car on the street. I use Performance Friction pads front (#1) and rear (#3). The biggest difference I notice is that I am not getting into the ABS all the time like with the Stoptechs. I used the same pad compound with the Stoptechs.

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I guess you are a lot harder on the brakes than me, as a lot of people are. I don't doubt what you are saying, just sharing my personal experience.

BTW, is there a way to check the Brembo fastener hole condition without disassembling them? If I disassemble them, do I need to use new fasteners to reassemble? (I will preorder them)

I re-used ST, DBA and Brembo fasteners on 2-piece rotors quite a few times (which is against manufacturers' recommendation). I have never had issues caused by that. I have seen StopTech fasteners loosen/back off at the track once, although I suspect improper assembly more than anything else. When I re-use rotor fasteners, I try to clean the outside barrels the best I can, soaking them with parts cleaner and maybe even scrubbing with something that would not scratch them. Of course, the right locking compound (it has to be the type that can "flow" in from the outside, not the usual thick stuff) needs to be re-applied.

There is a way to get a feel for how much the holes are worn without even taking the caliper off.

Remove the wheel and brake pads, and secure the hat to the hub by a couple of nuts (maybe with a spacer or some washers under them). Grab the studs with one hand, and try to rotate the ring against the hat with another. Also, try pulling on the ring in a few directions. A slight play/"click" is normal, especially if the rotors has seen some track use. If you can visibly see the ring rotate back and forth against the hat, the holes are getting damaged. This could also happen when all the fasteners are loose (i.e. not having been torqued right), but in this case, the ring will "flop" against the hat in other directions as well, if that makes sense.

You can also take out just 1 fastener, and inspect the outside of the hole, and even the inside (i.e. small mirror + flashlight)

was re-watching some videos and found a clip from my very last day on Brembos, just before the picture showing damaged holes was taken. you can see how much the front end is shaking on the straight, and especially when braking into turn 1 - check out 1.45 and 3.40 in the video.

https://www.youtube.com/watch?v=dXD65W_b1V0

I see what you are talking about although that could be ABS kicking in. Did you have the same issue in the dry?

oh yes, same, if not worse, in the dry.

I have now done 5 events on these rings, and they had held up admirably - no issues at all. I've driven the car around the block a few times after the last day and I am happy to report that there is no shimmer/vibration at all that I can notice (Brembos would have been a little rough at this point, and StopTechs would have been warped to the point of being unusable). I have been using RB XR7 pads for the last few events. Set my new personal best at 2 tracks while running this setup as well (although these are the tracks I've driven the least with this car in the past few years)

TreeSnake,

You better get you butt out to Hastings for sure this year as want to see all the cool stuff done to the Serpent. Really interested to chat about the Brembos, and do know the Carbotechs are available for that switch , and you know I do like those pads a bunch! Car is going to be wicked and need to get you interested in run time trials with NASA since you don't really want to run door to door.

what type of brake cooling are you guys using? do you have the carbon ACRX pieces that feed air to the caliper/rotor? i am trying to find a solution.

did you ever find any ta pads?

yes we all have the factory set up for the acr-x

BossGT said:

what type of brake cooling are you guys using? do you have the carbon ACRX pieces that feed air to the caliper/rotor? i am trying to find a solution.

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I have a new CF set of front ducts like used on the Comp Coupes, but you need to fab straps to hold them in place.

You will need to change the line fitting to come out parallel to the caliper though to fit them.

BossGT said:

what type of brake cooling are you guys using? do you have the carbon ACRX pieces that feed air to the caliper/rotor? i am trying to find a solution.

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The comp coupe ducts come with brackets that work, that's what I have. I also use the ACR-X Brembos and find myself rarely into the ABS whereas with the Stoptech ACR brakes i am constantly into the ABS, so despite the slight added weight my times are quicker with the Brembos which I think is due to the greater finesse or touch that is available when in heavy braking zones. I don't think the extra rotating mass hurts, and I have not had any issues with vibration, excessive wear or anything like Longdaddy is reporting. I like the Brembos with PF1/3 pads and nobody has beaten my times at my local track (HPR) in a Viper that I know about, fwiw. A little extra $$$ but I don't like ABS coming on. Smoother is better. Just my 2c. (Judge everything with lap times!)

so you are using performance friction factory fill acr-x pads in front? factory part number?

bluesrt said:

so you are using performance friction factory fill acr-x pads in front? factory part number?

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Check post #31