New kit under development, improving GenIII+IV brake balance for track/autocross use

[MomentaryRacing]

We are excited to announce the joint effort with RB Performance Brakes (http://www.racingbrake.com), to design and develop replacement rear caliper kit for Gen III/IV Viper.

In our testing this season, it became apparent that the stock ACR/ACR-X system has issues with brake bias/balance, which prevent the car from reaching its full potential under heavy use/race conditions.

Consultation with a professional race engineer has confirmed that this is a known limitation of the stock system.

The kit will allow use of the stock rotor and stock, unmodified spindle.

Stay tuned for further updates, we are looking to run the first test in a few weeks.

Attached screenshot demonstrates behavior of the stock ACR/ACR-X (gen IV) system - color of data points corresponds to rate of deceleration (heaviest braking is red), while the vertical axis represents front/rear brake bias - 0 is perfect front-rear balance, negative number (where most data points are) represents rear brake bias - which is very unusual for a car of this type. We also logged excessive rear ABS activations due to this (not shown on this chart).

[Racingbrake]

Good introduction for this improved set up on rear brake, and your sharing the feedback from racing experience is truly apprecaited.

I wonder if anyone race their Viper (G3,4,5) with factory 4 pot calipers (front and rear @355/355mm rotors) felt/had the same issue or concern but not knowing what to do.

[J TNT]

Subscribed . :fpopcorn::fpopcorn:

[Racingbrake]

Probably never been discussed before. For most street driving and event days you might not feel it, but some serious track/racing people already noticed that Viper has too much bias on the rear, and looking for a solution.

First let's take a look on how Viper caliper piston size stacked up, and the change of rear calipers we proposed to make.

http://cimg8.ibsrv.net/gimg/rennlist.com-vbulletin/694x404/80-piston_analysis_a0244af3b3a873772bf1469279c04cd4d7 0bc87b.jpg

Up until now Viper racers were looking for installing "proportioning valve"', "smaller rear rotors", "less aggressive" rear pads etc., but I can say none of these can effectively change the front and rear brake bias unless a "smaller piston" rear caliper is in place.

This rear RB caliper kit is being developed as our pot caliper would require an adaptor (below) for installing to OE spindle.

http://cimg5.ibsrv.net/gimg/rennlist.com-vbulletin/650x216/80-ad820_a21b6e8c3681a9085a1de73667a6d424b0e8d869.jpg

[XSnake]

I believe the trick was to install front calipers on the rear. That's what some did in the X series.

[Racingbrake]

We are making a production run next week on the rear adaptor for RB rear 4 pot calipers.

Anyone races with their Viper should feel the need to reduce the rear bias as proposed here, which has never been offered by any brake company before.

Any Viper racer here?

[MomentaryRacing]

Track test is scheduled for next week :)

[Racingbrake]

This is the kit we have just made it ready to ship to Momentary Racing.
http://www.racingbrake.com/RB-Rear-Aluminum-Caliper-and-Iron-Rotors-for-Dodge-p/2546.htm

http://cimg6.ibsrv.net/gimg/www.mbworld.org-vbulletin/640x480/80-img_0493_69ae81740e650ca089dfc49ea418ee67c62607ac. jpg


Two heavy duty RB 4-pot rear calipers - Using the same pad as Viper
Two upright adaptors and 2 assembly bolts
4 ea high strength caliper bolts


Any serious track racer who has been troubled with too much rear bias but can't find a solution. This is your answer and we guarantee the result.

[Racingbrake]

More discussions on this rear balanced kit in this thread:

Anybody tried the 370 mm rotor upgrade?
http://driveviper.com/forums/threads/14268-Anybody-tried-the-370-mm-rotor-upgrade?p=248628&viewfull=1#post248628

In fact the front 370mm oversized rotor plus this rear balance kit will be the best combination for Viper G3/4/5.

[MomentaryRacing]

OK, this will be fairly detailed post, as the development of the kit has been wrapped up, and we wanted to share the results.

First of all, big thank you to RB Performance for working through the development of the kit, Buddy Fey who helped us with some of the calculations, fellow Viper racers who shared their experience with brake bias issues, and Jon B. of Viper PartsRack, who came through on the last moment delivery of a tie link part that saved our weekend (which was the last opportunity for an extensive test this season).

Cliff's notes: The kit delivers, and the car FINALLY has that "Racecar Feel" under hard braking.

Details:

We finally had a chance to test Rear Brake Bias/Balance kit, developed by RB Performance. Last weekend was a great chance to test it against OEM configuration, as we were using same tires and brake pads, and similar aero setup, as our last test day on the same track (when we had OEM calipers on the rear axle), with nearly identical weather conditions as well - alternating cool/dry weather, as well as some rain.

20054

We were using RB XR70 rear pads, and Sintered (100% Metallic – originally developed for CCM rotor kit) front pads, with the open slot, 2 piece RB rotors (ACR-X/wider annulus size in the front, OEM size in the back). The car was on BF Goodrich G-force R1S tires.

20055

From the first session with the kit, it was clear that the piston size calculation was spot on. Both initial engagement, and the car’s balance under moderate-to-hard braking was significantly improved.

As you can see in the snapshot (typical of many laps’ worth of data we reviewed), we can exert higher braking force on the rotors/tires, and, thus, achieve higher deceleration forces. As a result, we started to use later braking points in corners where significant braking was required (by 20 to 40 ft., on average), without loss of car’s balance. Not having rear ABS interfere on initial brake application was a critical part of being able to maintain the balance, and to build up optimal tire slip angle.

20056

Looking a little deeper into the data from the whole weekend, we can also see that there’s a reduction to rear ABS interfering (by about 30%), even though overall force applied to tires on deceleration, is greater.

20057

Even the front ABS engagement is slightly reduced (unexpected result), likely resulting from an overall improved balance of the car under hard braking.

Finally, statistical analysis of average forces applied per wheel, show a consistent shift towards 50-50 “loading” of front and rear wheels under hard braking. OK, this sounds a little complicated – the bottom line, is that the grip across all 4 tires is maximized as the balance of the car is improved.

20058

We improved our best time on this track by 0.9 seconds this weekend, with majority of gains coming from both shortened braking zones, as well as improved balance of the car under braking and on turn-in.

The weekend brought a mix of dry and rain conditions, and braking performance was consistent and predictable in all situations.

[Banzai88]

I do notice the rear end wiggle on hard braking with my stock brakes. With these rear calipers, can I use my same rotors and pads? how much for the calipers? Thanks

[Racingbrake]

I do notice the rear end wiggle on hard braking with my stock brakes. With these rear calipers, can I use my same rotors and pads? how much for the calipers? Thanks

You can place the order here for the item on our website:

http://www.racingbrake.com/RB-Rear-Aluminum-Caliper-and-Iron-Rotors-for-Dodge-p/2546.htm

[speedtactics]

Come on just suck it up and live with it :dude3:
I do notice the rear end wiggle on hard braking with my stock brakes. With these rear calipers, can I use my same rotors and pads? how much for the calipers? Thanks