This is exactly why high performance motorcycles have been switching over to radial mount calipers the past ~5 years.

Eric, got some questions I am going to send your way if you have time.

 

haha, yeah, measuring is always a good idea

i ended up going with Carbotech XP12/XP10 on fresh rotors...they worked great at the track once I got them bedded in

what i mean by warped is the pedal shaking and that dronedronedrone noise from the rotors...from all the reading i've been doing i'm pretty sure now that the issue was incompatible pad materials trying to share the same rotor...from now on i will always keep rotors and pads together, one set for track and one for street...just takes all the headache out of this stuff

 

Can you explain "caliper flex"? Our caliper is a humugous cast piece and am having a hard time thinking about it "flexing"? Do you mean the (what I'll call) 'fingers' of the calipers behind the pad bending... or what exactly....thanks.

 

Not sure what you mean about "humugous cast piece" (stock? aftermarket?)

Here is how you notice it---happens all the time with cars that get raced (all kinds of cars). The guys at Hawk pointed this out after we ran 8 hours on the same set of Hawk brakes at a Road Atlanta enduro in our #30 RX8 running R6 Hoosiers. We had some pretty noticable pad wear that was uneven. You could call this "tapered". If I recall correctly, the shorter or top part of the pad had noticably less material than the longer side or bottom of the pad. This is due to the calipers "opening up" after lots of use. They are a cast piece and designed for street cars---right?. We start with new calipers every season to reduce this and probably will replace ours mid season to maximize brake pad contact and therefore braking potential.

Advice: guys, when you pull your brake pads-----(ready for this Eric Meyer special??) MEASURE your pad wear. A little trick you can perform is swap out your pads (from the inside of the caliper to the outside of the same caliper) if you are getting uneven wear---this COULD give you a little more life if one pad is wearing out sooner than the other.

Did this answer your question?

 

nice Eric----and guys --please dont just swap pads out for the track---do a real cleaning on the rotor facing--hitting them with a light touch of emory cloth--to insure removal of the pad deposits already there. deposit buildup will give you the shakes--just like a warped rotor. Not only do i do a hot bedding in --i also drive with mine for a couple days before the event.
pay attention to the slider bolts--you wouldnt believe what i have seen--for example a slider bolt that was absoulutly stuck and causing so much caliper distorsion that there was a 1/4 inch difference on the pad. Seen people not changing fluid x 4 years--did only bleeding.
check the seals around the pistong --etc etc.
yall have heard of the tt guy in the s2000 that got killed--right? it was brake failure that lead to the tragedy.
I much rather have good brakes than anything else on the track.
olddragger

 

Just to add to that (that being Eric's post), the brake caliper is not ideally supported as it is only held on at one side and it needs to be able to go over a rotor so it cannot have any support between the two sides closer to the hub. That means that it has a cantilevered arm that sees a great deal of force from braking. The braking force effectively spreads the caliper open a little bit. The deflection is pretty small, but you can probably measure it by putting a dial indicator on it and stomping on the brakes (I've measured deflections in the 0.030" range on ATV calipers in a panic stop situation). And, like Eric said, these things are designed for street cars where they aren't seeing maximum braking every time the car slows down. Over time with such large loads applied over and over again, the caliper begins to permanently deform.

 

nicely said
OD

 

There are different types of calipers:

1. Floating type single piston CI caliper - Typically for stock OE calipers such as RX8 (Grand AM allows only stock calipers but can use two piece rotors).
2. Fixed type multiple piston aluminum/CI calipers - Axial (leg) mount like some stock caliper: RX7, Sti, EVO 8 (Al) or heavy trucks (CI)
3. Fixed type multiple piston aluminum calipers - Radial (top) mount like RB4000 caliper BBK for RX8.
4. Fixed type multiple piston aluminum calipers - Radial (top) mount but with differential bores like RB400 caliper BBK for RX7.

Caliper deflection is unavoidable due to cantilever stress; however several factors can affect the degree of flex or deflection:

1. The axial distance (disc center to spindle mounting surface) - The shorter the span the less of the deflection - RB’s center mount two piece rotor design requires less span than traditional surface mount two piece rotors.

2. Caliper design including how it’s mounted - Leg (part of aluminum body) mount will flex more than radial or top mount with high strength alloy steel blots.

3. The radial distance (diameter of the rotor), the smaller the rotor the less of the deflection.

4. The caliper material - A more rigid aluminum material means less flex.

Type of uneven pad wear:

1. Between inboard and outboard - Typically seen in stock floating caliper due to the sequence of applied pressure, inboard side is engaged with caliper piston before the outboard side is engaged by retracted claws.

2. Between outer and inner edge - This can cause due to caliper flex and uneven temperature, usually outer edge wears more than inner edge.

3. Between leading and trailing edge - Leading edge engaged with rotor before trailing edge, this can be alleviated by piston size differentials - smaller piston for leading and larger piston for trailing.

A better designed and well built brake system not only can provide a more responsive and powerful braking performance but also extend the life of pad and rotors.

We certainly appreciate all the supports and trust you put on RB brakes

Thanks

Warren - RB

 

Very well put

 

Thread revival:

Warren from RB mentioned they dont YET make a stock size 4-piston caliper kit to fit the 18 X 9.5 +45MM rpf1. Any chance things had changed? I dont like the wording on the rb website for the stock sized kit. It says: "This brake kit will fit most 17" wheels with the exception of 17” Enkei RPF1 wheels." But no mention of 18" wheels. For the 13" kit it is much more clear by saying:" Fits 18 inch stock & Enkei wheels"

My situation. I have the RB 2 piece open slot rotors on all four tires and have good success running the hp + pads at the track with 245 nt-01 tires. However, I am upgrading to the 18 X 9.5 +45MM rpf1 and will run a 275/35 r-comp tire or maybe a hoosier. With the extra tire grip I thought I might want some extra braking power along with some weight reduction but if I have to buy the 13" kit with all new rotors, then I will need to find some extra room in my buget.

 

Oh and a few question for those that do run the RB 4-piston caliper stock size and/or 13". Any problems with brake bias? Are stopping distances improved or just brake feel? Would it be benifical to run a rear pad with more bit to offset upgraded front brakes?

 

2 cents: question why you think possibly better gripping tires requires extra braking power if you're happy w/stock brakes? Isn't the point of sticky rubber to be able to enter & go round corners faster, not slow down even more before the turn/in the turn? Also with 275 tires, you'll probably be going slower regardless due to increased weight/friction losses, except perhaps in autox. On a race track, I've been there, tried that, came back. Track data shows striking a measured balance w/width, weight, and size feels better, goes faster.

 

I appreciate your 2 cents, lets see if I can answer your questions.

1- Q- Why do I think possibly better gripping tires require extra braking power?
A- I never said requires, I said I thought I might want. I dont think you can argue that a 275 nt-01 will have more grip then a 245 nt-01 or that a 275 hoosier r6 will have more grip then a 245 nt-01. So no matter what, I am going to have additional grip and with the extra grip I might want more powerfull because I could use them. Stock sized tires and on the street, there is no point to a BBK but on the track with big grippy tires, I could use them. Do i need them and would they help? I dont know yet thats why I asked if stopping distances were actualy improved.

2- Q- If I am happy with the stock brakes?
A- well not stock, upgraded rotors, pads, lines and fluid. Well I am happy with them because I can lock up the r-comps I am using and I have never gotten them to fade. With that said, I might not have the same experiance with the new tire/wheel combo. If I do, then I will have no reason (except weight and caliper flex) to go with a 4-piston caliper.

3- Q- Isn't the point of sticky rubber to be able to enter & go round corners faster, not slow down even more before the turn/in the turn?

A- that is 1 of the points, another is to provide more grip when braking so you can not slow down more, but rather slow down faster. If I can go 50 feet farther before applying the brakes because for 1 - I can stop faster and 2 - I dont have to slow down as much, then my tires and brakes are going to save many seconds of my lap times.

4- Not a question but: Also with 275 tires, you'll probably be going slower regardless due to increased weight/friction losses

A- My wheels will be 4 pounds lighter and the hoosiers are 2 pounds lighten then my 245 nt-01's and 4 pounds lighter then the 275 nt-01's. Either way, my 275 tires are going to be lighter then my current set up. I dont think I will be going slower but I will find out. I keep good record of my entry/exit speeds, braking points and lap times. If my speeds dont increase or they decrease I will go with a smaller tire. However, if I can stay on the gas for 20 extra feet times 15 turns, and carry 3 MPH more speed through every turn, then I will shave seconds off my lap times.

Yes its a balance and more and bigger are not always better but sometimes they are. The important part is to make 1 change at a time and document the results.

 

Nothing like a good lively discussion of tire/wheel/stick! very enjoyable ... I've put these ideas thru my head, read about them in countless books on racing, etc., theorized what might be best, and have tried quite a few combinations myself....just for fun!

1 - well actually not argue, but no, I wouldn't say it's a given that bigger (same but wider) tires offer more grip. Here's why I say that. Let's take the case you mention 245 vs 275. Each tire is pressed onto the road by the same amount of weight of your car. Two things come into play... one, the contact patches are different for each, skinny and wide for the 275, less skinny and not so wide for the 245. Possibly the sq inches of contact patch on the road are the same. Different brand/compound - yes different stick coeficient, but the same principles apply.

So same tire compound - here's food for thought. Case one, if they area is the same, then the coeficient of friction, based on the downward force per sq inch would be equal. On the other hand, (case 2) if one has a larger contact patch, well again there would be less weight per sq inch pressing into the road, so each sq inch would develop less grip. Now this doesn't work exactly for all different sizings, but when speaking of close sizing, I believe this is correct and as far as it goes.

The as far as it goes part is one that involves the rest of the cars geometry while using the coeficient of friction available to it from the tire. Another trouble as the tire gets wider (and outside stock width esp.) is they aren't kept on the ground uniformaly accross the tread width due to camber changes brought on by the extended lateral reach of the tire. Basically the tread tend to rock up on one edge compared to a smaller width tire, and esp. while again while turning due to the compromised suspension geometery that results.

Bottom line in these cases stopping distances may not get better going bigger depending on so many reasons, alignment, tire shape, edge design and shape, etc. combines with compound.

2 - My gut would be you'll never ever get to the point where you stomp on the brakes in the RX-8 and just feel the brakes fade soas to not lockup the tires, regardless. The stock brakes are good enough so that doesn't happen. I mean, really, this isn't some Volkswagon with mushy brakes were talking about lol!

3 - absolutely right - if you've got the guts, you'll get the glory!

4 - I encourage you to try it for yourself of course - it's only money. I can only tell you I went from 235/40/18s on stock 8" rims to 275/35/18s on Enkei 9.5x18s (yea they weighed a bit less on the scales) and I had slower times over a given distance at full throttle (approx 50-120mph straight runs). Why, can't say I know....possibly extra tire frontal wind resistance, or tire to road friction, or more weight further out on the rim (more rubber/belt mass at the furthest diameter). It's an open question, but I have the track data that tells me that's what happened.

Also neither my cornering forces or braking became markedly better, but that could just be me, and my pucker capability...

 

You will need to go to the deeper offset Rotors/BBK Kit.

The Adapter kit and deeper offset rotors are what are going to allow you to run the caliper upgrade with those wheels.

Let me know if you need any further help or would like to order, I do offer an extra 10% off of Racing Brake Orders so that could help out with your budget.

 

Well I am not sure what I will do, if I do anything at all with the brakes, but I know I will be getting some new wheels and tires. Which tires, I am not sure of yet but they will be wider then my current set. I guess I will find out for myself if they make a difference or not, you could be right and they might not be faster.

 

Personally, I went to 17x9" Enkeis using 255/40s and the RB 2-piece slotted front rotors w/Cobalt pads and I've been a happy camper ever since. The braking is amazing , things stay cool as I put in some cooling ducts from the front skirt . I recently did 2 days, 4 hrs/day on track in adv Porsche group with no problems or overheating from any systems and I hung in the corners pretty well using those NT-01s we both love.

Good luck with your mods and keep the sunny side up!

 

We already have 3 brake kits built for RX8;

1. Stock offset with stock size (12.7") rotor
   
2. Stock offset with 13" rotor
   
3. Enkei (deeper) offset with 13" rotor

#3 Enkei offset 13" BBK was added as part of our commitment to serving the RX8 community. However this also increased our development and inventory burden. Our stock size brake kit is offered as a progressive upgrade for those customers who already own our two piece stock replacement rotors (like Highway8) so they can add more brake power as they need but still retain their initial investment on our two piece rotors which are known to last.

To our knowledge, Enkei is the only aftermarket wheel that is less forgiving than stock, and our kits are designed and built for easy installation w/o requiring wheel spacers and longer studs. However from our low sales on 13" Enkei offset kits, we cannot justify adding another kit – (Stock rotor with Enkei offset).

We know our stock offset kits (#1 and #2 above) will not clear Enkei wheels - not 17" and probably not 18" either.

In fact our 13" Enkei kits will be discontinued. It should be known that we have some customers with newer RX8 (06+?) models reporting this deeper (Enkei) offset kit the rotor will interfere with ball joint.

Anyone with an earlier model RX8 that is interested in Enkei offset 13" kit may contact Brice at Fluid Motorsports for a special close out deal - Limited to stock units only.