Hey guys,

I was wondering about the options for lightweight rotors on 18 inch wheels. I'm aware of the Black Series conversion rotor kit, and while it sounds like an amazing option, it's expensive, I'd have to buy 19 inch wheels, and I prefer the look of silver rotors over black. I'm happy on 18s, partly because I drive a lot on terrible quality backroads. I have a 2013 C63 Sedan.

Right now it looks like the only option I've seen for lightweight rotors for 18s is the Girodisc brakes at around $1300 for the fronts and $1200 for the rear. However I have read several comments that you will destroy the rears quickly using the parking brake, which I do make use of frequently.

Do you recommend getting the Girodisc rotors for the front but going with the stock Brembos in the rear? Or are there other better options for 18 inch wheels? Thanks

 

I had girodisc and loved them. But for value, you can’t really beat the 2-piece brembos on FCP Euro. Buy them. Use them up. Then return them for free replacements. It sounds too good to be true but isnt.

 

I replaced my OEM aluminum hat rotors (p31 pack) with Brembo 2 piece and found the Brembo's are actually slightly heavier.

 

Racing Brake makes 2 piece rotors that have a steel sleeve insert in the rear rotor hub that allows normal use of the parking brake. I have had them on mine for a number of years now.

https://racingbrake.com/mb-irk-18/

 

Did you not have the rear parking brake issue?


Ah thanks, I guess I hadn't realized there was a non-Black series option, I guess I got confused by the rotors being black (I wish they made the stock replacements in silver though).

So it looks like those will work on 18s and the kit includes the rings?

 

The black becomes silver the first time you use the brakes.

 

@BLKROKT beat me to it.

Yes, the black colour on the rotor rings is just a protective coating that will come off within the first 10 minutes of driving as you bed in the brakes.

They are OEM sized rotors and fit under the OEM 18" wheels, and the rear hats (hubs) have steel rings permanently pressed into them for the drum parking brake shoes.

 

Alright guys thanks for kindly helping the noob out, I appreciate it. I'm going to grab the kit for 18s/stock replacement.

 

I'm a huge girodisc fan and user. I can also get you a slight discount on them as well. No issue with the parking brake? I have no idea what these people are talking about. They are direction rotors so the cooling fins are actually functional. You can also by replacement rings later on when they wear out. I've already had to replace mine after 40k. Mind you that's very hard street driving, multiple road course track days, drag racing and drifting events. I would highly recommend if they are in your budget. Also lighter than most 2pc rotors on the market.

 

Front Girodisc/Factory rotor mass. W204 C63 Girodisc Part #'s labeled on top hats

 

show some pics when you done

 

I bought the front and rear Racing Brake kit suggested in this thread and so far have been happy. They were installed/bedded by a reputable shop.

A few questions:

1) Is the above grooving normal? I didn't see anything like this on my old stock C63 rotors. I noticed that if I drive slowly these disappear, but if I go on a hard canyon run I see these.
2) I read that the squeaking that occurs due to being cold, and my experience matches that. When I go on a canyon run on the way home there's zero squeak at low speeds vs. when I start I definitely hear squeaks at early stop signs. Normal for performance rotors like these right?
3) I am thinking of going to my first track day, how much would one day wear these down (rough %/guess)? I know it depends on how hard I brake how long of a day, but I assume being new (never tracked) I am likely to not be using them up as much.
4) It feels like the wheel is slightly easier to move from center, is this a real thing due to reduced un-sprung weight or is this placebo?

I will say that the brake pads in the set produce more dust than stock, but I do really like the pedal feel/performance (though I have trouble separating what is the rotor or pad). I don't mind cleaning the wheels more often -- and yes, I cleaned my wheels after snapping these!

 

What you are describing as grooving is just pad material deposits STARTING to form on the rotor surface and is perfectly normal. Your rotors still have the cross-hatch machining marks visible so they are still obviously new - but there are no grooves and your your brakes are not yet fully bedded in. It will happen in good time.

The squealing is not from the rotors but rather from the pads. What pads are you using?

Rotor wear on the RBs will be negligible after a track day, or for that matter an entire season... ask me how I know. Your pads will wear out more, and depending on the pads you are using they may even disintegrate if they are not up to spec.

You feeling that the steering wheel is easier to turn is 99% placebo because the steering is power-assisted (hydraulically to boot). However, the lower combined wheel & tire mass (unsprung / rotational) will result in quicker spring / shock response and thus better grip as you go over bumps or undulations on the track and that will be real.

Aside from making sure you've got proper / enough brake pads left (if they are close to worn you CAN boil the fluid), the only things you may need to worry about is the brake fluid itself. Make sure that you do a flush and replace the brake fluid in a week of two before your track day.

Have fun!!!!

 

Thanks for your thorough response, I really appreciate it. I will flush the brake fluid before any track time. I can accept the wheel feeling lighter is placebo, was very suspicious of myself, haha. My backroad drives are all over very bumpy curvy roads and I think handling has improved, the car feels more nimble as you describe. Lightweight wheels are next, just gotta decide whether to drop the coin on some BC Forged or go for some flow-formed. I have a healthy budget as getting older (just turned 40) I finally realized it's better to be "over bankrolled" for a car than to buy one you barely can afford.

Glad the deposits are normal, was just making sure since I just dropped close to 3K shipped for the front/rear set. My stock rears still had 50% life but I just went for the full kit (Front/Rear Rotors + Pads) because I'd rather just get the performance now, in the past I've waited and regretted it because I sold the car before using up parts I waited on but I didn't get to enjoy them as long despite spending the same amount. It's also cheaper as a set.

The pads are the non-track ones that come in the Racing Brake kit, PD1291 and PD1373. https://racingbrake.com/mb-irk-18/

2 more unrelated questions:

1) For alignment, what do you suggest for best steering feel? I remember someone here suggesting zero toe and otherwise stock settings. This is for street, but I spend a high percentage of my time in the car on pleasure backroad drives, and don't mind some tramlining. I use my B8 S4 more for daily duty stuff. My research leads me to think of doing either zero toe or very mild toe-in, like 1/32nd.

2) When upgrading the wheels, should I go for 19s? I am most concerned with steering feel. I know 19s will be less comfortable, but if the tradeoff is better steering feel (and handling, but steering feel being the most important) I'd go for it and upgrade to some coil-overs with soft-ish dampening options (KW DDC perhaps) if I need a little more comfort. I tried reading a lot about different wheel sizes but there were so many different opinions I found it hard to be certain so I was just curious your opinion. I'll probably just buy flow-formed 19s to see how I like it before considering forged.

 

A few pieces of input. I would stick with 18" wheels. No performance gain will come from larger wheels unless you required larger wheels for even larger brakes, or only a specific tire compound is available in that size. Let the tires do the work. Stiff suspensions are often confused with better handling. Look at race cars, they are super stiff but have thousands of pounds in downforce at speed requiring stiffer spring rates and dampeners. If you're more concerned about handling and performance than tire wear, Toe out the front about 3-5 minutes. Rear toe 10-15 toe'd in. This will help in turn in and to reduce understeer. If you stiffen the front end more you'll just make understeer worse. Also keep in mind tire choice make a bigger difference in handling than any other modification. Dont cheap out on them or you defeat any realized gains.

 

The RB brake pad numbers you specified (PD1291 and PD1373) refer to the pad SHAPE for the front and rear pads respectively. They come in various COMPOUNDS, and for track duty - especially on a heavy car like the C63 - you'll want their motorsport compounds. I ran the XR70 front and XT960 rear.... everything else would pretty much disintegrate with decent track use. You can see the different compounds here: https://racingbrake.com/tech-info-reference/. This is not a "For Sale" thread and I don't want to peddle anything, but if you are interested I have a brand new set of RB pads (both front and rear) in those compounds (XR70 F & XT960 R). They will squeal on the street when cold, but on a heavy car like the C63 they are the perfect track day pads if you are going to track the car.

If you can get 18" wheels that are wide enough (8.5"-9" F and 9.5"-10" R) with the right offsets (around ET40 F and ET50 R respectively) and will also clear the front calipers, I'd also run 18s. All factory GT race cars (GT3/GT4) and LMP prototypes run 18s. There is no benefit to going with larger wheels unless you need to, but in your case the only downside is that there are probably ten times as many wheels that fit the car in a 19" size as there are in 18". Having said that, if you are ever going to run slicks 18" is the magic size, and furthermore very decent "dual use, track worthy" tires are indeed available in 245/40ZR18 F and 265/35ZR18 or 275/35ZR18 R sizes (the new "200 treadwear" tire compounds are pretty awesome... as in they are stickier than 100TW dedicated track-only tires like the Toyo R888s or RA1s used to be a few years ago). Hankook RS-4s come to mind, Bridgestone RE-71Rs, Yokohama A052, AD08Rs, AD09s, Nitto NT05s... you can't go wrong with any of them.

As for alignment, I'd start with the stock specs, and only deviate from there if you need to. Unless you are chasing those last 3/10ths of a second per lap, there really isn't much to be gained, and it will always come at the expense of daily driveability. When you get to the point when you are after those last 3/10ths, chances are you'll already have a dedicated race car or three.

 

Anyone here know how much heavier the 390mm Girodisc fronts are than the 360mm ones?

 

I appreciate all your thoughts, Diabolis. I have long been an "18s" guy for all the reasons you mentioned, but all the performance stuff lately has pushed towards higher wheels so that has made me wonder if I should consider 19s. I also have 19s on my 2010 Audi S4 and feel fine about the size (softer suspension though). It's frustrating how few wheels are the proper offset for this car, I see a lot of people running a 45 offset in the rear, which sounds like a big difference.

However, I realized that some of my interest in a change could be whetted by actually trying the stock tire sizes. The previous owner fitted 245/40 PS4S up front and 275/35 PS4S out back, both of which are much wider tread than the wheel itself. I have heard that can actually be a negative for both performance and steering feel, the latter of which I've had some minor complaints about (The rear just starts to go without much of a hint, but I feel it once it's kicking out). So the plan is to just order stock sized tires and a stock alignment. Both passenger side's tires are wearing heavily on the inside of the tire compared to the driver's side, so I am guessing I'm off on alignment. I'm not expecting a huge difference, but a slight improvement would be welcome.

In regards to the track pads:
1) Sorry I should have specified that I didn't pay to upgrade to track pads, so I shouldn't have them. I am still getting some squeak when cold.
2) I will shop for track pads when I decide on a track day, I have made a rule that I only buy stuff when I'm immediately going to use it or fit it to the car right away, I've bought stuff in the past and never installed it (sigh). If you still have them when I go to the track, I'm sure I'd buy them.

Also I see the choice when ordering tires of two sets (same sizes) -- DT1 "different tread" for the front and TPC spec for the back, or the pair without those designations. The DT1 tire is 7.8 inch tread width vs. the 8.1" non (and .5 inch more depth) and the TPC spec is 1" less tread depth. I assume I need the TPC spec for the tire pressure sensor? But that doesn't make sense, as it's only labeled that for the rears, and I know the fronts have TPC. Would any of these tires work with TPS working?