Steve Richo

I purchased these myself from Tal at ACG with a set of MX72 pads. Fitted them up in the garage without too many issues. They were significantly lighter than the std discs, so a significant weight saving over 4 discs, I honestly feel that I could feel a difference through the seat of the pants. The car felt like it accelerated and turned in with a little more vigour, so smiles all round. ACG were great to deal with, many thanks Tal! Minor issues, braking the calliper mounting bolts, you will need to have the front end raised so you can turn the wheels to give clearance for the breaker bar, and you will need a 300mm breaker (or similar). The only other issue was that the fixing screw hole did not line up with the hub thread but not a big deal as they are tight on the hub centric spigot. My advice is go for it, no downside that I am aware of.

ripnbst

One thing no one has mentioned yet on the weight savings is that you are saving weight on rotating mass. I am pulling this number out of memory, so it may be inaccurate, but it's something like 1 lb saved in rotating mass =100 lbs saved in stationary mass.

When the motor drives the wheels it is also having to spin the brake discs. Saving weight on them makes it easier for the motor to drive the wheels. The discs are smaller in diameter than wheels and tires are so lightweight wheels and tires make a bigger difference.

The improvements are so minor they likely cant be felt on the butt dyno but they are there.

Diabolis

Yes, the savings are on unsprung weight, which is quite important in the handling characteristics of the car as the wheel assembly has less mass (and thus inertia) and is better able to track the road surface, ultimately resulting in more grip. You're not going to either feel or register ANYTHING on a dyno, simply because a dyno measures power and doesn't take weight into account. A 150 hp car and 150 hp motorcycle will produce the same dyno readings, but one will obviously accelerate a lot faster than the other.

Your argument about the motor having to drive the wheels is somewhat misleading, as it ultimately has to drive the entire car, not just the wheels, so in a straight line the weight savings (and thus performance increase) are exactly what you would get by removing the mass that you'd measure on the scale, let's say 26 lbs over the P31 rotors, which is not very significant.

During cornering however (and especially on a bumpy track), you would indeed get better grip and thus the results would be akin to removing more weight from the car as you suggested, although IMHO the ratio is a lot closer to 10:1 instead of 100:1. So yeah, during hard cornering, the resulting level of extra grip you would get as a result of reducing the unsprung weight by 26 lbs would be closer to shaving off 260 lbs from the sprung mass of the vehicle. Your "butt dyno" can definitely feel this - you'll even feel it in the steering response right away.

Manofsteelpt

I got mine from Tal too (great to work with) and replaced the cals with freshly painted cals thru his exchange program while I was at it. I appearntly had the 2 piece fronts, so the weight savings wasn't as much for me. Though I did need new rotors, so it all worked out fine anyways.

Girard@ACGautomotive

You forgot to mention that the front pair of girodiscs cost about the same price as 1 OEM AMG performance rotor

Thank you again for all the kind words

Girard@ACGautomotive

Thank you for the kind words sir! I'm glad you are enjoying the new brakes

The performance gains on these rotors are significant in every way:

- Less weight: Almost 7 pounds per corner of unsprung mass
- Directional: Meaning they vent properly, versus the OEM AMG which do not
- Serviceable: Discs can be replaced
- Less expensive option for PP owners

Let me know if you guys have any questions. I personally run these on my E55 and will install a set on my C63 this coming weekend.

Pertplus

I thought you sold your E55

Girard@ACGautomotive

No sir. She's a keeper.

Pertplus

My bad I was thinking of the P40SC wheels she had and confusing the two.

Girard@ACGautomotive

Yeah, those are long gone. Got a new set waiting for the car once it's done at Chapparone.

Pertplus

Sweet. Lookin forward to pics of the C63

freefall

This is my set up and I love it. The rotors are for the E55 but work perfect on my 2012 C63 Coupe.