355x32 vs 370x36 BBK setup for track/race

[RalliartRsX]

Hey folks

So I am planning the next phase of the build and I am settling with either the Paragon 355x32mm or 370x36mm kit. The car will mostly be a sprint race car (think 15-20 mins long races) with the occasional longer session with SCCA (think 30-40mins)

Car weight will be anywhere from 3200 to 3600lbs at race weight, 200TW tires Mostly east coast tracks (Pitt, Summit main, VIR, LRP, NJMP, Glen) am wondering if the longevity of the 370x36 kit in regards to rotor and pad are worth the price difference over the lighter weight 355x32mm kit?

Looking to shed as much weight as possible, but will gladly plunk down for the 370 kit if 355x32 wouldn't suffice for cars our weighta Keep in mind; reading through Essex's posting from several years ago, they make an endurance kit for ther Z06 with 325x32mm setup (stock is 355x36) that has seen massive increases in rotor and pad longevity https://www.m3post.com/forums/showthread.php?t=921567

Offcourse, rotor and pad design (thickness and sweep for example) are every bit as important as size in regards to thermal capacity and not eating up pads and rotors

Thoughts

[M3SQRD]

I have two PFC brake kits on my e92 M3s.

PFC Z54/Z45 which uses F/R 372/355 mm OD slotted rotors. This is the best brake kit that was available for the e9x M but PFC stopped supporting the aftermarket brake kits except for Porsche GT cars. Front caliper uses a 29 mm thick brake pad. The 372 mm V3 rotor has performed flawlessly at SP Main and Shenandoah, VIR Full and WGI. I can’t speak to the longevity of Paragon rotors but the PFC 372 mm V3 rotors last at least 28 track days (with PFC pads).

Z31/Z31 which uses F/R 372/371 mm OD slotted or dimpled rotors and four pads/caliper. This kit was released ~3-4 years before the Z54/Z45 kit. The calipers are a monobloc design with a fixed bridge and, based on its compact size (18 mm thick pads), a PFC engineer told me it’s the stiffest caliper they’ve designed. Once again, the 372 mm V2 rotor has no trouble handling SP Main and Shenandoah, VIR Full and WGI. The 372 mm V2 rotors also last at least 30 track days with PFC pads. Fits under all 18” wheels, including OEM, I’m aware of (my wheels in addition to other people’s wheel setups). This kit is a step down compared to the Z54/Z45 due to the use of the V2 rotor hat retention design and the 18 mm thick pads (more frequent pad changes which requires the removal of the caliper).

Based on my experience with both PFC kits, I would not run a 355 mm OD rotor on the e9x M. I believe you’ll run into brake heating issues with a 355 mm OD rotor. There’s a good chance the brake bias will shift rearward which isn’t necessarily an issue. At times, I’ll run a more aggressive pad on the rear to move the brake bias rearward. Fits under all 18” wheels, including oem, with plenty of clearance.

In addition, on my f82 I’m running the Essex/AP Racing CP9668/CP9449 372/365 mm OD rotors. This kit performs extremely well but I’m thinking about getting new caliper brackets so I can run a 378 mm OD rotor. The 372 mm rotor has trouble with 45 min sessions but works great for 20-25 min sessions. I definitely would not step down to a front 355 mm OD rotor.

[RalliartRsX]

Great info here and just about aligns with my "hunch". These cars are...heavy.

What car do you bring to the MA events? I am focusing n FATTs and Seat time events as less headache, more track time for testing and I can be done a little after lunch (4 or so sessions) as I am focused strictly on W2W moving forward

Its interesting as the Paragon caliper is a yesteryear AP caliper it seems. I would much prefer the 25mm pad size, but beggars can't be choosers. It will mostly be a sprint racing car, so that few extra K spent on the current crop of APs is easily 3 race passes for GLTC, SCCA or more for NASA.

[tsk94]

I think a 355mm kit will be just fine, with appropriate ducting. Given it's a race car, adding proper brake ducting shouldn't be an issue. If it's a well designed kit it would be totally doable, and as you mentioned would save a bit of weight.
Yes, the cars are heavy, but they really don't have crazy power - so keep that in mind.

I say this with a grain of salt, as on my E92's I've run the PFC kit Z54 kit like M3SQRD above, and on my current car I went with Brembo's Pista system.

[M3SQRD]

Originally Posted by RalliartRsX

Great info here and just about aligns with my "hunch". These cars are...heavy.

What car do you bring to the MA events? I am focusing n FATTs and Seat time events as less headache, more track time for testing and I can be done a little after lunch (4 or so sessions) as I am focused strictly on W2W moving forward

Its interesting as the Paragon caliper is a yesteryear AP caliper it seems. I would much prefer the 25mm pad size, but beggars can't be choosers. It will mostly be a sprint racing car, so that few extra K spent on the current crop of APs is easily 3 race passes for GLTC, SCCA or more for NASA.

I use both cars. The Z54/Z45 has a MCS 2WR F/R 600/900 (or 600/1000) lbf/in suspension setup with a diffsonline multiclutch 3.62 FD DCT LSD with 8600 rpm raised redline. The Z31/Z31 has a JRZ RS1 street-biased setup with 500/800 lbf/in spring rates with an 8600 rpm raised redline. SP seat time events are great. I’ve been going to them since the early 1990s.

The Paragon 6-piston caliper does look identical to AP Racing calipers from the 90s. The AP CP5555 caliper on my e46 M3 track car has all of the same features as the Paragon caliper. This doesn’t mean the Paragon caliper is bad but it does help explain why their kits are less expensive than current AP Racing and Alcon track brake kits. I’d stick with the 372 mm rotor to ensure I have an extra reserve of braking performance, if you will, at the end of a session vs. a 355 mm rotor that won’t have much, or no, reserve braking. The rotating inertia of the 372 mm is ~9% higher than the inertia of the 355 mm but negligible compared to the rotating inertia of the wheels and tires. I’d definitely accept the ~9% higher inertia of the 372 mm rotor for W2W racing.

[danvitmon]

Originally Posted by M3SQRD

I use both cars. The Z54/Z45 has a MCS 2WR F/R 600/900 (or 600/1000) lbf/in suspension setup with a diffsonline multiclutch 3.62 FD DCT LSD with 8600 rpm raised redline. The Z31/Z31 has a JRZ RS1 street-biased setup with 500/800 lbf/in spring rates with an 8600 rpm raised redline. SP seat time events are great. I’ve been going to them since the early 1990s.

The Paragon 6-piston caliper does look identical to AP Racing calipers from the 90s. The AP CP5555 caliper on my e46 M3 track car has all of the same features as the Paragon caliper. This doesn’t mean the Paragon caliper is bad but it does help explain why their kits are less expensive than current AP Racing and Alcon track brake kits. I’d stick with the 372 mm rotor to ensure I have an extra reserve of braking performance, if you will, at the end of a session vs. a 355 mm rotor that won’t have much, or no, reserve braking. The rotating inertia of the 372 mm is ~9% higher than the inertia of the 355 mm but negligible compared to the rotating inertia of the wheels and tires. I’d definitely accept the ~9% higher inertia of the 372 mm rotor for W2W racing.

Off topic but you wouldn't happen to have any extra Z54 kit front hats I could borrow? I have the Z54 calipers/pads/rotor rings/retaining rings, but no hats. And PFC won't make them unless I order 10 or more. I would pay for your time and shipping if you could send me one hat. I have a friend who's an engineer and good with Solidworks who already created a rough model, but the V3 retaining ring style has a weird design and I don't want to screw the tolerances up.

[M3SQRD]

Originally Posted by danvitmon

Off topic but you wouldn't happen to have any extra Z54 kit front hats I could borrow? I have the Z54 calipers/pads/rotor rings/retaining rings, but no hats. And PFC won't make them unless I order 10 or more. I would pay for your time and shipping if you could send me one hat. I have a friend who's an engineer and good with Solidworks who already created a rough model, but the V3 retaining ring style has a weird design and I don't want to screw the tolerances up.

I stocked up on rotors for both kits but when I went to stock up on mounting hats none were available. Only set I have are on the car.

[pirategenes]

Just some perspective from my experience, as I have the Paragon BBK 378x36mm 72 vane Rotor - PA035 Caliper. I love it. For some context, I run mostly at Waterford Hills, which is a tight and technical track. I have brake ducts. The BBK has been great and my front rotor temps are always lower than the rear (stock with DS2500 pads). I've had the BBK on for 6 track days (4-5 20min sessions per day) so far and the Paragon R5 track/competition pads still have life left. I think the extra thermal capacity of the 378mm rotor is nice to have.

[RalliartRsX]

378 is similar in price to the 370. However you shed almost no weight going to that size

[M3SQRD]

Originally Posted by danvitmon

Off topic but you wouldn't happen to have any extra Z54 kit front hats I could borrow? I have the Z54 calipers/pads/rotor rings/retaining rings, but no hats. And PFC won't make them unless I order 10 or more. I would pay for your time and shipping if you could send me one hat. I have a friend who's an engineer and good with Solidworks who already created a rough model, but the V3 retaining ring style has a weird design and I don't want to screw the tolerances up.

Have you tried reaching out to SYT_Shadow? He’s the most likely person to have a spare e9x M z54 front hat.

[danvitmon]

Originally Posted by M3SQRD

Have you tried reaching out to SYT_Shadow? He’s the most likely person to have a spare e9x M z54 front hat.

Yup he was the first person I reached out to lol. I messaged some other people that he sold his used kits to but they're all in use. I also messaged Nick about his kit that he is currently selling but he doesn't want to help sadly.

If you ever have any downtime on the car I would pay to borrow the rotor just to get measurements to make my own hats.

[kolosy]

Originally Posted by pirategenes

Just some perspective from my experience, as I have the Paragon BBK 378x36mm 72 vane Rotor - PA035 Caliper. I love it. For some context, I run mostly at Waterford Hills, which is a tight and technical track. I have brake ducts. The BBK has been great and my front rotor temps are always lower than the rear (stock with DS2500 pads). I've had the BBK on for 6 track days (4-5 20min sessions per day) so far and the Paragon R5 track/competition pads still have life left. I think the extra thermal capacity of the 378mm rotor is nice to have.

what's your ducting setup? i'm running the 370mm setup and i'm overheating my pads and burning them up in a day as a result. i've got a gt4 lip with the burkhart backing plate, but i think it's pointed wrong, it' looks like it's pointing at the rotor face instead of the hub and so not really doing anything to cool the outside.

[RalliartRsX]

Are you running DSC and such? What's your pad setup? And what do you mean "burning up"?

[kolosy]

Originally Posted by RalliartRsX

Are you running DSC and such? What's your pad setup? And what do you mean "burning up"?

I don’t want to jack this thread too much, as I’ve talked about it in others. But tl;dr I’m running carbotech xp20s and going through a set of pads every two track day or so. Seeing caliper temps of 410-450F based on temp strips.

[pirategenes]

Originally Posted by kolosy

what's your ducting setup? i'm running the 370mm setup and i'm overheating my pads and burning them up in a day as a result. i've got a gt4 lip with the burkhart backing plate, but i think it's pointed wrong, it' looks like it's pointing at the rotor face instead of the hub and so not really doing anything to cool the outside.

I have a GT4 V2 front lip with 2" hose going to Ali Express backing plates that point directly into the hub. I run RE71RS's in 275/35/18 square, to help inform perspective on braking stress. I don't have super great data on temp effects (like one side + one side - hose) but I have more anecdotally noticed overall decreased rotor temps (based on infrared laser thermometer) and general great braking performance.

Given what you said about your backing plates, I wonder if the inside vs outside rotor temps are different. Do your outside pads wear faster than inside? Not sure what to say here since it seems like this Paragon kit is working great for me.

[RalliartRsX]

Pad wear or taper can be attributed to too may things that don't include temp (like caliper flex)

With that said, are you running temp strips and rotor paint?? If not, unless you have a real time temp reading from the brakes, it is all anectodal to say the GT4 lip and 2" hose is doing much...

Why?? We recently did some testing on a splitter design with the GT4 l3" lip and well...just using tufts of wool, the splitter/lip combo was actually directing air AWAY from the OEM ducting out front. Had to peel back some of the lip/splitter to gain that airflow back to the OEM side ducts and oil cooler that was placed there

Also, we cut an opening further up in the fender liner to aid in egress of high pressure air.

So yeah. Anecdotal evidence is tough if not properly monitoring temps

Are you monitoring temps in real time or using the infra red laser right off the track??

[M3SQRD]

I understand how caliper compliance can result in pad taper but how does compliance result in an increase in wear rate of a pad with uniform wear?

[roastbeef]

i have 355 rotors. the setup you'll be happy with kinda depends on your habits and style. i'm a mdm user, so my brakes see even more use. my ap's don't quit, and have a consistent feel. however, this will cause the pads to wear quicker. that is the penalty.
the penalty with larger rotors is obviously the weight... so those are your pros/cons. performance is potentially higher with the 355 rotors due to less rotating weight.

355- less weight, less pad life.
370- more weight, better pad wear.

[M3SQRD]

Originally Posted by roastbeef

i have 355 rotors. the setup you'll be happy with kinda depends on your habits and style. i'm a mdm user, so my brakes see even more use. my ap's don't quit, and have a consistent feel. however, this will cause the pads to wear quicker. that is the penalty.
the penalty with larger rotors is obviously the weight... so those are your pros/cons. performance is potentially higher with the 355 rotors due to less rotating weight.

355- more weight, better pad life.
370- less weight, worse pad wear.

Wear rate is more related to pad compound, not rotor diameter. PFC 11 has excellent wear rate and is gentle on rotors.

Why does the 355x32 weigh more than the 370x36? Why does the 355 have better pad wear?

[roastbeef]

Originally Posted by M3SQRD

Wear rate is more related to pad compound, not rotor diameter. PFC 11 has excellent wear rate and is gentle on rotors.

Why does the 355x32 weigh more than the 370x36? Why does the 355 have better pad wear?

i totally screwed that up and reversed my own talking points- 355 is less weight, more pad wear. i'm correlating the higher pad wear to the higher temperatures from using a smaller rotor to shed the heat. it might be a small amount, but its a talking point.

[M3SQRD]

Originally Posted by roastbeef

i totally screwed that up and reversed my own talking points- 355 is less weight, more pad wear. i'm correlating the higher pad wear to the higher temperatures from using a smaller rotor to shed the heat. it might be a small amount, but its a talking point.

LOL! Now that makes perfect sense. It happens to us all