"Is bigger better?" Stoptech 380 vs. Stoptech 355

[72dan]

I run the Trophy setup 380 mm/6 piston front, 355 4 piston rear.
It isn't overkill as street pads overheat very quickly with aggressive driving.

I use Stoptech street pads on the street and Pagid pads on the track.

When you go to a softer tire, an extreme performance street tire you can pull higher levels of friction under braking. It is the ability to generate higher friction without locking up that a bigger brake kit gives in addition to more overall heat capacity.

I run Yokohama Advan AD08R tires, 265/30/19 front, 275/35/19 rear.
3 way coilovers, monoball control arms, etc.

[XKxRome0ox]

so the dust shield was bent back instead of trimming away

and while taking this photo, i noticed something on the rotor ... is that rotor damaged?
seems to have been chipped

[jritt@essex]

Originally Posted by XKxRome0ox

is this something necessary on all ST60 kit to fit on the e9x m3?
where does the dust shield interfere with the kit?
would love a little more explanation

and i just realized this is an old old thread..... hopefully someone can chime in

This thread could very well take home the necropost of the year award!

Our recommendation for our Essex Designed AP Racing Brake Kits is always to remove the dust shield. If you track your car, the dust shield is hurting you more than helping you in just about all cases. It's handy if you're driving through lots of mud, dirt, dust, gravel, etc., which most of this crowd isn't doing regularly. You can think of the dust shield like a mirror/wall. Heat coming off of the brakes gets bounced back from the shield and lingers in the area, and it also blocks incoming fresh air. That doesn't help your brake cooling situation. We therefore recommend ditching it. While I was sales manager at StopTech we recommended the same. Hopefully that is helpful.

[wyatth]

Bumping this up... Any other ST40 front only users? Would love some more feedback and photos. Especially with stock rear brakes (matching pads, SS lines, oem rotors/calipers).
Does anybody have the bias calculations with this setup? I couldn’t find.

*For future searchers: https://www.m3post.com/forums/showthread.php?t=699892

st40 355 front = p1: 44mm p2: 42mm (44mm is max size for st40)
st40 355 back = p1: 34mm p2: 32mm
st60 380 front = p1: 36mm p2: 34mm p3:32mm (or 40 34 29 who knows?)

These sizes would allow mixing and matching stoptech and stock rotors with negligible change to brake balance.

Stock balance is: F/R = 1.74
Stoptech ST40 all around is: F/R = 1.69
Stoptech ST60/ST40 is: F/R = 1.70
Stoptech ST60/stock is: F/R = 1.78
Stoptech ST40/stock is: F/R = 1.77

(All the above given same friction material front and back). Hence, stoptech can rightfully claim they provide a balanced upgrade no matter what you go with. All the balances above are within at least 2.5% of stock. Nice!

[Richbot]

I’ve been running str40 front with stock rear calipers for ~60,000 miles. It’s fine

[wyatth]

Can you or others with ST40 front and OE rears post some profile photos? I know it’s not the glamour hard parker setup but I’m just curious if it just looks off. I’d prob go drilled for a little more match.
Odd that Stoptech sized the ST40 front with 355mm rotors when they also make 360mm AeroRotors for the stock calipers, albeit in stock width still.

[Richbot]

Here they are behind 17x10's. I have since changed to the RB rear rotors which are slotted (pictured are ECS OE-replacement rear rotors)

The big front caliper and narrower sweep of the 355x35 rotor disc makes the front rotor look a little smaller than the stock rear, even though it's 5mm bigger diameter. optical illusion but that's how my eye sees it

[wyatth]

Very interesting and helpful. Thank you!

[Richbot]

I just pulled the stoptech STreet Performance pads that came with my STR40 front kit out. The kit went on 4.5 years ago at 60,314 miles and I took the pads out at 114,633 miles. Everything came apart and will go back together very nicely, dust boots were still in perfect shape, etc. Impressive.

There's about 4-5mm of pad left with some taper and pitting here and there, they start at 16.5mm and these would not have been wise to track on with this little left, even if it was wise to track the street pad with this kit to begin with (it's not terrible, but wise isn't what I'd call it)

So there you have it. THe rotors still have >34mm of thickness. Minimum is 33mm.

DS2500's going back on, hope there's room for the thicker pad

[pbonsalb]

Have you ever wished you had ST60 (assuming you were willing to run bigger wheels)?

[Richbot]

no

The car would be 10lb heavier in about the last place it needs more weight, and I've never felt I need "more" f whatever a bigger rotor would get me. I also like the extra clearance to the bigger wheels. The 17's with these are a lot like 18's with the ST60 380mm kits, about 3/8" of clearance and I've had a few rocks and clags get caught between wheel and caliper on the 17's.

If the rotors were wearing fast I'd say yeah ok maybe there's a benefit here, but they're not, they're wearing like the proverbial iron they are and will last about twice as long as the stock ones, which at 60k when I changed them were closer to minimum thickness than the stock pads were

On a street car, the gigantic 35mm front rotors stoptech puts on either one of these kits ought to outlast most marriages

[MPower7]

I'm almost completely sold on a ST-40 but very worried about the knockback. Can anyone let me know if knockback is going to be an issue?

[SAMM3Y]

Yes bigger is better. Performs better, dissipates heat better, looks better.. might weigh more and limit wheel/tire choices but unless you're running a completely stripped race car very competitively who gives a shit.

[wyatth]

It is kind of ironic that the only people who don't care about or feel the extra weight up front of a bigger kit, are the same people that don't need the increased heat capacity.

I'm not saying bigger isn't better, but it's benefits have diminishing returns, and unless you're tracking a lot, the benefits simply don't materialize. They are no different on the street or in the canyons. And if you are tracking, then the weight and wheel fitment becomes more important. So for most, it comes down to looks. And we can all agree that bigger looks better, but what's that worth to you is subjective.

[Richbot]

Originally Posted by SAMM3Y

Yes bigger is better. Performs better, dissipates heat better, looks better.. might weigh more and limit wheel/tire choices but unless you're running a completely stripped race car very competitively who gives a shit.

Performs better? A 2.25lb heavier (that's the spec from stoptech on the rotor ring) rotor is going to accelerate, brake, turn faster than the lighter rotor? Unless your performance metric is "how long will it spin without stopping" because you need a big flywheel effect in your brake rotor, nope. Can take more and dissipate heat better, yeah, of course, but do you need it? Looks better? who gives a shit

These observations from a company that sells a line of right-sized brake kits for the E9x line up with mine in the real world.

Q: Why aren't the discs bigger?
A: Short answer: Because they don't need to be! Long answer: Our systems are built from a racing mentality. In the pro racing world, teams scrap and scream to remove ounces of weight from the cars. Anything that is larger than necessary to get the job done is simply dead weight to drag around. That is how we approach our design. If you want to go faster and a 14" disc will work, a 15" disc will simply add weight, increase the moment of inertia, and hinder wheel fitment. Sure it will look pretty behind 20" wheels, but that's not what this product line is about.

The 14" AP Racing CP5773 Heavy Duty J Hook discs we are using are the exact same discs that won the championship last year on the Action Express Corvette Daytona Prototypes. These discs are being tortured in endurance racing events every weekend at the hands of some of the top drivers in the world. Yes those cars are significantly lighter, but they're also significantly more powerful, and far faster. To give you an idea of the boundaries they're pushing, one recently hit 223 mph in testing! :O If you think you'll give these discs a harder workout in your 20 minute DE session than these guys will when running 24 Hours of Daytona...no offense, but you're probably wrong. Keep in mind that the amount of energy transfer (changing kinetic spinning energy from the disc into heat) in a braking event is most greatly impacted by speed....more so than by weight. I'm going to get a bit technical here, so feel free to skip ahead if you feel your eyes glazing over! The core formula for kinetic energy is:

kinetic energy = vehicle weight x vehicle speed2

Take note of that little superscript at the end. If you look at the equation above, you'll note that doubling the vehicle's weight would double the kinetic energy, but doubling the vehicle speed would increase the kinetic energy by a factor of four! So in plain English, that means a stop from 220mph on a lighter car is going to be tougher on the brakes than a stop from 140mph on a substantially heavier car.

When comparing discs, you can't simply look at the diameter and decide that one will be more effective than another. The number of vanes, air gap, wall thickness, vane shape, metallurgy, hat attachment design, etc. all have to be taken into account.

To give you another example, our small four piston C6 Corvette Kit has found its way onto quite a few C6 Z06's pushing 600hp at the track. That kit features a 325x32mm disc. The OEM front disc on a C6 Z06 is 355x32mm. With a disc that is 30mm smaller in diameter than stock, many of our customers are seeing huge increases in pad and fluid fade resistance, less disc cracking, longer disc life, pads that wear longer, etc. Again, it's not just disc size that matters. It's all about design and optimization.

Wheel fitment is also of critical importance in our design process. As mentioned above, most of our customers run the smallest, lightest wheels available for the platform. I won't go into all of the merits of doing so, but obviously unsprung weight, lower rotational mass, cheaper tires, etc. all factor in. Our systems are packaged tightly to allow for a wide range of wheel fitment. Using an extremely large diameter disc kills wheel fitment, and the utility of a track-optimized brake system.

Okay...I've beaten that one to death.

[SAMM3Y]

Well I've got both from st for fronts and I'll tell you first hand which one I prefer..

[macdude357]

Originally Posted by MPower7

I'm almost completely sold on a ST-40 but very worried about the knockback. Can anyone let me know if knockback is going to be an issue?

I know some drivers that have experienced knockback on the ST40's. I'm using the ST60 Trophy kit myself and have not had any issues with knockback but I don't use r-comps or slicks either so that might have something to to with it. You can get anti-knockback springs if that's a concern.

On the flip side, another bonus of running ST40 up front is you can rotate pads (assuming you have an ST40 kit in the rear). It would be nice to move my half used pads back to the rear where they will last a long time. It's a bummer that ST40 front uses a different thickness rotor than the fronts. Rotating rotors would be really beneficial. My fronts crack way before they get too thin.

[Timujin]

Looking at ST40 F&R to keep factory 18s. Kicked around getting Dinan/Brembo kit Deans has for sale, but I do not want to be locked into 19s. Great info here.

[Richbot]

worn 4-5mm remaining Stoptech STreet Performance ST40 pads: 790 grams per corner
New Ferodo DS2500 FCP560H with about 14mm of friction material - 959 grams per corner

Car gained 3/4 of a pound putting new pads in it. Damn and blast. Should have drilled some speed holes in them

Oh, the Ferodo pads for the ST40 caliper don't have the noise reducing thingie on the backing plate. So that'll be interesting to see if they're noisier or not. The stoptechs were starting to squeak when cold on light pedal application probably because they were so thin they were able to vibrate. My caliper bridges have the oval spring thingies like other st40 calipers

[Dr. Dre]

I went the total poser route. I don't care about a few more pounds. I think you're full of it if you can tell me that you can feel 10 pounds on a street car/production based car.


To say these brakes are being abused on race tracks. So what. After each race they are probably getting new pad and brakes are being bleed. Our cars are street cars. No matter how much modification you do they are still street cars.

Buy a set of brakes and enjoy it.

[Richbot]

You've started down a path you'll never be able to return from, soon your roof rack will never leave the car, your hood will be rusty, somehow, probably a rust-colored vinyl wrap, and the wheels and tires will be 4 different colors with 205's all around and you'll be back her asking about how to get the best poke with wheels that still fit over your brakes that are way too huge for your car because they're the same size the come on the 2015 version of the same car. hashtag poseur life

I don't think the 380's are poseur. I just don't think they're necessary or "better" it's just a different option. Having been to racetracks where real E92 racecars get perfectly acceptable life out of carefully ducted stock brake setups with careful pad selection, I don't think ANY brake kit is strictly necessary on these cars, or wouldn't be, if BMW hadn't sold a 400hp track-oriented car without brake ducts leaving the owners to hack up the frontend of the car to get air to the rotors

[jritt@essex]

I'll chime in on this necro-thread, since there weren't nearly as many available options back in the day.

A proper brake kit should be a good match to the needs of the car and driver. That is in terms of fade resistance, feel, longevity, etc. Bigger will last longer and gives more headroom for upgrades to other aspects of the car (added horsepower, stickier tires, etc...but bigger also weighs more and can limit wheel fitment (particularly with 380mm discs).

We believe our front 372mm kits are now the standard by which all others are judged. We have multiple pad options, stainless ventilated pistons with anti-knockback springs standard, high vane count discs, and the Radi-CAL caliper design is by far the most advanced technology available anywhere. Our kits are incredibly lightweight, while still fitting inside 18's. Our front 372mm kit shaves 14 unsprung lbs. off the nose vs. the OEM brakes despite being larger, and you can get them with 1" thick pads that last forever. You can see options here:

https://www.essexparts.com/my-vehicl.../BMW/M3/%20E92

Lots of customer feedback in our other thread: https://www.m3post.com/forums/showth...ighlight=essex

I also wrote an extensive comparison of our Essex Designed AP Racing Radi-CAL kits vs. Stoptech if anyone is interested in seeing it. Our kits are more money than StopTech, but you are also getting a lot more for your money. Thanks for your consideration.