posted on April 28, 2010 14:30
Project EVO X Part 2, Making Great Brakes Even Better!
By Mike Kojima
When we last worked on Project EVO X we installed a very comprehensive yet very streetable suspension system from KW and Whiteline. In continuing our theme for building the ultimate EVO X without compromising its daily driveabilty, we now turn our attention to the brakes, wheels and tires.
For more on Project EVO X Click Here!
The EVO X comes with pretty good brakes from the factory, big Brembo 4 piston front and 2 piston rear calipers squeeze big 13.8" front and 13" rear rotors. The front rotors are 2-piece floating type with alloy center hats and anti rattle clips. In other words the stock brakes are already quite good, what would have been state of the art just a few years ago. So why would we want to change them out with something else? The main reason is that since our car is going to see some occasional track use, we want to upgrade our brakes so we can drive our car to the track for an event without the hassle of having to switch pads at the track. The big brakes will allow us to run at speed on a streetable brake pad. Bigger more powerful brakes will also be easier to modulate. The third reason is admittedly that big brakes just plain look cool!
|When comparing the stock brembo 4-piston caliper to the much larger Stoptech STR caliper, it is easy to see that the Stoptech part can accommodate a much larger brake pad.
We chose Stoptech as the brake system of choice for its combination of daily driveability and track performance. We selected Stoptech's Trophy STR big brake kit. The Trophy kit features an enhanced version of Stoptech's venerable ST-60 six piston front calipers and ST-40 4 piston rear caliper. The Trophy calipers feature a forged aluminum alloy body. Forging is a superior method of forming aluminum when an aluminum billet is heated and basically smashed into shape using many tons of force into a die. Forging produces a part with compressive stress for increased strength. It also orients the metal's grain in alignment to the part's shape. Putting the grain in the right direction increases strength and dimensional stability, much like how putting the grain of a piece of wood in the direction of stress makes for a stronger wood part. The pressure and stress of working the metal during forging also refines the aluminum's grain making it finer and eliminating voids and other internal flaws that can weaken the structure. This also makes for a much stronger part.
| The rear 4-piston Stoptech caliper is considerably larger than the 2-piston Brembo part
All Stoptech calipers are forged but the Trophy STR calipers are additionally shaped optimized using finite element analysis or FEA. FEA allowed Stoptech's engineers to figure out where material could be pared from the caliper body without affecting stiffness. These areas were then hogged out using a CNC machine for a 20% reduction in caliper body weight without any loss in rigidity. A stiff caliper is important because it makes for a firmer brake pedal with better feel and modulation. After machining, the STR caliper bodies are hard anodized for a tough corrosion resistant finish. Hard anodizing is an electrically converted surface of aluminum oxide that is thicker and harder than regular anodizing. Aluminum oxide is used as an industrial abrasive so you can imagine how hard this is.
| The Stoptech STR caliper has a bridge assembly, (the black part in this picture which greatly increases the stiffness of the caliper). The silver things bolted to the bridge are anti rattle clips. They preload the brake pads reducing noise and brake squeal. Note the CNC milling of the caliper that reduces weight making the STR caliper weigh about 20% less than the standard Stoptech ST-60 caliper.
The STR calipers use standardized FMSI D1247 front and FMSI D372 pad shapes shared with Brembo, AP, Alcon and other common racing brakes. The important part about this feature is that this means that there are many pad choices from many manufacturers in this size so the end user can select pads from a pool of at least 15 different compounds. The calipers have a bolt in bridge to span the open area of the caliper where the pads are inserted which greatly contributes to caliper stiffness without contributing to additional bulk and weight. The STR calipers are also equipped with stainless steel abutments that the brake pad backing plates can ride upon to prevent them from gouging into the softer aluminum caliper body in long term use. The smooth hard stainless also makes the brake action smoother with a more consistent pedal as the pads can move more freely when the brakes are applied.
|The light gray brake pads are the Stoptech parts, note that they are much larger than the stock Brembo pieces. More pad area = more stopping power.
Thursday, April 29, 2010 7:49 AM
If those original EVO brakes need a happy new home, I would happily put the entire set on my 4G63 powered Mightymax truck. 13 inch rotors and Brembos would look outstanding on it! ;)
Thursday, April 29, 2010 9:28 AM
I swear by StopTech. They were very helpful last year when I was designing the brake system for my school's FSAE car. It's too bad they don't make SAE sized brake hardware, or we would switch to them from Wilwood.
Is the NT-05 a runflat? It sounds like with all that side rubber it would support itself nicely on its sidewall. It also sounds like with that low aspect ratio, those tires were a bitch to mount. Or does the soft rubber compound prevent all that?
Thursday, April 29, 2010 3:01 PM
Wow, pretty sweet. I'm impressed you guys got bigger brakes for less weight! I always thought that was a big detriment of big brake kits, along with the poorer-than-stock performance.
Also where do you get those FEA images of your wheels? For almost every project car that gets new wheels it seems like you guys have one but I haven't been able to find them on various manufacturers' sites. Unless all your project cars get the same wheels and you're just reusing one image.... =P
Thursday, April 29, 2010 4:54 PM
About the pads, I thought that more surface area didn't really affect stopping ability in relationship with the amount of pressure applied, but more about pad wear. My thinking was that big brake kits gave you more of a lever to give you more torque for the same amount of force applied, along with increased heat capacity.
Thursday, April 29, 2010 5:14 PM
I just happen to use the same FEA image in all the articles, look close, its a RE30 not a CE28N. The NT05 is not a run flat, the sidewall tricks are for better response and to hold the tread flatter under load.
Pad area makes a huge difference in brake performance. You are correct about the big rotors giving more of a torque moment and incresed heat capacity.
Thursday, April 29, 2010 10:13 PM
Big pads vs small pads: friction force is equal to coefficient of friction X area of pad X pressure. General equation relating pressure to area is: force = pressure X area. Say a pressure of 50 lbs per square inch, pad area of 5 square inches = 250lbs of force right? Doing a quick units check, lbs/in^2 X in^2 = lbs. Yup, checks out. It's late... have to make sure my brain still works :)
So what I'm getting to, with a bigger pad, you can use less pressure to get the same friction force. This should let you use a less aggressive pad I think.
Couple things with the bigger rotor: torque = force x distance. You want to apply torque to the wheel (through the brakes) to stop right? Well, with the larger diameter rotor, it just increased 'distance' increasing your moment arm/torque arm. So to get the same torque, you need less force as compared to the smaller diameter rotor.
So compared to a small rotor/small pad setup, the new big rotor/big pad setup requires a lot less pressure between the pad and rotor to get the same braking torque.
Also, big rotor equals more surface area for faster cooling.
Friday, April 30, 2010 7:39 AM
At the bottom of page 2 it says the rotor size for front and back are both 355x32mm. Is that correct?
Friday, April 30, 2010 10:16 AM
How big is the weight differance between the stoptechs vs stock?
Friday, April 30, 2010 10:57 AM
Dude read the article!, Ben, Yes both rotors are 355mm.
Tuesday, May 04, 2010 12:32 PM
My mistake the rear rotors are 345mm
Tuesday, May 04, 2010 1:38 PM
Did my previous comment get deleted?
I think those are all very valid points and observations.
I've been a fan of Mike Kojima's writing for a long time.
I was just offering an opinion to make it better, and more informative to people interested in BRAKES, but maybe not StopTech.
Tuesday, May 04, 2010 2:28 PM
I am deleting your comments, check your PM. I believe you are an employee of a competitor to Stoptech and your comments are not unbiased or appropriate. I also deleted some detailed counterpoints to your post made by some of our readers as I do not wish this to deteriorate into a flame war.
I am open to discuss this matter with you privately. Again see your PM. I can verify your identify by tracking so it would help to be straight with me. If you don't stop reposting the same stuff without discussing it with me I will delete your account.
Stoptech is not a MotoIQ advertiser and our opinion is based on the fact that every Stoptech system we have had track experience with has worked flawlessly with a high degree of performance and the information that we are supplied with from Stoptech.
Saturday, May 08, 2010 7:12 PM
Question related to the wheels. I have an EVO X and have aftermarket wheels with a 20 offset. I noticed yours have a 22. My feeling is that steering feels is lost by going away from the stock (I forget but think it's 40 ish at least on the GSR) offset. Do you have some thoughts on this. My thinking is if I went to forged wheels ( I have cast Work wheels) in the future to try to get closer to a stock offset. Also, I didn't catch the weight of the Volks vs stocks (assuming this had the BBS). I assume it's not that much different. Thanks much.
Monday, May 10, 2010 11:29 AM
Well remember that the wheels are wider as well. Generally the more the centerline is offset from the Dave point, the more feedback you well get through the wheel.
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