MX-3.com

just a bit of background, the 323 has the mx3 subframe, so all components are technically applicable to the mx-3 as well.

i did all the R&D and prototyping myself. it's a direct bolt-on application, retains stock calipers and lines, and takes all but 1 hr to install, dont even have to bleed the brakes, and only a very minor modification required on the calipers (cutting some dust boots). im quite proud of the work actually its probably a bit on the big/overkill side for the car, though it is KLZE powered, but it's something i wanted to do just for the hell of it. anyways, onto the pics

before:


now:








comes in handy too for towing:

i'll summarize some initial driving impressions:

1) based on some "unofficial" 60-0 tests, compared to stock, the new setup yielded about 1/2 car length.

2) fade is gone. during those 60-0 tests, the stockers started slipping and chattering after 2nd/3rd run, but the new setup never did during the tests.

3) while towing today, compared to previous times when i towed, the car definitely responded better.

4) oh yea, and a chihuahua decided to dive in front of the car today, this kit saves lives too (j/k - but sure as hell locked up my wheels)

overall, a more confident feel, im sure partially mental, but definitely an improvement.

Weight of big rotors vs stock?

that's one thing i forgot to do is to weigh them....they are def. heavier. do they make the car more sluggish? (i assume this is where the question was leading to), maybe slightly (?) it's definitely not significant enough for me to tell straight up that it is, but everytime u add unsprung weight to the wheels im sure it makes a difference. but the KLZE doesnt seem to show any significant signs of slowing down. on a the smaller v6 or the i4, it might be more obvious.

did you upgrade master cylinder as well?

no, the entire system (lines, calipers, pads) are all stock, only the rotors are bigger. keep in mind this is just a relatively simple and cheap upgrade. the main focus is on increasing the diameter for added leverage and the bigger rotor for higher threshold for heat. sure i can start upgrading the calipers, the master cylinders, but then it becomes a full blown upgrade that's gonna run over 1G. sure it's gonna be a better system, but where do u draw the line? a few hundred bucks, or over 1G? for me, this car doesn't warrant a full blown brake overhaul.

So if your calipers and pads are stock, they are still gripping the same amount of surface area as on a stock rotor. I don't see the point of this?

I see the point.

1) He doesn't look like a dork with minibike brakes in his 17's.
2) He does stop sooner
3) Less brake fade
4) Its awesome to do a unique fab job, and have it actually be an upgrade.

It's all about leverage. The closer to the outside diameter of the wheel that you can get the brakes to grab, the less leverage is working against them. Also, they will wear slower.
I would be interested in the extra weight, too.
Did you buy them with the 4x100 pattern, or drill them yourself?
It's a little unsettling to me that the holes were drilled in the existing holes. It seems the pattern could have been rotated a bit, so they wouldn't overlap.
They look great.

It's actually more about swept area than anything.

The stock front disk is 10.12" in diameter and the pad is 6.66sq-in in area (taken from the online manual)...so say about 2" x 3.33"...give or take. That rotor is ~13" in diameter with the same 2" high pad.

Torque = F(force due to friction) * d(the distance from the center of rotation to the point of application of the force) We don't know the actual value of the force applied at the pad, but we can express everything in terms of that unknown. I have also assumed that the point of application is the midline of the pad...4.12" from the center.

for the stock rotor... F * 4.12" = 4.12F

for the larger rotor... F * 5.5" = 5.5F

That's a 33.5% increase in the applied torque.

However...

A(swept area) = Pi*[D - d]^2/4 (D-d is the absolute diameter of the rotor minus the diameter which is not contacted by the brake pad)

for the stock rotor that's... Pi * [10.12 - 2]^2/4 = 51.78sq-in

For the larger unit that's... Pi * [13-2]^2/4 = 95.03sq-in

That's an 83.5% increase in the total area which makes contact with the pad on each revolution of the wheel under braking.

The change in torque is significant but what people don't realize is that the Work done by the pad is related to the swept area. Because the friction force is applied over a much greater area, much more work is done in each revolution of the wheel.

The weight is a huge consideration though. The change in weight is much greater than I suspected when we talked about this last time. The guy on CP who did the Miata brake upgrade said that they were way heavier. An extra pound or so would not be a big deal, but an extra 5 could affect handling. Changing the rears for the RX7 vented rotors might not be a great idea.

fowljesse wrote:It's all about leverage. The closer to the outside diameter of the wheel that you can get the brakes to grab, the less leverage is working against them. Also, they will wear slower.
I would be interested in the extra weight, too.
Did you buy them with the 4x100 pattern, or drill them yourself?
It's a little unsettling to me that the holes were drilled in the existing holes. It seems the pattern could have been rotated a bit, so they wouldn't overlap.
They look great.

thanks, that was my initial reaction too when i got them from the shop (hence i did not redrill them myself - i COULD'VE used our CNC machine at work but wouldve been too much work to have to write a program just to do that, the shop that did it do rotor work all day long) but once i put the rotors on the car, i can tell the overlap holes wasnt going to be that big of a deal. also, i saw some other pics online of other redrilled rotors, and there are other examples ive seen that have overlapped holes. i think the shop did that b/c it's better to have them overlapping so the "sides of the holes are still solid, than to rotate them and have all the holes close to the pre-existing ones and have thinner materials b/t them. sounds confusing.

as for the weight, next time i take the rotors down to do some check-up (to make sure nothing fishy is going on), i'll see if i can put them on our scale and do some weight comparison vs. stockers.

wytbishop wrote:It's actually more about swept area than anything.

The stock front disk is 10.12" in diameter and the pad is 6.66sq-in in area (taken from the online manual)...so say about 2" x 3.33"...give or take. That rotor is ~13" in diameter with the same 2" high pad.

Torque = F(force due to friction) * d(the distance from the center of rotation to the point of application of the force) We don't know the actual value of the force applied at the pad, but we can express everything in terms of that unknown. I have also assumed that the point of application is the midline of the pad...4.12" from the center.

for the stock rotor... F * 4.12" = 4.12F

for the larger rotor... F * 5.5" = 5.5F

That's a 33.5% increase in the applied torque.

However...

A(swept area) = Pi*[D - d]^2/4 (D-d is the absolute diameter of the rotor minus the diameter which is not contacted by the brake pad)

for the stock rotor that's... Pi * [10.12 - 2]^2/4 = 51.78sq-in

For the larger unit that's... Pi * [13-2]^2/4 = 95.03sq-in

That's an 83.5% increase in the total area which makes contact with the pad on each revolution of the wheel under braking.

The change in torque is significant but what people don't realize is that the Work done by the pad is related to the swept area. Because the friction force is applied over a much greater area, much more work is done in each revolution of the wheel.

The weight is a huge consideration though. The change in weight is much greater than I suspected when we talked about this last time. The guy on CP who did the Miata brake upgrade said that they were way heavier. An extra pound or so would not be a big deal, but an extra 5 could affect handling. Changing the rears for the RX7 vented rotors might not be a great idea.

excellent break-down, u did a much better job that i could've. again for the weight, i know the rotors are def. heavier, personally it wasnt an issue for me, as 1) the car has a ZE in it, 2) i dont really track the car so the handling aspect is secondary. i will do my best to get an actual number for the rotor weight soon here.

The volume of the pad could also be calculated to find how the heat absorption factor increased. I'll do that when its not 1:00 AM

Don't do it. You'll just confuse, and anger me.

It's okay, I'm sure it'll make sense to Wytbishop, and a couple others.

Nicely done. I was considering this style of upgrade for my rears (having done a wilwood 13" setup in the front).

You should paint the center caps and edges, and cross drill those rotors though. They're gonna rust somethin fierce. Should paint your calipers while you're at it.