Show me your wheels...

[mx-3_4evr]

Gold ones for sure!

[Ukrman]

wow, the gold ones look awesome

[mx3autozam]

heres mine. 16x7 Rota Subzero's

[timpronk]

Did you (mx3autozam) buy your rotas subzeros from fiero ? He is moving on to a 323 right?

[Ryan]

Way too much open space. Makes teeny brake rotor look silly Thats the main reason I dislike very open wheels over 16"

[wytbishop]

Very good reason to upgrade your brakes as well.

[Whisper]

Wouldn't bigger brakes with bigger rotors add more rotational mass and thus kind of null-out any gains you might get?

[wytbishop]

I"m not trying to win races. I'm happy to let others obsess over meaningless crap like that. I would rather have nice big brakes that stop like crazy.

[marcdh]

Hmm quite often the big brake kits use bells to hold the rotors, which reduce mass. But really, it's not going to matter as much as even heavy wheels, maybe like <5hp, and what use is that if you're in a hedge?!

[wytbishop]

My philosophy is to do things that make the car work better. Some of the things I want are just to make the car look better, but in general they also improve the cars condition. The wheels are mainly to improve the look of the car, but also to improve traction. The brakes will also look better, but improved braking is a big consideration too. I don't really care if they weigh an extra 5lbs. I'm not interested in being on the cutting edge of weight reduction or squeezing every ounce of power out of it. I want the car to be comfortable and fast and handle well and look great and last for 15 more years...that's all.

[Whisper]

Yeah, I forgot who it was, I think Steeb maybe, but it was mentioned that larger rotors are harder to stop, due to increased rotational mass (which is more significant than stationary mass). Kind of like the same principle as with larger, heavier wheels. And I remember it was said the optimal solution is keeping stock sized brakes and simply getting sticker pads, that way you get all the pros of improved braking, without all the cons of larger rotors.

I've kind of followed that philosophy by upgrading my pads, and getting stainless steel brake lines, and it made a huge difference in stopping power.

[wytbishop]

No offense to Steeb, whom I'm sure is a very smart fellow, or yourself, but from a physics perspective there is absolutely no way on Earth that is true.

There would certainly be an increase in the inertia and momentum of the rotating brake rotor due to it's larger mass, and I agree that upgrading your pads and brake lines is probably more than enough for a street going car. But when you combine the increase in swept area of a larger rotor and correspondingly larger pad, as well as a small, but calculable change in the moment arm of the friction surface and resulting increase in brake torque there is no question at all that the very significant increase in braking force would more than compensate for the increase in momentum of a larger rotor. It would most certainly improve braking.

Compared to the mass of the wheels, the change in mass of upgrading rotors would be small. Even if it was a whole pound heavier, that would only represent a 2-3% change in the total rotating mass.

And as I also said, I'm planning to upgrade the brakes at least partially because they will look really good.

[Whisper]

What you're saying does make sense, but I just want to link to this old thread where there was some discussion about bigger brake kits. I guess it wasn't Steeb, but Yoda, that brought up the drawbacks of increased brake size. It sounds rather counter-intuitive, but maybe it has merit...

I'll quote Yoda's post, just so it's easier.

Bigger diameter rotors and 4 piston calipers don't necessarily mean that there will be an improvement in stopping power. I fact the opposite maybe true. Even is the rotor is made of lighter material the greater percentage of the mass in farther out from the center of rotation. The inertia at 60mph would make these rotors with a 1" greater radius the equivalent to the stock rotors having the mass of about 10 times or more what they actually do. As rotational speed increases then the rotational mass also increases. In addition to taking more energy to stop they also require more energy to keep in motion. I have seen in dyno test were WHP was reduced by 5-8whp at peak after installing bigger brakes. What really counts is the compound of the pads. Most pads made for the multi piston calipers were formulated for racing where the brakes are constantly used hard and operate at much higher temp that are seen on a street driven car. The main advantage to a larger rotor is the greater mass and surface area to dissipate the heat. On the other hand for drag racing you would be better off with stock brakes and good quality street pads the reason being is less rotational mass and the pads and rotors don't need to be warmed up to achieve max stopping power much the same as a panic stop in street driving. Bigger calipers do not equal more stopping power either unless you increase the braking force at the master cylinder as well. Generally speaking if the hydraulics force of the fluid is going to more that one cylinder, the force is being divided by the number of cylinders. You could end up with less breaking force than with the stock brakes if the master cylinder doesn't supply enough fluid volume and pressure for the additional number of pistons. I don't know if any of you have seen or been on a brake dyno. They work the opposite of a chassis dyno where the rollers are spin the wheels you to a preset speed them the brakes are applied to stop the rollers in a preset time. Here as part of the vehicle inspection process this is one of the tests. I know of several people that failed this test with properly installed big brake kits but were retested with the old stock brake hardware and passed without problems. On the street aftermarket big brake kits have more to do with marketing hype than they do with performance. The need for big rotors was created by marketing people looking for you to break open your wallet not the aftermarket companies filling a need because the OE brakes need to be upgraded. SCC magazine just ran an article busting a lot of the tuning myths.

[Mooneggs]

I'm doing autocrossing this year and I just bought a set of powerslot slotted rotors, hawk hps plus front pads and ebc greenstuff rear pads. I will be upgrading the fluid to racing blue fluid and I already have SS brake lines. This setup is amazing for autocross (as I've driven stereoking15's mx-3 and it was much better than my current setup)...

I'll be curious to see how it holds up when I do some lapping at a real track where higher speeds are involved. I believe that a big brake kit will really only benefit if you have a high horsepower setup and/or heavy braking at high speeds. For normal mx-3 applications including the klze I believe our basic setup is pretty ideal.

[wytbishop]

What you're saying does make sense, but I just want to link to this old thread where there was some discussion about bigger brake kits. I guess it wasn't Steeb, but Yoda, that brought up the drawbacks of increased brake size. It sounds rather counter-intuitive, but maybe it has merit...

I'll quote Yoda's post, just so it's easier.

Bigger diameter rotors and 4 piston calipers don't necessarily mean that there will be an improvement in stopping power. I fact the opposite maybe true. Even is the rotor is made of lighter material the greater percentage of the mass in farther out from the center of rotation. The inertia at 60mph would make these rotors with a 1" greater radius the equivalent to the stock rotors having the mass of about 10 times or more what they actually do. As rotational speed increases then the rotational mass also increases. In addition to taking more energy to stop they also require more energy to keep in motion. I have seen in dyno test were WHP was reduced by 5-8whp at peak after installing bigger brakes. What really counts is the compound of the pads. Most pads made for the multi piston calipers were formulated for racing where the brakes are constantly used hard and operate at much higher temp that are seen on a street driven car. The main advantage to a larger rotor is the greater mass and surface area to dissipate the heat. On the other hand for drag racing you would be better off with stock brakes and good quality street pads the reason being is less rotational mass and the pads and rotors don't need to be warmed up to achieve max stopping power much the same as a panic stop in street driving. Bigger calipers do not equal more stopping power either unless you increase the braking force at the master cylinder as well. Generally speaking if the hydraulics force of the fluid is going to more that one cylinder, the force is being divided by the number of cylinders. You could end up with less breaking force than with the stock brakes if the master cylinder doesn't supply enough fluid volume and pressure for the additional number of pistons. I don't know if any of you have seen or been on a brake dyno. They work the opposite of a chassis dyno where the rollers are spin the wheels you to a preset speed them the brakes are applied to stop the rollers in a preset time. Here as part of the vehicle inspection process this is one of the tests. I know of several people that failed this test with properly installed big brake kits but were retested with the old stock brake hardware and passed without problems. On the street aftermarket big brake kits have more to do with marketing hype than they do with performance. The need for big rotors was created by marketing people looking for you to break open your wallet not the aftermarket companies filling a need because the OE brakes need to be upgraded. SCC magazine just ran an article busting a lot of the tuning myths.

A few things...

"The inertia at 60mph would make these rotors with a 1" greater radius the equivalent to the stock rotors having the mass of about 10 times or more what they actually do. As rotational speed increases then the rotational mass also increases."

The Mass Moment of Inertia is what he's talking about here and he's sort of right. If you increase the diameter of a 10" disc by 1" and its mass by 1/4lb its moment of inertia increases by ~30%. That means it's 30% more difficult to start and stop that mass in rotation. However, the 10X he suggests as the perceived mass due to rotation is a gross overstatement. If we were having a discussion about unsprung mass and it's affect on handling I would lean towards agreement. It has been shown that reducing the unsprung rotating mass by one pound is equivalent to reducing the sprung mass of the vehicle by a much greater amount. This is because of the cetrigugal affect of the moment of inertia. However as it regards the acceleration and deceleration of that unsprung mass, the affect is not so pronounced.

"The main advantage to a larger rotor is the greater mass and surface area to dissipate the heat."

While I agree that this is a considerable benefit, I believe that the increase in swept area is of greater braking importance. That same 1" increase in diameter increases the swept area of the rotor by 36%. That means that the contact area that the larger pad sees over the course of a complete revolution of the rotor is 36% greater. I think that's really significant.

"Generally speaking if the hydraulics force of the fluid is going to more that one cylinder, the force is being divided by the number of cylinders. You could end up with less breaking force than with the stock brakes if the master cylinder doesn't supply enough fluid volume and pressure for the additional number of pistons."

This is incorrect. The pressure in the hydraulic system is the same everywhere in the system. That is one of the basic principles of fluid mechanics. The pressure in the system is determined by the force of your brake application multiplied by the square area of the piston in the brake master cylinder. That pressure is simultaneously applied to every surface which it makes contact with. The walls of the brake lines, the passages in the calipers and every piston in every caliper. The force on each piston in each caliper is in turn determined by that pressure divided by it's square area. If the pressure in the hydraulic system is unchanged, and it is, any increase in surface area of the pistons in the caliper, whether by increasing the size or number of the pistons will result in greater braking force. That it scientific certitude.

The whole brake dyno thing I can't comment on. I've never seen or used one. It makes sense that you would have to demonstrate the cars braking performance in an inspection, but I've never even heard of this being done and I've been around.

There is no physics that suggests that swapping a 10" rotor for an 11" rotor and upgrading the caliper from 1 piston to 2 will do anything but improve braking. It won't make your car handle better and yes, it will be heavier. But unless you're trying to shave thousandths off your times it will be absolutely imperceptible.