The Truth about FOX FRONT BRAKES!

[miamifiveoh]

So why don't we drill our flywheels then?

I'd like to hear custom89stang's logic applied to this question.

FIRST, The job of the brake system is to CONVERT the kinetic energy of forward motion into heat. This is accomplished by the friction of the brake pad acting on the rotor.

THEN, The rotor's job is to absorb this heat. The more mass the rotor has, the more heat it can absorb, and hence, the more braking ability. If you remove mass from the rotor (by drilling or slotting), you are decreasing the mass of the rotor, thereby decereasing its ability to absorb heat, thereby decreasing it's braking ability.

NEXT, the rotor has to dissipate the heat it just absorbed. This is accomplished via the venting present in most brake rotors. Some, like '94+ GT's, still use solid REAR rotors, though.

Fortunately, there has been a lot of new technology in brake pads in the last 50 years, so we don't need to worry about outgassing as much as we used to. Therefore, cross-drillied rotors are primarily an aesthetic upgrade.

Many will point to the 'high-performance' vehicles that are factory equipped with cross drilled rotors. Keep in mind that these rotors are much larger than the typical 10.84" Mustang rotor, and can AFFORD to lose some mass in exchange for the high-performance cross-drilled look. They certainly do look cool.

Here is a quote from a a thread on the corral (I don't care to reinvent the wheel):

Regarding extra surface area provided by the holes:

quote:
------------------------------------------------------------------------
Sure you increase the surface area, but where? Not in the prime spots of cooling airflow, and perpendicular to the direction of the normal flow. I believe at best they would be turbulence generators for existing cooling air flow. Heat dissipation depends on airflow, and lots of it, over the rotors, and through the open center section of a vented rotor, the holes don't do anything to increase the amount of airflow, and the additioanl srface area they do provide, isn't in the best place to make use of the existing airflow anyway.

If you are really having that much of a heat dissipation issue in a given application, rather than make your rotors weaker, I would recommend improving the brake ducting.
-----------------------------------------------------------------------

Regarding the airflow improvement provided by cross-drilling:

quote:
-----------------------------------------------------------------------
Not nearly as much as you think. A vented brake rotor works much like a centrifugal air pump, as the rotor spins, it creates low pressure areas behind the vanes, and air is drawn in from the center of the rotor to fill that low pressure area. So basically air is pumped from the center of the rotor radially outward (this is why you direct the ducting to the center of the rotor, for it to pick up the colder air). When you drill holes in the face, it takes a lot away from the centrifugal pump effect by not allowing the low pressure area to build up nearly as effectively.
And proper ducting is always useful, well, as long as you are moving anyway.
-----------------------------------------------------------------------


Do you like drilled/slotted rotors? Go ahead and buy them. Nobody is telling you NOT to. However, recognize that your are performing an aesthetic modification and not a performance enhancing one. There is nothing wrong with that.

Here is some more for you guys that like this topic:
http://www.corral.net/forums/showthread.php?s=&threadid=355711
http://corner-carvers.com/altimathread.php.html

Bon apetit,

 

[93 teal terror]

Boy, what the hell was I thinking? maybe it was cause I was drinking No matter what the distributed load is on a pad, the equivelant loading will always be the same. So in conclusion, cross drilling/slotting wont do anything, nothing, nada to slow your car down faster.

 

[sleeper89]

Ok, who's ready for the Platnium VS Copper spark plug debate!!!!!!!!

wow, this thread is priceless. not only does custom89stang come out flaming but does so with very limited/incorrect info. then he proceeds to request factual testing info regarding solid vs slotted/drilled, and backs up his beliefs with statements like this:

But for real, so what if it has less rotor, it grabs more cause of the dimples all you dumba$$es

well, i for one am convinced...
[sarcasm]
matt90gt and blackfox, you guys are stupid. clearly drilling your rotors causes more friction
[/sarcasm]

custom89stang-it's great that you are passionate about the hobby and having knowledge in general, but if you're going to call someone a liar, or say they are wrong and need to edit their web page, you should have some factual evidence to back up your statements. you have great thoughts and i see where your logic lies, and to be honest i cant even base my opinions on personal experience because i've never used slotted/drilled rotors. i was going to get them when i overhauled my brakes but after a LOT of research i felt there wasn't any performance advantage. check out the previous link to cornercarvers.com. it's a very informative thread by people in the know when it comes to brakes. then do what you want to your brakes. however, DO NOT come out flaming if you cant back up your statements factually (the same thing for which you shun matt90gt and blackfox5.0)

in closing i'd like to say matt's site is very informative, granted the info may or may not be 100% accurate, but it is informative. even if i ran into a problem that matt neglected to mention on his site i would be thankful for all the info it did (and does) provide which is accurate and helpful.

later

-steve

 

[chaka]

Boy, what the hell was I thinking? maybe it was cause I was drinking No matter what the distributed load is on a pad, the equivelant loading will always be the same. So in conclusion, cross drilling/slotting wont do anything, nothing, nada to slow your car down faster.

Not true. Did you read your first post. (the large cut and paste)?

But for everyday drives that don't compete what is the point?

You guys all go buy your slotted rotors and fancy brake pads. I will stick with my cobra setup. It works for what I need.

 

[miamifiveoh]

in closing i'd like to say matt's site is very informative, granted the info may or may not be 100% accurate, but it is informative. even if i ran into a problem that matt neglected to mention on his site i would be thankful for all the info it did (and does) provide which is accurate and helpful.

Agreed.

Short of driving over to your house and holding your hand, that's about as detailed as anyone should need it...and it's FREE!

I know I've paid hard earned money for products that didn't "bolt-on" quite as easily as they were supposed to. You will always run into snags when modifying.

 

[93 teal terror]

Not true. Did you read your first post. (the large cut and paste)?

But for everyday drives that don't compete what is the point?

You guys all go buy your slotted rotors and fancy brake pads. I will stick with my cobra setup. It works for what I need.

I mean to increase friction...they do have some "benefits" but increasing the frictional force is not one of them

 

[chaka]

I mean to increase friction...they do have some "benefits" but increasing the frictional force is not one of them

gotcha

 

[GAU89LXStang]

I thought I had an article that showed the differences between slotted/cross drilled rotors and stock brakes, but both that I found are "Big brake conversions" so they would be invalid. I am not nearly as "brainy" as some of you guys on here, but if anyone can find a comparison between stock brakes and slotted drilled brakes of the same size, then please post it or where to find it.

Now if we want to argue about dog training and canine behavior I would probably be the resident expert...

Later,
Mo' Town

 

[latham83]

This is freakin crazy...i know its a good arguement but really...im not taking either side..but i think EVERYONE here should take some kind of vehicle..either friends or not lol..with stock PLAIN rotors...drive it..then buy some powerslots..or JUST slotted rotors, put them on, and then drive it again..i really think everyone will notice an increase and feel in braking...over a stock setup...ive heard it enough..and i even drove one myself...my buddy put slotted's on his 2000 stage 3 jetta...and i drove it before and after...big difference....??? thats just me..

 

[Matt90GT]

Here you go smart guy:

What are the benefits to Crossdrilling, Slotting, and Zinc-Washing my rotors?
In years past, crossdrilling and/or Slotting the rotor for racing purposes was beneficial by providing a way to expel the gasses created when the bonding agents employed to manufacture the pads began to break down at extreme temperatures. This condition is often referred to as “green pad fade” or “outgassing”. When it does occur, the driver still has a good firm brake pedal, but simply little or no friction. Since this normally happens only at temperatures witnessed in racing, this can be very exciting!

However, with today’s race pad technology, ‘outgassing’ is no longer much of a concern. When shopping for races pads, or even ultra-high performance road pads, look for the phrases, “dynamic surface treatment”, “race ready”, and/or, “pre-burnished”. When these or similar statements are made by the pad manufacturer, the pad in question will likely have little or no problem with ‘outgassing’. Ironically more pedestrian pads used on most streetcars will still exhibit ‘outgassing’, but only when used at temperatures normally only encountered on the racetrack.

Although crossdrilling and/or slotting will provide a welcome path to expend any gasses when and if they develop, it is primarily a visual enhancement behind today’s often wide-open wheel designs.

Crossdrilling offers the greatest gas relief pathway, but creates potential “stress risers” from which cracks can occur. Baer’s rotors are cast with crossdrilling in mind, from the material specified, to curved vanes, behind which the holes are placed to minimize potential crack migration. Slotted surfaces are what Baer recommends for track only use. Slotted only rotors are offered as an option for any of Baer’s offerings.

Zinc washing is then done to provide a barrier, which resists development of surface scales or rust.


http://www.baer.com/Support/FAQ.aspx#1


Maybe you should to work for Baer!

Now also learn something about how brakes work:

http://auto.howstuffworks.com/brake.htm

Lets get to the friction part of this real quick:

http://auto.howstuffworks.com/brake4.htm

More friction you can make, the more stopping power. With the slots and holes, you lose surface area to make friction on. It can be a small percentage, but you are still losing surface area!

 

[sleeper89]

This is freakin crazy...i know its a good arguement but really...im not taking either side..but i think EVERYONE here should take some kind of vehicle..either friends or not lol..with stock PLAIN rotors...drive it..then buy some powerslots..or JUST slotted rotors, put them on, and then drive it again..i really think everyone will notice an increase and feel in braking...over a stock setup...ive heard it enough..and i even drove one myself...my buddy put slotted's on his 2000 stage 3 jetta...and i drove it before and after...big difference....??? thats just me..

sorry latham83, but the butt-o-meter is highly inaccurate and doesn't hold much weight around here. if you can give me factual test results of decreased braking distance i'm sold, until then i'll stick with solid rotors.

-steve

 

[astronut1885]

unless you are going to ride your brakes like an old lady, you probably aren't going to get them hot enough for the drilled/slotted vents to be advantageous anyway. The main benefit is a loss of rotational mass, and that is minor. When I swapped over however, I did notice better braking than last time I did brakes and went with stock. I had less fade and quicker stops overall. Both sides have good arguments, but I think only a road test can settle it. I personally like slotted rotors. They've worked for me, and they look nice in the wheel well too. Just my .02

 

[Boss 351]

The whole thing about brakes you need to know is that brakes are meant to convert motion into heat. Less heat doesn't mean better braking directly. HOWEVER with the slotted discs the heat can dissapate (sp?) better thus allowing more motion to heat conversion. At least that's what I understand.

Bigger brakes will work for sure as long as you do it right with the proper proportion valve and master cylinder. Stainless braided lines will allow less expansion in the lines thus allowing less loss in oil pressure. I'd get the bigger brake setup with the braided lines, good ceramic or carbon fibre brake pads and, money permitting, some good drilled discs.

 

[chaka]

Lets get to the friction part of this real quick:

http://auto.howstuffworks.com/brake4.htm

With the slots and holes, you lose surface area to make friction on. It can be a small percentage, but you are still losing surface area!

Friction force has nothing to do with Surface area.
ForceofFriction=CoeffOfFriction*ForceNormal.

ForceNormal is the force of the brake pad on the rotor. You have the same friction force no matter what the area.

 

[yellow5.0cobra]

Who gives a 'Kiss Me''Kiss Me''Kiss Me''Kiss Me'?

 

[Mustang5L5]

I hope you guys aren't comparing out ancient Fox brake systems to high tech formula 1 braking systems. They are nowhere related. What would apply to production car brakes do not for racing brakes.

This thread was labeled "truth about stock fox front brake" so why are we brining formula 1 race cars into the mix? When your brake pads cost $10,000 a set and emit toxic gases, then you can say drilled rotors are worth every penny..any they are in that case.

As for porche and merceded benz...well how much do those cars cost. A lot more money was spent in the engineering department for those vehicles. They has the time to sit down and figure out that they could reduce the mass of their rotors a certain amount and not affect the structure and ability to channel heat because their rotors are probably still twice as massive as any other vehicles. It's all about finding a middle ground. Too large and you have greater rotational inertia. Cut out too much mass and you affect the ability to absorb heat. Plus the fact you have massive calipers doesn't hurt either.

The final verdict should be Fox Brakes SUCK period.

 

[Mustang5L5]

The whole thing about brakes you need to know is that brakes are meant to convert motion into heat. Less heat doesn't mean better braking directly. HOWEVER with the slotted discs the heat can dissapate (sp?) better thus allowing more motion to heat conversion. At least that's what I understand.

That's just it though. Slotted rottors cannot dissapate heat better. Solid face rotors have more surface area in the airstream so they can dissapate it better

 

[Mustang5L5]

Regarding extra surface area provided by the holes:

quote:
------------------------------------------------------------------------
Sure you increase the surface area, but where? Not in the prime spots of cooling airflow, and perpendicular to the direction of the normal flow. I believe at best they would be turbulence generators for existing cooling air flow. Heat dissipation depends on airflow, and lots of it, over the rotors, and through the open center section of a vented rotor, the holes don't do anything to increase the amount of airflow, and the additioanl srface area they do provide, isn't in the best place to make use of the existing airflow anyway.

If you are really having that much of a heat dissipation issue in a given application, rather than make your rotors weaker, I would recommend improving the brake ducting.
-----------------------------------------------------------------------

Regarding the airflow improvement provided by cross-drilling:

quote:
-----------------------------------------------------------------------
Not nearly as much as you think. A vented brake rotor works much like a centrifugal air pump, as the rotor spins, it creates low pressure areas behind the vanes, and air is drawn in from the center of the rotor to fill that low pressure area. So basically air is pumped from the center of the rotor radially outward (this is why you direct the ducting to the center of the rotor, for it to pick up the colder air). When you drill holes in the face, it takes a lot away from the centrifugal pump effect by not allowing the low pressure area to build up nearly as effectively.
And proper ducting is always useful, well, as long as you are moving anyway.
-----------------------------------------------------------------------


Bon apetit,

Thank you!

That's exactly what i said!

 

[sleeper89]

Friction force has nothing to do with Surface area.
ForceofFriction=CoeffOfFriction*ForceNormal.

ForceNormal is the force of the brake pad on the rotor. You have the same friction force no matter what the area.

so let me get this straight (as i'm not an engineer), you're saying that the coefficient of friction between the pad and rotor is equivalent (or very close) to the coefficient of friction between the pad and the (air in the) holes/slots? please do elaborate.

-steve

 

[Mustang5L5]

I think i have an idea for a very good experiment.

I have access to a wind tunnel. Also, i have a front spindle from my '88 along with a solid rotor and a crossdrilled rotor and a 73mm caliper to mount on it. Assuming i could find a way to mount the spindle in the wind tunnel and spin the rotor to a speed that would be approximate as if you were doing 60MPH, i would do the following things.

1.) Determe how the airflow flows along the face of the rotor on the solid design.

2.) position the smoke outlet on the backside of the rotor near the open "centrigial pump" area to see how airflow flows through the vented viens at speed.

3.) use the crossdrilled rotor and determine is any airflow from the surface of the rotor travels inside the drilled holes

4.) repeat step #2 for the drilled rotor and see if any of the air being pumped through the center travels through the drilled holes.

#5 and #6 See if i can get access to a stotted rotor and do the same tests

This would try to prove the "drilled/slotted rotors cool better" theory. If no airflow goes into these ares, how can you cool better.

This all assumes i can find a way to spin the rotor up to speed cheaply (in other words...without costing me any money)