Topic: Brakes- daily driver vs hard driving vs racing

[Gentleman Jack]

Slotted brake rotors

Some of you know I was at SEMA this past week.  There was all kinds of stuff there, but I found myself gravitating to some really nice brake set ups for all kinds of vehicles.  Most of the fancy high dollar versions were slotted and or cross drilled.  That got my brother and I talking. What we came up with is that slotted rotors decrease the surface area of the rotor by as much as 25%.  We understand how that helps in racing where heat is a HUGE issue.  What we can't wrap our heads around is how it helps a normal driver car.  It would seem to me that most people never heat up the brakes on their daily driver enough to take advantage of the better cooling effects of the slotted rotor.  Effectively, by installing them on the "average" car, you are reducing the surface area with which the pads can work, thereby reducing the overall effectiveness of the brakes (all else being equal: equal size rotors, same materials etc)
Is this one of those classic cases of marketing over common sense? 

GJ

[Arabas]

AFAIK drilled rotors are supposed to cool faster because of better air circulation.
slotted rotors have bigger friction factor because they are not flat but rather have these slots.

regarding daily drivers, i have a problem defining daily driver....
i mean it all depends on what your braking needs are, your own perception of the sense of security (or your limits) and what kind of driving you usually do.
i guess it's kind of tuning options (295hp, 310hp, 330hp or bigger turbo and what turbo etc etc)

usually bigger diameter rotors, mean better cooling and bigger friction, so i suppose anybody can benefit from brake upgrades (daily or race) unless someone chooses a radical solution which will work only after you have actually warmed up REAL good the brake rotors and pads.

once again, this is my experience and personal opinion

[Brazen17]

Slotted brake rotors

Some of you know I was at SEMA this past week.  There was all kinds of stuff there, but I found myself gravitating to some really nice brake set ups for all kinds of vehicles.  Most of the fancy high dollar versions were slotted and or cross drilled.  That got my brother and I talking. What we came up with is that slotted rotors decrease the surface area of the rotor by as much as 25%.  We understand how that helps in racing where heat is a HUGE issue.  What we can't wrap our heads around is how it helps a normal driver car.  It would seem to me that most people never heat up the brakes on their daily driver enough to take advantage of the better cooling effects of the slotted rotor.  Effectively, by installing them on the "average" car, you are reducing the surface area with which the pads can work, thereby reducing the overall effectiveness of the brakes (all else being equal: equal size rotors, same materials etc)
Is this one of those classic cases of marketing over common sense?  

GJ

You are probably right. Probably doesn't hurt or improve typical daily stopping performance. I know if I ever get some (slotted only) it would be more for the visual look than performance.

[melissadunagan]

  Where slotted rotors help is in getting the gases and brake dust away from the pads so the pads can grip the rotor better. This is how I understand this.

[Gentleman Jack]

  Where slotted rotors help is in getting the gases and brake dust away from the pads so the pads can grip the rotor better. This is how I understand this.

Agreed.  The question is whether or not that is even an issue in normal driving.  I doubt it.

You are probably right. Probably doesn't hurt or improve typical daily stopping performance. I know if I ever get some (slotted only) it would be more for the visual look than performance.

Totally understand and agree.  A neat visual mod.  the question is, if you don't upgrade to larger rotors, or different materials, are you actually HURTING braking performance by reducing the surface area?  Normal daily driving does not heat up the brakes the way aggressive driving or racing does.

AFAIK drilled rotors are supposed to cool faster because of better air circulation.
slotted rotors have bigger friction factor because they are not flat but rather have these slots.

regarding daily drivers, i have a problem defining daily driver....
i mean it all depends on what your braking needs are, your own perception of the sense of security (or your limits) and what kind of driving you usually do.
i guess it's kind of tuning options (295hp, 310hp, 330hp or bigger turbo and what turbo etc etc)

usually bigger diameter rotors, mean better cooling and bigger friction, so i suppose anybody can benefit from brake upgrades (daily or race) unless someone chooses a radical solution which will work only after you have actually warmed up REAL good the brake rotors and pads.

once again, this is my experience and personal opinion

Arabas,

Yeah, daily driving can be different for anyone.  I would guess you might fall in to the "aggressive" driving category at least half the time you are driving (as do I ) but the other half of the time, I wonder if I'd be hurting my braking performance.  If I'm rolling down the freeway, the brakes are cold because I haven't used them much and have to panic stop - all things equal other than slotted vs not slotted - is there any advantage?  does the improvement in heat dissipation really overcome the smaller effective surface area?  I don't think so.


GJ

[Arabas]

GJ, as i said, i think that slotted rotors are supposed to improve friction, that s why pads are supposed to last less on slotted rotors.
in normal daily driving, i think that it is more important that the tires are up to good temperature and the pads are in good condition rather than slotted or not.
if someone drives normally all the time (or 80% of the time), drilled or slotted rotors is a waste of money IMHO

[Uranium-238]

Same thing applies to spirited driving, I know I often push the car hard enough that I have to slow down to let the brakes come back, but others might only push their cars that hard racing.

Something else to point out is  installing some good brake pads will add many of the good effect of drilled/slotted rotors, and are a helluva lot cheaper.

[timlange3]

Hi.  I believe slotted rotors may be a good thing for daily drivers as a marketing issue.
I believe the slots/holes, will tend to keep the rotors and pads cleaner, less debris will be collected causing somewhat less wear on both.  I also think the brakes will be quieter do to less debris.  Would a slotted rotor cool faster or not, less surface area to get rid of the heat, less surface area to be heated?  Do slotted rotors warp less or not?

I had a certain motorcycle without slotted rotors, brakes would squeal unless I cleaned the pads and only last a couple hundred miles.  Switched to slotted rotors and never got another sound.  Braking did not appear to be affected.

Just thinking out loud, not saying what is best.

[TomatoSoup]

I had replaced the OEMs with slotted rotors on my old Audi A4 (2 cars ago) - mainly 'cos they looked cool and were cheaper aftermarket than the OEMs.  I didn't notice any detriment to braking in normal driving - or improvements either.  That is with the certain exception of braking in heavy rain or after deep puddle splashes.  The slots really seemed to clear water away instantly and braking was immediate - compared to a brief but noticeable hesitation with the OEM discs.

My 2cents.

[Brazen17]

GJ, as i said, i think that slotted rotors are supposed to improve friction, that s why pads are supposed to last less on slotted rotors.
in normal daily driving, i think that it is more important that the tires are up to good temperature and the pads are in good condition rather than slotted or not.
if someone drives normally all the time (or 80% of the time), drilled or slotted rotors is a waste of money IMHO

I don't think it is a waste if you are doing it for appearance purposes and realize any performance gain would be minimal at best. Seems they would be more of a visual mod to me unless you go with bigger rotors. 

[Critterman]

I think you and your brother are over thinking the issue.  I have them slotted and drilled, the DDM big brake kit and agressive pads front and rear.

Before these rotors brakes squealled like GJ down in the cabin after a night of drinking.  After the rotor change not a sound.  Do they stop better?  They stop when i press the petal and there is always room between my nose and the reason I was stopping.   The only thing I have noticed the abs isn't as active in hard braking, the car just stops

[Noal]

For typical daily driving: as long as the brakes are able to lock the tires there shouldn't be much difference in the types of brakes.  They might make a difference in how hard the pedal is pressed, but if the tires can skid during braking, then the road surface/tires/suspension is the limiting factor.

Cost, longevity, reliability, continuous usage performance & performance under extreme handling conditions will be where the major differences are.

 

[Uranium-238]

That's quite true, but you left brake fade out of the mix. It's something decent pads will fix. While I haven't encountered it during my commute, I have run into brake fade when traveling on an insterstate in stop and go traffic in 100* weather.

Make it "Able to lock up the wheels and resistant to brake fade" and I'm in perfect agreement. Slotted/drilled rotors have the benefits, but they're certainly not "needed."

[kennysabarese]

If your brakes fade on the street you need better brakes. If you don't, then you don't.

I put upgraded pads and fluid into my car and was on the track for 3 days at Watkins Glen, which is really tough on brakes because there's a lot of straights and hard braking. I experienced brake fade only on one lap.

[Gentleman Jack]

If your brakes fade on the street you need better brakes. If you don't, then you don't.

I put upgraded pads and fluid into my car and was on the track for 3 days at Watkins Glen, which is really tough on brakes because there's a lot of straights and hard braking. I experienced brake fade only on one lap.

Brake fade was not my original thought with all this.  The reduction in surface area of a slotted rotor causing decreased performance was where my random mind was headed.

GJ

[kennysabarese]

http://auto.howstuffworks.com/auto-parts/brakes/brake-parts/brake-rotors2.htm

[Gentleman Jack]

You know Kenny, If everyone just googles everything, no one will ever need to have a conversation again! 

Thanks for the article though.  I know 90% of the folks that buy are doing it for the fashion of it.  Some of the fancy looking slotted rotors at SEMA had so many slots in them that there was hardly any surface area left to work with.  They were very pretty, much in the same vain as the motorcylce rotors in the article you posted.  They just didn't seem like they would work well for the average consumer they were being marketed to. 

GJ

[Brazen17]

You know Kenny, If everyone just googles everything, no one will ever need to have a conversation again! 

Thanks for the article though.  I know 90% of the folks that buy are doing it for the fashion of it.  Some of the fancy looking slotted rotors at SEMA had so many slots in them that there was hardly any surface area left to work with.  They were very pretty, much in the same vain as the motorcylce rotors in the article you posted.  They just didn't seem like they would work well for the average consumer they were being marketed to. 

GJ

GJ - Has is occurred to you that stopping is over rated?       

[Critterman]

Handling is where it is at, swerve around the obstruction

[kennysabarese]

well let's be careful here. you are decreasing the amount of surface that touches the pad yes, but you are actually increasing the surface area that is exposed to air by cutting grooves.

an extreme example of this is a heatsink. it will cool faster than a solid block of metal with the same external dimension.

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BUT on the other hand, less metal will get hotter faster.

so it's always a compromise.

ok now you really got me thinkin here...

i don't think amount of metal surface area (i'll call it friction surface area from now on) that is available to touch the pad is of concern. the reason we see fancy things on rotors is all about heat dissipation.

if you have enough friction surface area to lock up the tires, then you don't need anymore braking power, because you can't slow down any faster than the tires will let you. SO, the reason the brakes get bigger and bigger is to deal with heat, not increase the friction surface area.

so if you don't brake often, you need brakes that are able to enough to stop the car once without fading. if you want to brake more often without a lot of time in between braking events to allow for cooling, you will need brakes that can handle the higher temperature levels, AND/OR dissipate it more quickly.

so if you can't dissipate the heat fast enough, than you need to be able to have the rotor heat up more slowly, which you do by giving it more mass.

so the slots are probably more affective at cooling by pulling heat and those gasses away from the rotor than you would get by not removing the metal in those places to allow for slower buildup of heat.

so i think the moral of the story is, yes, most aftermarket brake companies sell you things that you do not need. The manufacturers are more concerned about the whole package so they will give you enough brakes that is necessary for the task at hand. They don't want to add weight because it affects handling and comfort and fuel economy.

[Noal]

Just to throw in another  and muddle things up further 

Without changing the pistons, the same amount of force is applied regardless of pads and rotors.  So decreasing the surface area between the pad and rotor doesn't change the force applied, just the area...  so does applying the same force over a smaller area significantly change the overall braking force (coefficient of friction * force applied by pistons)?  I don't recall the appropriate equations at the moment that correlate the coefficient of friction to the surface area and the applied force.  Unless someone chimes in, I'll have to look into it over the weekend just to satisfy my own curiosity of the physics behind all of this.

[LatinVenom]

A lot of attention is put on the Brakes and Rotors but just as equally important are the Tires.
For street use I rather spend my money on much better tires, than pads or rotors.
The drill and slotted rotors are primarily for heat dispersion.

[JimVonBaden]

  The only thing I have noticed the abs isn't as active in hard braking, the car just stops

If your ABS is kicking in less, then your brakes are less effective, all other things being equal.

Jim

[Kuprito]

Forget all physics and theory.

Try a car with big brakes and take your own decision.

I tried different brake setups on my car, and this is the best:



 (19" rims, 330x30 front and 296x25 rear)

[2kwk4u]

OK, I'll throw in my 2 cents from what I've learned, and the physics - as I understand it.

Larger diameter rotors make for better braking for two important reasons:

They provide for a "longer torque arm."  What this means is that the farther from the center of a circle you apply a force, the less that force has to be to affect motion.  Think of it like trying to loosen your lug nuts with a short wrench versus using a tire iron.  The tire iron requires a lot less muscle.

They have more mass, and thus can sink a lot more energy (i.e. heat) - therefore taking longer to heat up to the point where they can no longer prevent brake fade.

The trade-off to bigger rotors is all that extra rotating mass negatively affects handling, fuel mileage and acceleration.  Though I'm not sure I've ever seen that quantified as to how much.

As Noal points out, the sizes of the pistons in a hydraulic system (in the master cylinder and at the calipers) ultimately determine the force applied at the business end.  The coefficient of friction is determined by the makeup of the pads and rotors.  The SURFACE AREA in contact doesn't figure into the equation for friction.  So theoretically, the size of the brake pad doesn't matter.  Smaller pads, however, will wear faster and heat up much faster to the point where the heat of the pad changes the coefficient of friction (and you get brake fade).  So larger pads are better, to an extent, for the same reason (#2) that larger rotors are better.  They can absorb more energy in the form of heat before they give up the ghost.

As for the original issue of slotted vs. cross-drilled vs. smooth, I think we've covered that pretty well.  I've always understood that slotted is the way to go - with the caveat that the slots should NOT be milled all the way to the edge of the rotor (weakens the structure more).  There's the argument that some performance cars/supercars come from the factory with cross-drilled rotors (or at least used to before carbon ceramic became the rage).  High end Porsche 911's were often the examples cited.  The thing is, those rotors are apparently CAST with the holes in them.  Drilling through rotors is said to weaken them to the point where they'll crack if they're cycled through heat extremes (highly unlikely that you'd heat them up enough to worry about it anyway...)

Anyway, the slots are supposed to give the gas layer that forms between the pad and rotor an escape route, as well as give the rotor more surface area exposed to air for cooling. 

The biggest benefit I noted going to slotted rotors is the one Tomato Soup pointed out.  The split second "oh $h*t" of waterlogged brakes went away when I switched to slotted rotors on three cars I've done that to so far.  I've only noticed waterlogged brakes once or twice in my Sol, though.  So far I'm on stock brakes with it...  so none of the stuff you just read is based on my personal experience with a kappa