grooved, cross drilled or dimpled thoughts please!?

[aceyx]

Originally Posted by 1996 328ti

DIMPLES ARE PURELY TO SIMULATE DRILLED.
THEY SERVE ABSOLUTELY NO PURPOSE OTHER THAN LOOKS.

Unless the pads you are using are from the early 1970s.

Cross-drilling, slotting, and dimpling are artifacts of engineering to solve a problem that no longer exists with modern brake pads. They are an aesthetic holdover.

If you claim that it looks good, you're spot on.
If you claim you're stopping any faster, you sir (or madam), have a car that defies the laws of physics.

[mohaughn]

I would say that most manufacturers that put drilled rotors onto a car are doing it for looks and to reduce the weight of the rotor... Of course by reducing the weight of the rotor you reduce material to help it cool faster.. As long as it is engineered properly you shouldn't have a problem with drilled rotors.. Given that the e46 M3 drilled rotors fit our car perfectly and were designed for a much much heavier car you could use those without any problems... UUC races them and I'm not aware of them having any out of the ordinary problems with them.

I make sure to completely inspect mine after each event... I'll probably try the motorsport floating rotors that are not drilled next time just to see if I notice a difference, and they are cheaper. If I do notice a difference for the worse I'd continue to use the motorsport drilled rotors.

[pdxmotorhead]

As the friction material gets hot it begins to give off
gasses that can reduce the friction between pad
and rotor. Hole or slots are to allow the gas layer
on the pad to escape. On cold brakes it make ZERO
difference. On street brakes it helps IF and only IF
you've got the brakes very hot, something thats
not likely, day to day. I've seen this tested o a high
speed video and you can see the effect. But your
talking about the last 2% of brake effectiveness,
its like the last 5 HP on a 1300HP dragster, that 5
likely cost as much as the other 1000 hp to get there..
If you want the gas relief I'd use the slotted ones
because they don't crack as often as the drilled
rotors, the dimples are still TBD on how they affect
the life of the rotors. BTW the ATE slotted ones
gave us a definite improvement on pad life. Probably
because on the enduro car we put them on it let you
brake less in terms of time on the pedal, and in an
8 hour race that matters.

None of the teams I've worked with use drilled unless
they are desperate, the cracking issues simply
out-weigh the benefit.

It also depends on the type of racing, All the sprint
cars and midgets seem to use the drilled rotors,
but they are running very very thin rotors that need
all the help they can get. Weight is the game there....

Good Luck
Dave

[1996 328ti]

I find once my pads are out gassed, I'm good until they are worn down.
Sure, grooved rotors will let the gas escape easier, but once the gas escapes, it's no longer an issue. If I use fresh pads on the track, all it takes is several hard stops and they are good to go. I usually do this before a track event, but sometimes there is not enough time.

[pdxmotorhead]

They out-gas any time the material melts. So yea you get rid of the worst of it by proper bedding and the other measures mentioned. I've driven quite a few different cars at Portland and even the Sentra we rent for track days with good pads, I can get to the point where the brakes give up after enough real hard laps... Especially since the car likes being trail braked. Of course we don't put anything exotic, Hawk blues usually.

Heavy cars see more problems than light ones.


Dave

[campaiar]

OE Blanks FTW.

While the drilled, slotted, dimpled, etc rotors look better, they do wear pads quicker, which means more pads have to be purchased. Not to mention how expensive the rotors are to begin with.

Its mostly about cash flow. They feed off of the exact opinions that have been exhibited here.

[mohaughn]

True enough... Unless you are a super competitive racer that really needs to save .25 seconds off of your lap time I don't think the cost of the drilled rotors is worth it... When I started my car I was kind of going for a really good looking street car that was also track capable... But I've kind of changed since then.. It is strictly about the track and I'm not really worried so much about how it looks.

If I hit all of the driving events I want to in the next six months I'll probably end up getting new rotors later in the year.. I can do a same car OE Blanks VS OE Crossdrilled comparison at that time.

[L84THSKY]

Lets' look at this from a cost perspective. What do front and rear OEM rotors cost? I agree drilled has downsides, so I will compare my slotted ATE disks to OEM ones. Of course ATE is OEM or OEM replacement anyway.

Originally Posted by 1996 328ti

And probably never bedded in properly.
DIMPLES ARE PURELY TO SIMULATE DRILLED.
THEY SERVE ABSOLUTELY NO PURPOSE OTHER THAN LOOKS.

[marko]

had crossdrilled/slotted (from Bav. Auto.) on the car and they were complete BS (in my humble opinion, anyway)... they got bent fast and were causing heavy vibration on the steering wheel no more than 3K post purchase and (professional) installtion, and thus became a very expensive set of paperweights rather quickly. further, they made this ridiculous grinding sound (due to holes/slots) which went through me like a knife... as for stopping power, didn't really feel much difference as I do not 'track' the car... in short, stick with OEM solid/vented... best deal & value.

[DustenT]

Originally Posted by L84THSKY

Lets' look at this from a cost perspective. What do front and rear OEM rotors cost? I agree drilled has downsides, so I will compare my slotted ATE disks to OEM ones. Of course ATE is OEM or OEM replacement anyway.

The swirls in the ATE ultimates are for looks. Your rotors are almost as good as OEM blanks, since they are missing a small amount of surface area from the swirls.

Everyone seems to have to learn this lesson the hard way, I did.

[L84THSKY]

One of the problems with comparing the effect of a specific item is that you don't swap just that item when making upgrades.

I replaced my OEM worn rotors with ATE power slot disks. At the same time, I replaced the generic cheap pads with Axxis Ultimate pads. If I recall, that alone made a huge difference. Then I switched to DOT4 fluid and installed stainless steel brake lines.

Now the only way to see what effect OEM rotors would have, is to replace my currrent ones with OEM rotors the next time I need them. Do I really wanna do that just to see if they are any better? I am VERY pleased with the braking on my car, no fading or warping. I will stick with what I have.

Originally Posted by DustenT

The swirls in the ATE ultimates are for looks. Your rotors are almost as good as OEM blanks, since they are missing a small amount of surface area from the swirls.

Everyone seems to have to learn this lesson the hard way, I did.

[DustenT]

Originally Posted by L84THSKY

I replaced my OEM worn rotors with ATE power slot disks. At the same time, I replaced the generic cheap pads with Axxis Ultimate pads. If I recall, that alone made a huge difference. Then I switched to DOT4 fluid and installed stainless steel brake lines.

Yep, same here. I went from cross-drilled non-vented rotors on factory pads to: OEM vented blanks, UUC stainless lines, ATE racing blue fluid and some sticky Kumho tires. The combination of all those new parts made the car feel way better than any factory car...

[aceyx]

Originally Posted by mohaughn

I'll probably try the motorsport floating rotors that are not drilled next time just to see if I notice a difference, and they are cheaper. If I do notice a difference for the worse I'd continue to use the motorsport drilled rotors.

A buddy of mine ran them on his (E36) M3 with Hawk HPS+ pads. Said the reason he got faster on the track was because he was scared people were going to ram into him entering corners.

[oakley]

so do the hoses make a big difference as well than...never really thought about replacing them before.... as for the fluid all my servicing is done at the main bmw dealer so not really an option for me..spose depends wether the hoses make a diff. on standard fluid?? kinda gettin out of my league mechanically now!!

[mohaughn]

I'm using wilwood H compound track pads up front with Hawk ceramics on the back. I don't really have an opinion on the rear brake pads, they work but are a bit noisy in low use braking. Once you start to push them they are quiet.

I have absolutely no complaints on the front drilled rotors though... 6 months of use with maybe 6-8 hours of heavy use on them by a novice-intermediate driver(me) and 1 hour of hard use by a very experienced driver. Maybe 300 miles of street driving. No cracks yet. Money no object I would buy these rotors again.